Department of Pure &Industi ral Chemistry ANDREW AONDOAVER- 16-10... · 3.2 Particle size distribution of standard sand used for preparation of mortar for determination of compressive

ANALYSES OF SOME CEMENT BRANDS IN THE NIGERIAN MARKET

Digitally Signed by: Content manager’s

DN : CN = Weabmaster’s name

O= University of Nigeria, Nsukka

OU = Innovation Centre

ORJI ANN N.

Faculty of Physical Sciences

Department of Pure &Industi

Chemistry


AND OPTIMIZATION OF LIMESTONE CONTENT OF

LIMESTONE COMPOSITE PORTLAND CEMENT

TYOPINE ANDREW AONDOAVER

B.Sc , M.Sc (BSU)

PG/Ph.D/09/51796

i

: Content manager’s Name

Weabmaster’s name

a, Nsukka

Department of Pure &Industiral


AND OPTIMIZATION OF LIMESTONE CONTENT OF

LIMESTONE COMPOSITE PORTLAND CEMENT


ii

ANA TYOPINE ANDREW AONDOAVER

B.Sc , M.Sc (BSU)

PG/Ph.D/09/51796

LYSES OF SOME CEMENT BRANDS IN THE

NIGERIAN MARKET AND OPTIMIZATION OF

LIMESTONE CONTENT OF LIMESTONE

COMPOSITE PORTLAND CEMENT

BY


B.Sc , M.Sc (BSU)

PG/Ph.D/09/51796

A THESIS PRESENTED TO THE DEPARTMENT OF

PURE AND INDUSTRIAL CHEMISTRY,

FACULTY OF PHYSICAL SCIENCES,

UNIVERSITY OF NIGERIA, NSUKKA

IN

PARTIAL FULFILLMENT OF THE

REQUIREMENTS FOR THE DEGREE OF

DOCTOR OF PHILOSOPHY OF THE

UNIVERSITY OF NIGERIA, NSUKKA

iii

JUNE, 2014

CERTIFICATION

We certify that this Ph.D research work titled “Analyses of some brands of cement in the

Nigerian market and optimization of limestone content of limestone composite Portland

cement” was undertaken and reported by TYOPINE ANDREW AONDOAVER

(PG/Ph.D/09/51796).

Supervisor Prof.C.O.B. Okoye ---------------------------------- -------------

Signature Date

Head of Department Prof. P.O. Ukoha ------------------------------- -------------

Signature Date

iv

DEDICATION

To all youths passionate about learning

To Akaadoo

To service to humanity

v

ACKNOWLEDGEMENTS

God is Almighty, merciful and kind, for through his kindness we are able to do all things. I

want to thank God for his mercies and protection throughout this work.

I gratefully appreciate the contributions of the following persons towards the success of this

research work:

• My supervisor, Prof. C.O.B. Okoye for indefatigably mentoring and supervising the

research work from beginning to the end

• The Head of Department , Prof. P.O. Ukoha

• My father, friend and mentor, Dr. V.E. Agbazue

• My colleagues and friends as the case may be for their moral and technical support;

Doose Akaakase, Denen Ende, Peter Agudu, Iorbee Terfa, Blessing Ocheni, Denis

Dura, Vincent Ikyuior, Okon Bassey, Mr .M.O. Abifarin, Kumafan Dzaan, Akosu

Joy, Fefa Joseph, Ishom Isaac, Akulegwa Igbalumun, Silas Avenda, Andrew Ada,

Engr. &Mrs Ade sugh, Dr. Omaka (HOD Chemistry Department, FUNAI), Anthony

Ekenia, Mrs Ada Nkwo, Nora Igbalumun, Dido Mann, Raymond Aernyi, Edward Nor

and all those that have not been mentioned for want of space

• My family: Tina (Wife), David (son) and Queen (daughter), Mr & Mrs E.T. Imande

(parents), Maureen Tyopine, Sandra Tyopine, Dorothy Tyopine and Timothy Tyopine

(siblings) for enduring patiently while this work lasted.

vi

TABLE OF CONTENTS

Title i

Certification ii

Dedication iii

Acknowledgements iv

Table of contents v

Table of abbreviations x

List of figures xi

List of tables xii

Abstract xiv

1.0 Chapter one: Introduction 1

1.1 The nature of cement 1

1.2 World cement production and consumption 1

1.3 Cement production in Nigeria 2

1.4 Limestone composite cement 2

1.5 Statement of the problem 3

1.6 Significance of the study 3

1.7 Aims and objectives of the study 4

1.8 Scope of the study 4

2.0 Chapter two: Literature Review 6

2.1 History of cement production 6

2.1.1 Production of Portland cement 6

2.1.2 Sources of raw materials for cement manufacture in Nigeria 7

2.2 Chemical composition of raw materials for cement production 8

2.2.1 Limestone 8

2.2.2 Clays 10

2.2.3 Minor and trace components 12

2.2.3.1 Magnesia, MgO 12

2.2.3.2 Alkalis 13

vii

2.2.3.3 Sulphur 13

2.2.3.4 Phosphorus 13

2.3 Types of Portland cement 14

2.3.1 Type 1 14

2.3.2 Type 2 14

2.3.3 Type 3 14

2.3.4 Type 4 15

2.3.5 Type 5 15

2.3.6 Other types of cements 16

2.3.6.1 Coloured cements 16

2.3.6.2 Air entrained cements 16

2.3.6.3 Masonry cements 16

2.3.6.4 Water proof cements 16

2.3.6.5 Hydrophobic cements 17

2.3.6.6 Oil wel l cements 17

2.3.6.7 Slag cements 17

2.3.6.8 High alumina cements 17

2.4 Composition of Portland cement 18

2.5 Estimation of clinker composition 18

2.6 Setting of Portland cement 19

2.7 Manufacture of Portland cement 20

2.7.1 Pre-blending of raw materials 20

2.7.2 Heat treatment 22

2.7.3 Clinker cooling and grinding 29

2.8 Properties of Portland cement 30

2.8.1 Fineness 30

2.8.1.1 ASTM C 115: Fineness of Portland cement by the turbidimeter 30

2.8.1.2 ASTM C 204: Fineness of hydraulic cement by air permeability apparatus 31

2.8.2 Soundness 31

2.8.3 Setting time 32

2.8.4 Strength 34

2.8.5 Loss on ignition 35

2.8.6 Specific gravity 35

2.8.7 Heat of hydration 35

viii

2.9 Environmental impact 36

2.9.1 CO2 emissions 36

2.9.2 Heavy metal emission into the atmosphere 36

2.9.3 Alternative fuels and by product materials 36

2.10 Cement in Nigeria 37

2.11 Blended cements 39

2.12 Supplementary materials used in the manufacture of blended cements 40

2.12.1 High calcium fly ash 40

2.12.2 Ground granulated blast furnace slag 40

2.12.3 Condensed silica fume 40

2.12.4 Rice husk ash 41

2.12.5 Volcanic ash 41

2.13 Benefits of blended (composite) cement 41

2.13.1 Economical benefit 41

2.13.2 Technical benefits 41

2.13.3 Environmental benefits 42

2.14 Limestone as a supplementary material in blended cement production 42

2.15 Effect of limestone on properties of Portland cement 43

2.15.1 Particle size distribution and fineness 43

2.15.2 Consistency 44

2.15.3 Hydration 45

2.15.4 Setting 50

2.15.5 Compressive strength 50

2.16 Limestone reactions in limestone cements 51

2.17 Effect of limestone on concrete properties 52

2.17.1 Workability 52

2.17.2 Sulphate resistance 53

3.0 Chapter three: Experimental 56

3.1 Materials and methods 56

3.1.1 Materials 56

3.1.2 Reagents 56

3.1.3 Apparatus 56

3.1.4 Material sampling and sample preparation 57

3.2 Methods 57

ix

3.2.1 Analysis of limestone 57

3.2.1.1 Determination of calcium carbonate in limestone 57

3.2.1.2 Determination of lime in limestone 57

3.2.1.3 Determination of loss on ignition 57

3.2.2 Analysis of gypsum 57

3.2.2.1 Determination of sulphite (SO3) 57

3.2.2.2 Determination of gypsum purity 58

3.2.3 Analysis of clinker 58

3.2.3.1 Determination of loss on ignition (LOI) and sulphite (SO3) of clinker 58

3.2.3.2 Determination of silica in clinker by baking method 58

3.2.3.3 Determination of iron (III) oxide and aluminium (III) oxide

in clinker by EDTA titration 59

3.2.3.4 Determination of calcium oxide in clinker by EDTA titration 59

3.2.3.5 Determination of free lime in clinker by hot ethylene glycol method 59

3.2.3.6 Estimation of clinker constituents using Bogue’s formulae 60

3.2.4 Preparation of Laboratory composite cements 60

3.3 Physical analyses of cements 60

3.3.1 Determination of water demand and consistency 61

3.3.2 Determination of setting time 61

3.3.3 Determination of soundness 61

3.3.4 Determination of cement residue (fineness) using sieve method 62

3.3.5 Determination of cement surface area using air permeability method 62

3.3.6 Determination of compressive strength 62

3.4 Chemical analyses of cements 64

3.5 Quality control and statistical treatment of data 64

4.0 Chapter four: Results and discussion 65

4.1 Results 65

4.2 Discussion 72

4.2.1 Clinker parent sample 72

4.2.2 Ordinary Portland cement (OPC) 73

4.2.3 Effect of added limestone on chemical composition of LCCs 74

4.2.4 Effect of added limestone on particle size and surface area 76

4.2.5 Effect of added limestone on soundness of Portland cement 78

x

4.2.6 Effect of added limestone on setting time and consistency

of Portland cement 78

4.2.7 Effect of added limestone on strength development of Portland cement 82

4.3 Comparison of some analysed market brands of cements MBCs 83

4.4 Conclusion 86

4.5 Recommendations 86

4.6 Contribution to knowledge 86

References 87

Appendices 93

xi

TABLE OF ABBREVIATIONS

Abbreviations/Symbols Definition

ASTM American standard for testing and materials

C2S Dicalciumsilicate

C3S Tricalciumsilicate

C3A Tricalciumaluminate

C4AF Tetracalciumaluminoferrite

EDTA Ethylenediaaminetetraacetic acid

LCC Limestone composite cement

LOI Loss on ignition

LSPC Limestone Portland cement

MBC Market brands of cement

OPC Ordinary Portland cement

UNICEM United Cement

WAPCO West African Portland Cement Company

XRF X-ray florescence

xii

LIST OF TABLES

2.1 Physical properties of limestone 8

2.2 Classification of limestone deposit 9

2.3 Chemical composition of some limestone samples 10

2.4 Clay members showing variation in components 10

2.5 Physical properties of clay minerals 11

2.6 Chemical composition of clay samples 11

2.7 Chemical composition of corrective additives used in the production of

Portland cement 12

2.8 Attack on concrete by soils and waters containing various sulphate

concentrations 15

2.9 Clinker mineral content estimated by Bogue’s method and

microscopic analysis 19

2.10 Theoretical heat of hydration of clinker constituents 20

2.11 Effect of calcite grain size on dissociation of limestone 26

2.12 Temperature profile of various clay minerals 28

2.13 ASTM C 150 specified set times by test method 33

2.14 Grinding parameters of limestone, natural pozzolana and fly ash

blended cements at 15 percent addition and compressive strength

values of strength values of samples prepared using cement types 44

2.15 Sulphate resistance of cement with limestone additions 54

2.16 Effect of 30 percent filler based on type and fineness on weeks to

failure of mortar bars in 5 percent sodium sulphate 55

3.1 Composition of limestone composite cements (LCCs) 61

3.2 Particle size distribution of standard sand used for preparation

of mortar for determination of compressive strength 64

3.3 Mixer speed during mortar production 64

xiii

4.1 Mean values of total carbonate and lime content (%) and loss

on ignition of limestone parent sample 65

4.2 Mean sulphite content and purity of gypsum 65

4.3 Mean chemical and mineral parameters of clinker parent sample 66

4.4 Mean chemical and physical characteristics of OPC 67

4.5 Mean values of chemical composition of ordinary Portland

cement (OPC) and limestone composite cements (LCCs) 68

4.6 Effect of added limestone on fineness of Portland cement 69

4.7 Mean values of soundness of Portland cement 69

4.8 Mean setting times and consistencies of Portland cement 70

4.9 Mean compressive strengths of limestone composite cements (LCCs) 71

4.10 Mean range of chemical and physical parameters of some

analysed market brands of cement 72

xiv

LIST OF FIGURES

2.1 Schematic presentation of reactions in the kiln at various temperatures 23

2.2 Le Chatelier test apparatus 32

2.3 Vicat test apparatus for setting time 33

2.4a Compressive strength testing machine 34

2.4b Prism mortars for compressive strength test 34

2.4c Prism after fractured by load 35

2.5 Schematic presentation of rates of heat evolution 47

2.6 Heat evolution curves of ordinary Portland cement

blended with limestone 49

4.1 Effect of limestone addition on loss on ignition of Portland cement 74

4.2 Plot of freelime against % added limestone in Portland cement 75

4.3 Plot of sulphite against % added limestone in Portland cement 75

4.4a Plot of residue retained on 90µm and 180µm against

% added limestone in Portland cement 77

4.4b Plot of surface area of Portland cement against % added limestone

in Portland cement 77

4.5 Plot of consistency of Portland cement against % added limestone


4.6 Plot of setting times of Portland cement against % added limestone


4.7 Plot of strength development of Portland cement against

xv

% added limestone 83

4.8 Effect of added limestone on strength of cement 83

ABSTRACT

Clinker, gypsum and limestone were obtained from an indigenous cement manufacturing

company. The clinker and gypsum were ground together to produce ordinary Portland cement

(OPC) which served as reference cement. Limestone composite Portland cements containing

5, 10, 15, 20, 25 and 30 % limestone were prepared by adding limestone to the OPC. Two

foreign and two local brands of cement were purchased from the local market in Gboko,

Benue state. The cement samples were subjected to chemical and physical tests using standard

methods of analyses. Data were analysed using SPSS version 18 to compare the experimental,

market and standard (OPC) cements. Analyses of clinker showed the following %

composition: Silicon dioxide (20.23), alumina (6.29), ferrite (3.30), lime (65.48), sulphite

(0.79), loss on ignition (2.17), free lime (0.87). The litre weight was 1274g/L. Percentage

compositions of limestone were: total carbonate (91.08), lime (51.00) and loss on ignition

(40.21). Percentage compositions of gypsum were: sulphite (42.31) and purity (90.97).

Analysis of OPC showed the following percentages: silicon dioxide (17.75), alumina (6.09),

ferrite (3.41), lime (64.62), sulphite (2.72), loss on ignition (1.50), free lime (0.88), particle

size [45 micron (21.73), 90 micron (3.33) and 180 microns (1.33)], Blaine 297m2/kg;

soundness 1.67 mm; consistency 27.97, Vicat plunger penetration 5.70 mm; initial setting time

107.33 mins; final setting time 180.67 mins; 2 days strength 26.27 MPa; 7days strength 31.07

MPa and 28 days strength 36.20 MPa. Analysis of various limestone composite Portland

cement (%) were: silicon dioxide (17.00-17.64), alumina (5.99-6.08), ferrite (3.12-3.37), lime

(64.70-64.97), sulphite (2.27-2.68), loss on ignition (3.69-13.25), free lime (0.55-0.83),

particle size [45 micron (19.87-30.33), 90 micron (2.13-5.93) and 180 microns (0.53-2.40)],

Blaine (316-413) m2/kg, soundness (0.67-1.17) mm, consistency (24.80-27.60), Vicat plunger

penetration (5.33-6.00) mm; initial setting time (115.33-126.00) mins, final setting time

(183.00-229.33) mins, 2 days strength (17.28-25.00) MPa, 7 days strength (22.68-32.07) MPa

and 28 days strength (28.47-34.77) MPa. Analysis of brands of Portland cement (%) showed:

silicon dioxide (17.69-17.93), alumina (5.99-6.06), ferrite (3.25-3.30), lime (64.45-64.85),

sulphite (2.70-3.46), loss on ignition (3.32-6.60), free lime (0.36-1.73), particle size [90

microns (0.93-7.07) and 180 microns (0.00-0.80)], Blaine (283-394) m2/kg, soundness (0.67-

1.17) mm, consistency (26.27-28.90), Vicat plunger penetration (5.33-6.00) mm, initial setting

time (105.33-125.33) mins, final setting time (184.67-191.33) mins, 28 days strength (41.62-

50.56) MPa. Statistical analysis revealed that OPC, limestone composite Portland cement

containing 5-15 % added limestone and market sampled Portland cement brands all satisfied

NIS specifications (28 days strength ≥32.5 MPa, soundness ≤ 10 mm, sulphite ≤ 3.5 %,

plunger penetration 5-7 mm and initial setting time ≥ 75 mins) for Portland cement. This

indicates that limestone composite cement containing not more than 15 % added limestone

could be used for construction work without fear of failure or building collapse.

xvi

1

CHAPTER ONE

1.0 INTRODUCTION

1.1The Nature of Cement

Cement is the widest known building material in the civil industry. Cement is a substance

used to bind solid fragments or masses of solid matter together to form one whole substance

for the purpose of building, for example in making building blocks and concrete. By this

definition the term cement embraces a large number of different substances having adhesive

property. However popular use of the term cement has been restricted to adhesives used to

bind stones, bricks, tiles etc in the construction of buildings and other civil works1. These are

largely adhesives consisting of a mixture of compounds of lime as their principal

constituents. These are termed calcareous cements1. Cements of this kind are finely ground

powders which when mixed with water set into a hard mass. Setting and hardening result

from hydration, which is a chemical combination of the cement compounds with water. As a

result of their hydrating properties, constructional cements, which set and harden in the

presence of water, are called hydraulic cements. Among these is Portland cement 2. Cement is

applied as mortar and/or concrete. Mortar is used in binding bricks, blocks and stones in

walls. Concrete is used for large variety of constructional purposes which include road

construction and dams. Cement application as mortar or as concrete has helped in solving the

durability needs of infrastructure such as houses and offices, roads, bridges etc.

1.2 World Cement Production and Consumption

The need for modern housing has generally increased the demand for cement. Consequently,

cement production has grown exponentially over the years. In 2002, the world production of

hydraulic Portland cement was 1,800 million metric tons. The three top producers were China

with 704 million tons, India, with 100, and United States of America, with 91 million metric

tons. These three countries produce about half the world’s total production 3. In 2005, China

led with 43.46 percent followed by India producing 6.38 percent, then United States of

America with 4.38 percent. For the past 18 years, China has consistently produced more

cement than any other country in the world 3. This explains why China has the highest carbon

dioxide emission in the world. In 2006 it was established that China manufactured 1.24

billion tons of cement which was 44 percent of the world total cement production 5. Demand

2

for cement in China is expected to advance by 5.4 percent annually and this exceeded 1

billion tons in 2008. Cement consumption in China is expected to hit

44 percent of global demand and China will remain the world’s largest national consumer of

cement by a large margin 6.

As the demand for cement increased over the years different types of Portland cement

evolved in order to meet the demand. Type 1 or ordinary Portland cement (OPC) is the best

cement. It has the highest strength, but it is expensive. Therefore cheaper cements of less

strength or quality have been produced. These cements differ in their properties due to the

various supplementary materials added to the raw materials, namely; limestone and gypsum.

Examples of these supplementary materials include fly ash, pozzolana, slag, condensed silica

fume, volcanic ash, rice husk ash, and limestone 7. Countries such as Britain, Spain, France

and Argentina based on research results, have set standards for inclusion of supplementary

materials like limestone and other pozzolanic admixtures to OPC 7. For example British

Standards (BS 882) allows up to 15 % inclusion of limestone to OPC 8.

1.3 Cement Production in Nigeria

In Nigeria, The Federal Ministry of Commerce and Industry estimates that the effective

demand is around 20 million tons. According to Ian Furnivall and Tunde Abidoye 4, acute

infrastructure deficit and significant demand for housing has driven domestic production

volumes up to 25 % over the last four years 4. However the Federal government in her effort

to improve the availability of the commodity in 2010 banned the importation of cement into

the country in order to encourage local production and existing companies are increasing

their capacities. Dangote Cement Company formerly Benue Cement Company in Benue State

for instance, increased its capacity from 0.45 million to 2 million per annum in 2008 and now

2.9 to 3 million. In 2010 UNICEM added 2.5 million tons of its capacity to local capacity

while Lafarge WAPCO added 2.2 million tons in 2011. With these improved capacities the

quantity of cement in the market has improved.

1.4 Limestone Composite Cement

Limestone composite cement is widely used in Europe, in fact according to Cement Bureau,

the production of limestone composite cement in Europe increased by 7% between 2000 and

2010 9. This is partly due to its high durability, economic and environmental advantages. In

some European countries like Britain and Germany, up to 35 % limestone addition to

3

ordinary Portland cement has been reported 10

. It was also reported that the inclusion of up to

5 % limestone does not affect properties of Portland cement markedly 11

.

Limestone blended cements present different properties compared to ordinary Portland

cement and it is necessary to investigate their physical and mechanical properties with

varying limestone contents. The inclusion of limestone as an additive to boost quantity in

Nigeria started around 2005. Benue Cement Company started adding it in 2006.

1.5 Statement of the problem

In recent years, there have been many cases of collapsed buildings in Nigeria. There exists

the feat that the collapse of buildings might have much to do with quality of the cement and

other building materials, as well as integrity. The use of cementitious materials as additive to

Portland cement could lead to poor quality depending on the amount added. Apart from

Nigerian manufactured cement, imported cement could also contain much of additives, with

lowered quality. Cement bags are not adequately labeled to show the actual composition and

content of the cement, whether it is OPC or blended cement. Meanwhile the price of a 50 Kg

bag of Portland cement has risen steadily in recent years. For instance a bag of Nigerian made

cement rose from N1,200.00 in 2006 to N1,500.00 in 2011, and N1,950.00 in 2012. In

Ghana, it was reported that the price of 50 Kg Portland cement doubles every four years 12

.

The need to explore suitable supplementary cementitious materials that could replace a

significant portion of clinker in OPC without compromising its quality could be a solution to

the rising cost of cement.

Limestone has been reported by some authors like Guemmadi et al 10

and Tsivilis et al 13

as a

suitable material which can be used to replace portions of clinker in OPC exist in large

reserves in Nigeria. These deposits include: Nkalagu in Ebonyi State, Tsekucha in Benue

State, Mfamosin near Calabar and Ashaka near Gombe. There is also limestone deposit at

Kalambaina near Sokoto. Since cement quality is affected by the variability of composition of

the raw materials, it is expected that a study of the use of our local limestone as additive in

cement making may solve the problem of increasing cement prices in Nigeria.

1.6 Significance of the Study

The duration of any block or concrete structure is almost entirely dependent on the quality of

the cement used. As a result, an evaluation of the effect of addition of the locally sourced

limestone on the strength of the cement and in order to achieve high quality, the optimum

4

limestone content must be determined for production of high quality composite Portland

cement in Nigeria.

The present study is therefore an attempt to optimize limestone addition to Portland cement to

produce limestone composite Portland cement (LCPC) of comparable strength as OPC.

1.7 Aims and Objectives of the Study

There are no published data on the effect of limestone addition on the properties of Portland

cement produced in Nigeria. Using the available raw materials, it is expected that since the

qualities of limestone differ, its effect as additive in cement will differ depending on source.

Obviously there must be a balance between quality and economics in the use of limestone as

additive in cement production. Therefore the objectives of this study are to: (i) prepare

laboratory cement; prepare OPC and limestone composite cements (LCCs) having 5- 30 %

limestone content. (ii) Carry out physical and chemical analyses of the laboratory cements

(OPC and LCPC) and compare the qualities, (iii) determine the optimum limestone content

for high quality LCC, (iv) carry out physical and chemical analyses of some cement brands

available in the Nigerian market, and evaluate their qualities and (v) compare their qualities

with those of the laboratory cements (OPC and LCCs) with the aim of determining optimum

limestone addition without harm to quality of the cement.

1.8 Scope of the Study

Reports on the effect of limestone addition on properties of ordinary Portland cement have

been made by Guemadi et al 10

and Tsivilis et al 13

. Their studies showed that limestone could

be a suitable material which can be used in the production of blended Portland cement. There

is currently no published data on the effect of indigenously sourced limestone on strength of

ordinary Portland cement produced in Nigeria.

The present study however was limited to the assessment of the effects of varying

percentages of added limestone (0, 5, 10,15,20,25 &30) on the chemical and physical

properties of locally produced ordinary Portland cement. The chemical properties include (i)

SiO2 (ii) Al2O3 (iii) Fe2O3 (vi) CaO (v) SO3 (vi) loss on ignition (LOI) (vii) free lime. The

physical effects include (i) fineness or particle size of cement (ii) soundness (iii) setting time

and consistency of cement paste and (iv) strength development at 2, 7 and 28 days of water

curing.

5

Comparative study of four brands of Portland cement marketed in Nigeria with OPC and the

various LCCs was limited to their physical and chemical properties.

6

CHAPTER TWO

2.0 LITERATURE REVIEW

2.1 History of Cement Production

The history of cements dates back to the era of ancient Greece and Roman civilizations. The

materials used were lime and volcanic ash. These materials have hydraulicity by slowly

reacting in the presence of water to form a hard mass. This formed the cementing material of

the Roman mortars and concretes of over 2000 years ago and of subsequent construction

work in Western Europe14

. Volcanic ash mined near the city of Pozzouli was particularly rich

in aluminosilicates and this gave rise to pozzolana cement of Roman era 14

.

Portland cement is a hydraulic lime that was first developed by John Smeaton in 1756 when

he was to erect the Eddystone lighthouse off the coast of Plymouth in England. The building

stood for 126 years before its replacement 14

. Other men noted for the development of

cements about that time include L.J. Vicat and Lesage in France and Joseph Parker and James

Frost in England. They experimented with materials obtained by burning nodules of clay and

limestone. These are natural cements and because they were mixed by nature, their properties

varied as widely as the natural resources from which they were made 2,14

. This class of

cement is used for the making of burnt bricks and erection of mud houses.

2.1.1 Production of Portland Cement

In 1824, Joseph Aspdin of Leeds, England, obtained a patent on a hydraulic cement he called

Portland cement because it had the colour of a stone quarried on the Isle of Portland off the

British coast. His method involved pulverizing and burning of a proportionate mixture of

lime and clay into clinker, which was ground into the product known as Portland cement 14

.

This cement had greater strength property than the natural cement produced by John Smeaton

which was made by plain crushed limestone 12

. Portland cement today as it was in Aspdin’s

day, is a predetermined and carefully proportioned chemical combination of calcium, silicon,

iron and aluminum. It is the first true Portland cement and since then has remained the

popular or dominant type of cement used in concrete making and general civil works.

7

2.1.2 Sources of Raw Materials for Cement Manufacture in Nigeria

Minerals of natural origin as well as industrial products can be used for the production of

cement. Materials for this purpose are compounds containing the main components of

cement: lime (CaO), silica (SiO2), Alumina (Al2O3) and ferrite (Fe2O3). Usually these

compounds are found in the needed proportions in more than one material. The practice in

cement manufacture is usually to mix a high lime component with a lower lime component

which contains more silica, alumina and iron oxide. This component of lower lime content is

largely clay or marl material. Therefore the two main components are generally limestone

(high lime) and clay or marl 15

.

Sources of lime are wide spread in nature. It is the product of decomposition of calcium

carbonate sourced from limestone. Calcium carbonate of all geological formations qualifies

for the production of Portland cement 15

.

In Nigeria there are substantial number of large limestone deposits grouped into Precambrian

limestones, marbles and dolomites. There are also cretaceous and tertiary limestones, as well

as concretionary calcretes known in northern Nigeria as Jigilin. Precambrian marble and

dolomitic marbles occur near Igbeti in western Nigeria. There are deposits with extensive low

magnesium to the west of Lokoja suitable for cement and steel companies. Paleocene

limestones occur in the coastal area close to Lagos which includes deposits at Ewekoro and

Shagamu. Cretaceous limestones occur at the coastal Basin and Benue trough. These include

limestone beds at Nkalagu in Ebonyi State, Tsekucha in Benue State, Mfamosin near Calabar

where United Cement plc is sited and Gombe- Ashaka near Gombe where Ashaka Cement

Company is built. There is also limestone deposit at Kalambaina near Sokoto. A geological

survey of limestone deposits in Nigeria estimated that a reserve of 100 million tons of

limestone exists in Kalambaina alone 16

. Limestone abounds in Nigeria more than in any

other West African country. It is estimated at 2.23 trillion tons 17

.

Gypsum has not been found in commercial quantity in Nigeria. The nearest potential source

of gypsum is found in Mali Republic in millions of tons. All except the cement plant at

Okpilla in Edo State, which uses marble, are sited close to limestone deposits. The cement

factory at D'Onigholo in Benin Republic is jointly owned by Benin (52 %) and Nigeria (46

%). It is located on the Ewekoro limestone deposit which extends from Ogun State in Nigeria

to as far as Ghana.

8

Limestone at Mfamosing, near Calabar, is the largest and purest deposit in Nigeria. It is about

50 m thick at the quarry site. West of Calabar, another carbonate body occurs in the

subsurface that is 450 m thick. The Calabar flank is the main carbonate province in Nigeria,

with well developed tropical karst and caves. The Mfamosing limestone has over 97 percent

total carbonate 18

.

2.2 Chemical composition of Raw Materials for Cement Production

2.2.1 Limestone

Limestones of the purest grade are Calcite and Aragonite. Calcite crystallizes hexagonally

and Aragonite is rhombic. Calcite however is not profitable to use for cement production

because it is marble. The most common forms of calcium carbonate most similar to marble

are limestone and chalk. Limestone is predominantly fine grained. Its hardness depends on its

geological age. Usually, limestones of older formation are harder. The purest of limestones

are whitish and they contain higher carbonate content. In the presence of clay substance or

iron compounds the colour is influenced 15

. Table 2.1 shows the typical physical properties of

limestone.

Table 2.1 Physical properties of limestone 15

Specific gravity

Refractive index

Moh hardness

Decomposition temperature

Brightness

Density

Solubility in acid

2.91

1.51

3 - 4

600 – 900 degrees Celcius

70 - 80

2.5 - 2.65 kg/m3

High

Chalk is a sedimentary rock which was formed during the cretaceous period. Geologically it

is younger than limestone and it is softer. This property makes it a raw material for wet

process of cement manufacture. It does not require blasting for its extraction so crushing is

omitted. In some deposits its carbonate content is 98 - 99 % with small admixtures of silica,

alumina and magnesium carbonate 1, 15

.

9

Marl is a limestone that contains silica, clay and iron oxide. Marls are sedimentary rocks

generated by simultaneous sedimentation of calcium carbonate and clay substance. It is a

softer limestone due to its higher clay content. Its colour depends on the clay substance and

ranges from yellow to grayish black. They contain lime and clay component in an already

homogenized condition. This makes them suitable for cement manufacture 15, 19

.

Calcareous marl usually has a chemical composition like a carefully prehomogenized raw

mix of Portland cement. This type of limestone is used for making of natural cement.

However deposits of such raw materials are not common 1.

The quantitative proportions of lime and clay components in cement raw materials are a basis

for their classification. The following classification is established in Table 2.2

Table 2.2 Classification of limestone deposits

Limestone class Percentage total carbonate

High grade limestone

Marlaceous limestone

Calcareous marl

Marl

Clay marl

Marlaceous clay

Clay

96 - 100

90 - 96

75 - 90

40 - 75

10 - 40

4 - 10

0 – 4

In order to achieve a raw mix of moderate lime and clay component, a measured proportion

of the various grades are chosen for the purpose of Portland cement manufacture 15, 19, 20

.

Table 2.3 below shows chemical composition of some samples of lime stone and marl used

for the manufacture of Portland cement. The figures were obtained with the aid of X-ray

fractionometer (XRF)

10

Table 2.3 Chemical composition of some limestone samples

2.2.2 Clays

Clays are another raw material of importance in cement production. They are formed by the

weathering of alkali and alkali earth containing aluminum silicates and their chemical

conversion products, feldspar and mica. The main component of clays is formed from

hydrous aluminum silicates. Based on these, clays are grouped as kaolin, montmorillonite,

and alkali bearing clays 15

. Components of clay samples are shown in Table 2.4.

Table 2.4 Clay members showing variation in components15

Clay groups Clay minerals Components

Kaolin Kaolinite Al2O3.2SiO2.2H2O

Dickite Al2O3.2SiO2.2H2O

Nacrite Al2O3.2SiO2.2H2O

Halloysite Al2O3.2SiO2.2H2O

Montmorillonite Montmorillonite Al2O3.4SiO2.nH2O

Beidellite Al2O3.3SiO2.nH2O

Nontronite (Al,Fe)2O3.3SiO2.nH2O

Saponite 2MgO.3SiO2.nH2O

Alkali clays Illite K2O.MgO.Al2O3.SiO2.H2O

Sample 1 2 3 4 5

Component

%

limestone limestone limestone marl marl

SiO2 3.76 4.91 4.74 27.98 33.20

Al2O3 1.10 1.28 2.00 10.87 8.22

Fe2O3 0.66 0.66 0.36 3.08 4.90

CaO 52.46 51.55 51.30 30.12 27.30

MgO 1.23 0.63 0.30 1.95 1.02

K2O 0.18 0.01 0.16 0.20 0.12

Na2O 0.22 0.01 0.28 0.33 0.18

SO3 0.01 0.21 0.01 0.70 0.37

Loss on

ignition

40.38 40.76 40.86 24.68 24.59

11

Minerals of kaolin group differ in content of SiO2 as well as by crystallographic structure and

optical properties. Kaolinites are the purest of the Kaolin group. Textually, clays are fine

grained; usually under 2 microns in diameter 21

. Table 2.5 shows the physical properties of

clay minerals.

Table 2.5 Physical properties of clay minerals 22

Minerals Specific surface (m2/g) Specific gravity g/cm

3

Kaolin Approx.15 2.60 - 2.68

Halloysite Approx.43 2.0 - 2.20

Illite Approx.100 2.76 - 3.00

Montmorillonite Approx.800 -

Chemically clay varies from those close to pure clay to those containing iron hydroxide, iron

sulphide, sand, calcium carbonate e.t.c. Iron hydroxide is the principal colouring agent in

clays. Also organic matter may give the clay different colours. Clay with no impurities is

white 15

. Chemical composition of clay samples used in the manufacture of Portland cement

is shown Table 2.6

Table 2.6 Chemical composition of clay samples

Component % Clay 1 Clay 2 Clay 3

SiO2 67.29 62.56 52.30

Al2O3 8.97 15.77 24.70

Fe2O3 4.28 4.47 6.10

CaO 7.27 4.80 4.40

MgO 1.97 1.38 0.10

SO3 0.32 0.02 1.10

K2O+Na2O 2.71 2.35 0.80

In almost every raw mix pile, there exists shortage of one or more of the essential chemical

components needed. To make up for these components, additives are used. Thus for

completion of silica content, materials like sand, high silica clay, diatomite and other known

siliceous materials are used as corrective ingredients. Materials such as pyrite cinders, iron

12

ore, laterite are rich in iron oxide and are suitably used to correct iron deficiency 15, 21

. Table

2.7 contains the chemical composition of some corrective additives used in the production of

Portland cement

Table 2.7 Chemical composition of corrective additives used in the production of Portland

cement 21

Component % Diatomite Bauxite Pyrite

cinders

Iron ore Blast

furnace

flue dust

Flue

dust

Sand

SiO2 77.0 19.21 15.8 24.25 11.52 31.62 99.2

Al2O3 9.6

51.03 9.0 6.00 9.23 8.5 -

Fe2O3 13.16 69.5 55.60 61.50 6.75 0.50

CaO 0.3 3.0 0.81 1.50 5.00 46.32 -

MgO 0.9 0.15 1.10 4.25 1.55 3.56 -

SO3 - - 1.02 0.45 1.58 2.75 -

K2O+Na2O 1.5 - - - - 2.65 -

2.2.3 Minor and Trace Components

There are other components whose quantities in cement are limited either by standards or by

manufacturing experience. These include:

2.2.3.1 Magnesia, MgO

This is combined up to 2 percent by weight with the main clinker minerals, beyond that

amount it manifests as periclase (free MgO). Periclase reacts with water to form magnesium

hydroxide

MgO + H2O → Mg(OH)2

This reaction is a slow one and because of this property, Mg(OH)2 occupies a larger volume

than MgO and is formed on the same spot where the periclase is located. An effect of their

sharing a common spot in the clinker space usually causes a splitting of the hardened cement

paste resulting in cracking or magnesia expansion. Magnesia appears in limestone mainly as

dolomite (CaCO3. MgCO3). High values of magnesia exist in blast furnace as seen in the

Table 2.7. Therefore when selecting such slags for replacement of clay, care is taken to keep

magnesia content in the clinker within permissible limits 21

.

13

2.2.3.2 Alkalis

Oxides of potassium and sodium originate from clay and marl, where these compounds are

present in feldspar, mica and illite particles. In Europe potassium oxide is dominant. In other

areas like in the United States of America sodium oxide dominates. To avoid alkali expansion

in cements low alkali materials are used. From experience, Total alkalis (K2O + Na2O) are

not allowed to exceed 0.6 percent in clinker 21

.

2.2.3.3 Sulphur

Sulphur appears predominantly as sulphide in pyrites and marcasite in almost all cement raw

materials. An investigation of more than 90 German limestone deposits showed a total

sulphhur content of maximum 0.16 percent and an examination of 67 clay samples showed an

average of 0.22 percent sulphur. The presence of alkalis in excess of amount which is already

combined with sulphur contained in the raw mix allows the use of fuels rich in sulphur like

low pour fuel oil (LPFO) without emitting substantial amount of SO2 when the raw material

undergoes thermal treatment in the kiln. The alkali sulphate combined by the clinker is of

advantage for the early strength development of cement 21

.

2.2.3.4 Phosphorus

The phosphorus content of commonly used cement raw materials is very low. In Germany for

instance, the phosphorus pentoxide (P2O5) in clinker is within limits of 0.05 and 0.25 percent

21.

Certain industrial waste products containing one or more of the four basic oxides may be

regarded as raw materials. For example, blast furnace slag from steel works 15, 20

. In fact

using industrial by products to replace natural raw material is key element in achieving

sustainable economic growth.

Gypsum is also an essential raw material used in the production of cement. About 5 percent

added to burned cement clinker during grinding controls setting time of the cement. Gypsum

contains natural anhydrite such as calcium sulphate as dihydrate, calcium sulphate anhydrate

and calcium carbonate or clay as impurities 20

.

Gypsiferous shales are found in the upper cretaceous Dukarnaje formation and the Paleocene

Dange formation in Sokoto State of Nigeria. The abundance of gypsiferous shales at these

14

locations is estimated at 1.46 million tons. Other deposits are found in Nafada, Gombe State,

at Fika in Yobe State and at Guyuk, Adamawa State 23

.

2.3 Types of Portland cement

Different types of Portland cement with different physical and chemical properties are

manufactured for specific purposes. The American Society for Testing and Materials (ASTM

C150) recognizes five types of Portland cement 20

:

2.3.1 Type 1

This is ordinary Portland cement (OPC) which is made of clinker and gypsum alone. It is the

best cement because of its strength development. It is mostly the widely used general

purpose. It is used where cement or concrete is not subject normal to specific exposures, such

as sulphate attack from soil or water, or to a temperature rise due to heat generated by

hydration. Its uses include pavements and sidewalks, reinforced concrete buildings, bridges,

railway structures, tanks, reservoirs, culverts, sewers, water pipes and masonry works. All

Nigerian cement companies produce this type of cement 20, 24

.

2.3.2 Type 2

This is also general purpose Portland cement. It differs from Type 1 due to the fact that

additives (other than gypsum) are included in its production. Examples of such additives

include limestone and pozollan. These additives do not alter the quality markedly, only that a

little of the cement portion is reduced. It is used where precaution against moderate sulphate

is important, as in drainage structures, where sulphate concentrations in ground waters are

higher than normal, but not severe. It minimizes temperature rise when concrete is placed in

warm weather because it generates less heat at slower rate than Type 1. With its moderate

heat of hydration, Type 2 cements can be used in structures of considerable mass such as

abutments and piers, and heavy retaining walls. Type 2 cements are sometimes referred to as

blended cements 20, 25

.

2.3.3 Type 3

This is ordinary Portland cements containing higher lime to silica ratio than Type 1 produced

to achieve rapid hardening. They contain higher tricalcium silicate which confers higher early

strength. Type 3 cements are used in concrete works for economic advantages to achieve

quick removal of form work or rapid turn- around of precast concrete units in a mould. Roads

15

constructed using this type of cement are put to use earlier than those constructed using

Type1 cement 20

.

2.3.4 Type 4

These are ordinary Portland cements produced to achieve lower heat due to lower tricalcium

silicate and tricalcium aluminate content. These cause a lower heat of hydration. The

tricalcium aluminate is lowered with addition of iron oxide which consequently increases

tetracalcium aluminoferrite. This is a condition that reduces heat evolution. This class of

cements is intended for mass structures like dam works when temperature rise is great on

continuous pour of cement. In such works, if temperature is not minimized, it will cause large

cracks in the structure, rendering it weak 20

.

2.3.5 Type 5

These are sulphate resisting Portland cements required in certain aggressive construction

environments where high sulphate resistance is desired. Its application is suitable where

concrete is to be exposed to severe sulphate attack by water or soil. Such sulphates in solution

usually attack the hydration product of tricalciumaluminate. The sulphate resistance is

achieved by reducing tricalciumaluminate by increasing tetracalcium aluminoferrite through

iron oxide addition. Tricalcium aluminate content, generally 5 percent or less, is required

when high sulphate resistance is needed 25

. Type 5 Portland cements are of lower tricalcium

aluminate 20

. Table 2.8 shows the sulphate concentrations requiring the use of Type 5

Portland cement 26

.

Table 2.8 Attack on concrete by soils and waters containing various sulphate concentrations 26

Relative degree of

sulphate attack

Percentage water

soluble sulphate in

soil samples

Sulphate in water

samples, ppm

Cement type

Negligible 0.00 - 0.10 0 – 150 I

Positive 0.10 - 0.20 150 - 1500 II

Severe 0.20 - 2.00 1500 - 10,000 V

Very severe ≥2.00 ≥10,000 V

16

2.3.6 Other Types of Cements

2.3.6.1 Coloured Cements

There are various other special types of Portland cement manufactured under definite

specifications. Coloured cements are made by mixing suitable pigments with white or Type I

cement 2. White Portland cement for instance is made from chalk and white clay. White

cement is extensively used for visual effect in white or coloured concretes which are to be left

exposed and white or coloured mortars for masonry 20

. Some pigments used in making

coloured cement are 20

:

Iron oxide ---------------- red, yellow, brown

Manganese dioxide-----------------black, brown

Chromium oxide-------------------green

Carbon pigments-------------------black

Cobalt blue--------------------------blue

Ultramarine blue-------------------blue

2.3.6.2 Air Entrained Cements

Air entraining cements are made by the addition of organic agent that causes the entrainment

of very fine air bubbles in concrete. This increases the resistances of the concrete to freeze

thaw damage in cold climates.

2.3.6.3 Masonry Cements

Masonry cements are used primarily for mortar. They consist of a mixture of Portland cement

and ground limestone or other filler together with an air- entraining agent or a water repellent

additive. They provide cement which gives more plastic mortar than Type 1 cement 1, 20

.

2.3.6.4 Water Proof Cements

Water proof cement is a water repelling Portland cement. It contains water repelling agent

like calcium stearate. The aim is to reduce water permeability of concrete 2, 20

.

17

2.3.6.5 Hydrophobic Cements

Hydrophobic cement is obtained by grinding Portland cement clinker with film forming

substance such oleic acid in order to reduce the rate of deterioration when the cement is

stored under unfavourable conditions or transported along distances20

.

2.3.6.6 Oil Well Cements

Oil well cements are used for cementing work in the drilling of oil wells where they are

subject to high temperatures and pressures. They usually consist of type1 cement made

coarser than usual mixed with organic retarders such as starch and sugar to prevent rapid

setting 15, 20

.

2.3.6.7 Slag Cements

The granulated slag made by rapid chilling of suitable molten slags from blast furnaces is

another group of constructional cements. Slag cement is a mixture of Type 1 cement and

granulated slag containing up to 65 percent slag. Properties of these slag cements are similar

to those of Portland cement but they have lower lime content and higher silica and alumina

content. Those with the higher slag content have increased resistance to chemical attack 2.

The super sulphated cement is another type of slag cement. This type contains lesser lime

than blast furnace cement. It contains up to 15 percent hard burned gypsum or anhydrite

(natural anhydrous calcium sulphate). The strength properties are similar to those of Portland

cement but it has an increased resistance to many forms of chemical attack 2. Slag based

cements can be used for general concrete construction, having the advantage of possible low

cost since their major raw material is a bye product of iron and steel industry. In addition,

such cements can be used in projects where low heat of hydration is essential 20

.

2.3.6.8 High Alumina Cements

High alumina cements are manufactured by fusing at 1500 to 1600 oC a mixture of limestone

and bauxite which contains iron oxide, silica, magnesia and other impurities in an electric

furnace or in a rotary kiln. They have several properties such as high early strength which can

compare to that at 28 days in Portland cement within 24 to 48 hours, good refractoriness and

good resistance to sulphate attacks from sea and sulphate bearing water. However, their

limitation is that higher temperatures tend to reduce their strength in the presence of moisture.

High alumina cements are used where high early strength is required and moderate

18

temperatures are desired like in refractory linings for furnaces. A white form of the cement

has excellent refractory properties 2, 20

.

2.4 Composition of Portland Cement

Ordinary Portland cement consists of clinker and gypsum ground together. Clinker consists

essentially of a mixture of four crystalline compounds of calcium. Two have silica, one has

alumina and one has both alumina and ferric oxide. Thus clinker has constituents, namely;

lime, silica, alumina and ferric oxide. There are also several minor constituents, including

alkalis, magnesia and sulphur, which together amount to between 2 and 6 % by weight. In an

abbreviated notation, differing from the normal atomic symbols, these compounds are

assigned the following symbols: C3S (tricalcium silicate), C2S (dicalcium silicate), C3A

(tricalcium aluminate) and C4AF (tetracalcium aluminoferrite). C stands for lime, S stands for

silica, A stands for alumina and F for ferrite. Small amounts of uncombined lime and

magnesia also are present, along with alkalis and minor amounts of other elements.

The most important hydraulic constituents are C2S and C3S. C3S hydrates with moderate of

heat of hydration; the rate of hydration is controlled by the rate of diffusion of water through

the layer of calcium silicate hydrate forming on each particle of hydrating C3S. Thus,

hydration slows as thickness of hydrate layer increases. This hydration reaction contributes to

early strength of concrete within a week and beyond.

C2S hydrates more slowly and contributes more to late strength of concrete at 28 days and

beyond in conjunction with residual unhydrated C3S.

C3A hydrates very rapidly and violently as well. This is responsible for very quick setting but

contributes little to strength. This explains the quick setting of high alumina cements like the

early Roman cements. C3A and C4AF contribute little to strength and structure of concretes.

2.5 Estimation of Clinker Composition

The composition of clinker minerals was calculated from chemical analysis by Bogue 27

. This

method however, could only estimate the quantity or bulk of the minerals, leaving out the

actual mineralogical composition. Such results obtained by this method were known as

potential clinker composition. The ASTM cement standards of the United States of America

is based on Bogue’s calculation 28

. Bogue estimated that C3S contains 73.69 % CaO and

19

26.31% SiO2, C2S contains 65.12 % CaO and 34.88 % SiO2. In C3A is contained 62.27 %

CaO and 37.73 % SiO2 while C4AF 46.16 % CaO, 20.98 % Al2O3 and 32.86 % Fe2O3.

Bogue assumed that in every mixture of the four compounds, CaO was the sum of all lime

percentages as shown

CaO = 0.7369 C3S+ 0.6512 C2S+ 0.6227 C3A+0.4616 C4AF 1

With similar analogy for the other oxides and solving for the potential clinker compositions

C3S= 4.071 CaO- 7.600 SiO2-6.718 Al2O3- 1.430 Fe2O3 2

C2S= 8.602 SiO2 + 5.068 Al2O3 -3.071 CaO+ 1.078 Fe2O3 3

C3A= 2.650 Al2O3+ 1.692 Fe2O3 4

C4AF= 3.043 Fe2O3 5

As a comparative analysis, Brown determined microscopically the mineral content of various

clinker samples 29

. The results obtained as compared with Bogue’s method are shown in

Table 2.9. Nevertheless practical experience still supports the wide spread usage of Bogue’s

method

Table 2.9 Clinker mineral content estimated by Bogue’s method and microscopic analysis 29

C3S C2S C3A C4AF

M B M B M B M B

1 57.7 55.1 12.8 19.4 5.4 12.6 2.8 7.3

2 60.3 48.9 16.9 26.3 6.3 14.0 3.9 6.6

3 70.2 63.5 4.2 12.4 10.0 11.2 4.3 7.9

4 39.6 46.7 44.5 36.5 1.0 4.0 6.3 9.8

M= Microscopic method, B= Bogue’s method

2.6 Setting of Portland Cement

Two processes occur simultaneously that lead to setting of Portland cement:

1 the calcium sulphate hydrate in gypsum is dissolved in water to form an alkaline

calcium sulphate solution,

2 the C3A begins its violent reaction with water to form calcium aluminate hydrate

represented as C3AH13

20

During these processes an intermediate, ettringite (calcium aluminate trisulphate hydrate) is

formed. As the pH of the system increases towards alkalinity, ettringite becomes insoluble,

and gets deposited on the surface of the hydrating C3A, providing a layer slowing the rapid

hydration. Since the rate of reaction is determined by the rate of diffusion of water through

the ettringite layer, rapid setting is controlled 1, 15

.

These reactions are progressive and so mortar becomes stiffer with time, leading to a rigid

framework within which further hydration, particularly of the C2S gives hardening and

progressive strength development. The highest heat of hydration is shown by C3A, followed

in descending order by C3S, C4AF and C2S. Table 2.10 shows the theoretical heats of

hydration of clinker constituents.

Table 2.10 Theoretical heats of hydration of clinker constituents 30

Constituents Heat of Hydration (kJ/kg)

C3S 222

C2S 42

C3A 1556

C4AF 494

2.7 Manufacture of Portland Cement

The manufacture of Portland cement undergoes three stages: raw material pre-blending, heat

treatment and clinker grinding. These stages describe the dry process of cement manufacture,

which was developed after the wet process had been long in use. Today dry process is more

popular and is the process applied in Nigeria 20

.

2.7.1 Pre-blending of Raw Materials

In the pre blending stage, limestone and clay in the dry state are sourced from the quarry. A

number of limestone phases (limestone of varying qualities or lime content) are worked

simultaneously or in rotation with stockpiling to produce a blend of desired lime content. The

winning of argillaceous (clay) materials is similarly controlled. By controlling the blending of

both limestone and clay, a first approximation to the required chemical composition is made.

The limestone phases are drilled ahead of crushing and chemical analysis of cores then

21

followed by blending proportion. This raw material (raw mix) preparation is done

arithmetically. The purpose of calculating the composition of the raw mix is to determine the

quantitative proportions of the raw components in order to give the clinker the desired

mineralogical composition. Methods of calculation include: allegation alternate method,

hydraulic module and lime saturation factor.

The most used is the allegation alternate method which shows the ratio of limestone to clay to

be used. In this case, lime is the only component under consideration. Hydraulic module is

applied when more than one component is considered with the hydraulic module selected for

the clinker. This means that the modules of both raw material and clinker are equated since it

is expected that the raw material must share module with clinker to achieve desired clinker

quality. Thus

HM= C/ S+A+F for clinker ………6

HM= C rm/ Srm +A rm+ Frm for raw mix ………7

Where HM is hydraulic module. C, S, A and F are symbols for lime, silica, alumina then

Ferrite.

Since HM for clinker and raw mix are equal;

HM= C/ S+A+F= C rm/ Srm +A rm+ Frm ………8

This method assumes that x parts of the first raw material are apportioned to one part of the

second raw material. Under this assumption, the quantities of the particular raw material

components can be calculated as follows:

Crm=xC1+C2/x+1 ………9

Srm= xS1+S2/ x+1 ………10

Arm=xA1+A2/x+1 ..……11

Frm= xF1+F2/x+1 ………12

Inserting the values of Crm, Srm, Frm and Arm into the hydraulic module formula, we get;

HM= (XC1+C2/X+1)/ (XS1+S2/X+1) + (XA1+A2/X+1) + (XF1+F2/X+1) …….. 13

22

The basis for calculation is the chemical composition of the raw materials. Since the oxides

are known, the only remaining unknown is X. After transforming the equation the value of X

becomes

X=HM (S2+A2+F2)-C2/C1-HM (S1+A1+F1) ………14

This means X parts of limestone with one part of another component is required to achieve

clinker of a desired HM.

The crushed material is laid in thin layers on long stockpiles. As crushing goes on samples

are taken and analysed to determine adherence to planned stockpiling of the raw material.

This reduces chemical variation during reclamation to a minimum for minimum usage of

corrective additives. The stockpiled raw mix is recovered and ground to fine powder to be fed

into the kiln tube as kiln feed.

2.7.2 Heat Treatment

Reactions and temperatures in rotary kilns are strictly checked in clinkerization. The basic

steps are (i) evaporating off any water,(ii) decarbonization of calcium carbonate at

temperatures up to 1000 0C, (iii) heating the decarbonated material long enough for cement

compounds to form between 1300 – 1500 oC, according to its composition and fineness and

(iv) cooling the resulting clinker.

Through a temperature profile from 100 0C to above 1280

0C different reactions take place as

follows:

100 0C evapouration of free water which is endothermic

500 0C and above endothermic dehydroxylation of clay minerals

900 0C and above exothermic crystallization of products of clay and decomposition of

calcium carbonate.

CaCO3 → CaO + CO2

CaO + Al2O3 → CaO.Al2O3

900-1200 0C lime reacts with aluminosilicates which are the dehydroxylation products of

clay. This is an exothermic reaction.

1250 -1280 0C this is the burning zone in the temperature profile. At

formation takes place and rates of reaction increase

phase increases to a maximum at the highest temperature. T

through crystallization from the liquid phase. C

2CaO.SiO

Above 1280 0C the cement compounds are formed signifying completion of

clinkerization. Below 12800C is the cool zone where C

3CaO.Al2O

Figure 2.1 Schematic presentation of reactions in the kiln at various temperatures

The independent effect of the raw mixes

easily understood due to the following limitations;

i. a raw meal is a multi-component system and the behavior

understood in every detail

2CaO + SiO2 → 2CaO.SiO2

this is the burning zone in the temperature profile. At this point

formation takes place and rates of reaction increases enormously as the amount of liquid

ximum at the highest temperature. This is where C

through crystallization from the liquid phase. C2S is a low temperature crystal.

2CaO.SiO2 + CaO → 3CaO.SiO2

the cement compounds are formed signifying completion of

C is the cool zone where C3A and C4AF are formed1

O3 + CaO + Fe2O3 → 4CaO.Al2O3.Fe2O3

tation of reactions in the kiln at various temperatures

The independent effect of the raw mixes chemical composition on their burnability is not

easily understood due to the following limitations;

component system and the behavior of such system is not easily

23

this point, liquid

the amount of liquid

his is where C3S is formed

the cement compounds are formed signifying completion of

1,15, 19,20,31,32

tation of reactions in the kiln at various temperatures

chemical composition on their burnability is not

such system is not easily

24

ii. the major components, mainly oxides, contain some other minerals in minor

quantities and all differ in their reactivity

iii. the mineralizing effect of some of the minor constituents cannot be predicted with

certainty in such a complex system 33

The oxides by which a clinker composition is represented usually come from the natural raw

material, made up of various compounds. For instance lime, CaO, in a raw mix is the sum

total of CaO coming from all lime bearing compounds present in the mix. Thus lime may

come from calcite, dolomite, ankerite, gypsum, phosphates, feldspars and clay compounds.

Similarly, it is estimated that half of silica in the raw mix comes from free quartz and the rest

from clay minerals like kaolinite, montmorillomite, hydromica etc which also simultaneously

supply the required alumina. Therefore, the reactivity of the raw material is determined by the

reactions of the constituent minerals which are controlled by temperature profile. The

reactions proceed over a wide range of temperature, depending on the intrinsic characteristics

of the raw materials, and any breach of concurrence of these steps leads to disturbance of the

reaction kinetics. The stages of reaction depend on the mineral form and microstructural

features of the materials.

At high temperature, calcium carbonate decomposes in accordance with the equation

CaCO3 → CaO + CO2 -42.52 Kcal

The dissociation temperature of pure calcium carbonate is 898 oC, and it is reported to vary

from 812 - 928 oC depending on grain size and solid solubility of CaO in CaCO3

37, 38.

Complete dissociation and release of free CaO are known to start from 550 oC and continue

up to as high as 1000 - 1100 oC. Such variations in the dissociation of carbonates are due to

i. forms of carbonate present,

ii. associated minerals, and

iii. degree of crystallinity and grain size of the carbonates.

As a result of these factors,

1 the dissociation of carbonates and reactivity of CaO decrease in the order

Calcite → Dolomite → Ankerite

25

Therefore if ankerite is present in the limestone used in making a clinker, it is expected to

release lime at relatively lower temperature and if there is no assimilation of this lime due to

non availability of other reactive components, the lime crystals tend to be more ordered with

rise in temperature and lose their reactive state.

It is observed that lime crystals obtained from dissociation of dolomite are 1.5 - 2 times

smaller than those obtained from calcite, thus providing greater surface area, which results in

faster reaction 33, 36

.

2 the effect of the associated minerals and oxides lower the decomposition temperature

of limestone. Thus the dissociation pressure of calcite is increased by oxides like SiO2, Al2O3

and Fe2O3. Therefore in the presence of such impurities, the dissociation of calcite starts at

about 550 oC, but the dissociation rate is controlled by the formation rate of compounds with

other oxides until the actual dissociation temperature of 898 oC is reached. At this point it is

observed that the rate of release of free lime from the calcite is more than its assimilation rate.

It is also observed that the presence of fluorides leads to higher rates of calcium carbonate

dissociation temperature and that phosphates also have catalytic properties 33, 35

. The catalytic

action on the dissociation of carbonates is accompanied by intensive mineralization of lime

crystals which becomes less reactive with acidic oxides 33

.

3 the rate of dissociation and the reaction temperature of calcite have a direct

correlation with grain size. The decomposition of calcium carbonate starts with the formation

of pseudo morphs of two dimensional lime crystals after calcium carbonate crystals. Only

after some time do three dimensional nuclei of CaO crystals appear. The coarser the crystals

and more perfect their structure the longer the time between the two and three dimensional

crystals formation. This period is induction period. This implies that there are two stages of

carbonate decomposition;

• kinetic stage in which the rate of which is determined by the energy of formation and

concentration of CaO nuclei

• Diffusive stage, in which the rate depends on the thickness of penetrable shells on

calcium carbonate particles as well as on the diffusion rate of carbondioxide through it.

The decomposition characteristics of limestone are affected by the grain size and

crystallinity, particularly in the second stage 33, 34, 37

. Table 2.11 shows the relationship

between calcite grain size and decomposition of limestone.

26

Table 2.11 Effect of calcite grain size on dissociation of limestone

Crystallinity Grain size mm Dissociation rate Reaction temp.

Very coarse 1 Lowest Highest

Coarse 1 - 0.5

Medium coarse 0.5 - 0.25

Fine grained 0.25 - 0.10

Very fine 0.10 - 0.01

Microcrystalline 0.01 Highest Lowest

Associated minerals like magnesian minerals, sulphate and alkali minerals also affect the

thermal reactivity of a raw mix in the kiln.

Magnesia in limestone is present in forms like magnesian silicates, dolomites, magnesites,

ankerites and brucite. Under identical conditions of grinding and rapid cooling, the presence

of magnesian silicates ensures even distribution of fine periclase crystals whereas limestones

with dolomites or magnesites are prone to yield coarse periclase (25 - 30 µm). As explained

earlier, the effect of coarse periclase is unsound cement. Similarly, dolomite dissociates at

700 - 750 oC with the formation of Magnesia. If ankerite, Ca (Mg.Fe) (CO3)2 and magnesite

(MgCO3) are present in the raw material amorphous grains of magnesia are available at 700

and 660 oC respectively. Periclase forms at 800

oC. With dehydration of brucite, Mg (OH) 2 at

379 - 490 oC and dissociation of magnesian siderite (Fe, Mg) (CO3) at 580

oC, free magnesia

forms at still lower temperatures 38

.

The amount of alkali retained in clinker depends upon the amount of alkali in the raw

materials, thermal stability of the crystal lattice of the alkali compounds that form during

burning, and susceptibility of the alkali matter to sublimation. The behavior of the

compounds is strongly governed by the sulphur compounds present in raw materials. In the

presence of alkalis, the absorbed sulphurous and sulphuric anhydrides form thermally stable

K2SO4 and Na2SO4 which delay the sublimation of the alkali and sulphur, and increase their

quantity in clinker. Sulphite, in the raw material is transferred to clinker without substantial

loss whereas pyrite is partially sublimated into the gas stream.

The alkali bearing minerals with increasing temperature of alkali volatilization are biotite,

muscovite then feldspars 36, 39

.

27

The diffusion rate of lime CaO in the lattice of silica is four to five times higher than that of

silica in CaO lattice 37

. It therefore means that silica bearing materials are the determining

factor in the reactivity of raw mixes. The reactivity of different forms of silica with CaO

increases in the order;

Quartz → chalcedony → opal → alpha-cristobalite → trydymite → silica from feldspars →

silica from amphiboles, mica and clay minerals → silica from slag

Quartz crystals under the action of catalysts like Na+, K

+, Fe

3+, Fe

2+, F

- and Cl

- even at 800 -

1000 oC are transformed into fine reticulate cristobalite. The cristobalite is of a higher

reactivity due to its low density and defect state caused by the loss of O2-

and formation of the

same amount of silicon monoxide 33

. The silica in free form and of least reactivity determine

the rate of mineral formation, therefore silica in amorphous and hydrosilicates is preferable to

silica in other forms.

Clays show similar pattern of changes with temperature; dehydration, dehydroxylation,

breakdown of crystal structures producing reactive amorphous metaproducts and formation of

new phases. In cement making, advantage is taken of clays reactive state before stable phases

are formed. The water obtained from removal of hydroxyl group of clays has favourable

effect on the dissociation of calcium carbonate 38

. Due to variation in composition of clay

minerals, as well as the simultaneous presence of several clay minerals in one clay,

correlation of clay mineral forms with their burnability and reactivity is difficult. The

following clay minerals have a decreasing order of reactivity:

(Montmorillonite, halloysite) → (kaolinite, nontronite, biotite) → (pyrophyllite, muscovite,

vermiculite)

Some observe increased reactivity of raw mixes with increased kaolinite than other clays. The

reason advanced for this observation is that the products of the breakdown of the kaolinite

structure are highly reactive with calcium carbonate 38

. Table 2.12 shows the reactivity of

different clays at corresponding temperatures.

28

Table 2.12 Temperature profile of various clay minerals 38

Clay mineral Temperature (oC)

Allophane 530

Kaolinite

Halloysite

Hydromica 600 – 800

Ferruginuous chlorites

Montmorillonites

Low iron chlorites

Glauconites

800 – 900

Mica

Amphibole 900 – 1150

The reactivity of raw materials is often influenced by the presence of iron oxide in ferrous

state. The temperature ranges of iron oxide are

Ferriferous chlorite------------------330 - 500 0C

Glauconite--------------------------- 450 - 500 0C

Siderite, biotite, hornblende-------500 - 900 0C

Phlogopite----------------------------1050 - 1250 0C

On the other hand minerals like goethite (Fe2O3 H2O), and lepidocrocite (Fe2O3. H2O) gives

ferric oxide at about 300 oC.

Iron ore in the raw mix appears either as haematite or magnetite and both are more reactive

with lime and alumina. Unlike goethite and lepidocrocite, limonite (FeO.OH.H2O), often

contained in laterites is associated mostly with amorphous silica and is of higher reactivity.

The reactivity of a raw mix is dependent on the nearness of the temperature range or

appearance of raw mix components in a reactive state after thermal dissociation. It is

suggested that it is inappropriate to use a highly reactive chalk with low reactive clay

containing higher amounts of quartz and other minerals of low reactivity. Similarly the use of

29

a massive crystalline coarse grained limestone with highly reactive aluminosilicates or

amorphous silica may pose problems in their joint reactivity 33

.

i.7.3 Clinker Cooling and Grinding.

The rate of cooling of clinker influences its structure, the mineralogical composition as well

as grindability and consequently the quality of the resulting cement. This is the last stage of

cement manufacture. Clinker cooling is necessary because;

i. Hot clinker has a negative effect on the grinding process

ii. The reclaimed heat content of hot clinker is a factor that lowers cost of production

iii. Faster cooling improves quality of cement

C3S is unstable below 1250 0C. Demonstrations have shown that slow cooling rate produces

unreactive gamma C3S. This leads to setting time difficulties due to large crystalline C3A

formation and unsoundness due to high volume of periclase (MgO). Cement produced with

such clinker gives poor strength. Cements made from rapidly cooled clinker sets normally 1,

15.

Cooling rates control the quality of Portland cement as the properties of clinker are affected.

The flash setting which is sulphate resistance of cements made from slowly cooled clinker is

attributed to too much of C3A formed and unsoundness due to large sizes of periclase (MgO).

The soundness of the hardening Portland cement depends on the size of the periclase crystals.

The hydration of the larger periclase crystals is slow and can cause expansion or rupture in

concretes. The maximum size of the periclase which hardly impairs the cement is about 5 - 8

microns. Slow clinker cooling can produce periclase crystals about 60 microns large. It was

found that 4 percent periclase crystals in the cement, up to 5 percent micron in size, showed

the same rate of periclase expansion in an autoclave test, than 1 percent periclase crystals,

which were 30-60 microns large 40

.The contents of C3A and magnesium oxide would be

lowered in a rapidly cooled clinker 1, 41

.

The speed of cooling influences the ratio between the content of crystalline and liquid phases

in the clinker. During slow cooling, crystals of almost all clinker components are formed

whereas fast cooling hampers formation of large crystals, causing part of liquid phase to

solidify.

30

The cooled clinker is then ground with gypsum to produce Portland cement. Gypsum’s role

is to retard setting time.

2.8 Properties of Portland Cement

Portland cements are commonly characterized by their physical properties essentially for

quality purposes. The Nigerian Industrial Standards for Portland cement provide standard

specifications for Portland cement in Nigeria. The NIS 444:2003 describes the more common

Portland cement physical tests.

These tests are in generally performed on “neat” cement pastes i.e., Portland cement and

water. Neat cement pastes are not easily handled and thus they introduce more variation into

the results. Cements may also perform differently when used as mortar (cement, water and

sand). Over time, mortar tests have provided better indication of cement quality and thus,

tests on neat cement pastes are typically used only for research purposes 42

2.8.1 Fineness

Fineness or particle size of Portland cement affects hydration rate and this translates into rate

of strength gain. Greater surface area available for water- cement interaction is enhanced by

smaller particle size. The effects of greater fineness on strength are generally seen during the

first seven days 43

.

Fineness is determined by any of the several methods:

2.8.1.1 ASTM C 115: Fineness of Portland cement by the Turbidimeter

Determination of fineness by turbidity was developed by L.A. Wagner. This method

measures turbidity of a cement suspension in kerosene. A beam of light is directed through

the cement suspension and intensity of the current generated is detected by a photoelectric

cell and recorded. A calibration is done by calculation of a calibration factor k which depends

on the cell used. To determine this factor a primary standard material known as calibrant is

used.

Using a calibrant, the fineness of a material is obtained by comparing the two relative levels

of turbidity 43

.

31

2.8.1.2 ASTM C 204: Fineness of Hydraulic Cement by Air Permeability Apparatus

The determination of fineness of hydraulic cement by air permeability was developed by

R.L., Blaine. The principle is that the rate of flow of air through a layer of compacted

particles is proportional to the fineness of the particles. Therefore the test measures the flow

rate of air through a bed of cement particles. This method is also comparative rather than

absolute since it requires a reference material 44

.

The test is carried out by compacting the cement under investigation in a cell of known

volume and fitting it onto a u-tube manometer that contains a non- hygroscopic liquid of low

viscosity and density, for example dibutylphthalate. The cell is attached to the u-tube with a

tight seal and a vacuum is created under the cement sample. Then the air is pushed through

the cement sample by the liquid in the manometer. The time taken by the liquid in the

manometer to travel through a set distance is used to calculate the fineness which is

dependent on sample surface area S defined by the equation

S=Ss √T/√Ts ………15

Where Ss is the surface area of reference material, Ts is time of flow by the reference

material, T is the time of flow of the material under test and S is the surface area of material

under test. Therefore the surface area of the material tested can be calculated from the

reference material 44

.

ASTM C 184: fineness of hydraulic cement by the 150 µm and 75 µm sieves

ASTM C 430: fineness of hydraulic cement by the 45 µm sieve

NIS 448:2003: determination of fineness

The various methods (ASTM C184, C430 and NIS 448:2003) describe fineness as a measure

of coarse particles in a particle size distribution. The content of coarse or/ and fine particles in

a sample is determined by the use of standard sieve meshes which includes: 45, 75, 90,

150,180 and 212 µm.

2.8.2 Soundness

In cement technology, soundness refers to the ability of a hardened cement paste to retain its

volume after setting without delayed destructive expansion 43

. This destructive expansion is

caused by hydration of excessive amounts of free lime or crystallization of free magnesia

32

(MgO) in cement paste, mortar or concrete. It is suggested that the late formation of ettringite

from reaction of calcium sulphates with calcium aluminate (C3A) could also result in

destructive expansion 45

. In a typical expansion test, a sample of cement paste is heated under

high pressure and temperature several hours before brought gradually to room temperature

and pressure. The change in specimen length is measured in millimeters or percentage.

ASTM C 150, standard specification for Portland cement specifies a maximum of 0.80

percent for all Portland cement types while NIS 444:2003 specifies a maximum of 10mm 46

.

There are two methods for soundness determination; autoclave and le Chatelier test. Both

methods provide index of potential delayed expansion caused by hydration of free lime and

magnesia in Portland cements. Autoclave test shows possible expansion caused by both free

lime and magnesia while le Chatelier is concerned with expansion caused by free lime only

45. Figure 2.2 is le Chatelier apparatus.

Figure 2.2 Le Chatelier test apparatus

In a study of sound and unsound cements, the effect of cement fineness on autoclave

expansion was demonstrated. High magnesia cement was ground to a fineness of 225 m2/kg

and it expanded by 7.06 %. When the cement was ground to a higher fineness of 350 m2/kg,

the autoclave expansion dropped to 1.39 %, and finally when the fineness was increased to

400 m2/kg, the resulting autoclave expansion was only 0.24 %

45.

2.8.3 Setting Time

Cement paste setting time is affected by cement fineness, water to cement ratio, and sulphite

content of gypsum. Setting time tests are used to characterize how particular cement paste

sets. For control purposes, the initial setting time is not sooner than 75 minutes as contained

in NIS 444:2003 46

and not later than 160 min

whether or not cement is undergoing normal hydration

defined: initial set which occur

occurs when the cement has hardened to the point at which it can sustain some load

These particular times are arbitrary points used to characterize

fundamental chemical significance. There are two common setting time tests: Gi

needle test and Vicat needle test. Both define initial set and final set

which a needle of particular size and weight either penetrates a cement

given depth (initial set) or fails to penetrate a

needle test is more common and tends to give short

Table 2.13 shows specified set times for both setting time methods for

(ASTM C 150)

Table 2.13 ASTM C 150 specified set times by test method

Test method Set type

Vicat Initial

Final

Gillmore Initial

F

Figure 2.

and not later than 160 minutes. Additionally, setting time indicates

is undergoing normal hydration 43

. Normally two setting times are

when the paste begins to stiffen considerably and final set

occurs when the cement has hardened to the point at which it can sustain some load

These particular times are arbitrary points used to characterize cement; they do not have any

fundamental chemical significance. There are two common setting time tests: Gi

needle test and Vicat needle test. Both define initial set and final set based on the time at

which a needle of particular size and weight either penetrates a cement paste sample to a

initial set) or fails to penetrate a cement paste sample (final set). The Vicat

needle test is more common and tends to give shorter times than the Gillmore needle test

shows specified set times for both setting time methods for Portland cement

ASTM C 150 specified set times by test method 42

Set type Time specification

Initial ≥ 45 minutes

Final ≤ 375 minutes

Initial ≥ 60 minutes

Final ≤ 600 minutes

Figure 2.3 Vicat test apparatus for setting time

33

setting time indicates

. Normally two setting times are

when the paste begins to stiffen considerably and final set

occurs when the cement has hardened to the point at which it can sustain some load 42

.

they do not have any

fundamental chemical significance. There are two common setting time tests: Gillmore

based on the time at

paste sample to a

final set). The Vicat

more needle test.

Portland cement

Time specification

2.8.4 Strength

Cement paste strength is typically defined in three ways: compressive, tensile

These strengths are affected by water

and compaction, curing conditions, size and shape of specimen, loading conditions and

curing age 42

. Since cement gains strength over time, the time at which a strengt

conducted is specified. Typical

taken when doing a cement strength

concrete strength. It is used as a

cement mortars and not on cement pastes

strength. It is usually carried out on cement mortar test specimen. The test specimen is

subjected to a compressive load until f

is described by NIS 446:2003 47

.

Figure 2.4( a) Compressive strength test

strength test

Cement paste strength is typically defined in three ways: compressive, tensile,

strengths are affected by water – cement ratio, cement fineness, aggregate ratio, mixing

, curing conditions, size and shape of specimen, loading conditions and

. Since cement gains strength over time, the time at which a strengt

test times are 2, 7 and 28 days 42

. Two considerations are

cement strength test; cement mortar strength is not directly related to

quality control measure. Secondly, strength tests are done on

cement mortars and not on cement pastes 42

. The most common strength test is compressive


subjected to a compressive load until failure. Standard test method for strength determination

Figure 2.4 shows a set up for compressive test determination

a

Figure 2.4( a) Compressive strength testing machine,( b) Prism mortars for compressive

34

, and flexural.

aggregate ratio, mixing

, curing conditions, size and shape of specimen, loading conditions and

. Since cement gains strength over time, the time at which a strength test is to be

iderations are

test; cement mortar strength is not directly related to

strength tests are done on

. The most common strength test is compressive


ailure. Standard test method for strength determination

shows a set up for compressive test determination

b

machine,( b) Prism mortars for compressive

35

c

Figure 2.4 (C) Prism fractured by load

2.8.5 Loss on Ignition

This is determined by heating up a cement sample to 900 – 1000 0C until a constant weight is

obtained which is lower than the initial weight before ignition. The weight loss of the sample

due to heating is then determined. The loss in weight due to loss on ignition indicates the

presence of volatile substances like CO2, which may be caused by incomplete decomposition

and prolonged storage or adulteration during transportation 43

. In the cement industry the

value of loss on ignition of the cement or its blend is roughly equivalent to the loss in mass

that will undergo thermal treatment. The standard loss on ignition test is contained in NIS

445; 2003 48

.

2.8.6 Specific Gravity

Specific gravity is normally used in mixture proportioning calculations. The specific gravity

of Portland cement is generally around 3.15 43

.

2.8.7 Heat of Hydration

The reaction of C3A and C3S in cement generates heat of hydration. The heat of hydration is

also influenced by water to cement ratio, fineness and curing temperature. Increase in any of

the factors increases heat of hydration. This is the case usually observed in the construction of

large mass concrete structures such as gravity dams. The rate of heat produced is significantly

36

faster than it can be dissipated. This in turn creates high temperatures in the center of these

large concrete masses that in turn may cause undesirable stresses as the concrete cools to

ambient temperature. The advantage of high heat of hydration is enjoyed in winter because

favourable curing temperatures are maintained 43

.

2.9 Environmental Impact

2.9.1 CO2 Emissions

Cement manufacturing releases CO2 in the atmosphere when calcium carbonate is heated 49

.

The cement industry is the second largest CO2 emitting industry after power generation. The

cement industry produces about 5 percent of global man made CO2 emissions of which 60

percent is from the chemical process and 40 percent from burning fuel 50

. The amount of CO2

emitted by the cement industry is about 900 kg of CO2 for every 1000 kg of cement produced

51.

2.9.2 Heavy Metal Emission into the Atmosphere

In some circumstances, the emission of heavy metal gases into the atmosphere is influenced

by the composition of the raw materials used, the high temperature calcination

(decomposition) process of limestone and clay minerals. Accompanying heavy metal gases

are dust rich in volatile heavy metals which include thallium, cadmium and mercury 52

. These

heavy metals are often in trace amounts present as secondary minerals in most of the raw

materials. The presence of heavy metals in clinker arises both from the natural raw materials

and from the use of recycled by products or alternative fuels. The high pH prevailing in

cement pore water (12.5 to 13.5) limits the mobility of many heavy metals such as nickel,

zinc and lead by decreasing their solubility and increasing their sorption onto the cement

mineral phases 53

.

2.9.3 Alternative Fuels and By Product Materials

Usually a cement plant consumes 3 to 6 Gigajoules of fuel per ton of clinker produced. This

depends to a large extent on the process used in cement production and also the raw materials

used. Majority of cement kilns today use coal and petroleum coke as primary fuels and to a

lesser extent natural gas and fuel oil. Waste and by products with recoverable calorific value

are suitable fuels used in kilns. These replace fossil fuels like coal. Waste and by products

containing calcium, silica, alumina and iron can be used as raw materials in the kiln,

37

replacing raw materials such as clay, shale and limestone. Because some materials have both

useful mineral content and recoverable calorific value, the distinction between alternative

fuels and raw materials is very slim. For example sewage sludge has a low but significant

calorific value and burns to give ash containing minerals useful in the clinker matrix 53

.

2.10 Cement in Nigeria

One of man’s most pressing needs is housing. The Federal government of Nigeria has

identified this and has set it as a millenium priority. The year 2020 is marked as target to

provide housing for all its citizens. The limitation to this project is the availability of high

quality cement to the construction industry. In fact to achieve this target 20 million tons of

cement is required annually but presently only about 13 million tons or less is in the market 4.

Obviously Nigeria is facing a serious housing and infrastructure shortage. This is largely due

to the inadequacy of cement in the country. The needs in cement are partly offset through

eight cement industries: Dangote Cement Company (Obajana, Ibese and Gboko Plants),

Ashaka cement plant in Bauchi, United cement (Unicem) in Calabar, Cement Company of

Northern Nigeria, Sokoto and Lafarge WAPCO (Ewekoro and Shagamu plants).

In 2008, cement availability to Nigerian market was estimated at 13.4 million tons of which,

54 % was imported 4. By implication the existing manufacturing plants are operating below

50 % of their collective installed capacity. This may explain Nigeria’s invisibleness among

the world leading cement manufacturing countries in the world.

In 2002 the world production of hydraulic Portland cement was 1,800 million tones. The top

three producers of Portland cement are china, India and United States of America. These

three combined about half the world total production with Nigeria producing far less than 0.5

percent 3. In 2005, China led with 43.46 percent followed by India producing 6.38 and then

United States of America with 4.38 percent and Nigeria sharing the final 10.23 percent with

the rest of Portland cement producing countries3.

For more than a decade, China has consistently being the highest producer of cement 3. This

explains why China has the highest carbon dioxide emission in the world. In 2006, China

produced 1.24 billion tons of cement which was 44 % of the world’s total cement production

5. Demand for cement in China is expected to advance 5.4 percent annually and this exceeded

1 billion tons in 2008. Cement consumption in China is expected to hit 44 percent of global

38

demand and China will remain the world’s largest national consumer of cement by a large

margin 6.

The Federal Ministry of Commerce and Industry estimates that the effective demand is

around 20 million tons. According to Ian Furnivall and Tunde Abidoye 4, acute infrastructure

deficit and significant demand for housing has pushed domestic production volumes up to 25

% over the last four years 4. However in 2010, the Federal government of Nigeria, in her

effort to improve the availability of the commodity banned the importation of cement into the

country in order to encourage local production and existing companies are increasing their

capacities. Dangote cement company formerly Benue Cement in Benue State for instance,

increased its capacity from 0.45 million to 2 million per annum in 2008 and now 2.9 to 3

million. In 2010 UNICEM added 2.5 million tons of its capacity to local capacity while

Lafarge WAPCO has planned 2.2 million tons for 2011. With these improved capacities the

quantity of cement in the market have improved slightly and limestone blended cements have

been introduced into the Nigerian market. Today type I or ordinary Portland cement is

substituted completely with limestone blended cement in order to address cement scarcity in

the Nigerian market. Other countries such as Spain, France and Argentina also experienced

similar shortage and based on research results, their standards allowed inclusion of limestone

and other pozzolanic admixtures 7 to allowable limits. For example British Standards (BS

882) allows up to 15 % of limestone to OPC 8.

Limestone Portland cement is widely used in Europe, in fact according to Cement Bureau the

production of limestone Portland cement in Europe increased by 7 % between 2000 and 2010

9. Precisely the inclusion of limestone as an additive to boost quantity in Nigeria started a few

years ago. Benue Cement Company started adding it in 2006. In some European countries

like Germany and Britain, limestone addition to OPC is as high as 35 % 10

. It is reported that

the inclusion of up to 5 % limestone does not affect properties of Portland cement 11

. Blended

cements have certain benefits which include Economic, Environmental and Technical.

The Economic benefit of limestone in Portland cement is the reduced cost of production and

investment which makes cement cheaper 54

. The Environmental advantages include reduction

of CO2 and NO2 emissions due to reduction in clinker content 10

. In terms of technical

benefits, Moir and Kelham observed increased fineness with increase in limestone addition

to OPC and this lead to greater water absorption, improved hydration rates of cement

compounds and consequently increased compressive strength 55

.

39

Investigations on limestone blended cement revealed that the inclusion of 12 to 18 % of

limestone has no significant deleterious effect on strength development and other physical

properties of Portland cement 55-59

.

2.11 Blended Cements

Blended cements usually contain ordinary Portland cement and another cementitious

material. They are made by intergrinding Portland cement with another material. Fly ash,

blast furnace slag, silica fumes and limestone are common cementitious components of

blended cements and each of them results in a different type of blended cement with unique

set of properties. They have gained so much application that the production of ordinary

Portland cements is really on the low side. With the advancement in civil works there is

increasing need for special Portland cements that meet specific requirements with cost of

production being a strong consideration. The American concrete Institute’s Cement

terminology defines blended cements as hydraulic cements consisting essentially of an

intimate and uniform blend of a number of different constituent materials. They are produced

by intergrinding or blending Portland cement with other materials 60

. The use of blended

cement is common in Europe, Canada, Mexico and many other parts of the world. Although

blended cements are used in the United States of America, it is more common for mineral

admixtures such as fly ash and slag. Fly ash generally constitutes 15 to 25 percent by weight

of cement and ground granulated blast furnace slag constitutes 5 to 60 percent and silica

fumes 5 to 12 percent 7. The use of blended cements in Europe is very common and is

continuing to increase. In fact according to Cement Bureau the production of limestone

Portland cement in Europe which is one of the blended cements common in Europe increased

by 7 % between 2000 and 2010 9. Because of the environmental benefits of blended cements

strict environmental regulations have forced European cement manufacturers to focus their

attention on blended cements. European countries promote specific types of blended cements

according to the availability of the cementitious material. For example pozzolana Portland

cement is very common in Italy, Spain and Greece. In Germany, The Netherlands and

Belgium slag Portland cement is widely used. Silica fume is largely blended with Portland

cement in Norway, Iceland and France 7.

In these countries and many others cooperation between cement manufacturers and the

producers of the cementitious or supplementary materials exists. This cooperation has lead to

improved quality of these materials used in blended cements 7.

40

2.12 Supplementary Materials Used in the Manufacture of Blended Cements

Most of the materials used in the manufacture of blended cements are waste products from

industrial processes and they vary in quality. Examples of such are: high calcium fly ash,

ground granulated blast furnace slag, condensed silica fume and rice husk ash. The natural

ones include volcanic ash. These are common amongst European countries. Elsewhere like in

Ghana of Africa and India limestone is widely used in the manufacture of blended cement.

Blended cements may be Portland cement and one supplementary material or Portland

cement with more than one supplementary material. When it is a two component material it is

a binary system blend and the other ternary system blend. These systems are designed to

attain desired performance characteristics that may be difficult to achieve in a binary blend or

only Portland cement or even in the ternary system blends 61, 62

.

2.12.1 High Calcium Fly Ash (HCFA)

HCFA is residue collected from smokestacks of coal fired power plants generally using

lignite and /or bituminous coals. They have been combined with lime to produce moderately

strong concrete 63, 64

. Cements made with this material are pozzolanic. Pozzolanic materials

are silica or alumina containing materials which react with calcium hydroxide at room

temperature to form cementious compounds. These blended cements are common in China

and the United States of America 64

.

2.12.2 Ground Granulated Blast Furnace Slag

This is a product of iron smelting. It is mildly cementitious in itself until combined with

cement and water. It is formed by the reaction of limestone with materials rich in silica and

alumina associated with the ore or present in ash from the coke 65

. It improves strength at

later age 66

. The chemical composition of granulated blast furnace slag is similar to that of

Portland cement. Compared with Portland cement, the contents of silica and alumina are

higher but its lime is lower. The composition of blast furnace slag varies depending on the

nature of the ore, the composition of the limestone, the coke and the kind of iron produced 1.

It is widely used in Europe 63

.

2.12.3 Condensed Silica Fume

This is obtained from silicon metal industries. It is a super fine powder of almost pure silica.

It is the favourite for very high strength concretes used in the construction of high rise

41

buildings. It is often used in combination with cement and fly ash 63

. Because they are so

effective at increasing performance of cement, it is usually used as secondary additive in

ternary blended systems to develop the overall quality of the cement.

2.12.4 Rice Husk Ash

This is the least considered in terms of quality but considered promising on a global scale.

The world’s primary stable crop is rice. The milling of rice generates 100 million tons of

husks annually in India. Rice husk ash behaves like silica fume if the ash is generated at low

temperature and ground to fine particle size 61, 63

.

2.12.5 Volcanic Ash

This material comes about as a result of volcanic activity when silica rich magma meets with

large quantities of underground water in volcanic conduits. Under high temperature and

pressure the steam reacts with the dissolved carbon dioxide and sulphur gases and during the

volcanic eruption the magma produces material with excellent cementing characteristics. This

is the pozzolan used prior to the discovery of Portland cement in Italy and Greece 63, 67

.

2.13 Benefits of Blended (Composite) Cements

Modern blended cements have come into their class as increasing care has been taken to

develop high quality composite cements which far out perform traditional cements. Certainly

their increased usage is a result of favourable benefits which when grouped together fall

under the following headings:

2.13.1 Economical Benefits

Blended cements have replaced up to 60 percent of ordinary Portland cement and are

successful in civil applications. When cheaper supplementary material replaces portion of

Portland cement there is low cost of production and low investment costs per ton of cement 7,

54.

2.13.2 Technical Benefits

In general terms siliceous materials react with the calcium hydroxide in hydrated cement

paste to produce calcium silicate hydrates that yield higher strength. This is brought about by

improved fineness which is a property of blended cements. Higher fineness increases

42

retention of water which consequently improves hydration rates 7, 55

. Others include improved

concrete workability and lower risk of thermal cracking.

2.13.3 Environmental Benefits

There is reduction in the emission of carbon dioxide and other greenhouse gases as quantities

of clinker are replaced with lime containing supplementary materials that do not undergo

thermal treatment 10

.

2.14 Limestone as a Supplementary Material in Blended Cement Production

The inclusion of limestone in Portland cement has both economic and environment friendly

benefits like other blended cements. It also improves the performance of concrete with

respect to strength, durability and workability 59

. European Nations standard (EN 197-1)

permits the addition of 6 - 35 % of limestone to OPC. Under the EN 197-1 classification of

cements limestone Portland cement is type II/AL for 6-20 % limestone and type II/BL for 21-

35 % limestone addition to OPC 66

.

Limestone as discussed earlier is a naturally existing mineral that consists primarily of

calcium carbonate. The chemical composition of limestone varies widely depending on the

route by which they were formed.

Standard EN 197-1 requires in Portland limestone cement limestone with at least 75 percent

calcium carbonate by weight, with less than 1.2 percent clay and less than 0.2 percent organic

material. One of the impurities in limestone is magnesium carbonate and is deleterious for

concretes. Consequently its content is required not more than 4 percent.

Since the European standard for common cement was first published in 1993 there has been

an increasing trend in the use of limestone as a mineral addition in cement not only in the

European countries but also in other parts of the world. Limestone is semi inert and

contributes to concrete’s microstructure. Limestone addition considerably influences the

characteristics of cement but this influence depends on a number of factors which include

clinker type, fineness and limestone quality 68

. When interground with Portland cement

clinker it improves particle size distribution. The fine limestone particles act as nucleation

sites increasing the rate of hydration of the silicates.

43

2.15 Effect of Limestone on Properties of Portland Cement

2.15.1 Particle Size Distribution and Fineness

Limestone is softer than clinker and therefore lesser energy is needed to grind it attain

comparable fineness with clinker. Studies showed a decrease in energy when clinker and

limestone were ground together to give same fineness either had when ground alone. It was

revealed that Portland limestone cement gave a wider particle size distribution than that of

cement interground with fly ash or natural pozzolana. Addition of limestone to OPC requires

higher fineness or increased grinding time to achieve strength of OPC. This was observed in

the same study as limestone did not only increase the grinding time required to obtain target

compressive strength of 40 MPa, but also increased fineness considerably 58

. The particle size

distribution of limestone and clinker after intergrinding was investigated and clinker

concentrated in coarser fraction and limestone in the finer. As the limestone content and

grinding time increased, the particle size distribution became wider and finer. This means that

longer grinding time change amount of coarse particle for lower limestone contents but affect

the entire size distribution at higher limestone content. Limestone composite cements are

usually ground to very high Blain (surface area) values in order to obtain the desired

compressive strength. However the trend of fineness and Blain values do not go parallel to

each other at higher limestone percentages 69

. Studies by Voglis et al reveal the easiness of

grinding between limestone, fly ash and natural pozzolana all at 15 percent. In order of

increasing ease of grindability, the raw materials were listed as limestone, fly ash, natural

pozzolana and finally clinker. However the targeted Blaine values in order to achieve

required strength and grinding times were found highest in the case of limestone blended

cements as can be seen in Table 2.14 58

. Grindability of limestone blended cements when

investigated at different limestone addition percentages of 10, 20, 30 and 40 and at different

grinding times (35, 50, 65, 85 minutes) showed a widening particle size with increasing

Blaine values 69

. However both the grindability of clinker and limestone were negatively

affected in the case of 40 % limestone addition and lower fineness values of clinker and

limestone were measured when compared to 30 % limestone addition 69

.

In a physical and mechanical properties investigation on cements prepared by replacing 0, 6,

21 and 35 % of clinker with limestone at constant blain showed limestone blended cement

having increased fineness 70

.

44

The particle size of limestone affects other properties namely: consistency, setting time,

hydration and mechanical properties of Portland cement most importantly compressive

strength.

Table 2.14 Grinding parameters of limestone, natural pozzolana and fly ash blended cements

at 15 percent addition and compressive strength values of samples prepared using various

cement types 58

Cement type Composition Grinding time

(mins)

Blain value

(m2/kg)

28 days

compressive

strength

Portland

cement

100% clinker 5%

gypsum

41 303 40.3

Limestone

blended

cement

85% clinker + 15

% limestone

5%

gypsum

60 511 40.5

Natural

pozzolana

blended

cement

85% clinker + 15

% natural

pozzolana

5%

gypsum

52 418 41.2

Fly ash

blended

cement

85% clinker + 15

% fly ash

5%

gypsum

40 388 41.0

2.15.2 Consistency

This is the percentage of water that is required to convert cement into a standard paste. NIS

444:2003 defines standard paste as one that will allow a Vicat probe penetration of 5 - 7 mm.

This water percentage is the quantity of water required for hydration of the silicates. Usually

best range is 25 - 27 %. Theoretically in order to achieve the same strength values, limestone

blended cement require a finer grinding compared to ordinary Portland cement which adds up

with a high specific surface area.

Tsivilis investigated effect of limestone on consistency using two types of cements and three

types of limestone. He observed that cement with lower tricalciumaluminate required more

water regardless of limestone type 13

. In the same research consistency decreased with

increase in added limestone and increased fineness. It was also noticed that calcite and

dolomite type of limestone decreased consistency more than the limestone with more clay

content. Vuk et al observed a slight reduction (0.5 %) in consistency with the use of 5 %

45

limestone. He agreed that the more important parameter influencing consistency was fineness

69. A possible explanation is that the limestone fills the voids between the clinker particles.

A study by Inan Sezer showed decrease in consistency when limestone and clinker were

ground together. In the study grinding time was kept constant for all cements. Blended

cements with higher Blaine values were found coarser compared to cement without any

additive when sieves 32 and 90 micron sieves were used 71

. It is reported that Erdogbu

prepared blended cements with 5, 10, 20 and 30 percent limestone additions and consistency

was observed decreasing with increased limestone percentage. The decrease in consistency

was attributed to the smooth surface and lower porosity of limestone particles after grinding.

However strength values of blended cements were found lower than the required strength in

higher limestone replacements. Erdogbu suggested that limestone blended cements must be

ground finer 71

.

A study on the effects of limestone replacement at 15, 25, 35 and 45 % where grinding of

ingredients was separately done before mixing revealed that consistency of 26 to 27 percent

was required to get a Vicat plunger penetration of 30±5 mm 72

.

2.15.3 Hydration

Portland cement when mixed with water, its compounds (C3S, C2S, C3A and C4AF) react

with water to form hydrates. These reactions lead to the setting and hardening of the cement.

It is assumed that the reactions of each compound take place independently. The main

reactions of the individual cement compound are described thus.

1. The C3S and C2S react with water to produce calcium silicate hydrate (CSH) and

calcium hydroxide (CH)

2. The C3A not only reacts with water directly but also reacts with gypsum

(CaSO4.2H2O) to produce ettringite. Once all the gypsum is used up, the ettringite

becomes unstable and reacts with remaining C3A to produce monosulphate aluminate

hydrate crystals

3. Like C3A, C4AF reacts with gypsum water to form ettringite, lime and alumina

hydroxides. The complete product is attained by further reaction of C4AF with

ettringite.

The above reactions are accompanied by heat liberation. The liberated heat of hydration is

one method to determine degree of hydration.

46

The hydration of cementitious materials generally is exothermic. A variation in the liberated

heat of hydration mirrors the hydration mechanism of the hydrating material. A heat

evolution curve illustrated by Mindess and Young41

shows the 4 stages of hydration

1. Pre-induction stage

The fast heat evolution was attributed to the hydration of C3A, the hydration of free lime

and the wetting of the cement. In this stage C3A is most active and reacts with gypsum to

produce ettringite. The main products are ettringite and calcium hydroxide. The duration

of this stage is only several minutes.

2. Dormant stage

In this stage, cement has a low reactivity. This period last for about 5 hours

3. Acceleration stage

This acceleration is due to hydration of C3S. The mechanism of this acceleration is

described as a transport of ions to and from the surface of anhydrous particles through a

gradually thickening shell. After about 12 hours this stage ends. The main products are

calcium silicate hydrates and calcium hydroxide. This is the initial setting of the cement.

4. Post- acceleration stage

After the second peak, the rate of heat liberation slows down. The hydration of C2S

becomes the main contribution to this stage. The presence of a shoulder was suggested to

be due to conversion of ettringite to monosulphate aluminate hydrate and the formation of

secondary ettringite. The main products in this stage (final setting) are calcium silicate

hydrate, calcium hydroxide and monosulphate aluminate hydrate crystals

Figure 2.5 Schematic presentations of rates of heat evolution 73

47

Degree of hydration α (t) is defined as the ratio between the amounts of cement that has

reacted (that has been dissolved) at time t, relative to the original amount of cement:

α (t) = amount of cement that has reacted at time t ………16

total amount of cement at time t=0

Several theories for the determination of the degree of hydration have been proposed. Among

these methods, isothermal conduction calorimetry is the most convenient and most useful one

73.

α (t)≈ α(Q(t)) = Q(t)/Qpot ……….17

Where Q (t) (J/g) is the total heat liberated at time t obtained by integration of rate of heat

evolution and Qpot (J/g) is the potential heat when all the cement has reacted. Qpot is

calculated from the clinker composition of the cement and the heat of hydration of the

individual constituents:

Qpot = q1×(C3S) + q2×(C2S) +q3× (C3A) +q4× (C4AF) +q5× (C) + q6 ×(MgO) ………18

Where, q1 to q6

(J/g) are the heats of hydration of the constituents.

The presence of limestone in Portland cement promotes nucleation as it acts as nucleation

sites for hydration products, therefore the inclusion of limestone could increase the rate of

hydration reaction. Hydration of cement pastes at various water- cement ratios (20 % - 50 %)

with 10 % and 20 % limestone addition showed a more rapid reaction at 7 days age curing in

water in the higher w/c ratio pastes containing limestone 57

. In a similar investigation with

concrete mixtures at 34 % and 50 % w/c containing 10 and 20 % limestone, hydration

increased with increase in limestone content 56

. A computer model was employed using

CEMHYD3D program to predict the hydration and strength development of low w/c cement

pastes with varying limestone percentage. Limestone was used to replace 20.5 % and 30.8 %

of clinker at 0.25 water to cement ratio, and 14.5 % and 22.3 % at 0.30 water to cement ratio.

This showed the degree of hydration of pastes containing limestone being higher than the

control sample i.e. cements without limestone at all curing ages. From a comparative study of

the computer model and that done in reference 56, it is observed that coarse cement particles

hydrate slower which may be attributed to large volume to surface area.

The mechanism of hydration was studied at early ages of finely ground limestone and quartz

powder intermixed with Portland cements with different compositions. It was determined that

48

both of these material additions activated or slowed down the hydration rate depending on the

cement compositions. When cement with high C3A content was used hydration reactions

sped up for both types of materials and it was determined that these materials act as nucleus

for rapid formation of hydration products. In the case of low C3A content cement, the

addition of these materials retarded hydration 74

. The hydration of fly ash and slag at selected

levels of addition to OPC were studies using X-ray diffraction and differential thermal

analysis in comparison with limestone added to OPC. It was concluded that the hydration

reaction of ordinary Portland cement in the presence of powdered limestone and lime sludge

was more accelerated and greater amount of calcium hydroxide was liberated. With further

investigation it was concluded that hydration of OPC with lime sludge is better than with

limestone due to better crystallinity and fineness of powdered sludge 75,76

.

An investigation using isothermal calorimetry revealed that more hydration activity occurred

in cement containing 50 % limestone than in the absence of it under comparable conditions

77. This is the accelerating effect of limestone. Xiong and Van Breugel using isothermal

calorimetry found that the limestone additions gave an earlier peak and faster rates of

hydration at 200C than those of control paste at water to cement ratio of 0.43. At higher water

to cement ratio the hydration was earlier but did not produce the same activity as the control

mixture 78

.

Limestone affects hydration of both C3A and C3S. The addition of limestone accelerates their

hydration. Barbara et al investigated the effect of limestone on blended cement using

isothermal calorimetry. The rate of heat liberated from the blended cement was higher than

that from OPC. An X-ray diffractionometry employed in the study to show hydrate formation

revealed the formation of calcium carbosilicate hydrate. Barbara et al concluded that calcium

carbonate (limestone) not only modifies the hydration of C3S but also reacts with it to form

calcium silicate hydrate 77

.

In a typical heat evolution curve of Portland cement blended with limestone shown in Figure

2.6, it is seen that the addition of the limestone shortened the dormant stage, accelerated the

early hydration and resulted in an additional peak in the heat evolution curve around 12 hours

hydration.

49

Figure 2.6 Heat evolution curves of ordinary Portland cement blended with limestone

The curve shows the heat liberations of four mixes. Mix 01 is the pure cement paste with

water to cement ratio of 0.48. In mix 02 the limestone content is 33.3 percent and water to

cement is 0.41. In mix 03 the limestone content is 42.9 percent and water to cement ratio is

0.48. In mix 04 is OPC with water to cement ratio is 0.33.

The phenomenon in the curve could be explained through the activity of fine limestone

particles which provide nucleation sites for hydration of cement clinker. It is reported that the

accelerated hydration could be attributed to partly physical and partly chemical effect of

limestone particles 77

. For the additional peak it is explained that it results from the

conversion of alumina phase to calcium monocarboaluminate which releases more heat 78, 79

.

2.15.4 Setting

It is suggested that the fineness of limestone is a factor that influences setting time of cement

pastes. However different observations have been reported among different studies. For

instance in a study conducted by Vuk et al, Cement pastes of different fineness and C3A

content at 0 % and 5 % added limestone showed a delay in initial setting time by 50 mins at 5

% limestone addition when compared to ordinary Portland cement as fineness increased. The

increased fineness made C3A less significant 72

.Observing the effect of added limestone on

sulphate content, Campiteli observed sulphite increase with fineness and decreased with

increase in added limestone content but this was not a linear relationship. This he noted that

when part of the clinker is replaced by limestone, the coarser fractions of the interground

cement will consist primarily of clinker, while limestone will be concentrated in the finer

fractions 80

. This was similar to what Guemmadi et al observed and he agreed with Campiteli

50

as he did not observe a clear trend as setting time varied with fineness 75, 81

. Hooton et al

reported that Moir and Kelham also observed that increased fineness gave longer initial set

time at 20 % limestone replacement55

.

2.15.5 Compressive Strength

The strength of concrete made with limestone composite cement is influenced by the quality

of limestone, manufacturing process and final particle size distribution of cement. Obviously

the soft nature of limestone will make limestone cement have finer particle size than OPC,

thus high strength at early stage is expected. Series of cement samples with limestone

contents 0, 3, 5.5 and 8 % prepared at approximately equal Blaine and equal sieve were

studied. In these test, limestone of 85 % total carbonate was used with clinker of C3A content

of 5.1%. The result of 3 and 5.5 % added limestone showed comparable strengths with OPC

but at higher limestone percentage the Portland limestone cement was ground to higher

surface area to have similar strength value 11

.

At higher limestone additions strength loss may be due to dilution of C3S and C2S and this

must be compensated for by finer grinding. This was illustrated in a study that showed

comparable strength for ordinary Portland cement and Portland limestone cement with 15 %

limestone. Portland limestone cement was ground to 511m2/kg compared with 303 m

2/kg for

ordinary Portland cement as shown in Table 2.14 58

. Three cements from the same

manufacturing plant with 0, 8.3 and 18 % limestone had Blaine values of 317, 372 and 420

m2/kg respectively. Concretes produced with these cements achieved 28 day strength as 40.2,

38.1 and 36.3 MPa 56

.

Data published by Benachour and Dhir agree that the strength of concrete is reduced when

ground limestone are blended with ordinary Portland cement. Benachour concluded that the

performance of concrete produced with cement containing 25 percent limestone was

equivalent to what would be expected due to a 25 percent replacement of the Portland cement

with an inert diluent 82

. Dhir concluded that there were minor differences in the performance

of concrete with Portland cement and Portland limestone cement containing 15 percent

limestone but that above this level the water to cement ratio of the concrete should be reduced

by 0.08 for every 10 percent limestone to achieve the same compressive strength at 28 days

curing 83

.

51

These studies have revealed with regards to strength development of limestone Portland

cement that the appropriate choice of clinker quality, limestone quality, and percentage

limestone and cement fineness can lead to the production of limestone composite cement

with desired properties. However higher rates of limestone addition usually reduces the

compressive strength.

2.16 Limestone Reactions in Limestone Cements

It is reported that low amounts of limestone reacts completely to form various carboaluminate

phases. The extent of limestone’s reactivity is controlled by the amount of sulphate in the

system. As the sulphate increases, the likelihood of unreacted carbonate increases. Campiteli

and Florindo were reported to have observed that increased limestone addition decreased the

optimum sulphate content in both fine and coarse cements. However they concluded that

decreases in sulphate would not be sufficient for complete reaction at high limestone addition

levels as they observed beyond 14 percent limestone addition 81

. This may possibly be as a

result of the decrease in quantity of the fine clinker particles, although this decrease may not

be linear as would be expected from addition of limestone. Compressive strength as shown in

a study by Caldarone decreased with increase in added limestone but increase was observed

at about 7.5 percent addition after one day strength development. He suggested that the ratio

of CO3 to C3A probably gives more of monocarboaluminate than sulphate aluminate species

and this contributes to cement strength 81

. Hydration of C3A in the presence of calcium

carbonate results in calcium carbosilicate hydrate and strength is enhanced 75, 76

.

Tsivilis determined the effect of reactivity of limestone with OPCs of varying C3A contents

as observed by measuring compressive strength. Clinker with lower C3A (7.54 %) and higher

C3S (65.15 %) gave lower compressive strengths at all curing times and at all percentages of

added limestone to OPC of higher C3A (11.74 %) and lower C3S (57.99 %) 13

.

Suggestions are that some CaCO3 could be incorporated in calciumsilicate hydrate formed by

hydration C3S. However, the formation of ettringite is under debate. Authors like Tsivilis and

Kakali are reported to have found delayed formation of ettringite where limestone was added

to OPC, while Ingram et al found that ettringite formation proceeded normally in a similar

system. Others observed accelerated formation of ettringite. In other words such limestone

composite cements had earlier setting than OPC. This is possible due to the production of

calcium hydrate which is produced during dilution of limestone. Limestone also acts as a

nucleation site for enhanced calcium formation. Thus the nucleation and dissolution of

52

limestone are possible factors that lead to accelerated ettringite formation. Furthermore, the

microscopic structures of the calcium hydrate crystals in limestone composite cements are

responsible for accelerated formation of ettringite. The rate of formation of ettringite easily

translates to high early strength development within few days and reduces as days go by. This

was observed in an investigation by Barker and Cory. They observed enhanced formation of

calcium hydrates at early age with 5 % and 25% added limestone 25 % added limestone to

OPC 55

. Be that as it may, there is co-formation of carboaluminate hydrate with ettringite.

Investigations by Ingram et al and Klem and Adams were concluded that though calcium

carboaluminate and ettringite form in a competitive fashion since CO3 and C3A compete for

sulphite ions, the calcium carboaluminate is less stable and so the formation of ettringite will

proceed normally 83,84

.

2.17 Effect of Limestone on Concrete Properties

Properties that characterize concretes include Workability, resistance to sulphate attacks,

permeability and drying shrinkage.

2.17.1 Workability

The effect of limestone on workability of freshly prepared concrete is much related to particle

size distribution of the limestone in relation to the cement. Generally, fine limestone particles

can enhance the overall particle packing of the cement resulting in less space for water

between the solid grains. By definition, workability is that property determining the effort

required to manipulate a freshly mixed quantity of concrete with minimum loss of

homogeneity.

Research showed that decrease in average particle size of limestone used to replace OPC

partially gave better early age properties. Finer particles accelerate hydration. In the study

torque viscosity and flow resistance in concretes with a water to cement ratio of 0.33 were

measured using limestone with particle size of 0.7 and 3 micrometers average size limestone

particles( up to 20 percent) blended with ordinary Portland cement with varying amounts of

silica fume. The amount of limestone did not significantly affect the flow resistance but the

torque viscosity decreased with increasing limestone additions. In the same study the finer

limestone particle sizes approached that of silica fume (0.26 microns) and it was postulated

that the absorption of admixtures is notably higher for silica fume than for limestone 82

.

Decreased workability was observed with increased limestone addition by Bonavetti . A 0.01

increase in water to cement ratio was required to achieve equal slump from 0 to 5 percent

53

limestone and another 0.01 increase for limestone addition from 5 to 25 percent 57, 78

.

Information from these investigations established that water requirement is primarily related

to inter particle space.

2.17.2 Sulphate Resistance

Structures exposed to soils or ground water containing high concentration of sulphate ions

often experience sulphate attack. This has a deleterious effect on concrete. It is reported that

proper initial curing of blended concrete made with Type V (low alumina content) cement

with low water cement ratio were recommended as methods to resist sulphate attack.

However significant changes in cement chemistry have resulted in cement with a low silicate

ratio for sulphate environments. This is because higher silicate ratio cements results in

increased calcium hydroxide content in the hardened cement matrix, consequently enhancing

the susceptibility of such cements to the softening ability of sulphate attack 85, 86, 87

.

Generally, limestone in cements dilutes C3A and other active aluminate content of cements.

The formation of carboaluminate from reaction of calcium aluminates and limestone reduces

available alumina participation in deleterious sulphate reactions. On the other hand the use of

limestone composite cements result in lower strength and it is believed that it could facilitate

the ingress of external sulphates. Hooton claims that there is no evidence of deleterious

effects of up to 5 percent limestone in cements. Thus increased quantities of finely ground

carbonates could increase the potential for sulphate attack 59

.

In an investigation to monitor sulphate resistance of limestone blended cements with other

mixtures, 10- 40 percent ground limestone were added to OPC and compared with cements

made with same additions of calcium fluoride. The mortar bars were exposed to 5 percent

sodium sulphate and length change and time it took to crack were monitored. The results

shown in Table 2.15 showed that time taken to crack increased with increased limestone

replacement where as calcium fluoride replacements had no effect in spite of both fillers

having increased strength at time of sulphate exposure. It was suggested that the

improvement in sulphate resistance is possibly due to the formation of calcium

carboaluminate, thus suppressing formation of monosulphate and therefore reducing the

potential for ettringite formation on exposure to sulphate solution 88

. From the data Table

2.15 it is seen that the calcium carbonate (CaCO3) has a more beneficial effect.

54

Table 2.15 Sulphate resistance of cement with limestone additions 91

Mortar Time to crack (weeks) Compressive strength at 28

days (MPa)

Reference mortar 6 25.3

With CaCO3 filler (wt %)

10

10

27.0

20 12 27.3

30 14 29.7

40 16 30.9

With CaF2 filler (wt %)

10

6

23.7

20 6 28.2

30 6 32.6

40 6 28.9

In a similar study 40 percent added calcium carbonate to OPC with fineness range 960 – 1120

m2/kg improved sulphate resistance as shown Table 2.16. This observation was attributed to

the likelihood of very fine limestone reacting to form carboaluminate hydrates 89

.

Table 2.16 Effect of 30 percent filler based on type and fineness on weeks to failure of mortar

Bars in 5 percent sodium sulphate 89

Fineness( m2/kg) Limestone Dolomite Basalt

115-130 12 12 4

370-300 10 6 4

660-710 10 6 4

960-1120 18 6 2

Reference 6 weeks

Mortar prisms with 35 % added limestone and 8 % C3A were exposed to magnesium sulphate

solution at 5 0C. They suffered damage in one year. Prisms with 15 % added limestone

showed strong signs of impending damage within the same period. The prisms with 35

percent limestone, exposed to sulphate environments at 5 0C showed 75 % loss in

compressive strength 89

.

Borsoi found that mixtures containing 10 % limestone filler exhibited surface damage due to

presence of ettringite and thaumasite after 5 years exposure to magnesium sulphate solutions

(3000 mg/L), but did not show evidence of strength reduction. When 8.2 percent C3A cement

55

was replaced with a zero percent C3A cement, the surface damage with 10 percent limestone

was mitigated. In lower sulphate exposures (300 and 750 mg/L), no damage was observed

after 5 years 86

.

In a study a comparative study of strength losses between a control paste mixture and mixture

containing 10 percent limestone, when subjected to 10 percent magnesium sulphate solution

at 60 oC, revealed that both samples exhibited similar loss in strength. When immersed in 10

percent magnesium sulphate at 20 oC, strengths after 180 days were similarly unaffected for 0

and 10 percent limestone pastes, while 5 percent limestone showed increased strength similar

to that of 40 percent slag paste 85

.

56

CHAPTER THREE

3.0 EXPERIMENTAL

3.1 Materials and Methods

3.1.1 Materials

The primary materials were clinker, gypsum and limestone.

3.1.2 Reagents

All reagents were analaR grade purchased from Tedia, Merck, Riedal de-Haen, Hopkins &

Williams, Fisher, BDH and Lab tech chemicals. Barium chloride, ammonium acetate, (98.0

% w/w), copper complexonate indicator and calcein indicator were purchased from Merck

company, Germany. Conc. Hydrochloric acid, (37 % w/v), ethylene glycol (1, 2-ethanediol)

and ethanol (0.79 g/cm3) were purchased from Tedia chemicals, USA. Silver nitrate and

ethylene diaminetetraacetic acid, EDTA (99.0 % w/w) from Fisher Scientific Company,

USA. Sulphosalicylic acid indicator and sodium hydroxide from BDH, England. Ammonium

hydroxide from Hopkins and Williams, England, PAN (1,2-pyridylazo-2-naphthol ) indicator,

triethanolamine and potassium hydroxide from Riedel-de Haen, Germany, while

bromocresol green (BCG) was purchased from lab tech chemicals.

3.1.3 Apparatus

Normal laboratory glass wares (borosilicate), polyethylene vessels, pH meter (Jenway, sr

30102), weighing balance (mettler toledo, ML 4002E/01) porcelain crucibles (GmbH),

electric furnace (CONTROLS,10- D1418/A) dessicator, magnetic stirrer and hotplate

(Gallenhamp, 14/ss-660), filter papers (Whatman No. 40 and 42), bunsen burner, retort stand

with wire gauze, 100 oC thermometer, thong, jaw crusher, disc mill (Retsch, BB200)

laboratory cement mill (H-Welte, BGSTAK 4E/S 1980 model), quartering machine (locally

fabricated), cement mixer (CONTROLS, 65-L0006/AM, EN 196-1), air permeability

apparatus (Toni-Teknik, 870 1992 model), sieve machine (Alpine 200LS-N), 45,90 and 180

µm sieves (BS 140-1). Compressive strength machine (CONTROLS, 65-L11V2), jolting

apparatus with prism gang (CONTROLS, 65-L0012/E), Vicat apparatus with plunger, needle

and ring pin attachment (Toni-Teknik), electric water boiler (CONTROLS, 62-L0025/F)

electric water bath (Memmert, W200), Erlenmeyer flask, Gooch crucible and suction pump.

57

3.1.4 Sampling and Sample Preparation

The limestone was obtained from Tsekucha quarry in Gboko, Benue state. It was crushed

with a jaw crusher and quartered using a quartering machine. The quartered portion was

stored in polyethylene sample bag as limestone parent sample (LPS). In similar way all

materials were labeled parent samples. Clinker and gypsum were obtained from a local

cement manufacturing industry. The clinker was sampled at two hours interval for a period of

24 hours. The sampled clinker was homogenized and quartered. The quartered sample was

crushed with the jaw crusher and stored in polyethylene sample bags and labeled as clinker

parent sample (CPS), to be used for formulation of composite and ordinary Portland cements.

The obtained gypsum was similarly stored and labeled gypsum parent sample (GPS).

3.2 Methods

3.2.1 Analysis of Limestone

3.2.1.1 Determination of Calcium Carbonate in Limestone

1g of limestone sample was dissolved in 20 mL 1M HCl and heated to decompose the

carbonate. The solution was cooled and titrated against 0.5 M NaOH using phenolphthalein

indicator.

3.2.1.2 Determination of Lime in Limestone

Calcium carbonate obtained in 3.2.1.1 multiplied by 0.56 gave % CaO.

3.2.1.3 Determination of Loss on Ignition (LOI)

1g limestone sample (m1) was introduced into a crucible and placed in a muffle furnace at

900 oC for 30 mins. The heated sample was allowed to cool to room temperature in a

desiccator and weighed (m2). LOI was computed as a percentage of m1

LOI= (m1-m2) × 100 % …3.1

3.2.2 Analysis of Gypsum

3.2.2.1 Determination of Sulphite (SO3)

1g sample of gypsum was introduced into a 250 mL beaker and mixed with 90 mL of cold

distilled water. 10 mL of concentrated hydrochloric acid were added to the mixture and

58

heated gently until decomposition of the sample was complete. The solution was allowed to

cool and then filtered through Whatman filter paper No. 40 into a 400 mL beaker. The filtrate

was made up to 250 mL and reheated to boiling point. While boiling, 10 mL 0.5M BaCl2

were added to the boiling solution. The solution was allowed to cool with minimum

disturbance for 1hour for proper precipitation of sulphate ions.

The precipitate was filtered through Whatman No.42 filter paper and washed with boiling

water until free from Cl- ions. Silver nitrate was used to confirm the absence of Cl

- ions. The

residue (precipitate) was weighed in a porcelain crucible, charred and ignited in a muffle

furnace at 900 oC for 30 mins. The residue was cooled in a desiccator and final weight taken.

The difference in weights was expressed as SO3

% SO3 �� .��

��

...3.2

Where 0.343 is the molar ratio of SO3 to BaSO4 or gravimetric factor of SO3

3.2.2.2 Determination of Gypsum Purity

The purity of gypsum was obtained by multiplying % SO3 by 2.15. Where, 2.15 is molar ratio

of CaSO4.2H2O to SO3 (Appendix 2).

3.2.3 Analysis of Clinker

3.2.3.1 Determination of Loss on Ignition (LOI) and Sulphite (SO3) of Clinker

Loss on ignition determination in clinker followed same procedure as for limestone in 3.2.1.3

and SO3 analysis of clinker followed same procedure as for gypsum in 3.2.2.1.

3.2.3.2 Determination of Silica in Clinker by Baking Method

1g sample of clinker was ground with 1g of NH4Cl (fusion agent), and diluted with 10 mL

concentrated hydrochloric acid in a glass dish, and heated to dryness. The dried mixture was

allowed to cool to room temperature and later dissolved in 50 % HCl. The mixture was

reheated until all particles dissolved. The solution was made up to 2/3 full of the glass dish

with hot distilled water and filtered using Whatman filter paper No.42 into 250 mL conical

flask. The filtrate was allowed to cool and transferred into 250 mL standard flask and made

up to the mark with cold distilled water. It was shaken thoroughly and preserved for analyses

59

of iron (III) oxide, Aluminium (III) oxide and lime. The residue on the filter paper was used

for SiO2 determination by gravimetry after washing it free of Cl- ions. SiO2 was calculated

from the equation 48

:

SiO2= ��

�� 100 % …3.3

3.2.3.3 Determination of Iron (III) Oxide and Aluminium (III) Oxide in Clinker by

EDTA Titration 48

50 mL of the filtrate obtained in silica determination were pipetted into a 250 mL beaker and

made up to 100 mL with cold distilled water. 10 drops of sulphosalicylic acid indicator were

added into the solution and its pH was adjusted to 1.5 using NH4OH. The solution was heated

below 50 oC on a hot plate with magnetic stirrer (Gallenhamp), to stir the solution

continously. 0.05 M EDTA in a burrette was ran into the solution in drops until a persistent

reddish yellow colour change was observed. Iron content was obtained by

Fe2O3= Volume of EDTA×1.99625 % …3.4

The titrated solution was retained for aluminium oxide determination. The solution’s pH was

adjusted to 3.2 using 50 % ammonium acetate (CH4COONH4). The solution was reheated

and 5 drops of copper complexonate indicator and 10 drops PAN (1, 2 –pyridylazo – 2 –

naphthol) indicator were added. The solution was titrated with 0.05 M EDTA until colour

changed from violet- pink to pale yellow.

Al2O3= Volume of EDTA×1.2745 % …3.5

3.2.3.4 Determination of Calcium Oxide in Clinker by EDTA Titration 48

10 mL of the filtrate obtained from silica determination was pipetted into a 250 mL beaker.

10 mL of aqueous triethanolamine (1:4) solution were added to the filtrate and made up to

100 mL mark with cold distilled water. The pH was adjusted to 12.5 using 0.5 M KOH

solution.

The solution was stirred gently and steadily by means of a magnetic stirrer and titrated with

0.05 M EDTA with 0.1g calcein indicator until colour changed from pink to a persistent pale

yellow

60

CaO = volume of EDTA ×7.01 % …3.6

3.2.3.5 Determination of Free Lime in Clinker by Hot Ethylene Glycol Method 48

0.750 g of sample was weighed in a 250 mL conical flask and 40 mL of ethylene glycol were

added. The mixture was heated to 70 oC for 30 mins. in a water bath, and was filtered into a

dry Erlenmeyer flask with a Gooch crucible having asbestos bed with the aid of a suction

pump. The filtrate was titrated with 0.1M HCl using bromocresol green indicator.

Free lime = Volume of 0.1M HCl×0.2804 % …3.7

3.2.3.6 Estimation of Clinker Constituents Using Bogue’s Formulae

The four main compounds of clinker and cement were estimated using the equations 90

:

C3S = 4.0718(CaO-free lime)-{7.6SiO2+6.71Al2O3+1.43Fe2O3}

C2S = 2.87SiO2-0.754C3S

C3A = 2.65Al2O3-1.692Fe2O3

C4AF =3.073Fe2O3

3.2.4 Preparation of Laboratory Cements

A portion of LPS was oven dried at 100 oC for 10 min. The dried sample was ground into fine

powder with the aid of a disc mill. 1g of it was used for calcium carbonate determination by

titrimetric method, while another 1g of the same limestone sample was used for

determination of loss on ignition.

The laboratory cements were made by milling varying quantities of clinker and limestone and

a fixed quantity (4 %) of gypsum with the aid of a laboratory cement mill, till the desired

particle size and Blain were attained. Various limestone composite cements were made by

varying % limestone content as shown in Table 3.1. The samples were labeled OPC, C5, C10,

C15, C20, C25 and C30 respectively.

In preparation for chemical analyses, 100 g of each cement blend were sieved through 90 µm

mesh (BS 410). The samples were shaken thoroughly in polyethylene bags and stored.

61

Table 3.1 Composition of limestone composite cements (LCCs)

LCC % limestone % clinker % gypsum

OPC 0 96 4

C5 5 91 4

C10 10 86 4

C15 15 81 4

C20 20 76 4

C25 25 71 4

C30 30 66 4

3.3 Physical Analyses of Cements

Standard methods were used for analyses of laboratory cements [ordinary Portland cement

(OPC) and limestone composite cements (LCCs)] and market branded cements (MBCs)

3.3.1 Determination of Water Demand and Consistency

500 g of cement sample were mixed with various amounts of water (Wg) within a maximum

time of 4 min. The resulting paste was put into a Vicat mould until it was full using a hand

trowel. The mould was placed under the Vicat plunger which weighed 300 g. The plunger

was lowered gently until it made contact with the surface of the paste, and then left to

penetrate into the paste. The amount of water contained in the very paste which was allowed

a penetration of 5-7 mm is taken as the water demand in accordance with NIS 444-1:2003 46

.

The consistency was then calculated using the formula

��

500�� 100 % ……..3.8

Where Wg is weight of water

3.3.2 Determination of Setting Time

The initial and final setting times were determined using the Vicat needle (NIS 447:2003).

The needle which is attached to the Vicat apparatus was calibrated by lowering it to rest on

the base plate of the instrument and then adjusting the pointer to read zero on an attached

scale. The needle was later raised to stand in position.

62

The cement paste which has gone through standard consistency test was transferred into an

open mould on the base plate of the Vicat instrument. The needle was released to penetrate

vertically into the paste. When penetration ceased, the scale on the Vicat instrument was read

and the time recorded as the initial setting time, T0.

The mould was later inverted, and the needle was attached with a ring, and allowed to rest on

the reverse face of the paste. The final setting time Tf was recorded as that time, starting from

onset of experiment when the ring failed to make a mark on the reverse surface.

3.3.3 Determination of Soundness

Cement paste of standard consistency was used to fill a Le Chatelier mould, which has two

indicator needles. After filling the mould, the distance (do) in millimeters, between the

needles was measured and recorded. The filled Le Chatelier mould was heated in boiling

water for 30 min., and after allowing to stay in a humidity cabinet for 24 hours, the soundness

was later determined by measuring the new distance (df) between the two needles. The

soundness was obtained by the difference, df – d0.

3.3.4 Determination of Cement Residue (Fineness) Using Sieve Method

100 g of cement sample were sieved through 45 µm, 90 µm and 180 µm sieves (BS 410). The

residues were expressed as percentage of the initial weight.

residue = �� of residue

�� 100 ……..3.9

3.3.5 Determination of Cement Surface Area Using Air Permeability Method

118 g of cement sample were carefully introduced into an air permeability cell which has a

filter paper on a disc with holes (1mm diameter) under it. The sample was covered by another

filter paper disc on its top to avoid loss of material by sticking onto the surface of a plunger.

The sample was compacted with a plunger which was inserted gently but firmly into the cell

until the plunger cap made contact with the cell.

The cell was inserted into the socket at the top of the manometer, and the stop cock of

the manometer was opened to adjust the manometer liquid to a lower etched line. The stop

cock was released and the timer started automatically and it stopped when the liquid reached

the upper etched line. The time for the liquid to move from the lower to the upper etched line

was recorded as ts.

63

Blaine (specific surface), or B is then calculated by the formular:

B = K√ts … 3.10

Where K is apparatus constant and B is in m2/kg

To determine K, a reference sample of known B was compacted and subjected to air

permeability test, and the time taken for the liquid to move from lower to higher etched line,

tsav was recorded. Thus K was obtained by the relationship;

K= B/ √tsav …3.11

3.3.6 Determination of Compressive Strength

Mortar consisting of one part by weight of cement (450g) and, three parts by weight of

standard sand (1350g) with water to cement ratio of 0.5 (225g of water) was produced. The

particle size distribution of standard sand used for the mortar production is shown in the

Table 3.1

Mortar production was by mechanical mixing as follows: Water was poured into a

mechanical mixer bowl and cement was added gently into the water. The mixer was

immediately started at low speed and the sand was steadily added during the next 30 seconds.

The mixer was switched to high speed and mixing continued for additional 30 seconds, after

which the mixer was turned off and mortar was allowed to rest for 90 seconds. During the

rest time, the sides of the mixer bowl were scrapped down to the bottom, before mixing

resumed at high speed for another 60 seconds. Table 3.2 shows the mixer speed during

mortar production.

The mortar samples produced were moulded immediately using a prismatic mould on a

jolting apparatus (NIS 446-2003)47

. With the mould firmly clamped to the jolting apparatus,

the prismatic test specimens were made in pairs for each mortar. The moulds were labeled

accordingly and stored for 24 hours in a humidity cabinet for the prisms to acquire strength

enough to be demoulded without risk of damage.

All demoulded prism specimens were water cured at 20 oC for various periods of time after

which, their compressive strengths (RF) were determined in MPa as follows:

64

RF=F/A,…….3.12

Where F is maximum load at fracture in Newtons and A is area of prism (40 mm × 40 mm)

subjected to compressive load.1 MPa is equivalent to 1 N/mm2

Table 3.2 Particle size distribution of standard sand used for preparation of mortar for

determination of compressive strength 47

Sieve mesh (mm) of sand

particle

% weight Weight (g)

2.0 7 95

1.6 26 351

1.0 34 459

0.5 20 270

0.16 13 175.5

Total 1350

Table 3.3 Mixer speed during mortar production 47

Rotation min-1

Planetary movement

Min-1

Low speed 140 62

High speed 285 125

3.4 Chemical Analyses of Cements

Loss on ignition (LOI) determination for cement and clinker followed same procedure as for

limestone in 3.2.1.3 while analysis for SO3, SiO2, Fe2O3, Al2O3, CaO and free lime for

cements followed the same procedure as for clinker.

3.5 Quality Control and Statistical Treatment of Data

The accuracy of results was ensured by the use of analytical grade chemicals to prepare

standard solutions and reagents. Titrations were conducted thrice for every sample and

averaged. In all cases, measurements were done in triplicates, averaged and standard

deviations reported.

65

SPSS version 18.0 windows data editor software program was used in determining the

significance in variation of OPC, LCCs and MBCs.

66

CHAPTER FOUR

4.0 RESULTS AND DISCUSSION

4.1 Results

Total carbonate in limestone revealed 91.08 % while lime was 51.00 %. The limestone

sample is of calcite formation and belongs to the marlaceous grade of limestone as shown in

Table 2.2 19

. By the European and Nigerian standards EN197 and NIS 444.2003 respectively,

the minimum calcium carbonate requirement is 75 %. Table 4.1 shows the mean values of

parameters of the parent limestone sample (PLS) analyses.

Table 4.1 Mean values of total carbonate and lime content (%) and loss on ignition of

limestone parent sample (n=3).

TC

Lime

LOI

91.08±0.14

51.00±0.17

40.21±0.09

*LOI (loss on ignition), TC (total carbonate)

The sulphite content of gypsum was 42.31%, which translates to a purity of 90.97 %. These

are shown in Table 4.2. Sulphite content of gypsum is related directly to its purity; high

sulphite content shows high purity.

Table 4.2 Mean sulphite content and purity of gypsum (n=3)

%

SO3 42.31±1.40

Purity 90.97

*purity = % SO3 multiplied by2.15

The parent clinker sample was characterized in terms of chemical and mineralogical

properties. The mineralogical properties are 3CaO.SiO2 or (C3S), 2CaO.SiO2 or (C2S),

3CaO.Al2O3 or (C3A) and 4CaO.Al2O3.Fe2O3 or (C4AF). The values of the chemical and

mineralogical compositions are shown in Table 4.3 while the chemical and physical

67

properties of the OPC, namely (compressive strengths, fineness, soundness or expansion,

consistency and setting time) are shown in Table 4.4. The behavior of cement depends both

on chemical and physical properties. These physical properties indicate quality of the

cement.

Parameters shown in Table 4.3 indicates that the clinker is good for high quality Portland

cement. The free lime content of 0.87 % indicates that there was proper reaction of lime with

the oxides to form the mineral compounds. Furthermore, cement made from the clinker will

likely be sound i.e will have expansion less than 10 mm as specified by NIS when hardened.

Good clinker is expected to contain atleast 55 % C3S and not less than 70 % sum of C2S and

C3S.

Table 4.3 Chemical and mineral parameters of clinker parent sample (n = 3)

Chemical composition Mineral composition

Chemical % content Mineral % content

SiO2 20.23±0.06 C3S 62.41

Al2O3 6.29±0.02 C2S 11.01

Fe2O3 3.30±0.02 C3A 11.08

CaO 65.48±0.04 C4AF 10.14

SO3 0.79±0.01 Litre weight, g/L 1274±0.58

Free lime 0.87±0.01 - -

LOI 2.17±0.02 - -

68

Table 4.4 Mean Chemical and physical characteristics of OPC (n=3)

Chemical composition Physical Composition

Chemical % content Fineness(µm)

SiO2 17.75±0.06 45 21.73±1.67

Fe2O3 3.41±0.01 90 3.33±0.46

Al2O3 6.09±0.01 180 1.33±0.23

CaO 64.62±0.06 Blaine (m2/Kg) 297±3.06

SO3 2.72±0.14 Soundness,S (mm) 1.67±0.29

LOI 1.50±0.14 Consistency (%) 27.97±0.45

Free lime 0.88±0.01 Plunger (mm) 5.70±0.58

Setting time (mins)

Initial (T0) 107.33±2.5

Final (Tf) 180.67±6.81

Compressive strength (MPa)

2days 26.25±0.51

7days 31.07±0.80

28days 36.20±0.85

The OPC as shown in Table 4.4 complies with standard specification for good quality. The

low free lime caused a low (less than 10 mm) expansion. Initial setting was above 75 minutes

and 28 days strength was more than 32.5 MPa being minimum specification for Portland

cement.

Table 4.5 shows the effects of limestone addition on the mean chemical contents of OPC.

69

Table 4.5 Mean values of chemical composition of OPC and LCCs (n=3)

%SiO2 %Al2O3 %Fe2O3 %CaO %SO3 %LOI %Freelime

OPC 17.75±0.06 6.09±0.01 3.41±0.01 64.62±0.06 2.72±0.14 1.50±0.14 0.88±0.01

C5 17.64±0.04 6.08±0.006 3.37±0.02 64.70±0.08 2.68±0.07 3.69±0.10 0.83±0.006

C10 17.53±0.02 6.08±0.01 3.33±0.006 64.77±0.05 2.49±0.11 5.65±0.04 0.81±0.006

C15 17.44±0.01 6.05±0.06 3.29±0.01 64.82±0.01 2.63±0.03 7.95±0.10 0.69±0.02

C20 17.20±0.13 6.02±0.02 3.22±0.02 64.78±0.08 2.72±0.21 10.22±0.03 0.65±0.01

C25 17.12±0.02 6.01±0.006 3.17±0.01 64.96±0.02 2.27±0.08 11.12±0.05 0.71±0.02

C30 17.00±0.03 5.99±0.006 3.12±0.006 64.97±0.06 2.31±0.08 13.25±0.08 0.55±0.02

Addition of limestone to OPC increases surface area and fineness because it is finer and

softer to grind than clinker. In terms of the chemical content, it leads to reduction of all

except CaO, with the consequential increase in LOI as shown in Table 4.5. Table 4.6 shows

the effect of limestone addition on particle size and surface area of OPC.

Table 4.6 Effect of added limestone on fineness of Portland cement

% Standard sieve residue

Composite 45(µm) 90(µm) 180(µm) Blaine (m2/kg)

OPC 21.73±1.67 3.33±0.46 1.33±0.23 297±3.06

C5 19.87±1.51 2.13±0.23 0.80±0.69 316±2.00

C10 19.87±0.83 2.27±0.23 0.53±0.23 338±3.51

C15 28.20±3.22 4.33±0.64 0.93±0.23 343±4.16

C20 23.00±4.50 2.40±0.40 0.67±0.46 383±5.51

C25 28.33±1.42 5.33±0.61 2.13±0.83 399±3.06

C30 30.33±1.42 5.93±0.42 2.40±0.69 413±11.24

70

Table 4.7 shows no significant effect of added limestone on mean values of soundness of

OPC. All soundness values are less than 10 mm as specified by NIS.

Table 4.7 Mean values of soundness of Portland cement (n=3)

OPC C5 C10 C15 C20 C25 C30

1.67±0.29 0.67±0.29 1.00±0.00 1.00±0.00 1.00±0.50 0.83±0.29 1.17±0.29

The setting times, consistencies and plunger penetrations (PP) of the LCCs are shown in

Table 4.8. Limestone addition increased setting times and reduced consistency of OPC but

did not affect PP significantly. For quality cement, NIS prescribes initial setting time not less

than 75 minutes, consistency 26 – 30 % and plunger penetration of 5 – 7 mm.

Table 4.8 Mean setting times and consistencies of Portland cement (n=3)

Composite

cements

Setting time (mins) Consistency % PP(mm)

Initial T0 Final Tf

OPC 107.33±2.52 180.67±6.81 27.97±0.45 5.70±0.58

C5 115.33±1.53 183.00±2.00 27.60±0.17 5.67±0.58

C10 117.33±4.73 183.67±2.52 27.30±0.20 6.00±1.00

C15 125.33±1.53 187.67±2.89 26.80±0.30 6.00±1.00

C20 122.00±2.00 185.00±3.61 26.53±0.31 5.67±1.15

C25 119.67±1.53 189.67±3.06 26.10±0.96 5.33±0.58

C30 126.00±1.00 229.33±7.09 24.80±1.22 5.33±0.58

*PP (Plunger penetration)

71

The effect of added percentages of limestone on strength development of the various LCCs is

shown in Table 4.9. Addition of limestone to OPC reduced compressive strength significantly

beyond 15 % added limestone. Limestone composite cements containing 5-15 % added

limestone satisfied compressive strength of not less than 32.5 MPa as prescribed by NIS.

Table 4.9 Mean compressive strengths of LCCs (n=3)

Composite

cements

2 days(MPa) 7days(MPa) 28days(MPa)

OPC 26.25±0.51 31.07±0.80 36.20±0.85

C5 25.00±1.12 31.34±1.74 34.77±0.60

C10 23.61±0.49 32.07±0.62 33.13±1.12

C15 21.78±0.69 28.46±0.45 33.63±1.58

C20 20.54±1.27 27.61±1.31 32.45±0.37

C25 20.08±0.60 26.14±0.39 31.39±0.92

C30 17.28±0.93 22.68±1.24 28.49±0.05

The mean range chemical and physical parameters of some analysed MBCs are shown in

Table 4.10. All brands of the cements satisfied NIS specification for 28 days strength (not

less than 32.5 MPa) therefore they are of good quality.

72

Table 4.10 Mean range of chemical and physical parameters of some analysed MBCs (n=3)

Local (Cla&Clb) cements Foreign (Cfa & Cfb) cements

SiO2 (17.83-17.93) ± (0.01-0.04) (17.66-17.69) ± (0.01-0.06)

Al2O3 (6.00-6.06) ± (0.01-0.006) (5.99-5.99) ± (0.006-0.02)

Fe2O3 (3.23-3.30) ± (0.01-0.02) (3.27-3.31) ± (0.006-0.07)

CaO (64.45-64.79) ± (0.02-0.03) (64.84-65.85) ± (0.03-0.03)

SO3 (2.70-3.70) ± (0.07-0.28) (3.32-3.89) ± (0.10-0.21)

LOI (3.75-6.60) ± (0.01-0.57) (3.32-3.60) ± (0.06-0.26)

Free lime (%) (0.36-1.60) ± (0.03-0.03) (1.25-1.73) ± (0.02-0.03)

Initial setting (mins) (105.33-119.3) ± (3.21-6.60) (111.3-125.33)± (1.53-3.06)

Final setting (mins) (184.67-191.33)± (1.25-6.66) (176.0-189.0) ± (1.53-4.00)

Fineness: 90 (µm) (0.93-7.07) ± (0.23-1.89) (3.33-7.07) ± (0.23-0.61)

180 (µm) (0.00-0.80) ± (0.00-0.40) (0.40-0.13) ± (6.8e-17

-0.23)

Blaine (m2/ kg) (332-394) ± (15.01-60.06) (283-287) ± (0.00-1.15)

Consistency (%) (26.27-27.40) ± (0.42-1.25) (27.00-28.90) ± (0.26-1.15)

Soundness (mm) (0.33-0.67) ± (0.58) (1.00-1.17) ± (0.0-0.29)

PP (mm) (5.33-5.67) ± (0.58) (5.67- 6.00) ± (0.58- 1.00)

28days strength (MPa) (41.62-43.36) ± (1.70-5.98) (42.55-50.56) ± (0.77-1.33)

4.2 Discussions

4.2.1 Clinker Parent Sample

The chemical composition of the clinker is derived from the chemical composition of the raw

material used in producing the clinker. The values of the oxides are influenced by the

homogeneity of the raw meal, conditions of the kiln such as temperature and particle size

distribution of the raw meal.

The free lime content is an index showing the degree of reaction. It is the lime, CaO, left after

reacting with SiO2, Al2O3 and Fe2O3 and had a mean value of 0.87± 0.01 %. Free lime is a

result operational condition of temperature and material quality. The maximum specification

for free lime in Portland cement clinker is 1.5 %. Estimated values of mineral components of

the parent clinker sample showed: C3S 62.41 %, C2S 11.01%, C3A 11.08 % and C4AF 10.14

%. For good quality clinker, C3S of at least 55 % content is desired 50

. Litre weight and free

73

lime are related in the sense that when free lime gets low the litre weight increases. This free

lime of 0.87 % and litre weight of 1274 g/L may suggest that the raw meal was subjected to

excessive heat. Although there is no specified limit for litre weight, it is however a good

operational control measure for free lime control.

4.2.2 Ordinary Portland Cement (OPC)

The chemical and physical properties of the laboratory OPC are shown in Table 4.4. The

chemical parameters SiO2, Al2O3, Fe2O3 and SO3 vary from those in clinker. The final

composition of the cement is as a result of the contribution of the gypsum in Table 4.2 to the

various oxides. 4 % gypsum increased SO3 from 0.79 % in clinker as seen in Table 4.1.3 to

2.72 % in cement as shown in Table 4.4. This value satisfies Standards specification of 2.5 to

3.5 % for SO3 in Portland cement 50

. The reduction in oxides, from clinker to OPC suggests

that gypsum contributes more SO3 than other oxides. Free lime was not affected by the

introduction of gypsum. The introduction of gypsum did not increase LOI but reduced it from

2.17 % in clinker to 1.50 % in OPC in Table 4.4. This is because gypsum unlike limestone

contributes lesser lime and this reduced LOI.

The particle sizes of the OPC ranging from 45 to 180 microns added up to 26.39 % as shown

in Table 4.4. This means that finer particle sizes added up to 73.61 %. This would have

increased if Blaine value were to be higher than 297m2/kg. Since OPC has no other additive

other than gypsum higher Blain would not be necessary since the strength giving compounds,

C3S and C2S are in their concentrated states. The particle size distribution effect is

appreciated by the rate of hydration which translates into strength development within two

days. The strength of cement concrete or mortar develops with the rate of hydration. More the

rate of hydration, the faster will the development of strength be. This is because the finer

cement particles hydrate faster because of greater surface area (Blaine) hence faster the

development of strength. Table 4.4 shows a mean compressive strength of 26.25 MPa at 2

days and 31.07 MPa at 7 days and 36.20 MPa at 28 days. Nigerian Standard for compressive

strength specifies a minimum of 16.0 MPa at 7 days and 32.5 MPa at 28 days 50

.

Nigerian Standards specification for Portland cement specifies maximum of 10 mm for

soundness, 26 to 30 % for consistency, 5 to 7 mm Vicat plunger penetration and minimum of

75 minutes for initial setting for Portland cement50

.

74

4.2.3 Effect of Added Limestone on Chemical Composition of LCCs

Table 4.5 showed the effect of added limestone on chemical composition of OPC. As

portions of clinker reduced with increase in added limestone the parameters; SiO2, Al2O3,

Fe2O3 and SO3 reduced. This means that limestone of high lime and high CaCO3 contributes

insignificantly to SiO2, Al2O3, Fe2O3 and SO3. From the decomposition of CaCO3, 44% CO2

is lost and 56% CaO is retained therefore for every addition in added limestone 56 % CaO is

contributed. This increased the lime content of the limestone composite cements linearly.

Using the same analogy, it is expected that increased percentage of added limestone will

increase LOI of the limestone composite cements as shown in figure 4.1. There was no

significant variation in LOI of OPC and the LCCs (p>0.05).

Figure 4.1 Effect of limestone addition on loss on ignition of Portland cement.

Table 4.5 showed a reduction in free lime as added limestone increased. Lime is the product

of decomposition of CaCO3. The lime is usually most abundant than the other oxides required

for reaction to form the clinker compounds. The lime reacts with SiO2, Al2O3 and Fe2O3 to

form C3S, C2S, C3A and C4AF. The lime left after the reaction is free lime. Since CaCO3 in

the limestone is not decomposed it has no contribution to free lime of Portland cement.

Figure 4.2 shows a downward slope of free lime as clinker portion in limestone composite

cement reduced (Table 3.1) while limestone increased. The reduction in clinker affected free

lime significantly and this weakened compressive strength as shown in Table 4.9.

0

2

4

6

8

10

12

14

16

0 5 10 15 20 25 30 35

% L

oss

on

ig

nit

ion

% added limestone

75

Figure 4.2 Plot of free lime against % added limestone in Portland cement

The sulphate which is in form of sulphite reduced with increased added limestone. This trend

was observed in two different investigations. Both of them concluded that although sulphite

decreased with increase in percent added limestone, it was not a linear relationship. This can

be observed in Table 4.5 as the reduction is not with every increase in added limestone as is

depicted in Fig 4.3. The NIS 444:2003 specifies 2.5 - 3.5 % SO3 for Portland cement. As

presented in Table 4.5 SO3 was satisfied from 5 to 20 % added limestone. Limestone addition

beyond 20 % affected SO3 significantly. Therefore the depletion of SO3 could lead to the

formation of carboaluminate which retards activity of C3A hence delaying setting as shown in

Table 4.8.

Figure 4.3 Plot of sulphite against % limestone in Portland cement

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 5 10 15 20 25 30 35

% F

ree

lim

e

% Added limestone

0

0.5

1

1.5

2

2.5

3

0 5 10 15 20 25 30 35

% S

O3

% Added limestone

76

4.2.4 Effect of Added Limestone on Particle Size and Surface Area.

Table 4.6 shows variation in particle size and surface area with increase in added limestone.

Blaine values increased from 297 m2/kg to 413 m

2/kg. This increase in limestone addition

translated linearly to surface area of the LCCs as shown in Fig 4.4b. The addition of

limestone dilutes the strength giving compounds, i.e. C3S and C2S and so to achieve higher

strength i.e. above 32.5 MPa or strength close to that of OPC, greater surface area and

fineness are required. This explains the positive gradient on Figure 4.4b. The effect of higher

Blaine on strengths of Portland cement is shown on Table 4.9. Table 4.6 shows

corresponding increase in fineness as surface area increased. At 297 m2/kg coarse portion in

the particle size distribution from 45 to 180 micron sieves added up to 26.39 %, at 316 m2/kg

particle size from 45 to 180 micron sieves added up to 22.80%, at 338 m2/kg was 22.67 %, at

343 m2/kg was 33.46 %, at 383 m

2/kg was 26.07 %, at 399 m

2/kg was 35.79 % and at 413

m2/kg was 38.66 %. 5 % and 10 % added limestone sieve on 45 micron sieve did not decrease

even at increased grinding which raised Blaine value as shown in figure 4.4a. As presented

in Table 4.6, the sieve on 45microns the fineness values (amount retained on 45 micron

sieve) of cements prepared by using higher percentages of added limestone increased in line

with their increasing Blaine values. Observation of the coarse portion retained on 45 micron

sieve revealed the existence of coarse limestone particles in the cement powder. This

increased with increased limestone addition. This is against the rule but it occurs anyway. A

high Blaine value indicates proper grinding process. However, some limestone particles

remained coarser. Similar situation was observed when sieves with wider openings (90 and

180 microns) were used. For example, the amount retained by 90 and 180 microns sieves for

30 % added limestone were 5.93 % and 2.40 % respectively above OPC. The additions of

limestone did not affect particle size and surface area of the LCCs significantly (p>0.05).

In general, limestone particles are softer than clinker particles. However in order to provide

ease of grinding, limestone is to be absolutely dry. The difficulty here is that limestone sticks

to the surfaces of the grinding mill and grinding balls. Stickiness of limestone may be due to

hygroscopic nature of limestone. However during the initial grinding periods, the fineness of

both limestone and clinker particles increased (reduced sieve retention on 90 and 180

microns). At the following stages, the water bound in the limestone is detached due to

grinding energy and adhered onto the surfaces of the mill and balls. This adhesion of

limestone particles on the surfaces of balls and membrane creates a layer that reduces

grinding efficiency of the mill. In the case of a full scale mill, the water bound in limestone

77

evaporates at the stage of grinding due to inner mill temperature exceeding 100 oC and

sticking problem may not be observed. The effect of water bound in limestone on

grindability of limestone and clinker decreases in cement production. On the contrary, it is

not absolutely possible to reach the required temperature to evaporate the water content of

limestone in a laboratory mill.

Figure 4.4a Plot of residue retained on 90µm and 180µm against % added limestone in

Portland cement

Figure 4.4b Plot of surface area of Portland cement against % added limestone

0

1

2

3

4

5

6

7

0 5 10 15 20 25 30

Sie

ve

re

sid

ue

s (%

)

% added limestone

90

180

0

50

100

150

200

250

300

350

400

450

0 5 10 15 20 25 30 35

Bla

ine

m2/k

g

% added limestone

78

4.2.5 Effect of Added Limestone on Soundness of Portland Cement

The soundness of the limestone cements presented in Table 4.7 is satisfactory. The

soundness measured according to Le Chatelier procedure varied from mean value of 0.67 mm

to 1.67 mm while the limit according to NIS 444:2003 is not more than 10 mm. Soundness is

affected by high free lime and correlating Tables 4.5 and 4.7 satisfactory free lime generally

keeps soundness within acceptable range. Soundness for OPC was lower than those LCCs.

This may be as a result of reduced clinker portion in the cement samples. However added

limestone (not thermally decomposed) had no significant impact on soundness of LCCs.

4.2.6 Effect of Added Limestone on Setting Time and Consistency of Portland Cement

Table 4.8 presents the cement paste consistency, setting time and Vicat plunger penetrations

of OPC and the LCCs. The term consistency is generally considered to be the percentage of

water to cement ratio which is required to prepare a cement paste of standard consistency as

specified by NIS 444:2003. A standard cement paste will allow a Vicat plunger penetration

5-7 mm below the surface of the cement paste 50

. Table 4.8 presents Vicat plunger

penetration of various cement pastes ranging from (5.33 – 6.00) mm and there was no

significant variation among the Vicat penetration values.

The LCCs demanded less water than the OPC; this may be due to limestone’s inertness or

non involvement in the hydration reaction. In limestone composite cements containing 5 %

to 10 % limestone content there was a reduction in consistency from 27.60 % - 27.30 %.

This trend of near constancy was similar with results obtained by Helal and Mark 73, 91

. The

increase in limestone from 15 – 20 % caused a decrease in consistency from 26.80 – 26.53 %.

Further increase in added limestone reduced consistency to 24.80 %. These reductions as

shown in Fig 4.5 have a linear downward trend. This trend was observed oppositely by Helal

and Mark 73, 91

. They both reported increase in consistency with corresponding increase in

added limestone. The effect of added limestone on consistency of the limestone cements can

be attributed to the low water absorption of limestone since it is not involved in hydration

reaction and its increased fineness and surface area. The LCCs despite their higher surface

areas had wider particle size distributions probably due to the intergrinding of soft limestone

with the hard clinker. The drop from 26.10 – 24.80 % as added limestone rose from 25 % to

30 % could be attributed to fine particle size of limestone within the blended cement pastes as

suggested by Tsivilis 13

. This means that particle size distribution gets wider with added

79

limestone and 30% added limestone gave the widest particle size distribution and its particle

size required the least percentage of water for hydration.

Setting time is affected by (i) cement fineness and (ii) water to cement ratio (consistency).

Table 4.8 presents the consistencies and setting times of cement pastes as added limestone

increased. Table 4.8 shows that the blended cement paste had delays in initial setting times

more than OPC. The reactions involved in setting of cement are the hydration of C3A and

calcium silicates which change into their colloidal gels. At the same time, some calcium

hydroxide and aluminum hydroxide are formed as precipitates due to hydrolysis. Calcium

hydroxide binds the particles of calcium silicate together while aluminum hydroxide fills the

interstices rendering the mass impervious. These six reactions are responsible for initial

setting 92

(1) 3CaO. Al2O3 + 6H2O → 3CaO . Al2O3 .6H2O

Tricalcium Aluminate hydrated colloidal gel of tricalcium aluminate

(2) 3CaO SiO2 + H2O → Ca(OH)2 + 2CaO. SiO2

Tricalcium silicate Dicalcium silicate

(3) 2CaO. SiO2 + xH2O → 2CaO. SiO2. xH2O

Dicalcium silicate hydrated colloidal gel of dicalcium silicate

(4) 3CaO. Al2O3 + 6H2O → 3Ca(OH)2 + 2Al(OH)3

Tricalcium Aluminate

(5) 4CaO. Al2O3. Fe2O3 + 6H2O → 3CaO. Al2O3 6H2O + CaO. Fe2O3

Tetracalcium aluminoferrite Hydrated colloidal gel of tricalcium aluminate.

(6) 3CaO. Al2O3 + 3CaSO4 + 31H2O → 3CaO. Al2O3. 3CaSO4. 31H2O

Calcium sulphoaluminate or Ettringite

As shown in Table 4.5, increase in Limestone depleted SO3. It is expected that setting time

will be hastened. This was the trend observed by Mark 91

and this was contrary to trend

shown in Table 4.8. Fig 4.6 shows no clear trend in how added limestone affects initial

setting time of LCCs. From the observations in separate determinations, there was a non

80

linear trend on the effect of added limestone on setting of Portland cement 75, 81

. However the

delay in initial setting time could be attributed to decrease in sulphite contributed by gypsum

as added limestone increased. It is shown from Tables 4.8 and 4.6 that at higher limestone

additions and fineness, SO3 was depleted. Reduction in SO3 leads to faster setting and further

reduction could cause flash setting. However, the delay in setting could be attributed to

higher concentrations of calcium hydroxide due hydrolysis at equations 2 and 4 and

limestone itself which becomes the rate determinant of initial and final setting. Overall the

initial setting times conform to NIS 444:2003 specification that initial setting time of Portland

cement should not be sooner than 75 mins. Addition of limestone did not affect setting times

significantly.

The final setting times as shown in Table 4.8 also showed a similar trend as initial setting

times. The highest been at 30% added limestone, 229.3 secs. as against 180.7 secs. of OPC.

At this stage it could mean that there was excess dilution of the cement paste that resulted in a

delay of the final setting time. Helal and mark B et al observed differently as they observed

that final setting time of OPC paste was higher than the other cement pastes that contained

varying percentages of added limestone. They both agreed that decrease in final setting time

is due to the formation of increase calcium carboaluminate hydrates which has higher rate of

formation at early age of hydration 73, 91

. This probably could be due to particle size and

quality of limestone used in their investigation.

81

Figure 4.5 Plot of consistency of Portland cement against % added limestone

Figure 4.6 Plot of setting times of Portland cement against % added limestone

Vicat plunger penetrations decreased with increased added limestone. All penetration values

are within acceptable limits of 5-7 mm 50

. The penetration values suggest that the required

amounts of water were used in preparing the various cement pastes. Consistency of cement

24.5

25

25.5

26

26.5

27

27.5

28

28.5

0 5 10 15 20 25 30 35

% c

on

sist

en

cy

% added limestone

0

50

100

150

200

250

0 5 10 15 20 25 30

sett

ing

tim

es(

min

s)

% added limestone

T0

Tf

82

paste is expected to be less than 30 % since water affects setting time. The penetration values

at C25 and C30 are acceptable though, the consistencies suggest that the pastes were diluted

with excess water. The suspected over dilution might have also contributed to the prolonged

setting times of C30.

4.2.7 Effect of Added Limestone on Strength Development of Portland Cement.

The compressive strengths of OPC and LCCs are presented in Table 4.9. No significant effect

of added limestone on compressive strength was observed at 5% added limestone on all days

of curing. The strengths of all LCCs showed good early strength development within 7 days.

This is due to enhanced surface area and increased fineness. The strength of cement concrete

or mortar develops with the rate of hydration. The strength attained is a direct result of the

rate of hydration. A greater rate of hydration will produce higher strength. Standards

Organization of Nigeria does not specify minimum strength for 2 days but all 2 days strength

development are higher than 16 MPa minimum for 7 days. However, limestone addition

decreased the 28 days strengths. Bars illustrating strength gain at different percentages of

added limestone are given in Fig 4.10. Early age strength gain was higher for C5. The reason

for early age strength enhancement may be attributed to the nucleus forming effect of calcium

carbonate, CaCO3, particles for calcium hydroxide crystals at low concentration and

accelerating effect of limestone to the formation of calcium silicate hydrates, CSH 74

. At the

same time, limestone particles contribute to the strength development by forming

carboaluminate and by reducing the pore size of interstices thereby acting as inert filler 72, 74 &

80. However compressive strengths decreased with increased limestone addition in the long

term (28 days). It seems that beyond 2 to 3 days, calcium hydroxide concentrations decrease.

This may explain the drop in strength development with increase in added limestone

percentage for all the days of curing. Infact added limestone affected strength at 28 days

significantly beyond 15 % added limestone as shown in figure 4.8. By NIS 444:2003

specification, OPC satisfied 16.0 MPa for 7 days and 32.5 MPa for 28 days for Portland

cement.

83

Figure 4.7 Plot of strength development of Portland cement against % added limestone

Fig. 4.8 Effect of added limestone on strength of cement

4.3 Comparison of Some Analysed MBCs

The following are critical on the quality of cement.

(1) Imported cement contains additives employed in the manufacturing process and this

may affect their effectiveness at later ages.

(2) Some imported cement deteriorate due to long storage in transit 20

Therefore testing is required to confirm their compliance with Nigeria Industrial Standards

for cement. Table 4.10 presents mean ranges of physical and chemical parameters of sampled

cements sold in the Nigerian market. A comparative test of quality of local cements (labeled

Cla and Clb) and foreign cements (labeled Cfa and Cfb) was done for compliance with Nigerian

0

10

20

30

40

0 5 10 15 20 25 30

MP

a

% added limestone

2 days

7 days

28 days

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30 35

28

da

ys

stre

ng

th(M

pa

)

Composite cement blends %

84

Industrial Standards for cement. The range of loss on ignition (3.75 – 6.60) % for the local

brands of cement suggests that those cements samples were not OPC or type I cement. If

limestone were added to OPC it may have been between 5 to 10 % when compared with

Table 4.5. The loss on ignition of the foreign cement (3.32 -3.60) % suggest that the cements

most likely are Type I. this argument could be justified by the Blaine values of the foreign

cements. The Blaine range (283 – 287) m2/kg of the foreign cements are lower than those of

the local cements (332 – 394) m2/ kg but still have comparable if not higher 28 days

compressive strength. A higher Blaine indicates more proper grinding process. The higher

Blaines in the local cements could mean that higher surface area or greater grinding was

required to compensate for the dilution of C3S and C2S in OPC. This explains the high

strength in the foreign cement with lower Blaines.

Free lime values of both the foreign and local cement brands satisfied NIS 444:2003

specification of 2.5 % maximum limit for cements. The free lime values show optimum

condition for CaO to react with SiO2, Al2O3 and Fe2O3. Further more such clinker most likely

will not expand more than 10 mm as specified by NIS 444.2003.

Initial setting time of the local cement brands (105.3 – 119.3 mins.) were shorter than those

of the foreign cements (125.3 – 111.3 mins.). There is a relationship between SO3 and setting

of cement. A higher SO3 will delay in setting and vice versa. The wider range of SO3 in the

foreign cements is responsible for greater delays in setting than they are in the local cements.

All initial setting times are satisfactory as they satisfy NIS 444:2003 specification not sooner

than 75 minutes for Portland cement.

Obviously there was greater grinding in the local cements than the foreign cements. The

residue range on 90 µm for the local cements (0.93 – 7.07 %) as compared to foreign cements

(3.33 – 7.07 %) suggest that there was greater grinding process in the local cements.

Although residue when followed by higher surface area (Blaine) in the local cements, it

becomes obvious that it was necessary to compensate for adulteration of C3S and C2S. The

adulterated C2S and C3S require greater grinding to increase their surface area to hydration to

have high compressive strength. Residue on 90 µm of the local cements was 7.07 %. It is

characteristic of soft materials when interground with clinker. The soft material was retained

more even though it was subjected to greater grinding. This may be that the additive adhered

to the surface of the grinding membranes which in turn may have reduced grinding

85

efficiency. This increases residue retained on sieve. Conversely as observed in the foreign

cements the Blaine was less with expected higher residue range.

The absorption of moisture by finer particles is greater than coarser particles. When moisture

absorbed sufficiently it turns the material into paste. The paste is soft enough to allow for

plunger penetration (PP) into it. The extent of penetration indicates the consistency of the

material. When moisture absorbed increases there is greater plunger penetration into the

resulting paste. A deeper penetration indicates higher consistency 38, 39,40,41,42

. The consistency

range on the local cements (26.27 - 27.40 %) is greater than those of the foreign cements

(27.00 - 28.90 %). The consistencies agree with the various PPs. As prescribed by NIS

444:2003 standard consistency will allow PP limit to 5 - 7 mm and consistency range of 26 -

30 %.

Soundness of both the local and foreign cement samples is satisfactory. They are less than 10

mm as specified by NIS 444:2003. Concrete and mortar made with the cements can withstand

harsh weathers without cracking significantly.

Compressive strength at 28 days for the market cement brands all conformed to NIS

444:2003 specification above 32.5 MPa for Portland cement. Table 4.10 presents the mean

values of compressive strength of the cements. The highest values were produced by the

foreign cement (42.55 – 50.56 MPa). This is because the C3S and C2S in the clinker were not

diluted by additives and that may be the reason for low Blaine since not much grinding was

required unlike the local cement to achieve high compressive strength. There is no significant

variation (p˃0.05) in the strength of the market branded cements.

86

4.4 CONCLUSION

Limestone addition to ordinary Portland cement caused variations in the properties of the

OPC. However, the limestone composite cements (LCCs) with not more than15 % limestone

content compared favourably (p>0.05) with OPC. Further addition of limestone lowered the

quality of the LCCs (p<0.05) and made them unsuitable for high durable concrete works.

Therefore the range of 5 – 15 % was optimum for good quality limestone composite cement,

good enough to be used just as OPC in concrete and construction works. With this range 28

day compressive strength was good and satisfied NIS requirement for good Portland cement.

Quality parameters: setting time, soundness, sulphite and strength were good. These range of

LCCs, 5 – 15 % limestone content, compared favourably (p>0.05) with various analysed

brands of Portland cements obtained from Nigerian markets.

Composite cements that contained 20 - 30 % showed significant variation (p<0.05) in 28

days compressive strength and are unfit for high durable structures but can serve for masonry

works like plaster for walls.

4.5 Recommendations

1 Limestone content in limestone composite cement should not exceed 15%

2 Limestone composite cements containing not more than 15 % could be used in areas

where OPC is required

3 Since the LCCs (5 - 15 %) are comparable (p>0.05) with OPC, they can be used as

cheaper alternatives to minimize cost of construction works.

4 Consequently, cement manufacturers could be encouraged to produce this range of

LCCs to bring down cost of building.

4.6 Contribution to Knowledge

1 The optimum limestone content of limestone composite cement was found to be 5 –

15 %

2 This range of LCCs compared favourably (p>0.05) in quality with OPC

3 Beyond this range, the LCCs were found unfit for high durable civil and concrete

works, but could be used for masonry works

87

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95

APPENDIX 1

Preparation of Solutions and Indicators

Indicators

• PAN (Pyridylazon-napthol)

0.8 g PAN was dissolved in 400 ml ethanol in the presence of heat. After complete

dissolution it was allowed to cool to room temperature then transferred to indicator bottle and

made ready for use.

• Copper complexonate indicator

0.3977 g copper complexonate was dissolved in 100 ml distill water and allowed to stand.

The solution was stored and ready for use

• Phenolphthalein indicator

5 g of indicator was dissolved in minimum methanol and made up to 100 ml with distilled

water

• Bromocresol green (BCG) indicator

1g BCG in 75ml Ethanol and made up to 100 ml with distilled water

• Sulphosalicylic acid indicator

5 g of indicator was weighed into a 150 ml beaker and dissolved to 100 ml mark and made

ready for use.

• Buffer solution

35 g ammonium chloride was dissolved in 285 ml conc. Ammonia solution and made up to

500 ml with cold distilled water.

96

APPENDIX 2

Derivations of Constants

Purity constant for SO3

• CaSO4.2H2O →CaSO4+ 2H2O

• CaSO4→CaO+SO3

Theoretically,

CaSO4.2H2O→SO3

172 g/mol→80 g/mol

Therefore

CaSO4.2H2O/SO3 = 2.15

Sulphate molar ratio

CaSO4.2H2O→ CaSO4+ 2H2O 1

CaSO4 + BaCl → CaCl2 + BaSO4 2

BaSO4 → BaO + SO3 3

233 g/mol → 80 g/mol

(SO3/ BaSO4) ×100=34.3 % 4

Constant for CaO in EDTA titration

CaO → equivalent weight 56.08

1000 ml of 1M EDTA → 56.08 parts of CaO

1ml of 1M EDTA →56.08/1000 = 0.05608 parts of CaO

1ml of 0.05M EDTA → 0.05608 ×0.05= 0.002804 parts of CaO

1ml in 100 ml → 0.002804 ×100 = 0.2804 %

Weight of sample = 1g

97

Test solution =250 mls

Test solution taken = 10 mls

Weight in 10 ml = 10 ml × 1g / 250 ml =0.04 g

Parts of CaO in 100 ml/ weight of sample in 10 ml=7.01

Therefore in the equation

% CaO = 7.01 × volume of EDTA

• Constant for Fe2O3

Equivalent weight in Fe2O3 = 79.85 g

1000 ml of 1M EDTA→ 79.85 parts of Fe2O3

1ml of 1M EDTA → 79.85/ 1000=0.07985

1ml of 0.05M EDTA→ 0.07985×0.05= 0.0039925

1ml in 100 ml→ 0.0039925 ×100 = 0.39925 %

Weight of sample = 1 g

Test solution =250 ml

Test solution taken = 50 ml

Weight in 50 ml= 50 ml × 1g / 250 ml =0.2 g

Constant= 0.39925/0.2= 1.99625

Therefore in the equation

% Fe2O3= 1.99625 × volume of EDTA

Constant for Al2O3 in EDTA titration

Equivalent weight in Al2O3 = 50.98 g

(Molar weight /replaceable ions)

1000 ml of 1M EDTA→ 50.98 parts of Al2O3

1ml of 1M EDTA → 50.98/ 1000=0.05098

1ml of 0.05M EDTA→ 0.05098×0.05= 0.002549

98

1ml in 100 ml→ 0.002549 ×100 = 0.2549 %

Sample weight = 1g

Test solution = 250 ml

Test solution taken = 50 ml

Weight of sample in 50 ml test solution= 0.2 g

constant = 0.2549/0.2 =1.2745

Therefore the equation,

% Al2O3 = 1.2745 × volume of EDTA solution

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