PARTIAL CEMENT REPLACEABLE MATERIALS

BY

A.RAGHU TEJA B.K.CHAITANYA

III/IV B.Tech(civil) III/IV B.Tech(civil)

raghu_abhay2007@yahoo.co.in chaitu_trueman@yahoo.co.in

FaaDoOEngineers.com

CONTENTS

1. Abstract

2. Introduction

3. Experimental plan

a) part I

b) part II

4. Materials Required

5. Test results and discussions

6. Compressive strengths of mortars

7. Acidic resistance of mortars

8. Conclusions

9. References

FaaDoOEngineers.com

ABSTRACT

An experimental program is conducted to develop new kinds of pozzolana from

other agricultural wastes apart from rice husk and rice straw. The study

investigated the use of coconut husk, corn cob and peanut shell ash as cement

replacement materials. A series of tests were performed to determine the chemical

composition of coconut husk ash, corn -cob ash and peanut shell ash which are

referred to as CHA, CCA and PSA respectively. The mechanical properties of paste

and mortar containing different percentages of ash replacement were investigated.

``Experimental results revealed that coconut husk ash and corn cob ash cannot be

utilized as pozzolona while peanut shell ash can be classified as Class ‘C’ pozzolona

according to ASTM Standards. Corn cob ash mortars possessed higher compressive

strength. Among the four types of mortars tested for chemical attack, PSA mortars

showed higher resistance against acidic attack.

FaaDoOEngineers.com

INTRODUCTION

Many developing countries are attempting to develop substitutes for cement from locally

available raw materials like agricultural and industrial wastes. Fly ash (F.A) and rice-

husk ash (RHA) have already been proven to be economical as partial substitutes for

cement. These can replace cement up to 50 %. The researches carried out so far revealed

that reactive RHA could be produced by controlled burning of rice husk and grinding it to

a certain degree of fineness. Further more, RHA satisfies the minimum requirements of

ASTM class N, F and C pozzolona . Rice straw is another agricultural waste which is also

readily available in abundance in rice growing countries. But rice straw cannot be

considered totally as an agricultural waste since it can also be used in animal feeding,

mushroom production, paper manufacturing and pyrolosis. Rice straw ash (RSA) is also a

good partial substitute for cement. It was found that the compressive strength of RSA

concrete is slightly higher than ordinary Portland cement (OPC) and RHA concrete.

Other possible agricultural products which could be used as pozzolona are

coconut husk, corn cob and peanut shell. Coconut is readily available and abundant in

rural areas. Like rice straw, coconut husk is not totally regarded as agricultural waste

because it can be used for different purposes. Coconuts are the staff of life of tropics.

Some tropical people called it “THE TREE OF LIFE” because the meat and milk of the

nut give them food and drink; the trunk of the tree produces beautiful and durable wood

for their homes. Floor mats and clothing can also be made from the coconut husk ash.

The corn cob is about 16 % to 20 % by weight of the whole unshelled corn. Due

to the presence of many mechanical corn Sheller, a large volume of corn cob is produced

in one day operation and is normally utilized as fuel. One sack of dry corn cob weighs

approximately 25 kilogram.

FaaDoOEngineers.com

The shell of peanut is approximately 30 % by weight of a given amount of

unshelled peanut. Like corn, a mechanical Sheller has been developed for peanut. Peanut

shell can also be used as a fuel but most farmers dispose it in the field to improve the soil

condition for planting. Considering the abundance of coconut husk, and peanut shell in

rural areas, an attempt is made to utilize these three agricultural products as low-cost

construction materials. This research was conducted to investigate the potential of

coconut husk, corn cob, and peanut shell as partial substitutes for Portland cement. Figs

1-3 show different parts of coconut, corn and peanut respectively.

EXPERIMENTAL PLAN

The coconut husk ash, corn cob ash and peanut shell ash which are here in after

referred to as CHA, CCA, and PSA respectively will be obtained by burning the coconut

husk, corn cob and peanut shell in a ferrocement incinerator which .After burning the

ashes will be ground in the grinding machine .For simplicity, the time of grinding will be

kept constant at one hour through out the - experimental work.

FaaDoOEngineers.com

FaaDoOEngineers.com

The experimental program is dived in to two parts as follows:

PART 1 - Properties of Coconut Husk Ash, Corn Cob Ash and Peanut shell

Ash

An investigation on the physical and chemical properties of CHA, CCA and

PSA is conducted in this part. The physical properties considered are the strength activity

index, specific gravity and fineness. The chemical composition of each type of ash is also

obtained. All testing procedures are based on ASTM standards.

PART 2 - Compressive strengths and Acidic Resistances of Mortars

{a} The compressive strengths at different ages of mortars containing different types of

ash are determined. Four different mixes for OPC, CHA, CCA and PSA mortars having a

consistency equivalent to 105 % -- 115 %. Flow values are tested for 0 – 40 %

replacement by weight of cement. The samples are tested after curing for periods of 3, 7

and 28 days

{b} The resistance against acidic attack of mortars is determined by immersing the

tested specimen in 10 % HCL and 10 % sulphuric acid solution for 30 days and the

losses of weight are obtained. This was conducted for CHA, CCA, PSA, and RHA

mortars under saturated surface and oven dry conditions.

MATERIALS REQUIRED:

Coconut Husk, Peanut shell and corn cob .

CEMENT

Ordinary Portland cement. This was selected in order to compare the testing results with

previous researches on rice husk and rice straw ash.

MIXING WATER

Ordinary tap water was used for all mortars and pastes

FINE AGGREGATE

Natural river sand passing sieve number 30 and retained on sieve number 100 was used

through out the experiment.

FaaDoOEngineers.com

TEST RESULTS AND DISCUSSIONS:

PART 1 – Properties of Different types of Ashes.

Chemical Analysis of Ashes

The ash obtained by burning coconut husk in the ferrocement incinerator was

found to posses a darkish grey color. The ash produced is only 2.8 % by weight of the

unburnt coconut husk. This means that burning 25 kg of coconut husk which is the

capacity of the small ferrocement incinerator produces only 0.7 kg of ash in one hour.

The color of ash produced by corn cub is also darkish gray and its weight is only 1.43 %

of the unburnt corn cob it takes approximately two hours to burn 75 kg of corn cob.

Peanut shell when burnt in the same incinerator produces a brownish color ash which is

12% by weight of the unburnt peanut shell. The burning of 45 kg of peanut shell requires

approximately 5 hours. The maximum recorded temperature inside the ferrocement

incinerator was 750 degree Centigrade

The chemical analyses`of these ashes were performed by the laboratory of Siam

City Cement Co; Ltd. Factory located in Saraburi, Thailand. The results of chemical

analysis are shown in Table. These properties were also compared with different

pozzalanas namely rice husk ash, rice straw ash and sugar cane bagasse ash in Table 2. In

Table 3, a comparison of these ashes is made with the ASTM requirements for class N, F

and C pozzalans.

It can be observed from Table 1 that PSA has higher SiO2 , CaO contents which

are major composition of hardened cement gel than those of CHA and CCA. The

hardend cement gel than those of CHA and CCA. The hardened cement gel is composed

of Tricalcium silicate (C3S) , Dicalcium silicate(C2S), Tri calcium Alluminate (C3A),

Tetra calcium Alumino Ferrite (C4AF). Among these three ashes, PSA also has the lower

total amount of minor compounds namely Mgo,Mno,Cl respectively. The oxides of

sodium and potassium, Na2O, K2O, known as alkalis. They have been found to react with

some aggregates; the products of the reaction could lead to the disintegration of the

concrete. It has also been observed that the affect of the rate of the gain of strength.

Therefore the presence of large amount of these two alkalis requires special attention. As

FaaDoOEngineers.com

observed from the table, PSA shows lesser amount of these two alkalis than CHA and

CCA. Another which affects the strength is the loss of ignition. It was found that greater

amount of ignition loss results in loss of strength. Considering this factor, PSA is found

to be better than CHA and CCA.

Comparing with other pozzolanas, the silica content of PSA is lower than that of rice

husk ash.

TABLE 1:

Chemical composition Coconut

Husk Ash

(CHA)

Corn cob

Ash

(CCA)

Peanut shell

Ash

(PSA)

Ordinary

Portland

Cement(OPC)

Silicon dioxide

Aluminium oxide

Iron oxide

Calcium oxide

Magnesium oxide

Sodium oxide

Potassium oxide

Sulphate

Chloride

Manganese oxide

Loss on ignition

25.68

1.74

2.65

4.08

5.38

8.40

31.23

0.71

0.61

0.05

29.80

37.26

1.09

2.78

2.10

3.15

0.04

37.09

0.75

0.12

0.08

16.18

44.57

15.12

7.56

7.69

1.65

0.12

6.06

1.10

----

0.27

9.75

21.30

4.96

3.10

66.61

1.81

0.21

0.50

2.27

-----

-----

0.74

Physical properties

Blaine fineness

Specific gravity

2823.00

2.23

1036.00

2.21

5292.00

2.56

------

------

The test results for strength activity index of PSA and CCA mortars are tabulated

in table3. The results showed that the strength activity index of peanut shell ash with

Portland cement at 28 days is 95.02% and its water requirement is 99.6%. It can be

observed therefore that the addition of PSA to Portland cement reduces the amount of

water required for a given slump. Similar test was performed with ages of 3 and 7 days to

determine the early strength activity of PSA. The strength activity of PSA with Portland

FaaDoOEngineers.com

cement at ages 3 and 7 days is 117.34% and 106.4% respectively. It can be seen that PSA

has a greater early strengths compared to OPC at the ages of 3 and 7 days but becomes

lower at the age of 28 days. The high early strength of PSA is due to the presence of high

alumina. One feature of high alumina cement is its high rate of strength development.

The high rate of strength gained is due to C3A which has the highest rate of strength

development, resulting in the formation of CAH10 a small quantity of C2AH8 and alumina

gel. The strength activity index of corn cob ash at 28 days is 38.96% with a water

requirement of 102.4%. The addition of CCA in portland cement increases the amount of

water requirement. It can also be seen from table that its strength activity indices at ages

3 and 7 days are only 39.69% and 43.08% respectively. The low compressive strengths of

CCA are probably due to its high amount of alkalis and loss of ignition as in table2.

TABLE 2:

Chemical

composition

CHA CCA PSA SCBA RHA RSA

Silicon dioxide 25.68 37.26 44.57 65.8 92.05 65.94

Aluminium

oxide

1.74 1.09 15.12 5.5 0.94 0.99

Iron oxide 2.65 2.78 7.56 3.3 0.81 0.65

Calcium oxide 4.08 2.10 7.69 4.2 0.27 4.27

Magnesium

oxide

5.38 3.15 1.65 1.7 0.27 1.97

Sodium oxide 8.40 0.04 0.12 0.6 0.06 0.23

Potassium oxide 31.23 37.09 6.06 7.5 1.72 11.66

Sulphate 0.71 0.75 1.10 2.0 0.13 0.45

Chloride 0.61 0.12 ----- ----- ----- -----

Manganese

oxide

0.05 0.08 0.27 ----- ----- -----

Loss on ignition

29.80 16.18 9.75 9.4 3.19 13.46

Physical properties

Percent of ash

after burning

2.8 1.43 12 3.2 18-20 15

Blaine fineness 2823 1036 5292 15040 14300 12860

Specific gravity 2.23 2.21 2.56 2.308 2.085 2.240

FaaDoOEngineers.com

TABLE 3:

PART 2:Compressive Strength & Acidic Resistance Of Mortars

Compressive strength of Mortars:

Table 4 shows the comparison of compressive strengths at different ages of OPC,

CHA,CCA, PSA mortars having percentage of cement replacement. It can be observed

that among three types of ashes investigated in this study, coconut husk ash exhibits very

low compressive strengths as compared to corn cob ash and peanut shell ash. Evidently

the use of peanut shell ash as cement replacement up to 40% in mortar results in a high

strength matrix. It is of interest to note that for CCA mortars, the compressive strengths at

different ages of samples increase as the percentage of cement replacement is increased

from 20% to 40%. On the contrary, the compressive strengths of PSA mortars decrease as

the percentage of cement replacement is increased.

Property Pozzolona Class#

CHA CCA PSA

Chemical properties

N P C

Moisture content(%) 3.0 3.0 3.0 -- -- --

Loss of ignition % 10.0 12.0 6.0 29.80 16.18 9.75

SiO2+Al2O3+Fe2O3

(%)

2.65 2.78 7.56 3.3 0.81 0.65

SO3 4.0 5.0 5.0 0.71 0.75 1.10

MgO 5.0 5.0 5.0 5.38 3.15 1.65

Na2O 1.50 1.50 1.50 8.40 0.04 0.12

Physical properties

Fineness: Amount retained

On sieve no:325(%)

34 34 34 0.60 33.20 4.20

Pozzolanic activity index

With Portland cement at

28 days.

75 75 75 -- 38.96 95.02

Water requirement max % of

control

115 105 105 -- 102.5 99.6

FaaDoOEngineers.com

Acidic resistance of Mortars:

Resistance against sulphate attack:

Hardened concrete when present in sulphate solution results in expansion and

disruption of concrete. This phenomenon is called ‘sulphate attack.’ Attack of cement can

thus take place when sulphate reacts with Ca (OH)2 and with calcium aluminate hydrate.

The products of reactions which are the gypsum and calcium sulphoaluminate, having

considerably greater volume than the compounds they replace, so that the reactions with

sulphates lead to expansion and disruption of concrete.

Sulphate attack can also be reduced by the addition or even partial

replacement of cement by pozzolana. The effect of this is the reduction of free Ca

(OH)2 and rendering the alumina bearing phase inactive, but sufficient time must be

allowed for the pozzolanic activity to be developed before the concrete is exposed to the

sulphates. Another effect of pozzolana addition is the increase in impermeability of the

concrete. In table the values of percentage weight loss of different mortars are shown

after they were immersed in sulphate solution of 30 days. It can be seen in this table that

the resistance to sulphate attack increases in the following order:

1. Corn cob ash mortar

2. Ordinary Portland cement mortar

3. Rice husk ash mortar

4. Peanut shell ash mortar.

TABLE 4:

This trend

occurs also

for

specimen

under oven

AGE

Type of mortar Compressive

Strength(MPa)

Strenth activity

Index(%)

3-day Control mix

Peanut shell ash

Corn cob ash

18.34

21.52

7.28

100

117.34

39.69

7-day Control mix

Peanut shell ash

Corn cob ash

23.28

24.77

10.03

100

106.4

43.08

28-day Control mix

Peanut shell ash

Corn cob ash

30.11

28.61

11.73

100

95.02

38.96

FaaDoOEngineers.com

dried condition. However, specimen under oven dried condition, the mortars are more

resistant to sulphate attack than under saturated surface dry condition. This is because

hydration in the former part is accelerated and thus speeds up the pozzolanic activity.

Cement with high alumina content is indeed highly satisfactory to resist

sulphate attack. PSA contains 15% Al2O3 content and probably this leads to its higher

resistant to sulphate attack among the four types of mortars investigated. This resistance

to sulphates is due to the absence of Ca(OH)2 in hydrated high alumina cement and also

to the protective influence of the relatively inert alumina gel formed during hydration.

Resistance against acidic attack:

Acid solutions attack concrete by dissolving Ca(OH)2 and removing part of the

set cement, thus causing surface erosion. Cement having alumina content is not acid

resisting but can with stand well very dilute solutions of acid with pH greater than 3.5 to

4.0, found in industrial effluents, but not with HCl, HF or HNO3.

TABLE 5:

%loss of weight

Type of solution

Condition

Of

Specimen

Type

Of

mortar 10% HCl 10%H2SO4

Saturated

Surface

Dried

condition

OPC

RHA

PSA

CCA

5.23

4.26

8.94

15.04

73.74

48.59

46.26

75.46

Oven

Dried

condition

OPC

RHA

PSA

CCA

2.07

0.42

5.24

4.18

52.75

46.53

24.83

62.12

FaaDoOEngineers.com

From the table it can be observed that the resistance to acidic attack increases in the

following order:

1. Corn cob ash mortar

2. Peanut shell ash mortar

3. Ordinary Portland cement mortar

4. Rice husk ash mortar

It was that RHA is highly resistant to acid among the four mortars. This is due to the

higher silica content of RHA which reduces the free lime content of hydrated cement. It

can be seen also that OPC is more resistant to acid than PSA. Improved resistance against

acidic attack can then be obtained by treating the mortar in oven dried condition as

depicted from table 5.

FaaDoOEngineers.com

Conclusions:

1. The burning of peanuts shell produces a brownish ash while coconut husk and

corn cob produce grayish white ash.

2. Peanut shell ash has the highest silica content and lowest ignition loss among the

three raw materials and contains 15.12% Al2O3. According to ASTM standard,

only PSA can be classified as pozzolana class C respectively while corn cob ash

and coconut husk ash do not meet the requirements of pozzolana.

3. The strength activity index with Portland cement after 28 days of PSA is 95.02%

having a water requirement of 99.6% whereas CCA has a strength activity index

of 38.96% and a water requirement of 102.4%.

4. Peanut shell ash mortars have high early strengths compared to ordinary Portland

cement mortars. This is due to the presence of high amount of alumina in PSA.

5. PSA-cement mortar shows greater resistance to sulphate attack than OPC and

RHA but it has lower resistance to HCl attack than OPC and RHA.

References:

1. Journal of ferrocment: vol.25 No.1

2. Ranasinghe ,Arjuna 1985. Use of Rice straw ash as pozzolana . Asian institute of

technology, Bangkok.

3. Neville, A.M 1986. Properties of concrete .London: pitman publishing Ltd.

FaaDoOEngineers.com

FaaDoOEngineers.com