20320130406003 2-3

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308

(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME

17

STUDIES ON RICE HUSK ASH CEMENT CONCRETE

1Er. S. THIROUGNANAME,

2Dr. T.SUNDARARAJAN

1M.Tech., MIE., MISTE., FIAH., MIWWA., AMISE., MITArb., Assistant Engineer,

Public works Department, Puducherry, India 2Professor, Department of Civil Engineering, Pondicherry Engineering College, Puducherry, India

ABSTRACT

Rice husk which is an agricultural by–product is abundantly available all over the world.

Most of the rice husk, which is obtained by milling paddy, is going as a waste materials even though

some quantity is used as bedding material, fuel in boilers, brick kilns etc., The husk and its ash,

which not only occupy large areas causing space problems, but also cause environmental pollution.

In this experimental investigation, the strength of RHA- Cement concrete is evaluated for two

grades of concrete (M15, M20) at various replacement levels of RHA (ranging from 5% - 20%). The

results obtained are compared with conventional concrete. It is concluded that 20% of OPC can be

replaced with RHA to attain comparable compressive strength of M15 grade and that only 10% of

OPC can be replaced with RHA to attain the comparable compressive strength of M20 grade.

Keywords: Rice Husk, Mortar, Rice Husk Ash (RHA), Ordinary Cement (OPC).

INTRODUCTION

Cement is the most important binding material in structural constructions as it is used at

different stages of construction in the form of mortar or concrete. Conventional building materials

are becoming increasingly uneconomical. On the other hands, rapid industrialization has let to wide-

spread pollution of air, water and soil and accumulation of large industrial wastes (solid, liquid)

posing disposal and environmental problems. It would be worthwhile to make use of suitable waste

products to replace some of the conventional materials. The use of such materials would minimize

the use of scarce materials and hence, there will be economy in the cost of construction.

Most important and highly expensive building material is Ordinary Portland Cement (OPC).

The use of OPC attracted every one in the construction industry and its application in steadily

increasing when compared to other material used in those days.

INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND

TECHNOLOGY (IJCIET)

ISSN 0976 – 6308 (Print)

ISSN 0976 – 6316(Online)

Volume 4, Issue 6, November – December, pp. 17-30

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With the present level of OPC production, it is not possible to meet the dowelling needs of

the country and also for pavement of roads, bridges, canal works etc. M15 grade concrete is used in

general construction works, as this characteristic strength is sufficient for most of the building

elements. From above, it is clearly seen that a high strength binder like OPC is not needed for most

of the general works and hence it can be substituted partially or fully by producing a binder from

waste materials at lesser cost but with a desirable degree of strength and durability. The answer to the

above question has been realized in the form of Rice Husk Ash (RHA), which has been proved to be

a successful replacement up to 50% of OPC [1].

Rice Husk which is an agricultural by-product is abundantly available all over the world,

more so, in the countries like India, where it is a staple food. Due to this abrasive character, poor

nutritive value, very low bulk density and high ash content, a small portion only is used as bedding

material, fuel in boilers, brick kilns etc. To overcome the above problems, studies initiated by several

investigators on the use of RHA led to its use as a pozzolanic material, in view of its high silica

content (say about 90%).

LITERATURE REVIEW

In this chapter, the work carried out by various investigators (in India and abroad) on the use

of RHA for the production of cementitious material; use of RHA as partial replacement of OPC for

producing concrete and mortar are reviewed and presented.

HYDRAULIC CEMENT FROM RHA

As early as in 1974, P.K. Mehta [2] developed a process for making cement from Rice Husk

in which the rice husk is burnt under controlled conditions and the ash mixed with hydrated lime.

Since the silica in the amorphous RHA is already in a very reactive form, a hydraulic cement can be

produced simply by blending or by intergrinding the RHA with lime. As long as lime and silica are

present in active state in an anhydrous material, the cementing property can be obtained in aqueous

environments through formation of the calcium silicate hydrates. In some experiments, blends of

Portland Cement with RHA yielded good quality hydraulic cements.

One unique characteristic of RHA cement is a permanent black colour which is useful in

making black concrete for glare-free pavements or for architectural applications. The second unique

characteristic of RHA cements. is the excellent resistance of the materials to acidic environments.

Upon hydration of these cements, none of the lime would be present in the form of free Ca(OH)2.

The products of hydration consists of calcium silicate hydrates and silica gel and therefore more

resistant to acid attack.

CEMENTITIOUS BINDER FROM WASTE LIME SLUDGE AND RICE HUSK

CBRI, India has evolved a cementitious binder from waste lime sludge and rice husk. The

powder form of waste lime sludge and rice husk are dry mixed together roughly in equal amounts by

weight and the required quantity of water added to dry mix, for making cakes. After drying them,

they are fired in open with a grating base or in a trench. The fired material are then ground in a ball

mill to achieve sufficient fineness. The binder thus obtained had inherent characteristics of lime

based compositions. Some of the important properties of the above types of binders are given in

Table 1.



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Table 1: Properties of the Binder produced from Waste Lime and Rice Husk

S. No. Property Value

1.

2.

3.

4.

Bulk density (Kg/m3)

Setting times

Initial (min)

Final (min)

Water retention

1:1.5 (Binder:sand)

1:20 (BInder:sand)

Soundless (Le-Chatlier) (mm)

360(on firing)

700(on grinding)

60 - 90

480 – 600

71%(flow)

60%(flow)

1.50

Note: Water retention is tested as per IS :2250, ‘Code of practice for preparation and use of masonry

mortars’.

The crushing strength values of the above binder (tested as per IS: 712-1973, Specification

for building lime) using one part of binder and three parts of standard sand and using three types of

sludge, namely, sugar sludge, carbide sludge and paper sludge satisfied the requirement of

class-A lime i.e. eminently hydraulic (14 and 28 days stipulating strength being 17.5 kg/cm2 and

28.0 kg/cm 2).

The above binder was recommended for plastering and can be used as plain cement concrete

(PCC) works in foundations, floors, using conventional aggregates for use in precast hollow or solid

blocks for light loading purpose, for stabilizing soil; bricks with sand under pressure using semi-dry

mix. In spite of the above indicated uses, it did not gain popularity due to quick-setting nature of the

cementitious material and the process was found to be cumbersome and not suitable for large-scale

commercial production.

CEMENT FROM RICE HUSK ASH

At I.I.T., Kanpur, two alternate routes were developed for making cement from RHA namely

i)ASHMENT process and ii) ASHMOH process.

In the ASHMENT process, RHA is ground alone in a ball mill and mixed with Portland

cement in a specified weight ratio, in the range of 3/2 to ½ and the resulting blend called as

ASHMENT cement. However, in the planted ASHMOH process, RHA, lime and an additive are

ground together in a ball mill to form ‘ASHMOH cement’. The same plant can employ

‘ASHMOH’ and or ‘ASHMENT’ technologies without any modifications.

RAW MATERIALS, PROPERTIES AND APPLICATIONS OF ASHMOH

CEMENT

Raw Materials RHA obtained from the combustion process of rice husk as fuel or rice husk heaps burnt in

open fields, hydrated lime containing atleast 85% CaO content; OPC as an additive (8 – 10%) to

hasten the setting time, are the raw materials required (i.e. 64%; 27%; 9% - RHA; hydrated lime;

additive- OPC) ASHMOH cement obtained by the process had the properties as given in Table 2.



20

Table 2: Properties of ASHMOH Cement

Sl.No. Property Value

1

2

3

4

Setting times

Initial (min)

Final (hrs)

Compressive Strength (ASHMOH : sand = 1:3 and

W/B = 0.475 – 0.5) at

3 days ( Kg/cm2)

7 days ( Kg/cm2)

28 days ( Kg/cm2)

Compressive Strength of 1:2:4 ASHMOH concrete

W/c = 0.55-0.65) ( Kg/cm2)

Bulk density ( Kg/cm2)

60 - 90

6 - 7

110 – 150

140 – 180

220 – 280

140 – 190

700 - 750

Note: The loose bulk density of ASHMOH is about 50% of that OPC and hence when preparing

mixes by volume, 1.8 to 2.0 times the required volume of ASHMOH cement is taken, to maintain the

weight ratios constant.

Applications ASHMOH cement is not recommended for reinforced or prestressed concrete load bearing

structures, such as roofs, lintels etc. It is eminently suitable for non-critical routine applications such

as masonry work, sand-cement bricks and blocks, soil stabilization, village roads; water tanks, canal

lining, water conduits; foundation concrete etc., but not for RCC works.

ASHMOH is compatible with OPC in all proportions. A mixture of the two, containing more

than 30% OPC, is for all intents and purposes indistinguishable from conventional cement (OPC)

Inspite of the certain properties claimed by the investigators at IIT Kanpur, tests conducted at

Annamalai University (2) indicated that the initial setting time is about 30 minutes and the strength at

28 days of normal curing 120 kg/cm2 only, which was normally expected of a binder, such as

indicated above.

CEMENT FROM RICE HUSK, CLAY AND HYDRATED LIME

A process has been developed to make high quality pozzolanic materials from rice husk and

clay. The pozzalonic which mixes with lime gives a very good cementitous material and when

blended with Portland Cement gives a Portland Pozzolana cement. To make lime-pozzolana cement,

the finely ground Pozzolana as obtained is intimately mixed in the dry hydrated line in the ratio of

2:1 (by volume). This may be mixed insitu at the construction site or during grinding of the

pozzolana.

Following are the various properties of the rice husk clay pozzolana, obtained by the above process.

Loss of ignition - 1.5%

Specific gravity - 2.34

Lime reactivity (IS 1727 – 1967) - 64 to 106 ( Kg/cm2)

Lime pozzolana mortar - 44 to 72 (Kg/cm2)



21

The strength properties of Rice Husk Clay pozzolana are given in the Table 3.

Table 3: Strength Properties of Rice Husk Clay Pozzolana

Composition

Compressive Strength

( Kg/cm2)

Water Retention

7 days 28 days

1:6 (cement : sand) 12-20 20-30 30

1:2:6(lime:Pozzolana:sand) 24.4 45.2 72

1:2:9(lime:Pozzolana:sand) 13 22.5 67

The lime pozzolana has superior properties and chaper in cost and can replace OPC in normal

construction works as a mortar for masonry and for plastering. However, it should not be used for

any RCC work.

RESEARCH CARRIED OUT AT ANNAMALAI UNIVERSITY ON CEMENITIOUS

MATERIALS FROM RICE HUSK

During 1979-82, research work on the production of paddy husk cement from paddy husk

and lime was carried out in different stages at Annamalai University (2,3) Systematic experimental

studies were conducted on the type of furnace required to obtain good burnt clinkers of rice husk and

lime by open burning, the effect of various ratios of the blend of RHA and lime on the compressive

strength and on the effect of type of curing (normal and stem curing) on the strength attainment and

various strength characteristics. Gypsum was used as an additive (5% , 10% and 15%) to control the

setting times of the cementitious material and to study its effect on the strength of cement.

From the extensive test results obtained it has been concluded that the

i) Compressive strength of rice husk is the same both for normal and steam curing at 28 days

and it is the order of 90 ( Kg/cm2)

ii) The adhesive strength of the above mortar (1:4, by wt) is about 50% of that of conventional

cement.

iii) It is found that the rice husk cement has good setting properties when compared to that of

OPC.

iv) The bulk density of rice husk cement is only 790 ( Kg/m3) which is about 50% of the bulk

density of OPC. Thus, the rice husk cement mortar ratio of 1:1:5 (volume) is the same as 1:3

by weight. The above mortar can be recommended for wall plastering and floor etc.,

v) The compressive strength of brick masonry blocks plastered with rice husk cement on all the

sides was found to be equal to that of the strength of OPC blocks and,

vi) Stem curing produces a further rate of increase in hardening of cement and that the optimum

period of stem curing is 7 hours.

They have also suggested further studies on the effect of stem curing pressure (I,e, at low,

medium and high) on the various properties.

STUDIES ON RHA – CEMENT CONCRETE AND MORTAR

Studies in Taiwan Taiwan produces abundant quantity of rice husk containing primarily silica, rice husk

possesses reactive characteristics after burning and hence, large potential for use in concrete than for



22

soil stabilization. The reactive of RHA is dependent on both its origin and its treatment. The effect

of RHA on the microstructure, shrinkage, porosity and strength development characteristics of the

cement paste were studied by Hwang and Wu (4). They investigated the effect of temperature of

burning rice husk on the reactivity of the resulting RHA, which was quantitatively and qualitatively

investigated by means of X-ray diffraction and EDAX. In addition, the effect of RHA on cement

properties, was investigated covering the aspects such as workability, bleeding, setting times,

shrinkage, absorption, compressive strength and heat of evolution in the paste during hydration.

Moreover, ignition loss, optical microscopy, SEM and MIP investigations were employed to analyze

both hydration mechanisms and micro-structure.

From the above studies they have concluded that

i) Factors such as, heating rate, burning period, ambient furnace conditions will affect the

quality of ash,

ii) At a higher burning temperature of 700 C, rice husk forms ash primarily composed of SiO2

Higher temperature do no yield greater quantities of SiO2

iii) The heat of hydration varies inversely with the water-cement ratio (w/c) regardless of

whether or not the system contains RHA.

iv) The amount of bleeding is inversely proportional to the RHA content in the paste and

v) The water retaining effect of RHA and the increased quantity of C-S-H get generated by the

ash that fills the space previously occupied by free water both influence the strength and

physical properties. Cement paste containing RHA at a higher w/c (0.52 to 0.54), develops

higher ultimate strength than that without ash after 60 days, although their early strengths are

similar.

Studies in Japan Sugita and others (5) studied i) the temperature effect on the incineration of rice husk to

obtain large amounts of non-crystaline ash, ii) pozzolanic reactivity of RHA using the Ca(OH)2

solution in electric conductivity in relation to the X-ray diffraction method; iii) pulverizing property

of RHA iv) the relationship between the compressive strength of mortar with RHA and conductivity

data v) the porosity changes and drying shrinkage of mortar with RHA and vi) resistance to acid

attack and carbonation of mortar containing RHA.

From the above studies they concluded that

i) Lower combustion temperature over the flash point and shorter combustion periods, the

higher the amount of non-crystalline RHA.

ii) Higher the non-crystalline form of RHA, lower the energy required to pulverize it.

iii) Variation in electric conductivity indicates the amount of non-crystalline RHA present in the

sample.

iv) RHA obtained in electric hearth below 600°C and pulverized for 80 minutes, had a higher

pozzolanic activity than other pozzolanic materials, such as fly ash,

v) Drying shrinkage of mortar increased with the addition of RHA, which may be due to the

increase in fine pores in the mortar.

vi) There is improvement in the resistance to acid attack by using highly non-crystallized RHA.

vii) Depth of neutralisation of mortar with RHA was estimated to be similar to that of controlled

mortar (without RHA) and,

viii) Freeze-thaw resistance of mortar with RHA was similarly to that of controlled mortar, which

depends on the W/B and the amount of RHA.



23

Studies in Turkey Mazlum and Vyan(6) studied the temperature effect of incinerating rice husk in furnaces at

400° C and 500° C for 1, 5 hours to obtain silica of amorphous state by sudden cooling. They

studied the effect of environmental sulphate attack (Na2SO410H2O) on the flexural and compressive

strength of mortars after 4,8, 12 weeks of exposure in the above medium, for RHA contents in

cement ranging between 10% - 30% (by weight) at a constant W/B = 0.57 and using a super

plasticiser (naphthalene formaldehyde). The specimens were exposed to the medium only after 28

days of normal curing and the results were compared with that of controlled mortar.

From the above studies, they concluded that i) the flexural and compressive strengths of ash

mortars (cured in water) are greater than those of controlled mortars ii) the flexural strength of ash

mortars exposed to Na2SO4 medium have greater values than that of controlled mortars and ash

mortars kept under normal curing and iii) that RHA is an active pozzolana and it can be used in

sulphate environments, successfully.

Studies on RHA Cement Concrete in India Seshagiri Rao and others (7) carried out detailed investigations on RHA cement concretes to

evaluate its use as a structural material (i.e. for RCC applications and as a pavement material). The

investigations were carried out to find the influence of a) fineness of ash; b) water/cement ratio; c)

Cement-RHA content and; d) strength and durability of RHA concretes. Compressive strength,

flexural strength (on PCC beams), flexural strength of RCC beams and slabs were studied. In order

to study the durability, tests on permeability, abrasion resistance and resistance to dilute acids (5%

HCI, H2SO4 and Acetic acid; 30 – 90 days of immersion, change in weight) were determined for

RHA levels of 0-40%.

From the above studied they have concluded that

i) RHA fineness of 16,000 cm2/gm is optimum

ii) Upto 30% cement can be replaced by RHA for M15 and M20 grades.

iii) Flexural strengths are comparable with reference concretes.

iv) There is reduction in permeability.

v) There is improved abrasion resistance and to acid attack and,

vi) RHA reinforced concretes are in no way inferior to conventional reinforced concretes.

However, the above studies were not directed in evaluating RHA cement concrete as a

pavement material, excepting the abrasion resistance test, i.e. whether it conforms to pavement

quality concrete (PQC) has not be evaluated.

EXPERIMENTAL INVESTIGATIONS

The experimental investigations to study the compressive (cube and cylinder), tensile and

flexural strengths of RHA cement concrete.

PROPERTIES OF MATERIALS USED

Cement, graded coarse aggregate (CA) of maximum size of 20 mm; fine aggregate (FA)

(sand conforming to Zone-II gradation based on IS: 383-1970); Rice Husk Ash are the various

materials used in this study. The basic properties of the above materials are given below.



24

Cement 43 grade OPC (ACC brand) is used as the primary binder. The required quantity was

procured a single batch, stored and used throughout the whole programme. The physical properties

of cement obtained and used are given in Table 3.1.

Table 3.1: Physical Properties of OPC

Sl.No Property Results

1 Normal Consistency 29%

2 Initial setting time 110 min

3 Final setting time 160 min

4 Fineness (Blaines air permeability)

Fineness (by dry sieving)

285 m2/kg

9%

5 Specific gravity 3.15

6 Soundness value (Le-Chatlier 2.5mm

7 Compressive strength (*)

3days

7 days

28 days

20.87 N/mm2

25.88 N/mm2

36.02 N/mm2

Note (*) Standard sand is used

Coarse Aggregate (CA) Graded coarse aggregate (crushed granite stones) of maximum size of 20 mm is used. Table

3.2 shows the properties of the above CA.

Table 3.2: Properties of Coarse Aggregate

Sl. No. Property Results


2 Water absorption 0.45%

3 Particle shape Angular

Fine Aggregate (FA) Sand conforming to grading Zone-II of IS: 383 -1970 is used as fine aggregate (FA). Its

properties are given in Table 3.3

Table 3.3: Properties of Fine Aggregate

Sl. No. Property Results


2 Water absorption 0.55%

3 Fineness modulus 2506

Rice Husk Ash (RHA) Paddy husk obtained from PAPSCO, Puducherry is used to prepare ash. Only a mixed variety

of paddy husk could be obtained from the above source. Heaps of 25-30. Kg was burnt in open yard

for over 24 hours at a time and the ash obtained was collected in clean bags. Initial dry sieving

indicated the presence of large quantities of particles higher than cement size and hence, it was



25

decided to pulverize the ash so that cement sized particles could be obtained i.e. 90% of particles

passing through 90 micron sieve. The above process was done in M/s. Kumar Minerals

Mettupalayam Industrial Estate, Puducherry. Only such ash is used in the present study after again

dry sieving them to ascertain its fineness. Ash obtained by the above process was used for the partial

placement of OPC, the replacement levels ranging 5 – 20% (by weight). The various chemicals

properties of RHA are determined in the chemical testing and analytical laboratory Guindy, Chennai-

32 and the physical properties by standard laboratory methods. The above results are given

Table 3.4 and 3.5 respectively.

Table 3.4 Chemical Properties of RHA

Sl.No Property Value

1 Moisture 0.67%

2 PH of 5% solution 8.70

3 Electrical conductivity (EC) of 5% solution in

milli mohz

0.55

4 Total Carbon (C) 29.68%

5 Total Potassium as K2O 0.89%

6 Silicon as Si 35.65%

7 Total Phosphorus as P2O5 0.49%

Water

Ordinary potable tap water available in laboratory was used for making mortar and concrete

and for curing purposes.

Table 3.5: Physical Properties of RHA

Sl.No Property Value

1 Normal Consistency 30%

2 Fineness (before pulverizing) Dry sieving 77% (wt. retained on 75 µ)

3

Fineness (before pulverizing) Dry sieving

Wet Sieving

12.5% (wt retained on 75µ)

18.2%(Wt. retained on 75 µ)

17.9% (wt. retained on 45 µ)


5 Compressive strength (MPa) on mortar

Cubes 1:3 using standard sand ) at

3days

7 days

28 days

10.5/8.5/7.1/5.1

13.1/10.9/7.9/6.3

18.7/17.7/16.9/16.7

Note: The four values of compressive strength correspond to 5% 10%, 15% and 20% replacement

levels of RHA in OPC, in that order of occurrence, in the above table.

TESTS ON WET RHA –CEMENT CONCRETE

Normal consistency of RHA-Cement mortar, setting times (initial and final) and workability

studies (slump, compaction factor) were carried out on wet concrete.



26

Normal Consistency and Setting Times

Table 3.6: Consistency and Setting Times of RHA- Cement

The quantity of water required to produce a cement paste of standard consistency at various

replacement levels of OPC by 5, 10, 15 and 20% by RHA and their corresponding setting times were

determined by standard testing procedures. The above results are given in Table 3.6.

Workability Studies Workability tests on two grade of concrete (1:2:4 and 1:1.5:3) with partial replacement of

cement by RHA ( 5 – 20% by weight) and for W/B ratios varying 0.40 to 0.65 adopting standard

testing procedures were carried out and the above test results are given in Table 3.7.

Table 3.7: Results on Workability Studies on RHA-Cement Concrete

Sl

No. Mix

W/B

Ratio

RHA Replacement Level

5% 10% 15% 20%

Slump CF Slump CF Slump CF Slump CF

1

M15

0.40 0 0.81 0 0.80 0 0.82 0 0.81

2 0.45 0 0.82 0 0.82 0 0.83 0 0.82

3 0.50 0 0.85 0 0.83 0 0.83 0 0.82

4 0.55 0 0.86 0 0.84 0 0.84 0 0.82

5 0.60 5 0.86 7 0.85 3 0.84 0 0.82

6 0.65 10 0.88 8 0.86 10 0.85 5 0.83

7

M20

0.40 0 0.82 0 0.83 0 0.79 0 0.79

8 0.45 0 0.82 0 0.83 0 0.80 0 0.80

9 0.50 0 0.84 0 0.84 0 0.81 0 0.81

10 0.55 0 0.84 0 0.86 0 0.83 0 0.81

11 0.60 10 0.85 12 0.86 8 0.84 0 0.81

12 0.65 12 0.88 15 0.87 10 0.85 5 0.82

Note: CF – Compaction Factor

Mix Proportioning First reference mixes (M15, M20 grades) were proportioned using conventional materials

adopting IS method of mix design. The details of mix proportioning are given in Appendices A and

B. The mix proportions obtained are 1:1.838:3.489 for M15 grade with W/B = 0.575 and

1:1.493:3.031 for M20 grade with W/B = 0.50. OPC was replaced by RHA (5%, 10%, 15% and

20% by weight) in the above mixes and the mix proportions adjusted for the specific gravity of RHA,

to arrive at the mix proportion for each combination of RHA and OPC. The details of mix

proportioning for various levels of RHA replacement are given in Appendices. The mix proportions

thus obtained are given in Table 3.8.

Sl.No. Description Replacement of RHA levels

5% 10% 15% 20%

1 Normal Consistency (%) 35 39 43 45

2 Initial setting time (min) 169 150 105 90

3 Final Setting time (min) 203 195 190 185



27

Table 3.8: Mix Proportions of RHA – Cement Concrete

Sl.No. Binder Content

OPC : RHA Mix Proportion W/B Ratio

1

2

3

4

5

6

7

8

9

10

100 : 00

95 : 05

M15 90 : 10

85 : 15

80 : 20

1 : 1.838 : 3.489

1 : 1.831 : 3.477

1: 1.824 : 3.464

1: 1.818 : 3.451

1: 1.811 : 3.438

0.575

0.575

0.575

0.575

0.575

100 : 00

95 : 05

M20 90 : 10

85 : 15

80 : 20

1: 1.493 : 3.031

1 : 1.487 : 3.018

1 : 1.480 : 3.005

1: 1.474 : 2.992

1: 1.467 : 2.979

0.500

0.500

0.500

0.500

0.500

Test Conducted Following tests were conducted on hardened concrete after 28 days of normal immersed

curing i) compressive strength – cube and cylinder, ii) Split tensile strength (on cylinders) and iii)

flexural strength (on prisms) 150 x 150 x 150 mm cubes, and 150 mm x 300 mm height cylinders

for determining compressive strength; 100 x 200 mm height cylinders for split tensile strength and

100 x 100 x 500 mm beam specimens for determining the flexural strength were cast for each

combination of the mix proportion given in Table 3.8.

RESULTS, DISCUSSION AND CONCLUSIONS

The results of the various tests conducted on the two grades of concrete M15 and M20

considering partial replacement of cement by RHA in the range of 5 -20%

Workability Results of the above tests are given in Table 3.7. From the above results, it can be inferred

that slump test is not giving reliable results for all RHA levels. On the other hand, CF test yields

reliable results for all RHA content and for the two grades considered. As the RHA content

increases in the binder there is a decrease in workability for all water-binder ratios and there is a

increase for increase in water binder ratios.



28

Compressive Strength Cube Compressive strength of reference and RHA cement concrete (for 4 different %

replacements) for M15 and M20 are given in Table 4.1. From the above results, it can be seen that

the compressive strength (at 28 days) of RHA cement concrete yields comparable strength of

reference concrete, for RHA replacement levels upto 20% for M15 grade concrete and upto RHA

replacement levels upto 10% for M20 grade concrete.

However, the cylinder compressive strength of RHA cement concretes (given in Table 4.1)

has comparable strength as that of the cube compressive strength for all grades of concrete

considered in this study (i.e. M15, M20).

Table 4.1: Compressive Strength of Different Grades of RHA-Cement Concrete

Sl.No.

Description Average Compressive Strength (N /mm2) Ratio of

Cyl. To

Cubic

Comp.

Strength

Cube Cylinder

OPC RHA 7 Days 14 Days 28 Days 56 Days 28 Days

1 2

3

4

5

M15

100 95

90

85

80

0 5

10

15

20

15.53 20.81

19.93

17.04

16.82

21.07 25.41

24.82

22.15

20.66

23.00 29.55

28.81

28.37

24.22

26.33 31.12

31.78

29.00

26.00

12.91 19.43

18.12

18.82

16.94

0.56 0.66

0.63

0.66

0.70

1 2

3

4

5

M20

100 95

90

85

80

0 5

10

15

20

23.57 22.15

22.52

19.56

21.55

27.93 26.96

26.44

22.96

25.41

31.28 32.96

30.74

27.41

29.56

34.47 35.78

36.11

30.45

31.56

18.71 22.36

21.67

20.28

21.88

0.60 0.68

0.70

0.74

0.74

Split Tensile and Flexural Strengths

The results of the above tests for various types of concretes are given in table 4.2. All the

values, irrespective of RHA replacement levels and grades of concrete are always less than that of

conventional concrete.

Table 4.2 Split Tensile and Flexural Strength of RHA-Cement Concrete

Sl.No

RHA

Replacement

(%)

Avg. Split Tensile strength

at 28 days (N / mm2)

Avg. flexural strength at 28

days (N / mm2)

M 15 M20 M 15 M20

1 2

3

4

5

0 5

10

15

20

2.575 1.872

1.863

1.612

1.848

3.184 1.924

1.839

1.858

1.919

2.620 2.634

2.573

2.574

2.284

3.667 3.225

2.905

2.631

1.716



29

CONCLUSIONS

Based on the extensive experimental investigation carried out on RHA –Cement Concrete

and the following conclusions are drawn.

i) Normal consistency and setting times of RHA-Cement are comparable to that of OPC.

However, there is an increase in the consistency (value) of RHA-Cement due to increase in

RHA content in the above type of cement. This may be due to the presence of unburnt

particles, which absorb more water.

ii) As the RHA content increases, workability decrease, which may be due to absorption of

water by the unburnt (unhydrous) particles present in RHA. This phenomenon is the same

for M15 & M20 grades.

iii) Compressive strength of M15 RHA – Cement concrete attains comparable strength with that

of conventional concrete, upto 20% replacement level of RHA. However, for M20 grade

concrete RHA – Cement concrete attains comparable strength with that of conventional

concrete, only upto 10% replacement of level of RHA. This Phenomenon may be due to the

presence of unburnt rice husk, as the ash was obtained only by firing in open fields.

REFERENCES

1) Seshagiri Rao M.V. Saibaba Reddy E. Ramamohan Rao K. (1996) ‘Rice Husk Ask Cement

Concrete’ Proceeding of National Seminar on Alternate Construction Materials in Civil

Engineering held at REC Hamipur December 10-11, 1996, PP 321 – 330.

2) Lakshman S. (1980) Investigations on the Properties of Paddy Husk Cement, M.E. Thesis

submitted to the Annamalai University, Department of Applied Mechanics and Structural

Engineering PP.62

3) Subramanian C. (1982) ‘Further study on Cement from Paddy Husk’ M.E. Thesis submitted to

the Annamalai University, Department of Applied Mechanics and Structural Engineering

PP.55

4) Hwang C.L. Wu D.S. (1989) ‘Properties of Cement paste containing Rice Husk Ash’

Proceedings of the Third International Conference on Natural Pozzolans in Concrete

Trondheim, Norway, SP-114, published by ACI, Malhotra V.M. (Ed). Volume – I PP. 733 -

762.

5) Sugita S, Shoya M. and Tokuda H. (1992) ‘Evaluation of Pozzolanic Activity of Rice Husk

Ask’ Proceedings of the Fourth International Conference on Fly Ash, Silica Fume, Slag and

Natural Pozzolans in Concrete, Istanbul, Turkey, SP – 132, published by ACI, Malhotra V.M.

(Ed), Volume I, PP.495 – 512.

6) Mazlum F., and Uyan M. (1992) ‘Strength of Mortar made with Cement Containing Rice

Husk Ash and Cured in Sodium Sulphate Solution, Proceedings of (as in 5 above), PP. 513 –

532.

7) Seshagiri Rao M.v. Prasada Rao A. (1997) ‘Rice Husk Ash Cement Concrete for Rigid

Pavements’ Indian High ways, Volume 25, No.9, PP 13 – 22.

8) Mohammad Qamruddin and Prof.L.G.Kalurkar, “Effect of Unprocessed Rice Husk Ash as a

Cementitious Material in Concrete(A Comparison with Silica Fume)”, International Journal of

Civil Engineering & Technology (IJCIET), Volume 4, Issue 2, 2013, pp. 240 - 246,

ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.

9) Raju Sathish Kumar, Janardhana Maganti and Darga Kumar Nandyala, “Rice Husk Ash

Stabilized Compressed Earth Block-A Sustainable Construction Building Material – A

Review”, International Journal of Civil Engineering & Technology (IJCIET), Volume 3, Issue

1, 2012, pp. 1 - 14, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.



30

BIBLIOGRAPHY

1. SP:23 - 1982 Hand Book on Concrete Mix

2. IS:269 - 1976 Specification for Ordinary and Low Heat Portland Cement

3. IS:383 - 1970 Specification for Coarse and Fine Aggregate from Natural Sources for

Concrete.

4. IS:456 - 1978 Code of Practice for Plain and Reinforced Concrete.

5. IS:516 - 1959 Methods of Test for Strength of Concrete.

6. IS:1199 - 1959 Methods of Sampling and Analysis of Concrete.

7. IS:1727 - 1967 Methods of Test for Pozzolanic Materials

8. IS:2250 - 1981 Code of Practice for preparing and Use for Masonry Mortars’

9. IS:3812 - 1981 Specification for Fly Ash for use as Pozzolana and Admixture.

10. IS:4031 - 1988 Methods of Physical test for Hydraulic Cement (Part VII)

11. IS:5816 - 1970 Methods of Test for Splitting Tensile Strength of Concrete Cylinders.

AUTHOR’S DETAIL

Er. S.THIROUGNANAME, M.Tech., MIE., MISTE., FIAH., MIWWA.,

AMISE., MITArb., Assistant Engineer, Public works Department, Puducherry.