20320130406003 2-3

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME

TECHNOLOGY (IJCIET)

ISSN 0976 – 6308 (Print)
ISSN 0976 – 6316(Online)
Volume 4, Issue 6, November – December, pp. 17-30
© IAEME: www.iaeme.com/ijciet.asp
Journal Impact Factor (2013): 5.3277 (Calculated by GISI)
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IJCIET
©IAEME

STUDIES ON RICE HUSK ASH CEMENT CONCRETE
1

Er. S. THIROUGNANAME,

2

Dr. T.SUNDARARAJAN

1

M.Tech., MIE., MISTE., FIAH., MIWWA., AMISE., MITArb., Assistant Engineer,
Public works Department, Puducherry, India
2
Professor, 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 widespread 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.

17

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.

18

Table 1: Properties of the Binder produced from Waste Lime and Rice Husk
Property
Value
S. No.
1.
Bulk density (Kg/m3)
360(on firing)
700(on grinding)
2.

Setting times
Initial (min)
Final (min)

3.

60 - 90
480 – 600

Water retention
1:1.5 (Binder:sand)
1:20 (BInder:sand)

4.

Soundless (Le-Chatlier) (mm)

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 MATE RIAL S,
CEMENT

PROPERTIE S

AND

APPLICATIONS

OF

ASHMOH

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.
19

Table 2: Properties of ASHMOH Cement
Property
Sl.No.
1
Setting times
Initial (min)
Final (hrs)
2

3

4

Value
60 - 90
6 -7

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)

110 – 150
140 – 180
220 – 280

Compressive Strength of 1:2:4 ASHMOH concrete
W/c = 0.55-0.65) ( Kg/cm2)

140 – 190

Bulk density ( Kg/cm2)

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
Specific gravity
Lime reactivity (IS 1727 – 1967)
Lime pozzolana mortar

-

1.5%
2.34
64 to 106 ( Kg/cm2)
44 to 72 (Kg/cm2)
20

The strength properties of Rice Husk Clay pozzolana are given in the Table 3.
Table 3: Strength Properties of Rice Husk Clay Pozzolana
Compressive Strength
Composition
( Kg/cm2)
Water Retention
7 days
28 days
1:6 (cement : sand)
1:2:6(lime:Pozzolana:sand)
1:2:9(lime:Pozzolana:sand)

12-20
24.4
13

20-30
45.2
22.5

30
72
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
21

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.
22

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)
ii)
iii)
iv)
v)
vi)

RHA fineness of 16,000 cm2/gm is optimum
Upto 30% cement can be replaced by RHA for M15 and M20 grades.
Flexural strengths are comparable with reference concretes.
There is reduction in permeability.
There is improved abrasion resistance and to acid attack and,
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.

23

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.

Sl.No
1
2
3
4
5
6
7

Table 3.1: Physical Properties of OPC
Property
Normal Consistency
Initial setting time
Final setting time
Fineness (Blaines air permeability)
Fineness (by dry sieving)
Specific gravity
Soundness value (Le-Chatlier
Compressive strength (*)
3days
7 days
28 days

Results
29%
110 min
160 min
285 m2/kg
9%
3.15
2.5mm
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.

Sl. No.
1

Table 3.2: Properties of Coarse Aggregate
Property
Results
Specific gravity
2.60

2

Water absorption

3

0.45%

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

Sl. No.
1
2
3

Table 3.3: Properties of Fine Aggregate
Property
Results
Specific gravity
2.60
Water absorption
0.55%
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
24

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, Chennai32 and the physical properties by standard laboratory methods. The above results are given
Table 3.4 and 3.5 respectively.

Sl.No
1
2

Table 3.4 Chemical Properties of RHA
Property

3

Moisture
PH of 5% solution
Electrical conductivity (EC) of 5% solution in
milli mohz

4
5
6
7

Total Carbon (C)
Total Potassium as K2O
Silicon as Si
Total Phosphorus as P2O5

Value
0.67%
8.70
0.55
29.68%
0.89%
35.65%
0.49%

Water
Ordinary potable tap water available in laboratory was used for making mortar and concrete
and for curing purposes.

Sl.No
1
2
3
4
5

Table 3.5: Physical Properties of RHA
Property
Value
Normal Consistency
30%
Fineness (before pulverizing) Dry sieving
77% (wt. retained on 75 µ)
Fineness (before pulverizing) Dry sieving
12.5% (wt retained on 75µ)
Wet Sieving
18.2%(Wt. retained on 75 µ)
17.9% (wt. retained on 45 µ)
Specific gravity
2.14
Compressive strength (MPa) on mortar
Cubes 1:3 using standard sand ) at
3days
10.5/8.5/7.1/5.1
7 days
13.1/10.9/7.9/6.3
28 days
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.
25

Normal Consistency and Setting Times

Sl.No.
1
2
3

Table 3.6: Consistency and Setting Times of RHA- Cement
Description
Replacement of RHA levels
5%
10%
15%
20%
Normal Consistency (%)
35
39
43
45
Initial setting time (min)
169
150
105
90
Final Setting time (min)
203
195
190
185

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
RHA Replacement Level
W/B
Sl
5%
10%
15%
20%
Mix
Ratio
No.
Slump
CF
Slump
CF
Slump
CF
Slump
CF
1
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
M15
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
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
M20
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.

26


Sl.No.

Table 3.8: Mix Proportions of RHA – Cement Concrete
Binder Content
Mix Proportion
W/B Ratio
OPC : RHA
100 : 00

1 : 1.838 : 3.489

0.575

95 : 05

1 : 1.831 : 3.477

0.575

90 : 10

1: 1.824 : 3.464

0.575

4

85 : 15

1: 1.818 : 3.451

0.575

5

80 : 20

1: 1.811 : 3.438

0.575

6

100 : 00

1: 1.493 : 3.031

0.500

7

95 : 05

1 : 1.487 : 3.018

0.500

90 : 10

1 : 1.480 : 3.005

0.500

9

85 : 15

1: 1.474 : 2.992

0.500

10

80 : 20

1: 1.467 : 2.979

0.500

1
2
3

8

M15

M20

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.

27

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
Ratio of
Description
Average Compressive Strength (N /mm2)
Cyl. To
Sl.No.
Cubic
Cube
Cylinder
Comp.
OPC RHA 7 Days 14 Days 28 Days 56 Days 28 Days
Strength
M15
100
95
90
85
80
M20
100
95
90
85
80

1
2
3
4
5
1
2
3
4
5

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

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
Avg. Split Tensile strength Avg. flexural strength at 28
Replacement
at 28 days (N / mm2)
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

28

2.620
2.634
2.573
2.574
2.284

3.667
3.225
2.905
2.631
1.716

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.
29

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Hand Book on Concrete Mix
Specification for Ordinary and Low Heat Portland Cement
Specification for Coarse and Fine Aggregate from Natural Sources for
Concrete.
Code of Practice for Plain and Reinforced Concrete.
Methods of Test for Strength of Concrete.
Methods of Sampling and Analysis of Concrete.
Methods of Test for Pozzolanic Materials
Code of Practice for preparing and Use for Masonry Mortars’
Specification for Fly Ash for use as Pozzolana and Admixture.
Methods of Physical test for Hydraulic Cement (Part VII)
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.

30

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