KSCE Journal of Civil Engineering (2012) 16(1):93-102
DOI 10.1007/s12205-012-0779-2
Structural Engineering
www.springer.com/12205
Compressive Strength and Durability Properties of Rice Husk Ash Concrete
V. Ramasamy*
Received February 11, 2009/Revised February 15, 2010/Accepted April 4, 2011
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Abstract
The paper presents the experimental investigation conducted on Rice Husk Ash (RHA) concrete to evaluate the compressive
strength and to study its durability properties. In the preparation of rice husk concrete, cement was replaced at various percentage
levels such as 5%, 10%, 15% and 20%. Besides control concrete was also prepared for comparison purpose. Two grades of concrete,
namely M30 and M60, were prepared. The strength of the concrete increased with the levels of percentage of replacement of 10% at
which the increase in strength was 7.07% at 90 days compared to normal concrete. In the case of M60 grade concrete the
compressive strength increases with the addition of super plasticizer. In general, Saturated Water Absorption (SWA) increased in the
case of RHA Concrete up to 10% replacement level, but the same diminished with addition of super plasticizer. The porosity of RHA
Concrete decreased from 4.70% to 3.45% when the replacement level increased from 5% to 20%. There is a further decrease with the
addition of super plasticizer. The chloride ion permeability value of RHA Concrete was very low between 100-1000 coulomles, as
compared to normal concrete. It was observed from tests that RHA concrete was more resistant to HCl solution than that of control
concrete. The percentage of resistance against alkaline attack of M30 grade RHA concrete varied from 25 to 67 and the
corresponding value for M60 grade was from 35 to 70 for replacement levels varying from 5% to 20%. Addition of 20% RHA
showed higher resistance against sulphate attack for both continuous soaking and cyclic conditions. On the whole addition of RHA as
CRM improves the strength and durability properties of concrete to considerable extent.
Keywords: rice husk ash concrete, experimental investigation, compressive strength, durability, Rapid Chloride Permeability Test
(RCPT)
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1. Introduction
Concrete making materials come from the earth’s crust. Thus,
it depletes the natural resources every year creating ecological
strains. On the other hand, human activities on earth produce
solid wastes such as industrial wastes, agricultural wastes and
wastes from rural and urban societies in considerable quantities
of over 2500 million tons per year. Among the solid wastes, the
most prominent materials are fly ash, blast furnace slag, rice
husk (converted into ash), silica fume and materials from construction demolition. Substantial energy and cost savings can
result when industrial by-products are used as a partial replacement for the energy intensive Portland cement. The use of byproducts is an environmental–friendly method of disposal of
large quantities of materials that would otherwise pollute land,
water and air. By reducing the use of Portland cement, CO2 emission may be controlled. Due to growing environmental concerns
and the need to conserve energy and resources, efforts have been
made to utilize the waste material of industrial and agro products
in the construction industry as a pozzolanic mineral admixture to
replace ordinary Portland cement. The utilization of RHA as a
pozzolanic material in cement and concrete provides several
advantages, such as improved strength and durability properties,
reduced materials cost due to cement savings, and environmental
benefits related to the disposal of waste materials. In the present
investigation, Portland cement was replaced by Rice Husk Ash
at various percentages and its effect on the compressive Strength
and its Durability properties like water absorption, porosity, permeability, resistance to acid attack, alkaline attack and sulphate
attack was studied.
2. Experimental Programme
2.1 Materials Used
2.1.1 Cement
Ordinary Portland cement of 53 grade conforming to Indian
standard IS: 12269 (1987) was used for the present experimental
investigation. Its specific gravity is 3.15. The cement was tested
as per the procedure given in Indian standards IS 4031 (1988).
2.1.2 Fine Aggregate
Natural river sand conforming to Zone II as per IS 383(1987)
was used. The fineness modulus of sand used is 2.64 with a
specific gravity of 2.6.
*Professor, Dept. of Civil Engineering, Adhiparasakthi Engineering College, Melmaruvathur, Tamil Nadu, India (E-mail: rams_apec@yahoo.co.in)
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V. Ramasamy
2.1.3 Coarse Aggregate
Crushed granite coarse aggregate conforming to IS: 383 (1987)
was used. Coarse aggregate of size 20 mm down having the
specific gravity of 2.8 and fineness modulus of 7.20 was used.
2.1.4 Rice Husk Ash
Commercially available rice husk ash was procured and used
in the experimental investigation Physical and Chemical properties of rice husk ash obtained from K.C. CONTECH (P) Ltd.
Chennai are given in Table 1.
2.1.5 Superplasticizers
In this investigation Sulphonated Naphthalene (SNF) based
Super Plasticizer (SP) was used. The super plasticizers used for
the study conforms to IS 9103 (1999).
2.2 Mix Proportioning
The mixture proportions for the controlled concrete of M30
and M60 grades were arrived at from the trial mixes. M30 grade
was selected based on the consideration as medium strength
concrete and it is used normally in the design of columns. M60
grade was selected based on the consideration of high strength
concrete, which is generally used for prestressed concrete work.
The identification mix proportions and quantity of materials of
concrete mixture are given in Tables 2 and 3, respectively. Table
2 also contains the measured slump both with and without SP
and its dosage for different percentage of cement replacement.
For M60 grade concrete the trials were carried out to improve
workability and cohesiveness of the fresh concrete by incorporating SP.
2.3 Preparation of Test Specimens
The ingredients for various mixes were weighed; required water
was added and mixed by using a tilting drum type concrete mixture
machine. Precautions were taken to ensure uniform mixing of
ingredients. The specimens were cast in steel mould and compacted on a table vibrator. The specimens of 100 mm × 100 mm
Table 1. Physical and Chemical Properties of Rice Husk Ash
Sl. No
Parameters
Values
1
Fineness passing 45 micron
2
Specific gravity
3
Specific surface (nitrogen absorption) m2/ kg
27400
4
Silicon dioxide (SiO2)
87.20%
Table 2. Mix Proportion for M30 Grade Concrete Mixtures
Mix Designation
BC
BR1
BR2
BR3
BR4
Rice husk ash as CRM (%)
0
5
10
15
20
w/b ratio
0.43
0.43
0.43
0.43
0.43
Cement (kg/m3)
420
399
378
357
336
0
21
42
63
84
Rice husk ash (kg/m3)
3
Sand (kg/m )
621
582
542
503
464.
Coarse aggregate (kg/m3)
1108
1108.
1108
1108
1108
Water (lit/m3)
180.60 180.60 180.60 180.60 180.60
SP (%)
Slump (mm)
0.4
0.4
Without SP
15
10
With SP
20
20
0.8
1.40
2.80
5
0
0
15
10
7
Note: BC - Control Concrete
BR1 - 5% Rice husk ash
BR2 - 10 % Rice husk ash BR3 - 15% Rice husk ash
BR4 - 20% Rice husk ash CRM - Cement Replacement Material
Table 3. Mix Proportion for M60 Grade Concrete Mixtures
Mix Designation
Rice husk ash as CRM (%)
w/b ratio
Cement (kg/m3)
3
Rice husk ash (kg/m )
CC
CR1
CR2
CR3
CR4
0
5
10
15
20
0.35
0.35
0.35
0.35
0.35
474
447
420
391
366
27
54
81
108
0
Sand (kg/m3)
636
Coarse aggregate (kg/m3)
1113
1113
1113
1113
1113
Water (lit/m3)
166
166
166
166
166
SP (%)
1.8
2.0
3.2
4.5
5.8
585.10 535.61 483.21 433.72
Note: CC - Control Concrete
CR1 - 5% Rice husk ash
CR2 - 10 % Rice husk ash CR3 - 15% Rice husk ash
CR4 - 20% Rice husk ash CRM - Cement Replacement Material
× 100 mm size of cube were cast as per Indian standard IS: 516
(1959) according to which it is the size to be used for coarse
aggregate size of up to 20 mm for the determination of compressive strength at different ages and for the durability properties.
Curing of the specimens was started as soon as the top surface of
the concrete in the mould was hard enough. Spreading wet gunny
bags over the mould for 24 hours after the casting was carried
out for the initial curing. The specimens were later demoulded
and placed immediately in water tank for further curing.
96%
2.06
5
Aluminium oxide (Al2O3)
0.15%
6
Ferric oxide (Fe2O3)
0.16%
7
Calcium oxide (CaO)
0.55%
8
Magnesium oxide (MgO)
0.35%
9
Sulphur trioxide (SO3)
0.24%
10
Carbon (C)
5.91%
5.44%
11
Loss on ignition
12
Pozzolanic activity
84%
13
Particle size (µm)
7
3. Test Conducted
3.1 Compressive Strength Test
Cube specimens of 300 numbers each size of 100 mm × 100
mm × 100 mm for each grade of concrete were cast and tested
under compressive load at various ages. All the specimens were
tested in saturated surface dry condition, after wiping out the
surface moisture. For each mix combination, three identical
specimens were tested at the ages of 7, 28, 56, 90 and 180 days
using Compression Testing Machine (CTM) of 2000 kN capacity
under a uniform rate of loading of 140 kg/cm2/min. and the
compressive strength was calculated as per IS: 516 (1959).
− 94 −
KSCE Journal of Civil Engineering
Compressive Strength and Durability Properties of Rice Husk Ash Concrete
3.2 Saturated Water Absorption and Porosity
The water absorption and porosity values for various mixtures
of concrete were determined on 100 mm × 100 mm × 100 mm
size cubes as per ASTM C 642. The specimens were taken out of
curing tank at 60 days to record the water saturated weight (Ws).
The drying was carried out in an oven at a temperature of 105oC.
The drying process was continued until the difference between
two successive measures becomes small. Oven dried specimens
were weighed after they were cooled to room temperature (Wd).
Using these weights, Saturated Water Absorption (SWA) was
calculated by the equation:
SWA = [(Ws − Wd)/Wd] × 100
(1)
where, Ws: Weight of specimen at fully saturated condition
Wd: Weight of oven-dried specimen
The porosity obtained from absorption test is designated as
effective porosity.
It is determined by using the following formula,
Effective porosity
= (Volume of voids)/(Bulk volume of specimen)
The volume of voids was obtained from the volume of water
absorbed by an oven dry specimen or the volume of water lost on
oven drying of a water saturated specimen at 105oC to constant
mass. The volume of specimen is given by the difference in mass
of the specimen in air and it’s mass under submerged condition
in water.
3.3 Rapid Chloride Permeability Test
Corrosion is mainly caused by the ingress of chloride ions into
concrete annulling the original passivity present. The Rapid
Chloride Permeability Test (RCPT) has been developed as a
quick test able to measure the rate of transport of chloride ions in
concrete. This test was conducted as per ASTM C 1202(94).
Two halves of the specimens are sealed with PVC container of
diameter 90 mm. One side of the container is filled with 3%
sodium chloride solution (that side of the cell will be connected
to the anode terminal of the power supply) and on other side
sodium hydroxide solution was poured and connected to cathode
terminal. The Current passed was noted at every 30 minutes over
a period of 6 hours. From the results using current and time,
chloride permeability is calculated in terms of total charge
passed in Coulombs at the end of 6 hours by using the formula
given in Eq. (2).
Q = 900 × 2 × (Io + I30 + I60 + ········· + I330 + I360)
(2)
where, Q: Charge passed (Coulombs)
Io: Initial current
I30: Current at the 30 minutes
water cured for 28 days. After 28 days curing, the specimens
were taken out and allowed to dry for one day. Weights of the
cubes were taken. For acid attack, 5% dilute Hydrochloric Acid
(HCl) with pH value of about 2 was used. (Malhotra et al.,
1994). After that, cubes were immersed in the above said acid
water for a period of 60 and 90 days. The concentration of the
solution was maintained throughout this period. After 60 and 90
days, the specimens were taken from the acid water. The surfaces
of the cubes were cleaned, weights of the specimens were
registered and then they were tested in the compression testing
machine of 2000 kN capacity under a uniform rate of loading of
140 kg/cm2/min. The loss in compressive strength of the concrete cubes without rice husk ash and the improvement of resistance of acid attack of rice husk ash concrete cubes were analyzed.
3.5 Alkaline Attack Test
This test is not conducted on normal concrete. However, as
rice husk ash is used in this investigation, it was thought fit to
study the influence of alkanity on RHA concrete A total number
of 120 cubes of size 100 mm × 100 mm × 100 mm were cast and
demoulded after 24 hours. At the end of 28 days of curing
period, the specimens were taken from the curing tank and initial
weight was taken. Five percent by weight of water (Sekar, 2006)
of sodium hydroxide (NaOH) was added with water to prepare a
solution and the specimens were immersed in this solution for a
period of 60 days and 90 days to determine the alkaline resistance of the concrete with and without rice husk ash.
3.6 Sulfate Attack Test
This test was carried out on 240 specimens of size 100 mm x
100 mm × 100 mm after 28 days of curing period. The specimens were taken from the curing tank and initial weight was
taken. A solution containing five percent of sodium sulphate
(Na2SO4) and five percent of magnesium sulfate (MgSO4) by
weight of water was prepared as per Sekar (2006) and a set of
controlled and RHA concrete specimens were immersed in this
solution continuously for a period of 60 and 90 days to study the
effect of sulphate attack of the concrete with and without rice
husk ash. Another set of specimens were kept for alternate wet
and dry tests and were repeated for 30 and 45 cycles.The concentration of the solution was maintained throughout this period by
changing the solution periodically. The specimens were taken
out from the sulphate solution after 60 and 90 days of continuous
soaking and also after 30 and 45 cycles of alternative wetting and
drying. The surface of the cubes were cleaned, weighed and then
tested in the compression testing machine under the uniform rate
of loading of 140 kg/cm2/min. Strength was measured as per IS:
516 (1959), and change in strength was calculated.
4. Results and Discussion
3.4 Acid Attack Test
A total number of 120 cubes of size of 100 mm × 100 mm ×
100 mm size were cast and stored in a place at a temperature of
27oC ± 2oC for 24 hours and then the demoulded specimens were
Vol. 16, No. 1 / January 2012
4.1 Compressive Strength
The compressive strength variations with respect to the percentage of replacement of cement by RHA and number of days
− 95 −
V. Ramasamy
of curing are shown in Figs. 1 to 4. The effect of RHA content of
both concrete mixtures on compressive strength with and without
superplasticizer is discussed. It is observed that there is reduction
in compressive strength at earlier ages with the increasing RHA
content in both M30 and M60 grade concrete. However, the
required strength could not be achieved even at 90 and 180 days
for 15% and 20% replacement of cement by RHA.
Addition of SNF based super plasticizer improves the compressive strength of M30 concrete with 5% and 10% cement replacement by RHA. The increase in compressive strength of
RHA concrete over that of the control concrete for M30 and
M60 grades for a range of replacement levels of rice husk ash
and dosage of Sp is presented in Table 4 and 5, respectively.
In M60 grade concrete mixtures, the compressive strength values
were reduced without adding superplasticizer. The addition of
RHA increases the compressive strength due to pozzolanic reaction and micro filler effect of the RHA. The micro filler effect of
RHA distributes the hydration products in a more homogeneous
fashion in the available space, which make the matrix much
denser. Thus, the mechanism of increasing the compressive
strength of RHA concrete is believed due to the effect of both
pozzolonic reactivity and micro filler effect. Similar observations
have been made by Rao and Rao (2003) who have obtained
compressive strength with 10% RHA as an admixture over
conventional concrete. M30 grade concrete mixtures with SNF
based SP showed higher strength than the concrete without SP at
all the ages. At the earlier ages there is lesser strength development than at later ages for all the concrete mixtures. The pozzolanic reaction of RHA would come into play at later stages, improving the strength properties. Zhang and Malhotra (1996),
Fig. 1. Compressive Strength of M30 Grade Concrete at Different
Ages with Different RHA Content without SP
Fig. 3. Compressive Strength of M60 Grade Concrete at Different
Ages with Different RHA Content without SP
Fig. 2. Compressive Strength of M30 Grade Concrete at Different
Ages with Different RHA Content with SP
Fig. 4. Compressive Strength of M60 Grade Concrete at Different
Ages with Different RHA Content with SP
Table 4. Effect of Rice Husk Ash on Compressive Strength of M30 Grade Concrete
Change in Compressive Strength compared to Control Concrete Strength in respective Ages (%)
Mix ID.
7 Days
28 Days
56 Days
90 Days
180 Days
without SP
with SP
without SP
with SP
without SP
with SP
without SP
with SP
without SP
BC
-
-
-
-
-
-
-
-
-
-
BR1
4.69
2.94
3.37
4.26
2.15
4.53
1.03
5.05
2.86
2.52
BR2
-6.25
7.35
6.74
5.32
5.38
6.17
4.74
7.07
4.69
5.61
BR3
-14.06
-11.77
-13.48
-12.77
-15.05
-17.70
-15.46
-18.18
-14.29
-20.70
BR4
-28.13
-23.53
-32.58
-29.79
-32.26
-27.98
-29.90
-23.23
-27.55
-24.57
− 96 −
with SP
KSCE Journal of Civil Engineering
Compressive Strength and Durability Properties of Rice Husk Ash Concrete
Table 5. Effect of Rice Husk Ash on Compressive Strength of M60 Grade Concrete
Change in Compressive Strength Compared to Control Concrete Strength in Respective Ages (%)
Mix ID.
7 Days
28 Days
56 Days
90 Days
180 Days
with out SP
with SP
with out SP
with SP
with out SP
with SP
with out SP
with SP
with out SP
CC
-
-
-
-
-
-
-
-
-
with SP
-
CR1
-13.46
1.89
-4.03
1.43
-3.18
1.68
-3.88
2.78
-3.08
2.45
CR2
-20.19
5.94
-9.68
3.57
-9.84
2.67
-10.08
4.17
-8.46
4.49
CR3
-25.00
-3.77
-22.58
-11.42
-21.43
-10.24
-20.93
-9.72
-19.64
-9.52
CR4
-35.39
-6.98
-32.26
-31.43
-31.75
-29.17
-31.01
-26.39
-29.23
-26.53
Mehta and Malhotra (1997) have shown similar results on compressive strength in concrete with substitution of 10% RHA
instead of Portland cement.
Saraswathy et al. (2007) reported the coefficient of water absorption to be less for rice husk ash concrete with 0 to 30% replacement level when compared to control concrete.
4.2 Saturated Water Absorption
Saturated Water Absorption (SWA) is a measure of the pore
volume or porosity in hardened concrete, which is occupied by
water in saturated condition. The test results of saturated water
absorption of concrete with and without superplasticizers for
various percentages of rice husk ash are shown in Tables 6 and 7.
SWA values for 0, 5, 10, 15 and 20% of rice husk ash as CRM
are 1.62, 1.68, 1.74, 1.88 and 2.15% for M30 grade concrete
mixtures without superplasticizer. But the addition of superplasticizer showed lesser SWA values up to 10% rice husk ash content. In M60 grade concrete the reduction of SWA values up to
15% of rice husk ash content was observed. The water absorption characteristics of rice husk ash based concrete have been
reported by only a few investigators. Ganesan et al. (2004) reported that water absorption of controlled thermally treated RHA
blended mortars improved the micro structural characteristics to
a greater extent when compared to open air fired RHA concrete.
4.3 Porosity
The porosity test values of control concrete and different percentage of rice husk ashas CRM in concrete after 60 days are
shown in Tables 8 and 9. From the results it is observed that the
porosity value decreases as the percentage of replacement increases. The porosity values at 0, 5, 10, 15 and 20% rice husk ash
contents 3.45, 3.90, 4.20, 4.50 and 4.70% respectively, for M30
concrete mixtures without superplasticizers. But the addition of
superplasticizers showed the porosity values vary from 3.80 to
5.20% and 2.95 to 4.20% for M30 and M60 grade concrete mixtures, respectively, with SP. The small RHA particles improved
the particle packing density of the concrete mixture leading to a
reduced volume of larger pores. Saraswathy et al. (2007) have
reported the same trend.
Table 6. Saturated Water Absorption of M30 Grade Concrete Mixtures with and without RHA and SP
RHA SP content by
Weight of
Content
Binder (%)
(%)
Saturated Water
Absorption @ 60 Days (%)
4.4 Rapid Chloride Permeability Test
RCPT is based on the principle that negatively charged chloride
Table 8. Porosity of M30 Grade Concrete Mixtures with and without RHA and SP
Sl.
No.
Mix
ID.
without SP
with SP
Sl.
No
1.
BC
0
0.40
1.62
1.40
2.
BR1
5
0.40
1.68
1.34
3.
BR2
10
0.80
1.74
1.20
4.
BR3
15
1.40
1.88
1.56
5.
BR4
20
2.80
2.15
1.98
Table 7. Saturated Water Absorption of M60 Grade Concrete Mixtures with and Without RHA and SP
Sl.
No.
Mix
ID.
Mix
ID.
RHA
Content
(%)
SP Content by
Weight of Binder
(%)
1.
BC
0
0.40
3.45
4.20
2.
BR1
5
0.40
3.90
3.90
3.
BR2
10
0.80
4.20
3.80
4.
BR3
15
1.40
4.50
4.40
5.
BR4
20
2.80
4.70
5.20
Porosity @ 60 Days (%)
without SP
with SP
Table 9. Porosity of M60 Grade Concrete Mixtures with and without RHA and SP
Saturated Water
SP Content by
RHA
Content Weight of Binder Absorption @ 60 Days (%)
(%)
(%)
without SP
with SP
Sl.
No
Mix
ID.
RHA
Content
(%)
SP Content
by Weight of
Binder (%)
Porosity @ 60 Days (%)
without SP
with SP
1.
CC
0
1.80
1.18
1.38
1.
CC
0
1.80
2.70
3.80
2.
CR1
5
2.00
1.50
1.32
2.
CR1
5
2.00
2.90
3.40
3.
CR2
10
3.20
1.61
1.29
3.
CR2
10
3.20
3.40
2.95
4.
CR3
15
4.50
1.74
1.32
4.
CR3
15
4.50
3.80
3.50
5.
CR4
20
5.80
1.92
1.78
5.
CR4
20
5.80
3.90
4.20
Vol. 16, No. 1 / January 2012
− 97 −
V. Ramasamy
ions are attracted to a positive electrode and consists of measuring the total charge passed through a sample over the six
hours test duration when a direct current potential difference of
60V is applied across the end of the samples. The quality of material is quantitatively assessed based on the total charge passed
during the test, which is considered to be the measure of the
chloride permeability of concrete. Test results for the resistance
to penetration of chloride ions into concrete of 28 and 90 days
after casting, measured in terms of the electric charges passed
through the specimens in Coulombs for M30 and M60 grade
concrete mixtures with and without SP are given in Fig. 5 and 6.
From the figures it is observed that most of the chloride ion permeability values fall in the range of very low (100-1000 Coulombs)
category.
The charge passed through the M30 grade concrete mixtures
without SP are 2420, 910, 675, 570 and 420 Coulombs at the age
of 28 days and 1340, 720, 428, 380 and 290 coulombs, at the age
of 90 days, respectively for the cement replacement levels of 0,
5, 10, 15 and 20%. But with the addition of SP, the values are
980, 740, 590, 470 and 380 Coulombs at the age of 28 days and
945, 640, 370, 290, 210 Coulombs at the age of 90 days
respectively. The same behavior was observed in M60 grade
concrete mixtures with and without SP. From the test results, it is
found that as the cement replacement by rice husk ash level
increases, the charge passed decreases. The incorporation of the
RHA in concrete results in a finer pore structure in the hydrated
Fig. 5. Rapid Chloride Ion Permeability in M30 Grade Concrete
with and without RHA and SP
Fig.6. Rapid Chloride Ion Permeability in M60 Grade Concrete
with and without RHA and SP
cement paste especially at the aggregate and paste interface. As
per Do Silva et al. (2008) even though water penetrates in pores
of concrete with addition as evidenced by water absorption test,
the chloride ions do not penetrate due to the small pores
diameter. As per ASTM C1202, RHA reduced the rapid chloride
penetrability of concrete from a low to very low rating from
higher to lower replacement levels. The same trend was reported
by Nehdi et al. (2003) in RHA replaced concrete. Zhang and
Malhotra (1996) reported that RHA concrete (10% replacement
of cement) had excellent resistance to chloride ion penetration
and the charge passed in Coulombs was below 1000 both at 28
and 91 days.
4.5 Effect of Rice Husk Ash and Superplasticizers On Acid
Resistance
The action of acids on hardened concrete is the conversion of
calcium compounds into the calcium salts of the attacking acid.
Hydrochloric Acid (HCl) with concrete produces calcium chloride.
As a result of these reactions, the structure of concrete gets
destroyed. For this test nine cubes were cast for each mix. All the
cubes were cured normally for 28 days. Out of these 3 cubes
were taken out and tested for their strength. Remaining six cubes
were immersed in HCl solution for 60 and 90 days. At the end of
60 days the 3 cubes were taken out and tested for their strength.
Similarly remaining cubes were tested at 90 days. The loss in
compressive strength was worked out for each specimen. The
loss of strength of concrete under HCl curing after 60 and 90
days as found to be 12.45, 8.75, 7.10, 6.80 and 5% after the
immersion period of 60 days and 20.50, 17.40, 15.60, 13.00 and
10.00% at 90 days, respectively, for M30 grade concrete with
replacement level of 0, 5, 10, 15, and 20%. The addition of SP in
M30 grade concrete mixtures show the loss of compressive
strength of 10.50, 6.50, 5.80, 4.30 and 3.90% after the immersion
period of 60 days and 18.00, 13.70, 11.50, 8.50 and 6.80 at 90
days, respectively, for the cement replacement levels of 0, 5, 10,
15, and 20%. In M60 grade concrete, the loss of compressive
strength for 0, 5, 10, 15 and 20% RHA as CRM concrete mixtures are 18.50, 14.80, 13, 12.70 and 10.50% after the immersion
period of 60 days and 25.50, 21.80, 20.80, 18.00 and 14% at 90
days without SP. The reduction in compressive strength in concrete mixtures with SP due to acid attack are 16.50, 12.90, 11.70,
10.20 and 9.80% at 60 days and 23.00, 18.60, 16.40, 13.40 and
10.80% at 90 days, respectively, for 0, 5, 10, 15 and 20% RHA
as CRM. From the test results the concrete containing RHA was
found to be more resistant to the HCl solution than the control
concrete. The improved acid resistance of the rice husk ash
concrete can be attributed in part to the significant reduction in
permeability imparted by the use of RHA. Also the pozzolanic
reaction triggered by the use of RHA resulted in the conversion
of calcium hydroxide (which is readily attacked by HCl) to
C.S.H, thus, increasing the overall acid resistance of the concrete
(Mehta, 1996). The weight loss and resistance against acid attack
based on loss in compressive strength of M30 and M60 grade
concrete with and without RHA are given in Figs. 7 to 8. Table
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KSCE Journal of Civil Engineering
Compressive Strength and Durability Properties of Rice Husk Ash Concrete
Table 10. Effect of Rice Husk Ash on Resistance against Acid
Attack of M30 Grade Concrete Compared to Control Concrete
Percentage of Resistance against
Dosage
Acid Attack
Sl. Mix RHA
of SP
Concrete without SP Concrete with SP
No. ID. Content
(%)
60 days 90 days 60 days 90 days
Fig. 7. Loss in Weight for Acid Attack on M30 Grade Concrete with
and without RHA and SP
1
BC
0
0.40
-
-
-
-
2
3
BR1
5
0.40
29.71
15.12
38.00
23.88
BR2
10
0.80
43.00
23.90
44.76
36.11
4
BR3
15
1.40
45.38
36.58
59.04
52.77
5
BR4
20
2.80
58.54
51.12
62.85
62.77
Table 11. Effect of Rice Husk Ash on Resistance against Acid
Attack of M60 Grade Concrete Compared to Control
Concrete
Sl.
No.
1
Fig. 8. Loss in Weight for Acid Attack on M60 Grade Concrete with
and without RHA and SP
Fig. 9. Resistance of M30 Grade Concrete against Acid Attack: (a)
Normal Concrete, (b) RHA Concrete
10 and 11 shows the effect of RHA on resistance against acid
attack.
It has been found for M30 grade concrete, that there is a conVol. 16, No. 1 / January 2012
Percentage of Resistance against
Dosage
Acid Attack
Mix RHA
of SP
Concrete without SP Concrete with SP
ID. Content
(%)
60 days 90 days 60 days 90 days
CC
0
1.80
-
-
-
-
2
CR1
5
2.00
20.00
14.50
21.80
19.15
3
CR2
10
3.20
29.72
18.43
29.90
28.69
4
CR3
15
4.50
31.35
29.41
38.18
41.73
5
CR4
20
5.80
43.24
45.09
40.60
53.04
tinuous increase in resistance up to 20% replacement of cement
by RHA. The above behaviour found to be true with and without
addition of SP and immersion period of 60 and 90 days. M60
grade concrete also showed the trend of increase in resistance
against acid attack. It appears more than 20% replacement may
also give better resistance. Fig. 9(a) shows the appearance of the
normal concrete after immersion in HCl solution up to 90 days. It
has been found the edges were eroded and deterioration pockets
are found on the surface of the concrete. The colour has been
found changed. In the case of RHA concrete, the periphery of the
specimen was found intact without any erosion as shown in Fig.
9(b). Further the faces of the specimens were found without any
deterioration.
4.6 Effect of Rice Husk Ash and Superplasticizers On
Alkaline Resistance
The results of alkaline resistance of concrete in terms of loss in
compressive strength of M30 and M60 grade with and without
SP and RHA are presented in Tables 12 and 13. In M30 grade
concrete the loss of compressive strength for replacement of
cement by rice husk ash content of 0, 5, 10, 15, and 20% are
12.00, 9.00, 7.90, 6.20 and 4.60% after the immersion period of
60 days and 17.00, 12.00, 9.00, 6.80 and 5.00% at 90 days,
respectively, for the mixture without superplasticizers. The addition of superplasticizer shows the loss of compressive strength
for replacement of cement by rice husk ash content of 0, 5, 10,
15, and 20% are 10.00, 8.70, 7.20, 5.30 and 3.20% after the
immersion period of 60 days and 15.80, 10.00, 7.50, 5.90 and
− 99 −
V. Ramasamy
4.10% at 90 days, respectively. The addition of superplasticizers
shows much resistance against the alkaline attack. The weight
loss and compressive strength loss due to alkaline attack of M30
and M60 grade concrete with and without RHA attack are
presented in Figs. 10 to 11. From the Table 12 and 13, it has been
found for M30 grade concrete that there is continuous increase in
resistance against alkaline attack up to 20% replacement of
cement by RHA with and without addition of SP. M60 grade
concrete also showed the trend of increase in resistance against
alkaline attack.
Table 13. Effect of Rice Husk Ash on Resistance against Alkaline
Attack of M60 Grade of Concrete Compared to Control
Concrete
Percentage of Resistance against
Dosage
Alkaline Attack
Sl. Mix RHA
of
Concrete without SP Concrete with SP
No ID. Content
SP (%)
60 days 90 days 60 days 90 days
1
CC
0
1.80
-
-
-
-
2
CR1
5
2.00
34.60
33.33
33.33
50.71
3
CR2
10
3.20
43.07
46.66
41.66
56.42
4
CR3
15
4.50
58.46
61.30
55.00
65.00
5
CR4
20
5.80
70.00
69.33
73.33
78.90
In M60 grade concrete mixtures the loss of compressive
strength are 13.00, 8.50, 7.40, 5.40 and 3.90% after the immersion period of 60 days and 15.00, 10.00, 8.00, 5.80 and 4.60% at
90 day for 0, 5, 10, 15 and 20% of rice husk ash content,
respectively. The addition of SP shows the loss of compressive
strength of 12.00, 8.00, 7.00, 5.40 and 3.20% after the immersion
period of 60 days and 14, 6.90, 6.10, 4.90 and 2.95% of 90 days,
respectively, for the cement replacement levels of 0, 5, 10, 15
and 20%.
Fig. 10. Loss in Weight for Alkaline Attack on M30 Grade Concrete
with and without RHA and SP
Fig. 11. Loss in Weight for Alkaline Attack on M60 Grade Concrete
with and without RHA and SP
Table 12. Effect of Rice Husk Ash on Resistance against Alkaline
Attack of M30 Grade of Concrete Compared to Control
Concrete
Sl.
No.
Percentage of Resistance against
Alkaline Attack
Mix ID.
Dosage
RHA
of SP Concrete without
Concrete with SP
Content
SP
(%)
60 days 90 days 60 days 90 days
1
BC
0
0.40
-
-
-
-
2
BR1
5
0.40
25.00
29.40
13.00
36.70
3
BR2
10
0.80
34.16
47.08
28.00
52.53
4
BR3
15
1.40
48.33
60.00
47.00
62.65
5
BR4
20
2.80
66.66
70.00
68.00
74.05
4.7 Effect of Rice Husk Ash and Superplasticizers On Sulphate Resistance
Sulphate attack is caused by the chemical reaction between
sulphate and calcium hydroxide (Ca(OH)2), forming gypsum.
The gypsum may react with tricalcium aluminate (C3A) in the
concrete to form Ettringite and monosulphoaluminate. These reactions result in a substantial increase in volume with subsequent
cracking and peeling. The sources of sulphate ion are seawater,
sewage industrial waste, salts in ground water and delayed
release of clinker. The reaction of rice husk ash with calcium
hydroxide released during cemen thydration results in the formation of additional CSH and the accompanying reduction in
permeability of the concrete.
The effect of rice husk ash content on the sulphate resistance of
concrete under continuous soaking condition was studied by
replacement of rice husk ash from 0 to 20% in concrete mixtures.
The loss in compressive strength decreases with increase of rice
husk ash content. In M30 grade concrete the loss in compressive
strength after the immersion period of 60 days and 90 days at
sulphate solution are 9.50, 7.90, 6.00, 4.90 and 3% at 60 days
and 11.20, 9.50, 7.50, 6.20 and 4.50% at 90 days without SP,
respectively. But the addition of superplasticizer might improve
the resistance against sulphate attack.
In M60 grade concrete mixtures without superplasticizer show
the percentage loss in compressive of 10.50, 7.00, 5.90, 4.00 and
2.40% after the immersion period of 60 days and 12.80, 10.90,
8.80, 6.50and 3.60%, respectively, at 90 days for 0, 5, 10, 15 and
20% rice husk ash content. The addition of superplasticizer improves the resistance due to sulphate attack Figs. 12 and 13
shows the loss in weight for sulphate attack under continuous
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KSCE Journal of Civil Engineering
Compressive Strength and Durability Properties of Rice Husk Ash Concrete
soaking condition on M30 and M60 grade concrete with and
without RHA and SP.
The loss in compressive strength in M30 grade concrete
mixtures without SP are 9.20, 8.50, 6.90, 5.30 and 3.80% at 60
days and 9.70, 8.90, 7.60, 6.50 and 4.70% at 90 days, respectively, for 0, 5, 10, 15 and 20% of rice husk ash as a CRM in
concrete mixes. The addition of SP improves the resistance due
to sulphate attack. In M30grade concrete the loss in compressive
strength of concrete with SP are 8.70, 7.30, 5.90, 4.80 and 2.70%
at 60 days and 8.90, 8.00, 6.90, 5.40 and 3.80% at 90 days, respectively. The loss in compressive strength in M60 grade concrete
mixtures without SP are 12.20, 10.90, 8.70, 7.20 and 2.20% at 60
days and13.20, 11.70, 9.90, 8.60 and 2.40% at 90 days, respectively, for 0, 5, 10, 15 and 20% of rice husk ash as a CRM in
concrete mixes. The addition of SP improves the resistance due
to sulphate attack. In M60 grade concrete the loss in compressive
strength with SP are 11.50, 10.20, 7.80, 5.40 and 1.80% at 60
days and 11.90, 10.80, 8.70, 6.30 and 2.20% at 90 days, respectively. Figs. 14 and 15 show the percentage of weight loss due to
cyclic sulphate attack for 60 and 90 days specimens of concrete
mixtures with and without SP and rice husk ash. Even though the
duration of sulphate attack test is short, in order to collect some
Fig. 14. Loss in Weight by Sulphate Attack under Cyclic Wet and
Dry Condition on M30 Grade Concrete with and without
RHA and SP
Fig. 15. Loss in Weight by Sulphate Attack under Cyclic Wet and
Dry Condition on M60 Grade Concrete with and without
RHA and SP
quick results on the effect of sulphate on rice husk ash similar to
some kind of accelerated testing in the case of conventional
concrete, this test was conducted.
Fig. 12. Loss in Weight for Sulphate Attack under Continuous Soaking Condition on M30 Grade Concrete with and without
RHA and SP
Fig. 13. Loss in Weight for Sulphate Attack under Continuous Soaking Condition on M60 Grade Concrete with and without
RHA and SP
Vol. 16, No. 1 / January 2012
5. Conclusions
Being on organic and fibrous material rice husk ash .absorbs
more water and hence necessity as addition of SP to improve the
workability properties of RHA concrete. The increase in compressive strength for 5% and 10% of cement replacement by RHA
are 4.10% and 5.00% at 28 days, respectively, for M30 grade
concrete. The addition of superplasticizer shows a 9% higher
compressive strength than the control concrete at the RHA
content. The saturated water absorption was decreased when the
mixture containing 10% RHA by 16.60% and 7.00% for M30
and M60 grade concrete, respectively, when compared to concrete. The addition of SP shows 11.00% and 28.80% reduction in
porosity for M30 and M60 grade concretes respectively at the
RHA content 10% when compared to control concrete. The
presence of RHA in the concrete mixtures caused considerable
reduction in the volume of the large pores at all ages and thereby
reducing the chloride ion penetration. The loss of compressive
− 101 −
V. Ramasamy
strength on alkaline resistance was 4.60% and 5.00% at 60 and
90 days, respectively, for M60 grade concrete with 20% replacement of cement by RHA. The incorporation of RHA improved
resistance to acid attack compared to OPC because of the silica
present in the RHA, which combines with the calcium hydroxide
and the amount susceptible to acid attack. The addition of 20%
RHA shows higher resistance of upto 11.20% against sulphate
attack for both continuous soaking conditions and cyclic conditions. From the strength studies namely compressive strength, it
has been reflected that about 10% of cement replacement by
RHA is the optimum level. From the durability studies namely
chloride permeability, acid attack, alkaline attack and sulphate
attack it has been observed that there is an increase in resistance
up to 20% replacement of cement by RHA.
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KSCE Journal of Civil Engineering