Experimental Investigation on the Mechanical Properties of Grade 40 Concrete Incorporating Rice Husk Ash (RHA)

EXPERIMENTAL INVESTIGATION ON THE MECHANICAL PROPERTIES
OF GRADE 40 CONCRETE INCORPORATING RICE HUSK ASH (RHA)


G. A. HABEEB*
MEngSc Student, Dept. of Civil Engineering, Faculty of Engineering, University of Malaya, Malaysia.

H. B. MAHMUD
Professor, Dept of Civil Engineering, Faculty of Engineering, University of Malaya, Malaysia.

*Corresponding author Email: civilgx@gmail.com

ABSTRACT:

This paper reports an investigation on the behaviour of concrete produced from blending ASTM type I
cement with RHA. The properties of fresh concrete and the effect of replacing 5%, 10%, 15%, and 20% of
cement with RHA on the compressive strength were investigated. The optimum mix was chosen for further
investigation on the mechanical properties, selection of the optimum mix was based on the maximum level
of cement replacement that gives a comparable strength to that of the control mix. Incorporation of RHA in
concrete resulted in increased water demand, for the hardened properties, RHA concrete gave excellent
improvement in strength for 10% replacement, and up to 20% of cement could be valuably replaced with
RHA without adversely affecting the strength. Inclusion of RHA provided similar or enhanced mechanical
properties when compared to the control OPC mix.

Keywords: rice husk ash; workability; compressive strength; mechanical properties


1. INTRODUCTION
material that in itself possesses little or no cementitious

value but in finely divided form and in the presence of
From 1880 to 1996, the world’s annual consumption of
moisture will chemically react with alkali and alkaline
Portland cement rose from 2 million tons to 1.3 billion
earth hydroxides at ordinary temperatures to form or
tons. This is associated with major environmental
assist in forming compounds possessing cementitious
issues which include: i) cement manufacturing is the
properties [7].
third largest CO2 producer and this accounts for over

50% of all industrial CO2 emissions (for every ton of
cement produced, 1.25 ton of CO2 is released to the
air); and ii) 1600 ton of natural resources are consumed
to produce 1 ton of cement [1]. This calls for the use of
sustainable binders. One of the most promising
materials is rice husk ash (RHA). Rice husk is an
(a)
(b)
(c)
agricultural residue from the rice milling process, see
Figure 1. According to the United Nations FAO [2], the
annual world rice production for 2007 was estimated at

650 million tons, the husk constitutes approximately

20 % of it. The chemical composition of rice husk vary
Fig. 1: (a) The rice husk, (b) burnt RHA, and (c) RHA

due to the differences in the type of paddy, type of

after grinding
fertilizer used, crop year, climate and geographical

conditions [3]. Burning the husk under controlled

temperature below 800?C can produce ash with silica
2. EXPERIMENTAL PROGRAM
mainly in amorphous form [3-5].


The work presented in this paper reports an
A state-of-the-art report on rice husk ash (RHA) was
investigation on the behaviour of concrete produced
published by Mehta [6] and contains a review of the
from blending ASTM Type I cement with RHA. The
physical and chemical characteristics of RHA, the
physical and chemical properties of RHA were first
effect of incineration conditions on the pozzolanic
investigated and compared to OPC and silica fume.
properties of the ash, and a summary of the research
Mix proportioning was performed to produce high
findings from several countries on the use of RHA as a
workability RHA mixes (200-240 mm slump) with
supplementary cementing pozzolanic material. ASTM
target strength of 40 MPa. The properties of fresh
defines pozzolan as a siliceous or alumino-siliceous

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International Joint Conference: 7th APSEC (Asia Pacific Structural Engineering and Construction Conference) &
2nd EACEF (European Asian Civil Engineering Forum). Langkawi, Malaysia. 2009
concrete investigated were workability and fresh

density. The effect of replacing 5 %, 10 %, 15 %, and
20 % of cement with RHA on the compressive strength
was also investigated. The optimum RHA mix was then
chosen to study the mechanical properties such as
compressive strength, tensile splitting strength,
modulus of rupture and static and dynamic modulus of
elasticity. Results of these tests were compared to the
control OPC mix. The criterion of choosing the
optimum mix was based on the maximum level of
cement replacement that gives a comparable strength to
that of the control mixture.

2.1 Materials



2.1.1 Cement
Fig. 2: The X-Ray spectrum



An ASTM type I cement was used; its physical and
chemical properties are given in Table 1.


Table 1: Physical and chemical properties of

RHA, SF and cement
Material
OPC
RHA
SF
SiO2 (%)
20.99
88.32
92.06
Al2O3 (%)
6.19
0.46
0.48
Fe2O3 (%)
3.86
0.67
2.11
CaO (%)
65.96
0.67
0.4
MgO (%)
0.22
0.44
0.6
Na2O3 (%)
0.17
0.12
0.2
K

2O (%)
0.6
2.91
1.2

LOI (%)
1.73
5.81
2.54
Fig. 3: RHA particle shown by electron microscope.

Specific Gravity
2.94
2.11
2.18

Fineness (Blaine)
351.4
-
-

(m2/kg)
The physical and chemical properties of RHA, SF and
Fineness (BET)
-
27.4
25.2
cement are shown in Table 1. The chemical
(m2/g)

composition of the RHA and SF was determined using

the XRF (X-ray fluorescence spectrometry).
2.1.2 Rice Husk Ash


2.1.3 Aggregates
The rice husk ash used in this work was made in the

laboratory by burning the husk in a ferro-cement
The fine aggregate used was mining sand passing the
furnace [8], with incinerating temperature not acceding
4.75 mm sieve. The coarse aggregate was crushed
700?C. The ash was then ground using a Los Angeles
granite with size ranging from 19-4.75 mm. The
mill for 180 minutes. XRD analysis was performed to
properties of the aggregates are shown in Table 2.
determine the silica form of the produced RHA powder

samples using an X-ray diffractometer with CuK?
2.1.4 Chemical Admixture
radiation at 40 kV/20 mA, CPS= 1 k, width 2.5, speed

2?/min and scanning from 2? = 3-70?. The result
To maintain high workability of the concrete mixes of
showed that the ash was mainly in amorphous form
200 – 240 mm slump, an ASTM C494 type-A high
(Figure 2).
range water-reducing admixture was used. The R1000

superplasticizer was dark brown, water-soluble,
The specific surface area of the RHA and silica fume
chloride free sulphonated naphthalene formaldehyde,
(SF) was measured using the BET nitrogen adsorption
having 40% solid content with specific gravity of 1.2.
test. The results showed that RHA had higher surface

area than SF due to RHA’s multilayered and
2.2 Mixture Proportioning
microporous surface (Figure 3).

Mixture proportioning was done according to the DOE
mix design method [9]. The target mean strength for the
OPC control mixture was 40 MPa, the total binder
content was 391 kg/m3, fine to coarse aggregate

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International Joint Conference: 7th APSEC (Asia Pacific Structural Engineering and Construction Conference) &
2nd EACEF (European Asian Civil Engineering Forum). Langkawi, Malaysia. 2009

Table 2: Aggregates Properties
Properties
Fine Aggregate
Coarse Aggregate
App. Specific gravity
2.61
2.65
Water Absorption%
0.76
0.50
Size
Sieve size
Cumulative
Sieve size
Cumulative
mm
retained%
mm
retained %

4.750
0.00
19.00
0.00

2.360
16.91
13.20
43.80

1.180
35.31
9.50
68.69

0.600
58.12
4.75
100.00

0.300
81.39
-
-

0.150
93.10
-
-

0.075
97.18
-
-

Pan
100.00
-
-



Table 3: Mixture Proportioning of Control and RHA Concrete Mixes
w/b
Sp
Water
Cement
RHA
F Agg.
C Agg.
Mix
ratio
(% of binder)
(ltr)
(kg)
(kg)
(kg)
(kg)
CM
0.53
0.63
207
391
0
750
994
05RHA
0.53
1.12
207
371
20
750
994
10RHA
0.53
1.35
207
352
39
750
994
15RHA
0.53
1.60
207
332
59
750
994
20RHA
0.53
1.83
207
313
78
750
994



cont ent ratio was 75.4%. The water to binder ratio was
dynamic modulus of elasticity were conducted. Results
kept constant at 0.53 and the superplasticizer content
of these tests were compared to the control OPC mix.
was varied to maintain a slump of 200-240 mm for all

the mixes. The total mixing time was five minutes, the
3. RESULTS AND DISCUSSION
samples were then levelled and left for 24 hours before

demoulding. They were then placed in the curing tank
3.1 Phase I Investigations
until the day of testing. Details of the mix proportion of

the concrete mixes are presented in Table 3.
3.1.1 Effect of percentage of cement replacement

with RHA on workability
In Phase I of the study the effect of replacing 5 %, 10 %,

15 %, and 20 % of cement with RHA on the properties
The fresh properties of all the concrete mixtures are
of fresh concrete i.e., workability and fresh density
given in Table 4. The slumps were in the required range
were conducted. Then the effect on the compressive
of 200-240 mm. Bleeding was negligible for the control
strength at the ages of 1, 3, 7, 28 days was also
and RHA mixes and no segregation was detected. The
investigated. 100 mm cubes were cast from each
fresh density of RHA concrete was in range of
mixture. Specimens were kept in the moulds for 24
2250-2328 kg/m3, lower than the control, due to the
hours and then placed in water for curing until the age
low specific gravity of the RHA particles. The Sp
of testing.
content had to be increased with increasing RHA

content, due to the high specific surface area of RHA
Based on the Phase I works, the optimum mix based on
which would increase the water demand [5, 10]. To
the maximum level of cement replacement that gave
maintain similar workability, Sp content had to be
comparable strength to that of the control mixture was
increased up to 1.83 % of the binder content for the
chosen for further investigation. In this Phase II, the
20% RHA mix.
mechanical properties such as compressive strength,

tensile splitting strength, modulus of rupture, static and

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International Joint Conference: 7th APSEC (Asia Pacific Structural Engineering and Construction Conference) &
2nd EACEF (European Asian Civil Engineering Forum). Langkawi, Malaysia. 2009



Table 4: Fresh concrete properties
RHA
Sp
Slump
Fresh
Mix
Content
(% of
(mm)
Density
(%)
Binder)
(kg/m3)
CM
0
0.63
230
2347
05RHA
5
1.12
200
2328
10RHA
10
1.35
210
2293
15RHA
15
1.60
220
2270
20RHA
20
1.83
220
2253





Fig 4: Effect of RHA content on compressive
3.1.2 Effect of cement replacement with RHA on

strength of concrete
compressive strength



The strength development of the control and RHA
3.2 Phase II Investigations
mixes are given in Table 5. At 28 days, strength

increases for RHA concrete was noted at all
3.2.1 Effect of curing on compressive strength
replacement levels compared to the control OPC mix.


The data shown in Table 6 represent the strength of
Maximum strength was noted at 10% replacement level
concrete up to 90 days. Two curing regimes, i.e water
and at 20% RHA content, the strength of the concrete
curing and air drying were adopted. The results showed
achieve equivalent value to that of the control.
that specimens subjected to air-drying showed slightly
Replacement level above 20% was avoided in this
higher strength at early age. This may be due to the
study because the Sp content needed would be much
laboratory conditions, whereby the high relative
higher than the permitted level by the manufacturer
humidity and temperature of ~ 90%R.H and 30 °C
(maximum of 2% by weight of the cementitious
respectively, may accelerate the hydration reaction of
materials), which can bring about an adverse retarding
concrete. From 28 days onwards, the specimens cured
effect to the fresh concrete. Furthermore, the strength
in water had a marginally higher strength because
would decrease to a value lower than that of the control.
sufficient moisture was available for the concrete to
Based on the results shown in Table 5, mix 20 RHA
hydrate.
was chosen on the basis that it contains the optimum

level of cement replacement and its strength was
The advantage of using RHA in blended concrete is
comparable to that of the control OPC concrete. The
highlighted in Table 6. Irrespective of the curing
relation between the RHA content and strength of
method, RHA concrete exhibited higher strength than
concrete is shown in Fig 4.
the control, especially at later ages. This is due to the

pozzolanic reaction of the RHA with lime produced

from cement hydration which led to an increase in the

cementing compound C-S-H, thus contributing to the
Table 5: Strength Development for OPC and RHA

higher long term strengths.
concrete

Mix
RHA
Compressive Strength MPa

content
Table 6: Effect of curing on strength development of
1day 3days 7days 28days
control and RHA concrete

Mix
CM
20RHA
CM
0%
19.1
26.7
30.2
39.6
RHA content (%)
0%
20%
05RHA
5%
17.9
25.3
30.0
40.2
7days
30.7
30.5
10RHA
10%
19.4
28.1
34.3
48.4
Water
28days
39.9
40.5
15RHA
15%
18.2
25.1
31.3
42.4
Curing
Compressive
90 days
44.1
45.2
20RHA
20%
17.3
24.5
29.8
40.6
Strength
7days
31.3
32.6

(MPa)
Air

28days
39.1
40.0
drying

90 days
43.0
44.1

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International Joint Conference: 7th APSEC (Asia Pacific Structural Engineering and Construction Conference) &
2nd EACEF (European Asian Civil Engineering Forum). Langkawi, Malaysia. 2009
3.2.2 Other Mechanical Properties
compressive strength, tensile splitting, flexural strength

and the static and dynamic modulus of elasticity.
The results of the other mechanical properties such as
Enhancement in these properties can be attributed to the
tensile splitting, modulus of rupture and the static and
pozzolanic reaction of the RHA particles.
dynamic moduli are shown in Table 7. Generally, it can

be seen that incorporation of RHA enhanced the
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