A cost-reduction of self-compacting concrete incorporating raw rice husk ash

Abstract

The higher material cost of self-compacting concrete (SCC) as compared to normal vibrated concrete is mainly due to its higher cement content. In order to produce economical SCC, a significant amount of cement should be replaced with cheaper material options, which are commonly found in byproduct materials such as limestone powder (LP), fly ash (FA) and raw rice husk ash (RRHA). However, the use of these byproduct materials to replace the high volumes of cement in an SCC mixture will produce deleterious effects such as strength reduction. Thus, the
objective of this paper is to investigate the optimum SCC mixture proportioning capable of minimizing SCC’s material cost. A total of fifteen mixes were prepared. This study showed that raw rice husk ash exhibited positive correlations with fly ash and fine limestone powder and were able to produce high compressive and comparable to normal concrete. The SCC-mix made with
quaternary cement-blend comprising OPC/LP/FA/RRHA at 55/15/15/15 weight percentage ratio is found to be capable of maximizing SCC’s material-cost reduction to almost 19% as compared with the control mix

Full text

Journal of Engineering Science and Technology
Vol. 11, No. 1 (2016) 096 - 108
© School of Engineering, Taylor’s University
96
A COST-REDUCTION OF SELF-COMPACTING
CONCRETE INCORPORATING RAW RICE HUSK ASH
H. AWANG*, M. N. ATAN, N. ZAINUL ABIDIN, N. YUSOF
School of Housing, Building and Planning, Universiti Sains Malaysia,
11800 Minden, Penang, Malaysia
*Corresponding Author: hanizam@usm.my
Abstract
The higher material cost of self-compacting concrete (SCC) as compared to
normal vibrated concrete is mainly due to its higher cement content. In order to
produce economical SCC, a significant amount of cement should be replaced with
cheaper material options, which are commonly found in byproduct materials such
as limestone powder (LP), fly ash (FA) and raw rice husk ash (RRHA). However,
the use of these byproduct materials to replace the high volumes of cement in an
SCC mixture will produce deleterious effects such as strength reduction. Thus, the
objective of this paper is to investigate the optimum SCC mixture proportioning
capable of minimizing SCC’s material cost. A total of fifteen mixes were
prepared. This study showed that raw rice husk ash exhibited positive correlations
with fly ash and fine limestone powder and were able to produce high
compressive and comparable to normal concrete. The SCC-mix made with
quaternary cement-blend comprising OPC/LP/FA/RRHA at 55/15/15/15 weight
percentage ratio is found to be capable of maximizing SCC’s material-cost
reduction to almost 19% as compared with the control mix
Keywords: Self-compacting concrete, Powder, Additives, Strength, Cost reduction.
1. Introduction
Self-compacting concrete (SCC) is described as an innovative concrete with the
ability to flow under its own weight and completely fill the formwork, even in the
presence of dense reinforcement, without the need for any vibration whilst
maintaining homogeneity [1]. Self-compacting ability is achieved by employing
high volume of paste made possible by blending cement with mineral additives
such as limestone powder (LP), fly ash (FA), silica fume (SF), ground-granulated
blast-furnace slag (GGBS), rice husk ash (RHA), or meta-kaolin (MK) [2].

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Journal of Engineering Science and Technology January 2016, Vol. 11(1)
Incorporating mineral additives in SCC is found to be capable of not only
regulating the cement content but also enhancing the fresh state properties [3].
LP is reported to reduce cost and environmental load due to cement
production and to enhance all engineering properties [4, 5]. High economic
impact is reportedly gained with 70% to 85% FA addition in low strength SCC
[6], while SCC containing 15% SF is reported to produce high compressive
strength [7]. Hence, these additives have long found usages in actual concrete
applications. RHA on the other hand, is an agricultural by-product obtained
from burning the husk under controlled temperature of < 800ºC. The process
produced about 25% ash containing 85%–90% amorphous silica plus about 5%
alumina which made it highly pozzolanic. As reported, for about 1000kg of
paddy milled, 55kg of RHA was produced. India, being the highest rice-
producing country, generates about 20 million tons of RHA annually [8, 9].
Thus, the potential of using RHA in concrete production could become an
important economic endeavour. It was reported that concrete containing
up to 30% RHA attained a compressive strength of 30MPa [10]. They
were discovered that a binary blend powder material comprising 85%
ordinary Portland cement (OPC) and 15% RHA in an SCC mix produced
compressive strength of 42.5MPa after 90 days of water curing and flexural
strength of 6.5 MPa.
Meanwhile, a number of researchers associate RHA addition with increased
compressive and flexural strengths [11-13], but the most useful characteristic of
RHA is that it is derived from cultivated crops making it a value-added product
due to its capacity as a renewable mineral additive. Despite the advantages and
potential that RHA could offer as cement replacement material, cement and
concrete manufacturers in the developed regions of the world are concerned with
the problems of transportation and production [14].
Few researchers have explored ways of producing low-cost concretes by
incorporating unprocessed or raw RHA (RRHA) with some measures of
success. Brown [15] revealed that it is possible to use RRHA obtained from
uncontrolled burning of rice husk to produce concrete that achieves similar
strength to that of a control mix. Sua-iam and Makul [16] revealed that
incorporating a FA/RRHA blend in ternary SCC improves compressive strength
development due to the smaller particles of FA filling voids, thus; decreasing
porosity and water demand.
This research shall expand the field of knowledge on RRHA by
incorporating it in binary, ternary and quaternary SCCs so that its influences in
low, medium and high volume cement replacement SCCs can be evaluated. The
findings shall shed lights on the potential of CO
2
emissions reduction into the
atmosphere due to concrete production, the production of cost-effective SCC
and the utilization of cheaper RHA in bulk quantities. The uniformity of an
SCC mixture reduces permeability and enhances the overall durability of the
concrete. One of the most important benefits of SCC is the increase durability
associated with the effects of mineral addition because it enhances the lifespan
of the SCC beyond that of conventional concrete thereby reducing the
environmental footprint on a unit time basis [17]. These are vital economic and
environmental benefits which will help SCC to achieve the status of a
sustainable construction material.

98 H. Awang et al.
Journal of Engineering Science and Technology January 2016, Vol. 11(1)
2. Materials
The basic constituents of an SCC mix were similar to that of normal vibrated
concrete, i.e., powder, water, fine & coarse aggregates and super-plasticizer (SP).
The base powder material was Type 1 OPC, manufactured by Tasek Cement
Corporation Berhad, whilst the additives were fine limestone powder (LP),
pulverized fuel ash (FA), silica fume (SF) and raw rice husk ash (RRHA) by rice
milling plant, Permatang Pauh, Penang; all obtained from local sources (Fig. 1).
The physical and chemical properties of OPC and additives are shown in Table 1.
(a) Fine Limestone powder
(Pulai Calcium Sdn. Bhd., Johor)
(b) Fly ash (Infinity Global
Carbonate Venture,
Kuala Lumpur)
(c) Silica fume
(ScanFume Sdn. Bhd.Kuala Lumpur)
(d) Raw rice husk ash
(Bee Guan Rice Mill, Penang)
Fig. 1. Additives used in the mixture.
Table 1. The physical and chemical properties of OPC and additives.
OPC LP FA SF RHA
Oxide Composition (%)
SiO
2
Al
2
O
3
Fe
2
O
3
CaO
MgO
SO
3
21.28
5.60
3.36
64.64
2.06
2.1
1.84
1.37
-
52.98
0.42
0.08
56.2
20.17
6.69
4.24
1.92
0.49
90.36
0.71
1.31
0.45
-
0.41
92.99
0.18
0.43
1.03
0.35
0.10
Physical properties
Specific gravity
Blaine (m²/kg)
3.15
340
2.80
443
2.20
290
2.10
20,000
2.16
351

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Journal of Engineering Science and Technology January 2016, Vol. 11(1)
Washed river sand was sieved to produce fine aggregates with a maximum
particle size of 4.75 mm. The sand gradation test, shown in Fig. 2 was performed
in accordance with ASTM C33 [18]. Crushed granite, graded between 4.75 mm to
12.5 mm, was used as coarse aggregate. The SP was ADVA 181; a high range
water-reducing polymer-based admixture and was formulated in accordance with
BS5075 Part 3:1985 specification [19]. The water used was piped water supplied
by the local authority.
Fig. 2. Sand sieve analysis performed in accordance with ASTM C33.
3. Mixture Composition and Experimental Setup
A total of fifteen mixes were prepared comprising one control mix (designated
CM), four binary SCC mixes (designated BM), six ternary SCC mixes
(designated TM) and four quaternary SCC mixes (designated QM). Mixture
proportioning for the control mix and SCC mixes is presented in Table 2. CM
contained the maximum amount of OPC, 475 kg/m
3
. Binary SCC mixes contained
403.75 kg/m
3
OPC, 15% lower as compared with the CM. The reduction in OPC
is replaced with equivalent weight of LP, FA, SF or RHA. Ternary SCC mixes
contained 332.5 kg/m
3
OPC, 30% lower as compared with the CM. The reduction
in OPC is replaced with equivalent weight of two mineral additives. Quaternary
SCC mixes contained 261.25 kg/m
3
OPC, which is 45% lower as compared the
CM. The reduction in OPC is replaced equivalent weight of three mineral
additives.
All materials which used for the production of SCC mixes are stored in dry
and covered area and kept under room temperature. Prior to the actual process,
fine and coarse aggregates are sieved accordingly. All solid constituent materials;
OPC, LP, FA, SF, RHA, sand and crushed granite rocks are weighed in
accordance with the requirement of each they are prepared for Mixing water and
SP are then made available for use. The water to blended cement ratio is set at 1.0
by volume, which is in accordance the proposal made by Okamura and Ouchi [2]
and guidelines in EPG [3].
The mixing process starts by placing fine and coarse aggregates in an
appropriate concrete mixer. Once the aggregates are thoroughly mixed, OPC and/or
appropriate mineral additive/s are added to the aggregates’ mixture. The concrete

100 H. Awang et al.
Journal of Engineering Science and Technology January 2016, Vol. 11(1)
mixer is left to run for about five minutes or until coarse and powder particles are
fully blended. Once this happens, water is gradually added to the dry mixture until
the mixture starts to show sign of viscosity. Small dosages of SP are gradually to
the mixture while observing the fluidity and viscosity of the wet mixture. Water
and/or SP are continually added while maintaining visual observation on the
physical state of the wet mix. The wet mix is cast into 100 mm cubic moulds and
left to stand for 24 hours under room temperature. After 24 hours, the hardened
specimens are demoulded and immersed in a container filled with water.
Table 2. Mixture compositions.
Legend:
OPC – ordinary Portland cement; LP – limestone powder; FA – fly ash; SF – silica fume;
RRHA – raw rice husk ash; G – crushed granite rock; CM – control SCC mix; BM –
binary SCC mix; TM – ternary SCC mix; QM – quaternary SCC mix.
Compressive strength tests are performed after 7, 14, 28, 60 and 90 days, in
accordance with BS EN 12390-3:2009. The tests using a universal testing
machine (UTM) are represented in Fig. 3. Three 100 mm cubic specimens used in
dry in dry density tests are reused for compressive strength tests.
Fig. 3. Compressive strength test using universal testing machine.
Symbol
Label OPC LP FA SF RRHA
Sand
G
kg/m
3
CM 100C 475 - - - - 1005 838
BM1
BM2
BM3
BM4
85C/15LP
85C/15FA
85C/15SF
85C/15RRHA
403.75
403.75
403.75
403.75
71.25
-
-
-
-
71.25
-
-
-
-
71.25
-
-
-
-
71.25
1000
990
988
989
834
826
824
825
TM1
TM2
TM3
TM4
TM5
TM6
70C/15LP/15FA
70C/15LP/15SF
70C/15LP/15RRHA
70C/15FA/15SF
70C/15FA/15RRHA
70C/15SF/15RRHA
332.5
332.5
332.5
332.5
332.5
332.5
71.25
71.25
71.25
-
-
-
71.25
-
-
71.25
71.25
-
-
71.25
-
71.25
-
71.25
-
-
71.25
-
71.25
71.25
986
983
985
973
975
972
822
820
821
812
812
810
QM1
QM2
QM3
QM4
55C/15LP/15FA/15SF
55C/15LP/15FA/15RRHA
55C/15LP/15SF/15RRHA
55C/15FA/15SF/15RRHA
261.25
261.25
261.25
261.25
71.25
71.25
71.25
-
71.25
71.25
-
71.25
71.25
-
71.25
71.25
-
71.25
71.25
71.25
970
972
969
959
809
810
808
800

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Journal of Engineering Science and Technology January 2016, Vol. 11(1)
4. Compressive Strength
Figure 4 represents the development of compressive strength with age for the binary
SCC mixes. As shown, the control mix exhibited high hydration activities on the
first 10 days where it gained 82% of the 90-days strength and increased by a mere
2% after 28 days. Hence, the control mix gained a further 18% of the 90-days
strength during late ages. Meanwhile, BM1 and BM2 are shown to gain 90% and
94% of their respective 90-days compressive strengths after 14 days, while BM3
and BM4 gained 91% and 94% of their respective 90-days strength after 28 days.
BM4 exhibited moderate rates of strength gain at an early age but is able to
sustain the rate till around 28 days. RRHA has large amounts of water stored in its
porous particles which is released to the surrounding concrete matrix when
needed for further hydration of anhydrous cement grain. The water released from
the pores of the RRHA particles is also utilized for RRHA-lime reaction which
provides additional strength to hardening SCC. Thus, the combined effects of
slow cement hydration, constant supply of water from porous RRHA particles and
RRHA-lime pozzolanic reaction enable BM4 to sustain a moderate rate of
strength gain from early age up to 28 days, and to generate further gains up to and
beyond 90 days. BM1 and BM2 exhibited relatively high rates of strength gain
during early ages which are sustained up to 14 days. Both mixes continued to
generate strength gains up to and possibly beyond 90 days. Since LP is inert while
FA-lime pozzolanic reaction to occur during later ages [20], then early age
compressive strengths are generated by cement hydration primarily and the
physical effects of LP and FA additions.
Fig. 4. The compressive strengths of the control
mix and binary SCC as a function of curing age.
The development of ternary SCCs compressive strengths with maturing ages
is represented graphically in Fig. 5. Although the synergic effects of FA/RRHA
are able to produce higher 90-days compressive strength as compared with those
of LP/RRHA and FA/SF additions, the later additions have the advantage of

102 H. Awang et al.
Journal of Engineering Science and Technology January 2016, Vol. 11(1)
being able to generate measurable linear gains during the late ages which, in a
probabilistic point of view will enable their compressive strengths to surpass that
of TM5 in due course. TM3 exhibits linear strength gain of 9.5MPa between day-
28 and day-90 which corresponds to a daily increase of approximately 0.15MPa.
If it is able to sustain the rate of linear gain for another month, its compressive
strength would be higher than those of the control and TM5.
Thus, in the view point of compressive strength development, LP/RRHA
additions exhibited better synergic effects as compared with FA/RRHA and LP
producing better physical effects than FA. When LP replaces part of OPC, it
produces a dilution effect on the cement particles due to its chemically inert
characteristic. This effect increases the distance between each cement grain in the
paste solution and increases their specific surface that come in contact with water.
As a result greater numbers of cement particles are hydrated and greater numbers
of CaOH crystals are thus made available for RRHA-lime pozzolanic reaction.
Hence, the physical effect of LP particles is able to enhance the chemical effect of
RRHA particles. However, the main cause for using LP in concrete is to enhance
particles packing density through its filler effect where its fine particles are used
to fill up large pores between the aggregates causing them to be segmented into
finer pores and their volume reduced significantly.
Fig. 5. The compressive strengths of ternary SCC as a function of curing age.
TM4, which incorporates FA/SF addition exhibited a similar mode of strength
development with TM3, except in the early period of 7 days, it generated higher
strength gain. The mechanism of early strength gain for TM4 may be explained as
follows; dissolution of cement grains due to physical reaction with water,
deflocculation of cement particles in cement paste due to physical effects of FA
particles, hydration of cement grains and SF-lime pozzolanic reaction. This

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Journal of Engineering Science and Technology January 2016, Vol. 11(1)
mechanism is enhanced by synergic effects of FA/SF additions resulting in high
strength gain in the early age.
During late ages, FA is more reactive chemically when FA-lime reaction starts
to take place while SF is more reactive physically when its un-reacted ultra-fine
particles fill the interfacial transition zone (ITZ) between aggregates and cement
paste. Thus, FA-lime reaction provides additional strength during late ages and
SF’s physical effect densifies the ITZ leading to increased bondage between
aggregates and paste. Therefore, the synergic effects of FA and SF additions
during late ages are able to generate significant increases in compressive strength.
The development of quaternary SCCs with maturing ages is represented in Fig.
6. QM3 and QM4 exhibited relatively high rates of strength gain during the early
ages and yield 33.5MPa and 32.3MPa respectively after 28 days, enabling them to
be classified as G30 strength grade concretes. Both mixes continue to generate
measurable strength development during the late ages up to and possibly beyond 90
days. QM1 and QM2 are also shown to exhibit similar mode of strength
development but yield lower compressive strengths during the early period causing
them to obtain lower ultimate strengths as compared with QM3 and QM4
Based on Fig. 4, it is revealed that the incorporation of LP/SF/RRHA
additions to replace 45% of OPC produces optimum synergic effects leading to
better performing SCCs from a compressive strength development perspective,
while the incorporation of FA/SF/RRHA additions produces the next best
performance. The main observation when viewing the ingredients of both
mixtures is the inclusions of SF and RRHA in each mixture. Despite their
apparent incompatibility when mixed in ternary cement-blend, they showed
optimum co-operation and interaction when a less reactive additive is included in
quaternary mixture. Hence, it is shown that the inclusion of a less reactive
additive is able to overcome the deleterious effects of SF/RRHA mixture.
Fig. 6. The compressive strengths of ternary SCC as a function of curing age.

104 H. Awang et al.
Journal of Engineering Science and Technology January 2016, Vol. 11(1)
5. Material-Costing
The cost of every individual material used in this study is given as a ratio from
OPC’s cost in Fig.7. The cost is represented as a dimensionless quantity. It shows
that the majority of the materials are cheaper than OPC except for the SF and SP.
Fig. 7. Cost individual materials as a ratio of OPC’s cost.
5.1. Material-costing for the binary SCC mixes
The material-costs for the control and binary SCC mixes are presented in Fig. 8.
The cost is represented as a dimensionless quantity and is expressed as a ratio of the
control mix. As shown, the material-cost for the control mix is 1/m
3
, while those of
BM1, BM2, BM3 and BM4 are 0.918/m
3
, 0.919/m
3
, 1.01/m
3
and 0.921/m
3
respectively. Thus, the incorporations of LP, FA and RRHA in binary SCC mixes is
able to reduce SCCs cost by around 8% as compared with the control mix.
Fig. 8. Material-costs for one cubic meter of the control and binary SCC mixes.
Mineral additives affect SCCs costing in a number of ways based on their
varying retail prices, their effects on SP’s consumption and their effects on
aggregate’s volume. The costs of LP, FA and RRHA are cheaper than that of

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Journal of Engineering Science and Technology January 2016, Vol. 11(1)
OPC compared to SF. Therefore, the more the amount of OPC that is replaced
with LP, FA and/or RRHA the greater will be the reductions in material-cost,
whereas replacement with SF will be associated with increases in material-cost.
The incorporation of different types of mineral additive is also found to affect the
amount of SP required in the given mixtures. By replacing 15% of OPC’s weight
with LP is shown to require 3.75L/m
3
of SP which is 6.75L/m
3
lower as compared
with that of the control mix. Since SP is an expensive chemical admixture, any
reduction in its amount of usage can produce a significant impact on SCC’s
costing. Apart from LP, the incorporation of FA is also found to cause significant
reduction in SP’s requirement, but little effects are observed with the
incorporations of SF and RRHA.
5.2. Material-costing for the ternary SCC mixes
The material-costing for ternary SCC mixes are presented in Fig. 9. TM2, TM4 and
TM6 are mixes which include SF as one of the additions and their cost is between
5.2% and 6.7% cheaper in comparison with the control mix, while TM1, TM3 and
TM5 are mixes without SF as one of the additions and their cost is between 11.7%
and 13.1% cheaper. Among ternary SCC mixes, TM5 which incorporates
FA/RRHA mineral additive mixture to replace 30% of OPC’s weight is shown to
exhibit the highest amount of saving in material-cost as compared with other SCC
mixes. The breakdown of savings in cost is as follows: 12.4% reduction from
replacing 30% of OPC’s weight with FA/RRHA mixture, 1.1% reduction due to
reduction in aggregate’s volume and 0.4% increase in cost due increase in SP’s
dosage. Hence, the incorporation FA/RHA mixture in ternary SCC mix produces a
net cost-saving of 13.1% as compared with the control mix and more than 90% of
the saving comes from incorporating cheaper mineral additives such as FA and
RRHA. When SF is incorporated as one of the additions, saving in material-cost is
reduced by almost 50% due its high retail price.
Fig. 9. Material-costs for one cubic meter of ternary SCC mixes.
It is shown that incorporating mineral additives in ternary SCC allows up to
13% saving in material-cost as compared with the control mix. Most of the saving

106 H. Awang et al.
Journal of Engineering Science and Technology January 2016, Vol. 11(1)
comes from utilizing cheaper mineral additives such as LP, FA and RRHA. But
the saving is reduced to almost half when SF is included as one of the additions.
5.3. Material-costing for the quaternary SCC mixes
The material-costs for quaternary SCC mixes are presented in Fig. 10. QM1,
QM3 and QM4 are quaternary SCC mixes which incorporate SF are found to be
between 9.4% and 12.1% cheaper as compared with the control mix. On the other
hand, QM2 is found to be 18.8% cheaper as compared with the control mix.
Fig. 10. Material-costs for one cubic meter of quaternary SCC mixes.
One of the important reasons for replacing OPC with mineral additives in
SCC’s production is to reduce the material-cost by employing ingredients which
are cheaper than OPC such as LP, FA and RRHA. Thus, the greater the amount of
OPC that is replaced by these additives the lower will be the cost of SCC’s. One
of the ways in which higher amounts of OPC may be replaced is by employing a
mixture of three mineral additives to form a quaternary cement-blend. Therefore,
when 45% of OPC’s weight is replaced with a quaternary cement-blend
comprising of OPC/LP/FA/RRHA at 55/15/15/15 weight percentage ratio,
material-cost for the quaternary SCC mix is found to be reduced by 18.8% as
compared with the control mix. Hence, SCC’s components that influence the total
material-cost are cement-paste, chemical admixture and aggregate. With respect
to QM2 mix, it is thus revealed that 85% of the total reduction in material-cost is
due to the reduction in the cost of cement-paste, 10% is due the reduction in the
cost of chemical admixture, while the remaining 5% is due the reduction in
aggregate’s volume. However, in order to enhance SCC’s engineering properties
it may be advantageous to incorporate a highly reactive component in the
quaternary-cement blend, such as SF even though it is at the expense of its
material-cost. As a result, QM1, QM3 and QM4 all of which incorporate SF as
one of the additions are found to be between 8.3% and 11.6% more costly than
QM2 which does not include SF as one of the additions.

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Journal of Engineering Science and Technology January 2016, Vol. 11(1)
6. Conclusions
Analysis of test results for binary SCC mixes revealed that RRHA possesses great
potential as a cement replacement material and better than LP, FA and SF. SCC
mix which is made with ternary cement-blend that comprises of OPC/LP/RRHA
at 70/15/15 weight percentage ratio is found to have produced optimum mixture
proportioning due to its ability to produce the highest performance with respect to
SCC’s engineering properties. SCC mix which is made with quaternary cement-
blend comprising OPC/LP/FAS/RRHA at 55/15/15/15 weight percentage ratio is
found to be capable of maximizing SCC’s material-cost reduction to almost 19%
as compared with the control mix. Hence, the goals of reducing a significant
amount of OPC in the production of SCC and of producing economical SCC are
achievable when RRHA is incorporated as one of the additions in ternary and
quaternary cement-blends.
Acknowlegment
The authors are thankful for the financial support in this research granted by
Universiti Sains Malaysia under USM RU Grant (Ref. No. 1001/ PPBGN/
811234)
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