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Strength of Concrete Containing Rice Husk Ash Subjected to Sodium Sulfate Solution via Wetting and Drying Cyclic
Che Norazman Che Wan1,a, Ramadhansyah Putra Jaya2,b, Dewi Sri Jayanti3,c, Badorul Hisham Abu Bakar4,d and Mohd Fadzil Arshad5,e
1School of Civil Engineering, Polytechnic Tuanku Sultanah Bahiyah, Kulim Hi-Tech Park, 09000 Kulim, Kedah, Malaysia
2Faculty of Civil Engineering and Construction Research Alliance, Universiti Teknologi Malaysia, 81310 Skudai, Johor Bahru, Malaysia
3Faculty of Agriculture, Department of Agricultural Engineering, Universitas Syiah Kuala, 23111 Darussalam, Banda Aceh, Indonesia
3School of Civil Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia
3Faculty of Civil Engineering, Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia
achenorazmanchewan@yahoo.com, brsyahputrajaya@gmail.com, cdee_jayanti@yahoo.com, dcebad@eng.usm.my, efadiil2003@yahoo.co.uk
Keywords: Strength; Rice Husk Ash; Sodium Sulfate; Wetting; Drying.
Abstract. The influences of different replacement levels of rice husk ash (RHA) blended cement
concrete subjected to 5% Na2SO4 solution via wetting-drying cycles was evaluated in this study.
RHA was used as a Portland cement Type I replacement at the levels of 0%, 10%, 20, 30%, and
40% by weight of binder. The water-to-binder ratio was 0.49 to produce concrete having target
strength of 40 MPa at 28 days. The performance of RHA blended cement concrete on compressive
strength, reduction in strength and loss of weight was monitored for up to 6 months. The results of
the compressive strength test have been shown that use of RHA in blended cement has a significant
influence on sulfate concentration. When increasing the replacement level of RHA, the strength of
concrete also increases in comparison to OPC concrete (except RHA40) even exposed to 5%
Na2SO4 solution. On the other hand, the reduction in strength and weight loss of specimens
increased with increase in the exposure time. Generally, it can be said that the incorporation of rice
husk ash as cement replacement significantly improved the resistance to sulfate penetration of
concrete. Finally, RHA cement replacement in concrete mixed provided better resistance to sodium
sulfate attack up to 6-month exposure.
Introduction
Sulfate attack is one of the most important problems concerning the durability of concrete
structures [1]. The effect of sodium sulfate attack on concrete can be divided into two principal
reactions: the reaction of sodium sulfate and the reaction of magnesium sulfate with calcium
hydroxide to form gypsum [2]. The formed gypsum reacts with calcium aluminate hydrates to form
ettringite [3]. Several researchers [4, 5] have confirmed that limiting C3A and C4AF contents is not
the ultimate solution to the problem of sulfate attack. However, the incorporation of pozzolanic
materials such as RHA, slag, FA, MK, POFA, silica fume, etc. as partial replacements for OPC has
been found to be a beneficial technique for enhancing the resistance of concrete to sulfate attack [6,
7].
Applied Mechanics and Materials Vol. 534 (2014) pp 3-8© (2014) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMM.534.3
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 161.139.220.113, Universiti Teknologi Malaysia - UTM, Skudai, Malaysia-17/02/14,04:27:30)
Limited experimental data reported by Torii and Kawamura [8], found that FA and silica fume
appear to increase the resistance significantly, but only when the amount is above a certain level,
which is dependent on the type of sulfate solution. In a related study, Jaturapitakkul et al. [9]
discovered that POFA fineness also contributes to the sulfate resistance of concrete. It was noted
that the finer the POFA, the lower is the expansion and loss in compressive strength of concrete
immersed in sulfate solution.
Based on the available current literature, it can be seen that the use of supplementary
cementitious materials such as silica fume, blast-furnace slag, volcanic-ash, fly ash, silica fume, etc.
as partial replacement cement is an advantageous technique to improve the resistance of concrete
under sulfate attack. However, limited data is available on the effects of RHA as a replacement of
Portland cement subjected to sodium sulfate solution via wetting and drying cycles. For this reason,
the purpose of this study is evaluate the performance of RHA blended cement concrete exposed to
Na2SO4, especially with wetting and drying cycles under laboratory simulation.
Materials
Raw Materials. The ordinary Portland cement (Blue Lion Cement) was used as the major binder
material in the production of moderate-strength concrete (40 MPa). The chemical composition of
OPC is in the standard range as shown in Table 1. The mean particle size of OPC is 10.11 µm and
the density is 3.12 g/cm3. The surface area of the OPC is 359 m
2/kg tested and determined by using
Blaine test. The chemical composition of OPC is in the standard range, with 70% CaO, 17.8% SiO2,
3.9% Al2O3, 3.2% Fe2O3, 1.5% MgO, and 3.6% SO3. Furthermore, the rice husk was incinerated in
a gas furnace at a heating rate of 10°C/min until it reached 700°C and maintained at this
temperature for 6 hours [10]. After the completing burning process, the ash was left inside the
furnace for cooling and removed it in the following day. The ash will then be taken into grinding
process and it was performed by the laboratory ball mill with porcelain balls. The chemical
compositions of RHA evaluated by X-ray fluorescence (XRF) analysis are given in Table 1. Data
from Table 1 shows that the main component of RHA is SiO2. The combined total amounts of SiO2,
Al2O3 and Fe2O3 are 93%. American Society for Testing and Materials C618-12 requires that
pozzolanic material must contain a minimum of 70% of total amount of the three main oxides. This
indicated that RHA have met the requirement of ASTM C618-12 [11] to be categorized as
pozzolanic materials. Table 1: Chemical composition of the OPC and RHA
Component
(wt.% as
oxide)
SiO2 Al2O3 Fe2O3 CaO MgO SO3 Na2O K2O LOI
OPC 17.0 3.90 3.20 70.0 1.50 3.60 0.02 0.53 0.25
RHA 93.0 0.20 0.13 0.49 0.73 0.15 0.02 1.30 3.98
Aggregates. The coarse aggregate was crushed blue granite stone with size of 5 to 14 mm. On the
other hand, the fine aggregate used was natural river sand passing by 4.75 mm sieve. The specific
gravities of coarse and fine aggregates are approximately 2.665 and 2.715, respectively.
Sample Preparation and Tested Program. A laboratory study was undertaken to investigate the
effects of reagent-grade Na2SO4 on the OPC and RHA-blended cement concrete. The control mix
was prepared using OPC. RHA replacement levels of 10%, 20%, 30%, and 40%, by weight of
cement were used in this study. Constant water to binder ratio (w/b) of 0.49 was used throughout
the investigation. In the blended cement, the RHA material was thoroughly mixed with the ordinary
Portland cement, and water was then added into the mixer. However, to maintain slump values,
superplasticizer was added into the mix. After mixture was ready, the concrete were cured in water
maintained at room temperature for a minimum of 28 days to achieve strength of 40 MPa. After 28
4 Advances in Kinematics, Mechanics of Rigid Bodies, and Materials Sciences
days of curing under water, the specimens were transferred to sodium sulfate solution with wetting
and drying cyclic. In the cyclic test, the specimens were subjected to an average to 15 hours of
wetting and 9 hours of drying per day, considered to simulate the Malaysian tidal zone conditions.
This method has been successfully used by Ramadhansyah et al. [3]. On the other hand, the
compressive strength test of all the concrete mixes was performed on 100×100×100 mm cubes. The
specimens were compressed by a compression machine with maximum capacity of 3000 kN with a
loading rate of 150 kN/min. The reported compressive strength was the average of the three
samples.
Results and Discussions
Compressive Strength. Fig. 1 represents a graphical illustration of the compressive strengths of
OPC concrete and RHA blended cement concrete subjected to 5% sodium sulfate (Na2SO4) solution
via drying-wetting cycles at the age of 3, 7, 28, 56, 90, and 180 days. There were no differences in
strength observed in OPC concrete and RHA blended cement concrete up to approximately 90 days.
However, the compressive strength of concrete initially increased during the period between 3 to 90
days, and then started to decrease until the specimens eventually deteriorated after 180 days. The
increase in strength may be attributed to two following reactions. First, the continuous hydration of
un-hydrated cement components to form more hydration products in addition to the reaction of
RHA blended cement with the liberated lime to form more calcium silicate hydrate (CSH) leading
to increasing compressive strength. Second, the reaction of sulfate ions with hydrated cement
components to form gypsum and ettringite. These two reactions lead to a denser structure as a result
of precipitation of the products within voids and micro-pores [12]. Still, the decrease in compressive
strength observed in this experimental work was due mainly to the severity of the drying-wetting
cycles. The sodium sulfate (Na2SO4) reacted with cement hydrates, and repetitive crystallization of
sulfate by repeated hydration occurred. The reactions of sulfate ions with hydrated cement become
more dominant leading to formation of micro-cracks and this decreases strength. Finally, it can be
concluded that the strengths of OPC concrete and RHA concrete subjected to 5% Na2SO4 with
drying-wetting cycles were observed in four stages: (i) the increased between 3–28 days, (ii) the
slowly increased between 28–56 days, (iii) the linearly increased between 56–90 days, and (iv) the
accelerating failure after 180 days.
Fig. 1. Strength of OPC and RHA-concrete subjected to Na2SO4 via wetting-drying cyclic
Applied Mechanics and Materials Vol. 534 5
Reduction in Compressive strength. The reduction in compressive strength of concrete subjected
to sulfate solution was calculated using Equation (1) as follows:
Reduction in compressive strength (%) = (1)
Where ƒ΄dw is the average strength of the specimens cured in tap water and ƒ΄sl is the average
strength of the specimens subjected to sulfate solution with drying-wetting cycles.
The reduction in the compressive strength of OPC and RHA blended cement concrete subjected to
sodium sulfate solution with drying-wetting cycles are presented in Fig. 2. The reduction in
compressive strength of specimens increased at the earlier age of exposure. For instance, the
reduction in compressive strength after 28 days was 0.72% for OPC concrete, followed by 0.49%,
0.35%, 0.42%, and 2.74% for RHA-10, RHA-20, RHA-30 and RHA-40 concrete, respectively.
However, the reductions of all the specimen concrete after 90 days of immersion were significantly
lower than those at 56 and 180 days. This can be explained as follows: as the pozzolanic reaction
proceeds, Ca(OH)2 was consumed to react with silicon dioxide (SiO2); the reaction then produced a
number of C–S–H and sulfate ions, which led to the reduction of compressive strength [3].
Fig. 2. Reduction in strength of OPC and RHA-concrete subjected to Na2SO4 via wetting-drying cyclic
Weight loss due to sulfate attack. In this study, the weight loss of the specimens was calculated
using Equation 2 as follows:
Weight loss (WL) (%) = (2)
Where WLdw is the average initial weight of three specimens cured in tap water and WLsl is the
average weight of the specimens subjected to sodium sulfate solution with wetting-drying cycles.
In general, the weight loss of the OPC concrete and RHA concrete initially increased with increase
in the exposure time as illustrated in Fig. 3. For instance, at the age of 28 days, the weight loss of
OPC, RHA10, RHA20, RHA30, and RHA40 concrete is about 2.57%, 3.71%, 1.77%, 1.80%, and
1.29%, respectively. However, at longer exposures, for example, 180 days, the value of weight loss
6 Advances in Kinematics, Mechanics of Rigid Bodies, and Materials Sciences
due to sulfate attack for OPC, RHA10, RHA20, RHA30, and RHA40 concrete was about 6.66%,
5.92%, 3.07%, 3.13%, and 2.16%, respectively. The increasing weight loss with exposure time may
due to the filling up of pores by the reaction products, thereby densifying the hardened concrete
mix, resulted in a decrease in the weight of specimens, thus increasing the weight loss with
immersion period [13, 14].
Fig. 3. Weight loss of OPC and RHA-concrete subjected to Na2SO4 via wetting-drying cyclic
Conclusions
The results obtained in this study clearly indicate that the addition of RHA as cement replacement
materials provides additional improvements in compressive strength to sodium sulfate solution via
wetting and drying cycles. A high degree of replacement (30% or 40%) leads to low calcium
hydroxide levels due to low cement content. Addition of RHA, as of the pozzolanic reaction,
increases the strength of specimens, and hence increases the concrete durability. This is because
higher replacement of cement leads to lower levels of calcium silicate hydrate, which is the
compound that gives concrete its compressive strength. The high level replacement of RHA has the
advantageous effect in improving resistance in Na2SO4 solution through wetting and drying cycles
(i.e. decrease in calcium hydroxide, magnesium hydroxide, ettringite, and gypsum). Therefore,
RHA can be used as pozzolans to replace part of Portland cement in making concrete with relatively
high strength and good resistance to sulfate attack. These can be explained by the higher content of
RHA, which could undergo greater pozzolanic reaction as well as good sulfate resistance.
Acknowledgements
The support provided by Universiti Sains Malaysia in the form of a research grant for this study is
very much appreciated.
Applied Mechanics and Materials Vol. 534 7
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8 Advances in Kinematics, Mechanics of Rigid Bodies, and Materials Sciences