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

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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