Durability of conventional concretes containing black rice husk ash

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Journal of Environmental Management 92 (2011) 59e66

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Journal of Environmental Management

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Durability of conventional concretes containing black rice husk ash

B. Chatveera a,*, P. Lertwattanaruk b

aDepartment of Civil Engineering, Faculty of Engineering, Thammasat University, Rangsit Campus, Khlong Luang, Pathumthani 12121, Thailandb Faculty of Architecture and Planning, Thammasat University, Rangsit Campus, Khlong Luang, Pathumthani 12121, Thailand

a r t i c l e i n f o

Article history:Received 3 November 2009Received in revised form5 July 2010Accepted 7 August 2010Available online 21 September 2010

Keywords:Black rice husk ashCementConcreteDurability

* Corresponding author. Tel.: þ66 2 5643001x3105E-mail addresses: [email protected] (B. C

(P. Lertwattanaruk).

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a b s t r a c t

In this study, black rice husk ash (BRHA) from a rice mill in Thailand was ground and used as a partialcement replacement. The durability of conventional concretes with high waterebinder ratios wasinvestigated including drying shrinkage, autogenous shrinkage, depth of carbonation, and weight loss ofconcretes exposed to hydrochloric (HCl) and sulfuric (H2SO4) acid attacks. Two different replacementpercentages of cement by BRHA, 20% and 40%, and three different waterebinder ratios (0.6, 0.7 and 0.8)were used. The ratios of paste volume to void content of the compacted aggregate (g) were 1.2, 1.4, and1.6. As a result, when increasing the percentage replacement of BRHA, the drying shrinkage and depth ofcarbonation reaction of concretes increased. However, the BRHA provides a positive effect on theautogenous shrinkage and weight loss of concretes exposed to hydrochloric and sulfuric acid attacks. Inaddition, the resistance to acid attack was directly varied with the (SiO2 þ Al2O3 þ Fe2O3)/CaO ratio.Results show that ground BRHA can be applied as a pozzolanic material and also improve the durabilityof concrete.

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1. Introduction

The use of agrowaste ashes as cement replacement canproduce concrete of standard quality and also improve thedurability (Ganesan et al., 2008). Various types of agrowaste ashessuch as rice husk ash, bagasse ash, palm oil fuel ash (POA) andothers have been widely studied and used in the constructionindustry for the ecological and economical aspects (Chatveera andLertwattanaruk, 2009; Cordeiro et al., 2009; Coutinho, 2005;Ikpong and Okpala, 1992). Agrowaste ashes have pozzolanicproperties in which amorphous silica combines with lime(calcium hydroxide) and forms cementitious materials. Thesematerials can also improve the durability of concrete (Jauberthieet al., 2000, 2003).

Rice husk has been widely used as fuel in the rice paddymilling process. The use of this fuel generates a large volume ofrice husk ash (RHA) usually discarded into landfills, and causingpollution and contamination to water resources. To preserve theenvironment, the interest in using rice husk ash (RHA) inconstruction industry has increased tremendously (Nehdi et al.,2003; Chindaprasirt et al., 2008; Saraswathy and Song, 2007;Ganesan et al., 2008). By burning rice husk at controlled

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burning temperatures below 700 �C, amorphous silica in RHA isformed which is highly reactive (Chindaprasirt et al., 2007; deSensale, 2006). The analyses showed that the highest amountsof amorphous silica occur in rice husk burnt in the range of500e700 �C (Nair et al., 2008). For RHA processed with higherburning temperature with some crystalline silica, reactive RHAcould be obtained by fine grinding (Rodriguez-Camacho, 2002;Mehta, 1977; Zhang and Malhotra, 1996). The properly burntand ground rice husk can be used as a mineral admixture incement production (Ganesan et al., 2008; Chindaprasirt andRukzon, 2008; Chindaprasirt et al., 2008), and the behavior ofcementitious products varies with the source of RHA (Jauberthieet al., 2000, 2003; Chatveera and Lertwattanaruk, 2009). Highamounts (up to 30%) of RHA could be blended with cementwithout adversely affecting the strength and permeability ofconcrete (Chatveera and Lertwattanaruk, 2009). For durability,RHA often improves the concrete’s resistance to deteriorationfrom sulfates and chlorides, and also lowers the temperature offresh concrete (Huang et al., 2005; Gastaldini et al., 2007).

With the long term goal to develop criteria for using rice husk toproduce alternative low-cost but high-quality building materials,this research focuses on investigating the influence of black ricehusk ash (BRHA) from a rice mill in Thailand on the quality anddurability of conventional concrete at different ages. OrdinaryPortland cement Type 1 was partially replaced with 20% and 40% ofBRHA by weight of binder in concretes with high waterebinderratios (between 0.6 and 0.8). The studies presented include

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B. Chatveera, P. Lertwattanaruk / Journal of Environmental Management 92 (2011) 59e6660

chemical and physical properties of BRHA, drying shrinkage,autogenous shrinkage, depth of carbonation reaction, and weightloss of concretes exposed to hydrochloric (HCl) and sulfuric (H2SO4)acid attacks. The results of the study would be beneficial for futureapplications of BRHA in increasing the durability of concrete.

2. Experimental program

2.1. Materials

The materials used in this study included ASTM Type 1Portland cement. Graded river sand with fineness modulus of3.12 and specific gravity of 2.54 conforming to ASTM C33 wasused as fine aggregate. Crushed limestone with a nominalmaximum size of 25 mm, fineness modulus of 7.35 and specificgravity of 2.71 was used as coarse aggregate. Hydrochloric (HCl)and sulfuric (H2SO4) solutions with the pH equal to 1.0 were usedas acid substances.

The BRHA was collected from a rice mill in Nakornpathomprovince in central Thailand. In the production process, rice huskwas fed by air to the furnace chamber of a boiler. The rice husk wasburned at a temperature of 850 �C with short residential time,approximately 10e15 min. The steam was used to drive theturbines of a rice mill. An electrostatic precipitator was used tocollect ash. The rice husk ash was then ground in a laboratory rodmill for 75 min to reasonable fine particles with Blaine fineness of6200 cm2/g and BET surface area of 110 m2/g. Cement and BRHAsamples were subjected to particle size analysis by a laser-basedparticle size analyzer. A small amount of sample was mixed withdeionized water and made into an aqueous solution with the aid ofa surfactant. The solution was then fed into the analyzer.

Table 1Mix proportions of concrete.

Mix Water-to-binderratio

g Portlandcement(kg/m3)

BRHA (kg/m3) Coarse aggre(kg/m3)

OPCe0.6e1.2 0.6 1.2 305 0 929OPCe0.6e1.4 0.6 1.4 358 0 866OPCe0.6e1.6 0.6 1.6 410 0 802



20Re0.6e1.2 0.6 1.2 235 59 92920Re0.6e1.4 0.6 1.4 276 69 86620Re0.6e1.6 0.6 1.6 316 79 802

20Re0.7e1.2 0.7 1.2 213 53 92920Re0.7e1.4 0.7 1.4 250 62 86620Re0.7e1.6 0.7 1.6 287 72 802

20Re0.8e1.2 0.8 1.2 195 49 92920Re0.8e1.4 0.8 1.4 228 57 86620Re0.8e1.6 0.8 1.6 262 65 802

40Re0.6e1.2 0.6 1.2 170 113 92940Re0.6e1.4 0.6 1.4 200 133 86640Re0.6e1.6 0.6 1.6 229 153 802

40Re0.7e1.2 0.7 1.2 155 103 92940Re0.7e1.4 0.7 1.4 181 121 86640Re0.7e1.6 0.7 1.6 208 139 802

40Re0.8e1.2 0.8 1.2 142 94 92940Re0.8e1.4 0.8 1.4 166 111 86640Re0.8e1.6 0.8 1.6 191 127 802

Remarks: g is the ratio of paste volume to void content in compacted aggregates.

2.2. Concrete mix proportions

In this study, concretes were mixed with high waterebinderratios (w/b) of 0.6, 0.7 and 0.8, and ratios of the volume of paste tovolume of minimum voids content of total aggregates (g) were 1.2,1.4 and 1.6. The ratio by volume between fine aggregate to totalaggregates (s/a) was 0.5 and percentage of minimum voids volumecontent was 24.6. The BRHA replacements were varied at 0%, 20%and 40% by weight of binder. The concrete mixture proportions aresummarized in Table 1. Results of slump and compressive strengthat 28 days of the concretes were also given. OPCew/beg denotesa control concrete mixed with Portland cement Type 1. XRew/begdenotes a concrete in which BRHA was used as Portland cementreplacement at the percentage of X by weight. The total mixingtime was 5 min; the samples were then casted and left for 24 hbefore demolding.

2.3. Testing procedures

2.3.1. Drying shrinkageThe drying shrinkage was performed by applying the method

proposed by Japan Concrete Institute (JCI, 1998) by using100 � 100 � 500 mm specimens with two LVDT displacementtransducers contacted on the embedded stud at both ends of thespecimen. The specimens were removed from the mold at 24 hafter casting. Then the specimens were cured in water and thelength measurements were taken periodically until the age of28 days. After 28 days of wet curing, the specimens were stored atconstant temperature (25 � 2 �C) and constant relative humidity(60 � 5%). The measurements of length change were performed

gate Sand (kg/m3) Water (kg/m3) Slump (cm) Compressivestrength at28 days (kg/cm2)

929 183 7.0 27.5866 215 22.0 26.9802 246 24.0 22.0

929 193 9.0 22.4866 226 23.0 21.5802 259 25.0 16.1

929 201 11.0 19.2866 235 24.0 16.4802 270 26.0 11.7

929 176 4.5 29.3866 207 18.5 28.3802 237 20.0 26.6

929 186 6.5 22.4866 219 20.5 20.4802 251 22.0 17.9

929 195 8.5 16.5866 228 22.5 13.3802 262 24.0 10.3

929 170 2.5 26.9866 200 4.0 26.5802 229 7.5 26.2

929 180 5.0 21.4866 212 8.5 20.6802 243 10.0 20.2

929 189 7.0 15.3866 222 12.0 14.2802 254 13.0 11.0

Table 2(b)Physical properties of cement and black rice husk ash.

Physical properties Portland cement Ground BRHA

Moisture content (%) 0.19 2.35Blaine specific surface area (cm2/g) 3248 6200BET specific surface area (m2/g) e 110Specific gravity 3.11 2.02% Retained on sieve No. 325 9.35 14.77

Strength index compares with control mortars (%)At 7 days 100 76At 28 days 100 88

Water demand (%) 100 107

Table 3Chemical and physical properties of BRHA according to ASTM C618 standard fornatural pozzolan.

B. Chatveera, P. Lertwattanaruk / Journal of Environmental Management 92 (2011) 59e66 61

periodically until the age of 150 days. Three concrete specimenswere tested for each data.

2.3.2. Autogenous shrinkageThe autogenous shrinkage was performed in accordance with

the method proposed by Japan Concrete Institute (JCI, 1998). Foreach mixture, three concrete prisms of 100 � 100 � 500 mmwereprepared. Before the removal of the mold, two LVDTs contacted onthe embedded stud at both ends of the specimen were installed tomonitor the length change. Immediately after demolding at 24 h,the specimens were sealed with an adhesive polyester film to avoidmoisture loss. All specimens were stored in a curing room ata temperature of 25 � 2 �C and a relative humidity of 60 � 5%during the test. The measurements of length change were per-formed periodically until the age of 150 days.

2.3.3. Depth of carbonationFor long term reference carbonation tests, the 10 � 10 � 10 cm

concrete cubes were used. The specimens were cured in saturatedlime water. After curing for 28 days, the specimens were trans-ferred to a sealed chamber and subjected to carbonation at roughly0.03% CO2 concentration, a temperature of 23 �C and a relativehumidity of 70% for 180 days (De Ceukelairea and VanNieuwenburga, 1993). The concrete specimens were taken out ofthe carbonation chamber and split in a tensile splitting test. Aftersplitting the concrete specimens, the freshly split surface wascleaned and sprayed with a phenolphthalein pH indicator. A solu-tion of 1% phenolphthalein in 70% ethyl alcohol was used as theindicator for determining depth of carbonation (RILEM, 1988). Inthe non-carbonated part of the specimen where the concrete wasstill highly alkaline, a purple-red color was obtained. In thecarbonated part where the alkalinity of concrete was reduced, nocoloration occurred. The average depth of the colorless phenol-phthalein regionwas measured from three points, perpendicular tothe two edges of the split face, both immediately after spraying theindicator and at 24 h later. Three concrete specimens were testedfor each data.

2.3.4. Resistance to acid attackThis test was conducted in order to study the effect of BRHA

replacement on the resistance against acid attack. The10 � 10 � 10 cm concrete specimens were prepared and cured insaturated lime water. After curing for 28 days, the specimens weretaken out to measure the initial weights, and then transferred to 1%solution of hydrochloric (HCl) acid and the same amount of 1%solution of sulfuric (H2SO4) acid. The parameters investigated werethe time and weight loss of fully-immersed concrete specimens inthe respective acid solutions. The measurements of weight losswere performed at the age of 3, 7, 14, 21, 28 and 60 days. Threeconcrete specimens were tested for each data.

Properties Type of pozzolan Ground BRHA

N F C

Chemical propertiesMin. SiO2 þ Al2O3 þ Fe2O (%) 70.0 70.0 50.0 78.66Max. sulfur trioxide (SO3) (%) 4.0 5.0 5.0 0.04Max. Na2O þ 0.658 K2O (%) 1.5 1.5 1.5 0.71Max. loss on ignition (%) 10.0 6.0 6.0 8.31

3. Test results and discussion

3.1. Properties of ground black rice husk ash

The chemical compositions and physical properties of ordinaryPortland cement and black rice husk ash (BRHA) from a rice mill are

Table 2(a)Chemical compositions of cement and black rice husk ash.

Materials Chemical compositions (%)

SiO2 Al2O3 Fe2O3 CaO MgO K2O Na2O SO3 LOI

Portland cement Type 1 20.84 5.22 3.20 66.28 1.24 0.22 0.10 2.41 0.96Ground BRHA 78.12 0.31 0.23 0.08 0.34 0.82 0.17 0.09 8.31

given in Tables 2a and 2b. The ground BRHA contained high silicacontents (SiO2) of 78%, and very small proportions of other chem-ical compositions. Blaine fineness of the ground BRHA (6200 cm2/g)was finer than that of Portland cement (3248 cm2/g). BRHA hadlower specific gravity and more water demand than Portlandcement. Table 3 shows the properties of BRHA according to ASTMC618 (2008) specification for pozzolan materials. The results indi-cated that BRHA can be classified as a Type N pozzolan, and used asa partial cement replacement. An X-ray diffraction analysis (XRD) ofground BRHA was conducted to identify the crystalline phasesinvolved in the composite. From XRD pattern in Fig. 4, somereasonably sharp and intense reflections start to show up on top ofthe broad amorphous background, evidencing that crystallinecristobalite starts to form (Habeeb and Fayyadh, 2009; Nair et al.,2008; de Sensale et al., 2008). Researchers found that atcontrolled burning temperatures below 700 �C, a rice husk ash(RHA) in amorphous silica is formed which is highly reactive(Chindaprasirt et al., 2007; de Sensale, 2006). Even for higherburning temperature with some crystalline silica, reactive RHAcould be obtained by fine grinding (Rodriguez-Camacho, 2002;Zhang and Malhotra, 1996).

The SEM micrographs at the magnification of 200� and 7500�are shown in Figs. 1 and 2, respectively. It can be seen that BRHAparticles were larger than those of Portland cement, with multi-layered and microporous surfaces and angular particle shapes,resulting in the higher porosity and pore volume of BRHA (Habeeband Fayyadh, 2009). According to the Blaine fineness results, theground BRHA particles (6200 cm2/g) were finer than Portlandcement particles (3248 cm2/g), due to the shape, surfacemorphology and porosity of BRHA. On the other hand, it was foundthat the particle size distribution of ground BRHA was comparableto that of Portland cement in the range of 1e100 mm, as shown in

Physical propertiesMoisture content (%) 3.0 3.0 3.0 2.35% Retained on sieve No. 325 34 34 34 14.77Strength index at 7 days (%) 75 75 75 76Strength index at 28 days (%) 75 75 75 88Water demand (%) 115 105 105 107Blaine specific surface area (cm2/g) e 6185Specific gravity e 2.02

Fig. 1. Micrograph of ordinary Portland cement and black rice husk ash (BRHA) 200-time magnification: (a) ordinary Portland cement and (b) black rice husk ash.

Fig. 2. Micrograph of ordinary Portland cement and black rice husk ash (BRHA) 7500-time magnification: (a) ordinary Portland cement and (b) black rice husk ash.


Fig. 3. In addition, some cement particles had a fine-grained frac-tion (0.1e1.0 mm) resulting in an average particle size smaller thanblack rice husk ash. The results demonstrate that the shape, size,surface morphology and porosity play a very significant role indetermining the surface area and water demand.

3.2. Drying shrinkage

Fig. 5 shows the results of drying shrinkage of concretes withthewaterebinder ratio of 0.60 and the ratio of paste volume to voidvolume content of the compacted aggregates (g) of 1.2. It was foundthat drying shrinkage of the concretesmixedwith BRHAwas higherthan the OPC concrete. One source of drying shrinkage in concrete

0123456789

10

0.01 0.1 1 10 100 1000 10000

Particle Diameter (microns)

Cement

Ground BRHA

As-received BRHA

Parti

cle

Size

Dis

tribu

tion

by V

olum

e (%

)

Fig. 3. Particle size distribution of Portland cement and black rice husk ash.

is the loss of water held in capillary pores of the hydrated cementpaste to the environment (de Sensale, 2006). From the results,increasing the percentage replacement of BRHA (from 20% to 40%by weight of binder) tends to reduce the drying shrinkage ofconcrete. The incorporation of BRHA causes the segmentation oflarge pores leading to refinement of the pore structure, andincreases nucleation sites for the precipitation of pozzolanic reac-tion products in cement paste (Rukzon et al., 2009).

Fig. 6 shows test results of the drying shrinkage of concretesmixedwith 20% BRHA replacement and the ratio of paste volume tovoid volume content of the compacted aggregates (g) of 1.2. It wasfound that increasing the waterebinder ratios increased the watercontent of the mix and thus increased the shrinkage. The concretesare more porous and have additional capillary pores, resulting in anincreased loss of free water to the environment. Furthermore,increasing the waterebinder ratio lowers the cement content and

Fig. 4. XRD pattern of black rice husk ash.

Age (Days)

Fig. 5. Drying shrinkage of BRHA concretes (water-to-binder ratio of 0.6 and g of 1.2).

-500

-400

-300

-200

-100

0

100

200

0 30 60 90 120 150

Dry

ing

Shri

nkag

e(m

icro

-str

ain)

Age (Days)

r = 1.2 (mix 20R-0.6-1.2) r = 1.4 (mix 20R-0.6-1.4)r = 1.6 (mix 20R-0.6-1.6)

Fig. 7. Drying shrinkage of BRHA concretes (BRHA replacement of 20% and water-to-binder ratio of 0.6).

Age (Days)


hence the lower reaction, yielding less amount of the hydrationproduct. As a result, this leads to more permeability of concrete andcontributes to more free water evaporation and increasing thedrying shrinkage.

Fig. 7 shows test results of the drying shrinkage of concretesmixed with 20% BRHA replacement and the waterebinder ratio of0.6. It was found that increasing the ratio of paste volume to voidvolume content of the compacted aggregates (g) tends to increasethe drying shrinkage of concrete due to the increase of paste volumeand the smaller amounts of aggregates yielding more free water inthe capillary pores. As a result, a loss of water from the capillarynetwork in the concretes is progressive and proceeds at anincreasing rate leading to the highermagnitude of drying shrinkage.

3.3. Autogenous shrinkage

Fig. 8 shows test results of the autogenous shrinkage ofconcretes with the waterebinder ratio of 0.6 and the ratio of pastevolume to void volume content of the compacted aggregates (g) of1.2. The cement substitution by BRHA at the early age increases theautogenous deformation due to the pozzolanic effect, since chem-ical shrinkage of the silica reaction is much higher than Portlandcement reaction; but with time, probably due to its cellular struc-ture the autogenous deformation decreases in comparison withthat of the concrete without RHA (de Sensale, 2006; Miyazawa andTazawa, 1995). From the results, increasing the BRHA percentagereplacement (from 0% to 40% by weight of binder) tends to reducethe autogenous shrinkage of concrete. BRHA provides a positiveeffect on the autogenous shrinkage of concrete, which is attributedto the filler effect, when compared with the hydration effect of thecement paste without BRHA. Incorporation of BRHA causes thesegmentation of large pores leading to refinement of the porestructure and lower capillary stresses in these pastes (Rukzon et al.,2009; de Sensale et al., 2008). In the long period the behavior of theconcrete with BRHA was better than those of control concrete(OPC).

Age (Days)

Fig. 6. Drying shrinkage of BRHA concretes (BRHA replacement of 20% and g of 1.2).

3.4. Depth of carbonation

Fig. 9 presents the depth of carbonation of BRHA concretes at theage of 180 days. The depths of carbonation of the concretes mixedwith BRHA are higher than the OPC concrete. Increasing the BRHApercentage replacement (from 20% to 40% by weight of binder)tends to increase the depth of carbonation. The carbonation requiresthe presence of water because CO2 dissolves in water formingcarbonic acid (H2CO3). A chemical reaction of Ca(OH)2 in thehydrated cement pastewithH2CO3 to formCaCO3 leads to reductionof the alkalinity, thereby permitting corrosion of the embeddedsteel (Johannesson and Utgenannt, 2001; Papadakis et al., 1991).Incorporation of BRHA increases the rate of carbonation because ofthe lower concentration of cement and the increase in concreteporosity, allowingmore CO2 to infiltrate (Rukzon et al., 2009).WhenCa(OH)2 is removed from the paste, the hydrated CeSeH gel willliberate CaO, which will also carbonate (Gastaldini et al., 2007).

For comparison of the ratios of paste volume to void volumecontent of the compacted aggregates (g) of 1.2, 1.4 and 1.6, it wasfound that increasing the g tends to have an adverse effect ofcarbonation on concrete with the higher percentage BRHAreplacement due to the higher volume of cement paste. Whenincreasing the volume of paste, the degree of carbonation increasesdue to the higher porosity of concrete structure, allowing more CO2penetration into concrete. Increasing the waterebinder ratio tendsto increase the porosity and volume of capillary pores in concrete,and significantlyaffect the carbonationdepth. Asmore air enters thecapillary pores of the concrete the CO2 it contains reacts withthe hydroxides to form more CaCO3. Carbonation is also affected bythe moisture condition of the concrete. Dry Ca(OH)2 reacts veryslowly with CO2 and the reaction is much faster when a surface filmof water is present on the grains of the hydroxide. Damp concretetherefore carbonates at a faster rate than dry concrete (Mays, 2001).

-400

-350

-300

-250

-200

-150

-100

-50

0

0 30 60 90 120

egaknirhSsuonegotu

A)niarts-orci

m(

0% BRHA (mix OPC-0.6-1.2) 20% BRHA (mix 20R-0.6-1.2)

40% BRHA (mix 40R-0.6-1.2)

Fig. 8. Autogenous shrinkageof BRHAconcretes (water-to-binder ratio of0.6 andgof1.2).

a

b

c

Fig. 9. Carbonation depth of BRHA concretes at the age of 180 days: (a) g ¼ 1.2,(b) g ¼ 1.4 and (c) g ¼ 1.6.


3.5. Resistance to acid attack of concrete

Fig. 10 shows test results of the weight loss due to hydrochloric(HCl) and sulfuric (H2SO4) acid attacks of the concrete mixed withground BRHAwith the waterebinder ratio of 0.6 and g of 1.2. Fromthe results of HCl and H2SO4 attacks, the OPC concrete yieldedmore

-15

-10

-5

0

Immersed time (days)

-1

-1

-

0 15 30 45 60

20%BRHA40%BRHA

OPC

HCL

Wei

ght l

oss

(%)

Wei

ght l

oss

(%)

a b

Fig. 10. Weight loss due to HCl and H2SO4 attacks of BR

weight loss than those mixed with ground BRHA from a rice mill,and the rate ofweight loss of concrete increaseswhen increasing thereplacement level of BRHA (20e40%). For the HCl attack, the weightloss of OPC concrete is higher than those of concretes mixed withBRHA. In case of H2SO4 attack, the weight loss of OPC concrete ishigher than that of concretes mixed with 20% BRHA replacement,but lower than that of concretesmixedwith 40% BRHA replacement.

When immersed in HCl solution, concrete is chemicallyexposed to the pH that produces a progressive neutralization ofthe alkaline nature of the cement paste, removing alkalies anddissolving portlandite (Ca(OH)2) and CeSeH gel. The chloride(Cl�) dissolved in water speeds up the rate of the leaching ofCa(OH)2 transforming to CaCl2 which is very soluble, and thusincreases the porosity and permeability of concrete leading to theloss of stiffness and strength. In the presence of Cl�, the release ofcalcium from Ca(OH)2 and CeSeH could be controlled by theprecipitation of alteration solid phases (Huang et al., 2005;Gastaldini et al., 2007). In case of H2SO4 immersion, SO4

2� ionsreacted with Ca(OH)2 and transformed to gypsum (CaSO4$2H2O),leading to the expansion of cement matrix and further cracking ofthe interior of the concrete (Chatveera and Lertwattanaruk, 2009;Santhanam et al., 2003). This leaves the concrete susceptible todirect attack by H2SO4 solution.

As shown in Fig. 10, replacement of 20% of Portland cement byBRHA leads to a successive reduction of the corrosion of concreteunder both HCl and H2SO4 attacks due to the increase in pozzo-lanic reaction between BRHA and Ca(OH)2 yielding additionalCeSeH. As a result, this leads to increasing the density andimpermeability of concrete. In addition, the decrease of Ca(OH)2reduced the alkalinity and degree of reaction of HCl and H2SO4attacks, and contributed to less damage and improved durabilityof concrete. Replacement of 40% of Portland cement by BRHAimproves resistance to HCl attack, but it impairs resistance toH2SO4 attack due to a reduced amount of free lime and additionalunreacted silicon dioxide leading to the decrease in pozzolanicreaction. In addition, although increasing BRHA replacementreduced the amount of Ca(OH)2 used as a reactant in sulfuric acidreaction, SO4

2� ions can also react with other calcium compoundsin cement matrix. As a result, this leads to reducing the densityand increasing the permeability of concrete, and contributes tomore corrosion due to H2SO4 attack.

Fig. 11 shows test results of the relationship between chemicalcompositions and weight loss of concrete due to HCl and H2SO4attacks. It was found that the chemical compositions in eachconcrete mix proportion are an important factor for the damageof concrete due to acid attack. The concretes with the(SiO2 þ Al2O3 þ Fe2O3)/CaO ratio of 0.74, in which 20% of Portlandcement was replaced by BRHA, yielded lower weight loss due toHCl and H2SO4 attacks than the control concretes and those with40% BRHA replacement, with the (SiO2 þ Al2O3 þ Fe2O3)/CaO ratiosof 0.42 and 1.23 respectively. This is due to the amount of CaO andSiO2 available for optimizing the pozzolanic reaction in cement

5

0

5

00 15 30 45 60

Immersed time (days)

20%BRHA OPC

40%BRHA

H2SO4

HA concrete (water-to-binder of 0.6 and g of 1.2).

0

5

10

15

(SiO2+Al2O3+Fe2O3)/CaO

3 days

7 days

14 days

21 days

28 days

60 daysW0

5

10

15

0 0.5 1 1.5 0 0.5 1 1.5

(SiO2+Al2O3+Fe2O3)/CaO

3 days

7 days

14 days

21 days

28 days

60 days

HCl

Wei

ght l

oss

(%)

Wei

ght l

oss

(%)

a b

H2SO4

Fig. 11. Relationship between chemical compositions and weight loss due to HCl and H2SO4 attacks.

Fig. 12. Weight loss due to HCl and H2SO4 attacks of BRHA concrete at different water-to-binder ratios (BRHA replacement of 20% and g of 1.2).

a b

Fig. 13. Weight loss due to HCl and H2SO4 attacks of BRHA concrete at different g (BRHA replacement of 20% and water-to-binder ratio of 0.6).


paste of each mixture contributing to the density and permeabilityof concrete.

In addition to the replacement percentage of BRHA, the otherfactors which have effects on the corrosion of concrete due to acidattacks are the waterebinder ratio and the ratio of paste volume tovoid volume content of the compacted aggregates (g). As shown inFig. 12, the results of weight loss of concrete due to HCl and H2SO4attacks show that increasing the waterebinder ratio tends toreduce the weight loss due to the larger volume of free water fillingthe capillary pores. This leads to an increase in the internal porepressure of concrete to resist the diffusion of HCl and H2SO4 acidsinto the cement matrix, resulting in the positive effect on theimpermeability and durability of concrete.

As shown in Fig. 13, the results of weight loss of concrete due toHCl and H2SO4 attacks show that reducing the ratio of paste volumeto void volume content of the compacted aggregates (g) tends toreduce theweight loss due to the decrease in the amount of calciumcompounds available to react with HCl and H2SO4 solutions. Thisleads to the reduction of cracking in the interior of concrete,resulting in a positive effect on the durability of concrete.

4. Conclusions

Based on the results for conventional concretes with highwaterebinder ratios studied, incorporation of the ground black ricehusk ash (BRHA) from a rice mill into Portland cement results incomparable effects in the durability of concrete. The followingconclusions can be drawn.

1. According to the chemical compositions and physical properties,the ground BRHA in this study can be classified as a pozzolanicmaterial of Type N according to ASTM C618 since the sum ofcomponents SiO3, Al2O3 and Fe2O3 is higher than 70%, SO3 is nothigher than 4% and the loss on ignition (LOI) is close to 8%.

2. The use of BRHA replacing Portland cement has a negative effecton the drying shrinkage of concrete. However, the dryingshrinkage of concretewith40%BRHAreplacement is comparableto the OPC concrete. Increasing the replacement percentage ofBRHA (from 20% to 40% by weight of binder) tends to reduce thedrying shrinkage of concrete due to packing effect and segmen-tation of large pores leading to refinement of the pore structure.


3. The autogenous shrinkage of the concrete mixed with BRHA islower than the OPC concrete. Increasing the BRHA percentagereplacement (from 20% to 40% by weight of binder) tends toreduce the autogenous shrinkage of concrete.

4. The depths of carbonation of the concretes mixed with BRHAare higher than the OPC concrete. Increasing the BRHApercentage replacement (from 20% to 40% by weight of binder)tends to increase the depth of carbonation. The ratios of pastevolume to void volume content of the compacted aggregates(g) are an important factor for the damage of concrete.Increasing the g tends to have an adverse effect of carbonationon concrete with the higher BRHA percentage replacement dueto the higher volume of cement paste. In addition, increasingthe waterebinder ratio tends to increase the porosity andvolume of capillary pores in concrete, and significantly affectthe carbonation depth.

5. For the durability of concrete exposed to HCl and H2SO4 attacks,replacement of 20% of Portland cement by BRHA leads toa positive effect in decreasing the corrosion of concrete underboth HCl and H2SO4 attacks. Replacement of 40% of Portlandcement by BRHA improves resistance to HCl attack, but itimpairs resistance to H2SO4 attack. The chemical compositionsin concrete mix proportion are an important factor for thedamage of concrete due to acid attack. The concretes with the(SiO2 þ Al2O3 þ Fe2O3)/CaO ratio of 0.74, in which 20% ofPortland cement was replaced by BRHA, yielded the lowestweight loss of concrete due to HCl and H2SO4 attacks.

Acknowledgment

The authors acknowledge the support of Thammasat University.The authors also thank Dr. Natt Makul and Mr. Tavisan Kongsub fortheir assistance in the experimental program.

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Durability of conventional concretes containing black rice husk ash