Construction

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Construction and Building Materials 21 (2007) 1492–1499

and Building

MATERIALS

Strength and water permeability of concrete containing palm oil fuelash and rice husk–bark ash

P. Chindaprasirt a, S. Homwuttiwong b, C. Jaturapitakkul b,*

a Department of Civil Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen 40002, Thailandb Department of Civil Engineering, Faculty of Engineering, King Mongkut’s University of Technology Thonburi, Bangmod,

Tungkru, Bangkok 10140, Thailand

Received 1 May 2005; received in revised form 20 October 2005; accepted 30 June 2006Available online 1 September 2006

Abstract

In this paper, palm oil fuel ash and rice husk–bark ash, which are by-products from electricity generating power plants and disposed aswastes in landfills, were used as a partial cement replacement. They were ground and incorporated into concrete at the levels of 20%, 40%and 55% by weight of binder. Compressive strength and water permeability of concretes containing ground palm oil fuel ash (GPOA) andground rice husk–bark ash (GRBA) were investigated. From the tests, the replacement of Portland cement by both materials resulted inthe higher water demand in concrete mixtures as compared to ordinary Portland cement (OPC) concrete with compatible workability. Thecompressive strengths of concretes containing 20% of GPOA and GRBA were as high as that of OPC concrete and were reduced as theincrease in the replacement ratios. Although the compressive strengths of concrete with the replacement of GPOA or GRBA up to 40%were lower than OPC concrete, their water permeabilities were still lower than that of OPC concrete. These results indicate that both ofGPOA and GRBA can be applied as new pozzolanic materials to concrete with an acceptable strength as well as permeability.� 2006 Elsevier Ltd. All rights reserved.

Keywords: Compressive strength; Permeability; Palm oil fuel ash; Rice husk–bark ash

1. Introduction

It is known that the permeability controls deteriorationsof concrete in the aggressive environment [1,2], because theprocess of such deteriorations as carbonation, chloride andsulfates attack are governed by the fluid transportation inconcrete. The addition of fillers and pozzolanic materialsare introduced to improve the strength and other proper-ties of concrete for necessary conditions. A study on com-pressive strength and water permeability of concretecontaining a new material is therefore of considerableinterest.

Palm oil fuel ash (POA) is produced from burning offiber, shell, and empty fruit bunch of palm oil tree as a fuel

0950-0618/$ - see front matter � 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.conbuildmat.2006.06.015

* Corresponding author. Tel.: +66 2 470 9137; fax: +66 2 427 9063.E-mail address: chai.jat@kmutt.ac.th (C. Jaturapitakkul).

to heat the steam for electricity generation and palm oilextraction process. The palm oil fuel ash is so disposed inlandfills that the amount of ashes increases every yearand now becomes a burden. It is estimated that more than100,000 tons of palm oil fuel ash has been produced everyyear and increases annually in Thailand. The study of palmoil fuel ash was started by Tay [3] who used it to replacePortland cement with 10–50%. He found that in the rangeof 20–50% of cement replacement, the decrease in the com-pressive strength of concrete at various ages was almostproportional to amount of the ash in the concrete mixtures,except when only 10% ash was used. Later, Awal and Hus-sin [4] reported that palm oil fuel ash had a good potentialin suppressing expansion due to sulfate attack. In 2004, itwas found that palm oil fuel ash, which contained a sub-stantial amount of silica and was ground to a suitable fine-ness, could be used as a pozzolanic material to producehigh strength concrete as high as 100 MPa at 90 days [5].

Table 2Chemical composition of cement and replacement materials

Chemicalcomposition(%)

Cement(OPC)

Fly ash(OFA)

Ground palmoil fuel ash(GPOA)

Ground ricehusk–barkash (GRBA)

SiO2 20.9 41.1 57.8 74.8Al2O3 4.8 22.5 4.6 0.2Fe2O3 3.4 11.6 3.3 0.8CaO 65.4 15.3 6.6 5.9MgO 1.2 2.8 4.2 0.6Na2O 0.2 1.7 0.5 0.2K2O 0.3 2.9 8.3 2.0SO3 2.7 1.5 0.3 0.5LOI 0.9 0.2 10.1 11.2SiO2 + Al2O3 + Fe2O3 – 75.2 65.7 75.8

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However, results on the water permeability of concretecontaining palm oil fuel ash have been rarely reported.

Rice husk–bark ash (RBA) is also a waste from electric-ity generation power plant. In the fluidized bed powerplant, two parts of rice husk are used in conjunction withone part of eucalyptus tree bark by weight as fuel. Theburning temperature of the materials is between 800 and900 �C. The disposal of rice husk–bark ash is also becom-ing a problem due to its quantity. It is estimated that morethan 300,000 tons of rice husk–bark ash has been producedeach year in Thailand [6]. Effort has, therefore, been madeto utilize this ash. The study revealed that the ground ricehusk–bark ash conforms to the Class N pozzolanic mate-rial [7] as prescribed by ASTM C 618 [8]. Moreover, thecompressive strength of mortar containing very high fine-ness of rice husk–bark ash is equal or higher than the con-trol mortar. Although some properties of concretecontaining rice husk–bark ash have been reported [6], noneof them deals with a relationship between the strength andthe permeability.

The aim of this research is to study the compressivestrength and water permeability of concrete containingpalm oil fuel ash and rice husk–bark ash. The results arecompared to concrete containing fly ash, a well-knownpozzolanic material, and also compared to the control con-crete as well. The knowledge on the strength and perme-ability of concrete containing palm oil fuel ash and ricehusk–bark ash is of interest and could be beneficial onthe utilization of these waste materials in concrete work,especially on the topic of durability.

2. Experimental program

2.1. Materials

2.1.1. Cement and incorporated materials

ASTM Type I ordinary Portland cement (OPC) wasused for all concrete mixtures. Palm oil fuel ash and ricehusk–bark ash were ground by ball mill until the 95% ofthe particles passed a sieve No. 325 (opening 45 lm) andwere assigned as GPOA and GRBA, respectively. In addi-tion, fly ash (OFA) was collected directly from Mae Mohpower plant in the north of Thailand. These materials wereused partially to replace OPC to cast concrete. Physicalproperties and chemical compositions of the materials areshown in Tables 1 and 2.

Table 1Materials properties

Material Specific gravity Retained ona sieve #325 (%)

Median particlesize, d50 (lm)

OPC 3.14 – 14.7OFA 2.19 32.1 27.1GPOA 2.43 1.0 8.0GRBA 2.15 1.9 10.2

Note: OPC = Ordinary Portland cement Type I. OFA = Fly ash.GPOA = Ground palm oil fuel ash. GRBA = Ground rice husk–bark ash.

2.1.2. Aggregates

River sand with fineness modulus of 2.44 and specificgravity of 2.65 was used as fine aggregate. Crushed lime-stone with the maximum size of 20 mm and having specificgravity of 2.67 was used as coarse aggregate.

2.2. Concrete mixtures

OPC was partially replaced by ground palm oil ash(GPOA) and ground rice husk–bark ash (GRBA) at 20%,40% and 55%, while the replacement of OFA was 20%and 40% by weight of binder. The binder content of con-crete was set as a constant of 300 kg/m3 and mix propor-tions of concrete are presented in Table 3. The amountsof water in all concrete mixtures were adjusted in orderto control the slump of fresh concretes between 60 and90 mm.

2.3. Testing

2.3.1. Compressive strength

Concretes cylinders of 100 mm in diameter and 200 mmin height were used to determine the compressive strength.The samples were demolded 24 h after casting and cured inwater until the testing ages. The compressive strengths ofconcretes were determined at the ages of 28 and 90 days.

2.3.2. Water permeability

The penetration method and steady flow method areavailable for the investigation of water permeability of con-crete. The steady flow method was applied to test the per-meability of concrete. The coefficient of water permeabilitywas determined by measuring the amount of water passingthrough the specimen and calculated using Darcy’s law andthe equation of continuity [9],

K ¼ qLgQPA

ð1Þ

whereK = Coefficient of permeability (m/s)q = Density of water (kg/m3)g = Acceleration due to gravity (m/s2)

Table 3Mix proportions of concrete

Mixtures Cement (kg) OFA (kg) GPOA (kg) GRBA (kg) Fine aggregate (kg) Coarse aggregate (kg) Water (kg) Slump (mm)

OPC 300 – – – 915 1080 213 75OFA20 240 60 – – 904 1068 215 65OFA40 180 120 – – 893 1057 195 60GPOA20 240 – 60 – 907 1072 220 65GPOA40 180 – 120 – 900 1064 222 70GPOA55 135 – 155 – 894 1059 225 90GRBA20 240 – – 60 903 1068 214 80GRBA40 180 – – 120 891 1055 229 60GRBA55 135 – – 155 883 1046 240 70

Fig. 1. Permeability housing cell.

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Q = Flow rate (m3/s)L = Thickness of concrete sample (m)P = Absolute water pressure (Pa)A = Cross-sectional area of concrete sample (m2)Two days before testing the permeability, the samples

were prepared by sawing of 40 mm thick slice from themiddle of the cylinder. After drying in the laboratory for24 h, the slice was cast around with 25 mm thick of non-shrinkage epoxy resin to prevent the water leakage. Theepoxy resin was allowed to harden and dry for another24 h. The specimen was then installed in the housing cellas shown in Fig. 1, and then the water pressure of0.5 MPa was applied. This pressure was recommendedand used by Chan and Wu [10]. The time and the amountof water passed through the specimen were monitored untilthe constant flow rate was obtained.

3. Results and discussion

3.1. Properties and particle shape of materials

Considering the chemical compositions in Table 2, itrevealed that the fly ash and the GRBA can be assignedas class F and class N pozzolan as prescribed by ASTMC 618 [8], respectively. The GPOA cannot be classified asclass N pozzolan because the contents of SiO2 + Al2O3 + -Fe2O3 were less than 70%. It should be noted that the losson ignition (LOI) contents of GPOA and GRBA were

rather high as 10.1% and 11.2%, respectively and 74.8%of GRBA was SiO2.

Particle size distribution curves of OPC and the othermaterials are shown in Fig. 2. The median particle sizeof OFA was 27.1 lm, which was larger than that of theOPC (14.7 lm). Before grinding, palm oil fuel ash andrice husk–bark ash had median particle sizes more than100 lm. After grinding, the median particle sizes ofGPOA and GRBA were reduced to 8.0 and 10.2 lm,respectively.

The particle shapes of OPC and the replacement materi-als are presented in Fig. 3. The particle shape of OFA wasspherical and smooth surface indicating a rather completeburning. On the other hand, both of GPOA and GRBAhad an angular and irregular particle shape, which weresimilar to that of Portland cement Type I.

3.2. Water requirement in concrete mixtures

The amounts of water in the concrete mixtures forslump of fresh concrete between 60 and 90 mm are shownin Table 3 and the water-to-binder (W/B) ratios are shownin Table 4. The W/B ratio of OPC concrete was 0.71. Theuse of OFA could reduce the W/B ratio in the concretemixture and the W/B ratio was much lower than OPC con-crete as the increase in replacement ratios. This result wasaffected by the spherical particles of OFA. The oppositeresults were found in GPOA and GRBA concretes. The

Fig. 2. Particle size distribution of materials.

Fig. 3. Scanning electron microscopy (SEM) of materials: (a) Portland cement type I (OPC); (b) original fly ash (OFA); (c) ground palm oil fuel ash(GPOA); and (d) ground rice husk–bark ash (GRBA)

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W/B ratios of GPOA and GRBA concretes were higherthan that of the OPC concrete and tended to increase withthe higher replacement ratios. Because the particles ofGPOA and GRBA were angular and irregular with someporous particles, they needed more water to lubricate formaintaining the same workability than OPC concrete. Itwas noted that the W/B ratios of GRBA concrete were lar-ger than that of GPOA concrete.

3.3. Compressive strength

Compressive strengths and normalized strengths of con-cretes containing GPOA and GRBA are compared to OPCconcrete in Table 4. The compressive strengths at 28 and 90days of OPC concrete were 26.1 and 28.2 MPa, respec-

tively. At 28 days, the concretes containing 20% and 40%of original fly ash had the compressive strengths of 26.3and 20.9 MPa or 101% and 80% of the OPC concrete,and increased to be 28.7 and 24.4 MPa with the normalizedcompressive strength of 102% and 87% at 90 days, respec-tively. At the low replacement ratio (20%), the strength wasrelatively high owing to the reduction of the W/B ratio andthe dispersion effect as well as the pozzolanic reaction of flyash. At higher replacement ratio (40%), the strength of con-crete decreased since the amount of Portland cement wasgreatly reduced.

Compressive strengths of GPOA20, GPOA40 andGPOA55 concretes at 28-day were 23.9, 20.7 and18.1 MPa or 92%, 79% and 69% of the OPC concrete,respectively. At the later age, their strengths slightly

Table 4Compressive strength and permeability of concrete

Mixed W/B Compressive strength (MPa) –Normalized

Permeability · 10�12, k (m/s) – k/kcontrol

28 days 90 days 28 days 90 days

OPC 0.71 26.1 – 100 28.2 – 100 2.89 – 1.00 2.05 – 1.00OFA20 0.70 26.3 – 101 28.7 – 102 2.22 – 0.77 0.60 – 0.29OFA40 0.65 20.9 – 80 24.4 – 87 4.67 – 1.62 2.01 – 0.98GPOA20 0.73 23.9 – 92 29.4 – 104 0.59 – 0.20 0.25 – 0.12GPOA40 0.74 20.7 – 79 23.7 – 84 0.41 – 0.14 0.26 – 0.13GPOA55 0.75 18.1 – 69 22.3 – 79 3.30 – 1.14 2.38 – 1.16GRBA20 0.71 27.5 – 105 29.3 – 104 0.90 – 0.31 0.42 – 0.21GRBA40 0.76 22.7 – 87 25.6 – 91 1.74 – 0.60 1.33 – 0.65GRBA55 0.80 20.0 – 77 24.1 – 85 5.48 – 1.90 4.02 – 1.96

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increased, therefore, 90-day compressive strengths of theseconcretes were 29.4, 23.7 and 22.3 MPa or 104%, 84% and79% of OPC concrete, respectively. It was observed that thecompressive strength of GPOA20 concrete at 90 days wasslightly higher than that of OPC concrete, although theW/B ratio of GPOA20 concrete was higher. This is dueto the filler effects and the pozzolanic reaction of the highfineness of GPOA. Otherwise, the increase in replacementratio of GPOA to 40% and 55% decreased the strengthof concrete. However, the normalized compressive strengthof all GPOA concretes increased with the ages. This sug-gests that the contribution of compressive strength wasdue to the pozzolanic reaction of GPOA with calciumhydroxide released from hydration of cement.

For series of GBRA concretes, the 28-day compressivestrengths were 27.5, 22.7 and 20.0 MPa or had the normal-ized compressive strength of 105%, 87% and 77% forGBRA20, GBRA40 and GBRA55 concretes, respectively.Again, increasing in replacement ratio of GRBA, the com-pressive strength of concrete was reduced. At 90 days, thecompressive strength of GRBA20, GRBA40 and GRBA55concretes were 29.3, 25.6 and 24.1 MPa, respectively. Thenormalized compressive strength of GRBA20 concretewas 104%, which was slightly less than the 28-day value.However, the normalized compressive strengths ofGRBA40 and GRBA55 concretes increased and were91% and 85%, respectively.

From the results, it revealed that the incorporation of20% of these pozzolans did not adversely affect the strengthof concrete. An increase in the replacement ratios to 40%and 55% of binder, however, decreased the strength of con-crete. For the same replacement ratio, the strengths ofGPOA and GRBA concretes were slightly higher thanthose of OFA concretes, although their W/B ratios werehigher than the OFA concretes. This suggested that thestrengths of GPOA and GRBA concretes were affectedby the finer particles of GPOA and GRBA as comparedto OFA particles. Thus the faster pozzolanic reaction ofGPOA and GRBA occurred and the filler effect made theconcrete denser. In addition, the strengths of GBRA con-cretes were slightly higher than the strengths of GPOA con-cretes, although they needed more water in the concrete

mixtures. This indicated that GRBA was more reactivethan GPOA. This is due to the rice husk–bark ash containsa large amount of SiO2 (74.8%). It is known that the properburnt and ground rice husk ash (has the content of SiO2

more than 80%) develops the compressive strength of con-crete at the early age [11,12]. Although, the burning tem-perature of GRBA was quite high (800–900 �C) and somepart of the silica might become crystalline, it had beenfound that rice husk ash with this high temperature burn-ing could still be successfully used as a good supplementarycementitious material [12,13].

3.4. Water permeability of concretes

The water permeability of concrete and the ratio of per-meability are given in Table 4. The ratio of permeability isdefined as the permeability of concrete containing pozzola-nic materials divided by the permeability of OPC concreteat the same age of testing. The water permeabilities of OPCconcrete at 28 and 90 days were 2.89 · 10�12 and2.05 · 10�12 m/s, respectively and these agreed with theprevious research [14]. This study also found that the per-meabilities of all concretes reduced with the curing age. Forexample, the permeabilities of OFA20 concrete were2.22 · 10�12 and 0.60 · 10�12 m/s or had the ratio of per-meability of 0.77 and 0.29 at 28 and 90 days, respectively,these are lower than that of OPC concrete. These resultswere affected by the lower W/B ratio as well as the pozzo-lanic reaction of OFA20 concrete. The increase of OFA inconcrete resulted in a higher permeability of concrete sincethe permeability of OFA40 concrete was higher than thatof OFA20 but was lower than OPC concrete at the ageof 90 days.

The permeabilities of GPOA concretes were also lowerthan that of OPC concrete, except for GPOA55 concrete.At 28 days, the permeabilities of GPOA20, GPOA40 andGPOA55 concretes were 0.59 · 10�12, 0.41 · 10�12 and3.30 · 10�12 m/s or had the ratios of permeability of 0.20,0.14 and 1.14, respectively. At 90 days, the permeabilityof GPOA concretes decreased as compared to that of 28-day. It is interesting to note that the result showed thatGPOA20 and GPOA40 concretes gave the lower perme-

P. Chindaprasirt et al. / Construction and Building Materials 21 (2007) 1492–1499 1497

ability than the OPC concrete, even though the W/B ratiosof the two concretes were higher than the OPC concrete.The permeability of GPOA55 rapidly increased and washigher than the OPC concrete. This may result from thelow cement content and the high W/B ratio of GPOA55concrete.

The permeabilities of GRBA concretes were also lowerthan that of OPC concrete at 20% and 40% of cementreplacement and tended to be higher as the replacementratio to 55%. At 28 days, the permeabilities of GRBA20,GRBA40 and GRBA55 concretes were 0.90 · 10�12,1.74 · 10�12, and 5.48 · 10�12 m/s or had the ratios of per-meability of 0.31, 0.60 and 1.90, respectively. At 90 days,the permeability of GRBA concretes slightly reduced fromthe age of 28 days and the ratios of permeability ofGRBA20, GRBA40 and GRBA55 concretes were 0.21,0.65 and 1.96, respectively. It is noted that the ratio of per-meability of GRBA55 concrete at 90 days was slightlyhigher than the value at 28 days. This means that theimprovement of permeability of GRBA concretes areslightly less than that of OPC concretes at 40% and 55%of cement replacement. However, the use of 20% and

Fig. 4. Relationship between the permeability of concr

Fig. 5. Relationship between the permeability of concr

40% of GRBA to replace Portland cement still producesconcretes with lower permeability than the OPC one.

Figs. 4 and 5 show the relationship between the perme-ability of all concretes and the cement replacement levelsat 28 and 90 days, respectively. At 28 days, most of con-cretes had lower permeability than that of OPC concrete,except OFA40 and GRBA55 concretes and the lowestpermeability was observed in GPOA40 concrete. More-over, the permeabilities of GPOA concretes tended todecrease when the cement replacement ratio increasedup to 40%. On the contrary, the permeabilities of OFAand GRBA concretes increased as the cement replacementwas more than 20%.

At 90 days, the permeabilities of all concretes reducedand were lower than the values at 28 days. The ratios ofpermeability also had the similar result, except GRBA55concrete. This suggested that the development of perme-ation of OPC concrete was less than the other concretes.It was clear that the 20% replacement of each pozzolanicmaterial gave the most impervious concrete and the perme-ability tended to increase with the increasing of replace-ment levels.

etes and the cement replacement ratios at 28 days.

etes and the cement replacement ratios at 90 days.

Region IRegion II

Region III Region IV

OPC

1.0E-13

1.0E-12

1.0E-11

1.0E-10

15 20 25 30 35

Compressive Strength (MPa)

Perm

eabi

lity

(m/s

ec)

OPC

OFA-28

GPOA-28

GRBA-28

Fig. 6. Relationship between water permeability and compressive strength of concretes at 28 days.

Region IRegion II

Region III Region IV

OPC

1.0E-13

1.0E-12

1.0E-11

1.0E-10

15 20 25 30 35

Compressive Strength (MPa)

Perm

eabi

lity

(m/s

ec).

OPC

OFA-90

GPOA-90

GRBA-90

Fig. 7. Relationship between water permeability and compressive strength of concretes at 90 days.

1498 P. Chindaprasirt et al. / Construction and Building Materials 21 (2007) 1492–1499

3.5. Relationship between compressive strength and water

permeability of concrete

The relationships between the permeability and the com-pressive strength of concretes at 28 and 90 days are pre-sented in Figs. 6 and 7, respectively. It can be seen thatat 28 days, the relationship was more scattered than therelationship at 90 days. The permeability of concretetended to decrease with the increasing in the compressivestrength. The figures are divided into four regions in Figs.6 and 7 as passing the point of OPC concrete. Region I rep-resents concretes which have both compressive strengthand permeability higher than OPC concrete. It is foundthat there is no concrete mixture in this region at both agesof testing. Region II indicates concretes which have lowercompressive strength but higher permeability as comparedto OPC concrete. From the test results, GPOA55 andGRBA55 concretes at 90 days are observed within thiszone. The concretes contained 40% of OFA, GPOA andGRBA are located in region III, which are lower in bothof compressive strength and permeability than OPC con-crete. Concretes in region IV are the preferable concretes,which are more impervious or lower permeability and also

have higher compressive strength than OPC concrete.There exist OFA20 and GRBA20 concretes in this regionat 28 days and GPOA20 concrete at 90 days.

At 90 days, OFA20, GPOA20 and GRBA20 concreteshad the similarly strength (28.7–29.4 MPa) at the samereplacement ratio, but the values of permeability of theseconcretes were different. This suggests that the permeabilityof concrete is affected by the type of replacement materials.In summary, GPOA and GRBA are suitable as new pozzo-lanic materials to reduce the permeability of concrete.However, the ratio of cement replacement should be con-sidered for obtaining the desired compressive strengthand the permeability of concrete.

4. Conclusions

From the study of using ground palm oil fuel ash(GPOA) and ground rice husk–bark ash (GRBA) in con-crete, the following conclusions are drawn:

1. Although GPOA and GRBA increased the amount ofwater in concrete mixture, the compressive strength ofconcretes containing 20% of these materials as cement

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replacement were higher than OPC concrete. With 40%of cement replacement, the compressive strength ofGPOA and GRBA concretes were more than 84% ofOPC concrete at 90 days.

2. The optimum cement replacement by GPOA, GRBA andOFA in this experiment is 20%. The higher replacementthan this ratio results in the reduction of compressivestrength and tends to give higher permeability of concrete.

3. GRBA produces higher compressive strength thanGPOA at all cement replacement levels, although lowerof permeability of concrete was obtained with GPOA.

4. The permeability of GPOA and GRBA concretesdepends on the cement replacement ratios, and age ofconcretes. In general, the permeability of concretereduces with the increasing in the compressive strengthand age of concrete.

5. Both GPOA and GRBA are suitable as pozzolanicmaterials in concrete. This shows a good promise to uti-lize these waste materials.

Acknowledgment

The authors gratefully thank the financial supports ofthe Thailand Research Fund (TRF) under the Royal Gold-en Jubilee Ph.D. Program and TRF Advanced ResearchScholar.

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