Use of waste ash from palm oil industry in concrete

Weerachart Tangchirapat, Tirasit Saeting, Chai Jaturapitakkul *,Kraiwood Kiattikomol, Anek Siripanichgorn

Department of Civil Engineering, King Mongkut’s University of Technology Thonburi, Bangmod, Tungkru, Bangkok 10140, Thailand

Abstract

Palm oil fuel ash (POFA), a by-product from the palm oil industry, is disposed of as waste in landfills. In this study, POFA was uti-lized as a pozzolan in concrete. The original size POFA (termed OP) was ground until the median particle sizes were 15.9 lm (termedMP) and 7.4 lm (termed SP). Portland cement Type I was replaced by OP, MP, and SP of 10%, 20%, 30%, and 40% by weight of binder.The properties of concrete, such as setting time, compressive strength, and expansion due to magnesium sulfate attack were investigated.The results revealed that the use of POFA in concretes caused delay in both initial and final setting times, depending on the fineness anddegree of replacement of POFA. The compressive strength of concrete containing OP was much lower than that of Portland cement TypeI concrete. Thus, OP is not suitable to be used as a pozzolanic material in concrete. However, the replacement of Portland cement Type Iby 10% of MP and 20% of SP gave the compressive strengths of concrete at 90 days higher than that of concrete made from Portlandcement Type I. After being immersed in 5% of magnesium sulfate solution for 364 days, the concrete bar mixed with 30% of SP had thesame expansion level as that of the concrete bar made from Portland cement Type V. The above results suggest that ground POFA is anexcellent pozzolanic material and can be used as a cement replacement in concrete. It is recommended that the optimum replacementlevels of Portland cement Type I by MP and SP are 20% and 30%, respectively.� 2006 Elsevier Ltd. All rights reserved.

1. Introduction

Palm oil industry is one of the most important agroin-dustries in Thailand. Besides the production of crude palmoil, a large amount of solid waste is also an output from thepalm oil industry. Annually, more than 2 million tons ofsolid waste of palm oil residue, such as palm fiber, shells,and empty fruit bunches (as shown in Fig. 1a) are produced(Office of the Agricultural Economics, 2002). To solve theenergy problems, solid wastes from palm oil residue areused as fuel to produce steam for electricity generation.After burning, an ash by-product is produced, which isabout 5% by weight of the residue or about 0.1 million tonsper year. Utilization of palm oil fuel ash (POFA) is mini-mal and unmanageable, while its quantity increases annu-

* Corresponding author. Tel.: +66 2 470 9131/33; fax: +66 2 427 9063.E-mail address: chai.jat@kmutt.ac.th (C. Jaturapitakkul).

ally and most of the POFA is disposed of as waste inlandfills (Fig. 1b) causing environmental and otherproblems.

Many researchers have studied the use of agrowasteashes as constituents in concrete, namely rice-husk ash(Mehta, 1977), sawdust ash (Udoeyo and Dashibil, 2002)and bagasse ash (Singh et al., 2000). Their results haverevealed that these agrowaste ashes contained a highamount of silica in amorphous form and could be usedas a pozzolanic material. ASTM C 618 (2001) defines poz-zolanic material as a material that contains siliceous or sili-ceous and aluminous material by composition. In general,a pozzolanic material has little or no cementing property;however, when it has a fine particle size, in the presenceof moisture it can react with calcium hydroxide at ordinarytemperatures to provide the cementing property.

POFA is one of the agrowaste ashes whose chemicalcomposition contains a large amount of silica and thathas high potential to be used as a cement replacement

Table 1Physical properties of materials

Sample Specificgravity

Retained on 45lm sieve(No. 325) (%)

Median particlesize, d50 (lm)

Portland cement Type I 3.14 N/A 14.7Portland cement Type V 3.17 N/A 7.5

OP 1.89 94.4 183.0MP 2.36 19.5 15.9SP 2.43 1.0 7.4

Note: N/A, not applicable.

(a) Palm oil residues

(b) Palm oil fuel ash (POFA)

Fig. 1. Palm oil residues and palm oil fuel ash (POFA).

Table 2Chemical compositions of materials

Chemical composition (%) PortlandcementType I

PortlandcementType V

SP

Silicon dioxide (SiO2) 20.90 22.15 57.71Aluminium oxide (Al2O3) 4.76 3.51 4.56Iron oxide (Fe2O3) 3.41 5.57 3.30Calcium oxide (CaO) 65.41 62.43 6.55Magnesium oxide (MgO) 1.25 0.99 4.23Sodium oxide (Na2O) 0.24 0.06 0.50Potassium oxide (K2O) 0.35 0.17 8.27Sulfur trioxide (SO3) 2.71 1.07 0.25Loss on ignition (LOI) 0.99 1.69 10.52

Bogue compositions

Tricalcium silicate (C3S) 62.86 51.22 –Dicalcium silicate (C2S) 12.50 24.87 –Tricalcium aluminate (C3A) 6.84 0.00 –Tetracalcium aluminoferrite (C4AF) 10.38 16.95 –

(Tangchirapat et al., 2003). However, the use of POFA as apozzolanic material for partially replacing Portland cementis not well known and little research has been conducted.Tay (1990) used ash from palm oil waste to replace Port-land cement and showed that it had low pozzolanic prop-erties, and recommended that POFA should not be usedas a cement substitute in any quantity higher than 10%by weight of binder. The low pozzolanic property of palmoil fuel ash is due to the large particles and porous struc-ture, and thus its use results in a very low rate of pozzolanicreaction.

The aim of this research is to utilize the palm oil fuel ash(POFA) as a pozzolanic material in concrete in order toreduce the environmental problems and the landfill arearequired to dispose of POFA. If POFA, an agrowasteash from the palm oil industry, can be developed for usein concrete, it will form a new material for concrete pro-duction as well as a good way to eliminate the waste.

In this study, a grinding process is used to improve thereactivity of POFA. The effects of POFA at differentdegrees of fineness and levels of replacement of Portlandcement on the properties of fresh and hardened concretes,such as setting time, compressive strength, and expansionof concrete in sulfate solution, were investigated. The

results were compared to those of control concretes madefrom Portland cement Type I (CT1) and Type V (CT5).

2. Experimental program

2.1. Materials

2.1.1. Cement

Portland cement Type I and Type V were used in thisstudy. Their physical and chemical properties are providedin Tables 1 and 2, respectively. According to ASTM C 150(2001) for Bogue compositions, Portland cement Type Iand Type V have C3A content of 6.84% and 0%,respectively.

2.1.2. Palm oil fuel ash

Palm oil fuel ash (POFA) used in this study was col-lected from an industry located in southern Thailandwhere palm fiber, shells, and empty fruit bunches werecombusted at temperature about 700–1000 �C. The palmoil fuel ash from the industry was sieved through a sieveNo. 16 (1.18 mm opening) in order to remove foreignmaterials and uncombusted palm fiber (assigned as OP;original size POFA). The residue ash retained on a sieveNo. 16 was about 10% by weight. To improve reactivity,

OP was ground into two different levels of fineness byusing a ball mill. The abbreviations MP and SP were usedto identify the ground POFA as medium and small sizes,respectively.

The particle morphologies and the particle size distribu-tions of materials are shown in Figs. 2 and 3, respectively.It was found that OP had large particles with a median par-ticle size of 183.0 lm and most particles were rather of por-ous texture (Fig. 2a). After POFA was ground, MP and SPhad particles with irregular and crushed shapes (Fig. 2b

(a) Original size of pa

(b) Medium size of palm oil fuel ash (MP)

Fig. 2. Scanning electron micro

Fig. 3. Particle size distr

and c), and the median particle sizes were reduced to 15.9and 7.4 lm, respectively.

Fineness in term of percentage of particles retained on asieve No. 325 (45 lm opening) and specific gravity of mate-rials are shown in Table 1. It was noted that OP had largeconcentration (94.4%) of the particles retained on a sieveNo. 325, while those of MP and SP were 19.5% and1.0%, respectively. The specific gravity of OP was 1.89and increased to 2.36 and 2.43 for MP and SP, respectively.It was also noted that the grinding process increased not

lm oil fuel ash (OP)

(c) Small size of palm oil fuel ash (SP)

scopy of palm oil fuel ash.

ibution of materials.

only the fineness of POFA, but also the specific gravity.This is because the porous particles, which usually havelow specific gravity values, are crushed into smaller parti-cles with lower porosity. This result was confirmed by otherresearchers who ground fly ash or bottom ash (Cheerarotand Jaturapitakkul, 2004; Kiattikomol et al., 2001; Payaet al., 1996).

Tangchirapat et al. (2003) showed that the pozzolanicreactivity index of POFA is dependent on its fineness.The strength activity index of POFA with particles retainedon a 45 lm sieve of 41.2% is 74 and 73% at the ages of 7and 28 days, respectively. However, the strength activityindex of ground POFA (retained on 45 lm sieve of 1.5%)was 90% and 95%, respectively at the ages of 7 and 28 days.

The chemical compositions of POFA are reported inTable 2. The major chemical composition of ground POFA(SP) was 57.71% of SiO2. The total amount of SiO2, Al2O3,and Fe2O3 was 65.57%, which was lower than the mini-mum requirement (70%) specified by ASTM C 618 (2001)for pozzolanic material. The LOI, K2O, and SO3 were10.52%, 8.27%, and 0.25%, respectively. It should be notedthat the chemical composition of POFA in this study couldnot be classified as class N pozzolan as prescribed byASTM C 618 (2001). In the previous research efforts, how-ever, the chemical composition of POFA was satisfied as apozzolanic material class N (Hussin and Awal, 1996; Tay,1990).

2.1.3. Aggregate

Local river sand, having a fineness modulus of 2.68 wasused as a fine aggregate. Crushed limestone with a nominalmaximum size of 20 mm was used as a coarse aggregate.The fine and coarse aggregates had specific gravities of

Table 3Mix proportion and setting times of concretes

Mixes Mix proportion (kg/m3)

Cement POFA Sand Coarse aggregate

CT1 300 – 809 1031CT5 300 – 809 1031

OP10 270 30 803 1022OP20 240 60 796 1014OP30 210 90 789 1005OP40 180 120 783 997

MP10 270 30 804 1024MP20 240 60 799 1018MP30 210 90 794 1012MP40 180 120 789 1005

SP10 270 30 805 1026SP20 240 60 801 1021SP30 210 90 798 1016SP40 180 120 794 1011

Note: CT1 and CT5, control concretes made from Portland cement Type I anOP, MP, and SP, original, medium, and small sizes of palm oil fuel ash (POF10, 20, 30, and 40, percent replacement of POFA in Portland cement Type I b

2.60 and 2.71, and water absorptions of 0.63% and0.47%, respectively.

2.2. Mix proportions and test specimens

The mixture proportions of control concretes (CT1 andCT5) and concretes containing POFA (OP, MP, and SP)are summarized in Table 3. The compressive strength ofcontrol concrete CT1 (concrete mixed with only Portlandcement Type I) was designed at 28 days of 30 MPa withslump of fresh concrete between 50 and 100 mm. The ratioof fine to coarse aggregate was 45:55 by volume. Portlandcement Type I was partially replaced by OP, MP, and SP atthe rates of 10%, 20%, 30%, and 40% by weight of binder tocast concrete. Water to cementitious materials (cement andpalm oil fuel ash) ratio of concrete containing palm oil fuelash was adjusted to maintain the slump of fresh concrete asthat of the CT1 concrete (50–100 mm).

After mixing, the initial and final setting times of freshconcrete were determined by using Penetrometer in accord-ing to ASTM C 403 (2001). Concrete cylinders of 100 mmin diameter and 200 mm in height were used to determinecompressive strength. After casting for 24 h, all concretespecimens were removed from the molds and cured inwater at room temperature. They were tested for compres-sive strengths at the ages of 3, 7, 14, 28, 60, and 90 days.

For the determination of sulfate resistance, the expan-sions of concretes containing POFA were measured byusing specimens having a cross-section of 75 · 75 mm anda length of 285 mm. The concrete bars were immediatelyimmersed in 5% of magnesium sulfate solution after beingremoved from the molds (24 h after casting). The expan-sions of concrete bars containing POFA were measured

w/cm Slump (mm) Setting times(h:min)

Water Initial Final

210 0.70 65 4:10 6:30210 0.70 65 6:00 8:45

216 0.72 65 4:40 7:30231 0.77 60 5:00 8:30261 0.87 80 5:50 10:30285 0.95 80 6:50 12:20

216 0.72 80 4:35 6:40219 0.73 75 4:40 7:05219 0.73 70 4:55 7:25222 0.74 70 5:10 7:45

204 0.68 55 4:25 6:35210 0.70 60 4:35 7:00213 0.71 60 4:50 7:25216 0.72 60 5:10 7:40

d Type V, respectively.A).y weight of binder.

Fig. 4. Relationship between compressive strength and age of concretes.

every 14 days up to 364 days, and the results were com-pared to those of the control concrete bars (CT1 and CT5).

3. Results and discussion

3.1. Setting times

Table 3 presents the setting times of control concretesand concretes containing POFA. The results showed thatthe CT1 concrete had the initial setting time of 4 h10 min and the final setting time of 6 h 30 min, while theCT5 concrete had longer initial and final setting times thanthose of the CT1 concrete, which were 6 h and 8 h 45 min,respectively.

For concrete containing POFA, it was found that theinitial and final setting times increased with the increaseof POFA replacement. The highest retardation of the set-ting times occurred at 40% of OP replacement, whichresulted in 6 h 50 min for the initial setting time and 12 h20 min for the final setting time. This is due to a highreplacement of cement by OP. In addition, large particleswith high porosity of OP will increase the water-to-binderratio of concrete, thus resulting in increasing setting timesof concrete.

After grinding OP to increase the fineness as MP andSP, the setting times of concretes were reduced in compar-ison to the OP concretes. However, the setting times of MPand SP concretes increased when the replacement of MPand SP increased and the results were similar to OP con-cretes. The higher replacement of POFA results in thereduction of C3S and an increase in the loss on ignition(LOI) in concrete (POFA has a high LOI of 10.52%), thusincreasing the setting times of concrete. It is noted that thesetting times of concretes mixed with 10% of MP and SPare close to those of the CT1 concrete. They are 4 h35 min and 4 h 25 min for the initial, and 6 h 40 min and6 h 35 min for the final setting times, respectively. In addi-tion, the setting times of MP40 and SP40 concretes arelonger than those of the CT1 concrete, but less than thoseof the CT5 concrete.

The results of setting times of POFA concretes suggestthat the use of POFA to replace Portland cement Type Iin the mixture of concrete causes delay in both initial andfinal setting times, depending on the fineness and levelreplacement of POFA. The long setting times of POFAconcretes are due to the pozzolanic reaction between poz-zolan and calcium hydroxide (Ca(OH)2), which is usuallyslower than the hydration of cement. This behavior con-forms to the results of setting times obtained from usingother pozzolans, namely fly ash (Bouzoubaa et al., 2004)and sawdust ash (Udoeyo and Dashibil, 2002).

3.2. Compressive strength

Fig. 4 shows the relationship between compressivestrength and age of OP, MP and SP concretes. It was foundthat at 28 days, the OP10, OP20, OP30 and OP40 concretes

had the compressive strengths of 24.5, 21.2, 15.0 and9.9 MPa, respectively, while those of the CT1 and CT5concretes were 31.9 and 31.6 MPa, respectively. The resultsindicated that the higher the replacement of OP, the lowerthe compressive strength of concrete. The results alsorevealed that the compressive strengths of concretes con-taining OP were much lower than that of the CT1 concrete,especially when the replacement of OP was more than 20%.With 20–40% replacement of OP, the compressive strengthsof concretes at 28 days were between 31% and 66% of theCT1 concrete. This can be attributed to the fact that OPhas large particles with high porosity which causes anincrease in the water-to-binder ratio of concrete, resultingin a decrease in the compressive strength. Thus, the original

Fig. 5. Expansion of concretes bars in 5% of magnesium sulfate solution.

size of POFA (OP) is not suitable to be used as a substitutefor cement in concrete.

In the case of concretes containing MP (Fig. 4b), theycould produce a higher compressive strength than thoseof OP concretes. It is observed that at the ages of 28 and90 days the compressive strengths of MP10 concrete were30.1 and 37.6 MPa or about 94% and 101% of the CT1concrete, respectively. This indicates that MP contributedcompressive strength by pozzolanic reaction. In addition,the concrete mixed with 20% of MP had a compressivestrength of 26.9 MPa or 84% of the CT1 concrete at 28days, and increased to 33.4 MPa or 90% of the CT1 con-crete at 90 days.

For concretes containing SP (Fig. 4c), which was thehighest fineness of POFA used in this study, it was foundthat at 10% and 20% of cement replacement compressivestrengths were as high as that of the CT1 concrete at 28days. The compressive strengths of SP10 and SP20 con-cretes at 28 and 90 days were 31.9, 31.6 and 39.0,38.6 MPa or about 100%, 99% and 105%, 104% of theCT1 concrete, respectively. In addition, the compressivestrengths of SP30 concrete at 90 days was 36.8 MPa orabout 99% of the CT1 concrete. These results suggest thatthe higher fineness of POFA (SP) had greater pozzolanicreaction and the small particles could also fill in the voidsof concrete mixture, thus increasing the compressivestrength of concrete (Isaia et al., 2003).

The results of compressive strength of concrete suggestthat POFA has high potential for using as a pozzolanicmaterial in concrete when the material is ground to a fineparticle size. In addition, the optimum replacement ofMP and SP are 20% and 30% by weight of binder, respec-tively, for which the compressive strength of concretes con-taining MP and SP are not less than 90% of the CT1concrete at 90 days.

3.3. Expansion

Fig. 5 shows the expansion of concrete bars in 5% ofmagnesium sulfate solution. It was found that the CT1concrete bar had an expansion of 0.047% at 364 days, whilethat of the CT5 concrete bar was 0.038%. This suggestedthat the use of Portland cement Type V can reduce theexpansion of concrete due to sulfate attack. However, itwas observed that the expansion values of the CT5 con-crete bar were slightly lower than the CT1 concrete bar(�0.01%), although the CT5 concrete bar used Portlandcement Type V (C3A � 0%). These results indicate thatC3A was not the sole parameter that caused expansiondue to sulfate attack. Gonzalez and Irassar (1997) investi-gated the sulfate attack mechanism on four cements withlow C3A content (0–1%) and a C3S content that variedfrom 40% to 74%. Their results showed that the higherthe C3S content, the greater the expansion.

The expansion of OP concrete bars compared to thoseof CT1 and CT5 concrete bars is shown in Fig. 5a. Theuse of OP at all replacement levels had expansion values

higher than that of the CT5 concrete bar. At 364 days, con-crete bars mixed with 10% and 20% of OP had expansionvalues higher than that of the CT1 concrete bar. At areplacement rate of 30%, the OP30 concrete bar had thelowest expansion values (0.046%) and was close tothe expansion of the CT1 concrete bar (0.047%). Whenthe replacement of OP was 40%, the highest expansion ofconcrete bar occurred, which was 0.065%. This wasbecause the higher replacement of OP caused a higherwater-to-binder ratio, and resulted in a decrease in sulfateresistance of blended cement (Chindaprasirt et al., 2004).Although the expansion of concrete bar was reduced byusing OP to replace Portland cement Type I at 30% byweight of binder, the compressive strength of OP30concrete was too low compared to the CT1 concrete.

Therefore, OP is not suitable to be used as a pozzolanicmaterial in concrete.

Fig. 5b shows the expansion of concrete bars using MPto replace Portland cement Type I. The expansion values ofMP concrete bars were lower than those of the OP concretebars. At 364 days of immersing in magnesium sulfate solu-tion, the MP10, MP20, MP30, and MP40 concrete barshad expansion values of 0.053%, 0.049%, 0.045%, and0.043%, respectively. It was noted that the expansion val-ues decreased with the increase of MP replacement. Theconcrete bars mixed with MP of 10% and 20% had expan-sion values slightly higher than that of the CT1 concretebar. At the level of replacement up to 30–40%, the expan-sion values were less than that of the CT1 concrete bar.However, the MP30 and MP40 concrete bars had compres-sive strengths lower than that of the CT1 concrete (71%and 75% of CT1 at 28 days, respectively). Thus, it is notrecommended to replace Portland cement Type I by MPat rates higher than 20%.

Fig. 5c shows the expansion of concrete bars using SP toreplace Portland cement Type I. At 364 days, the concretebars containing SP had expansion values less than those ofMP concrete bars (0.046%, 0.042%, 0.040%, and 0.036%for the SP10, SP20, SP30, and SP40 concrete bars, respec-tively). It should be noted that the expansion at 364 days ofthe SP40 concrete bar was less than that of the CT5 con-crete bar (0.038%). Considering the expansion and com-pressive strength of SP concretes, it is recommended thatthe optimum replacement of SP is 30% which has theexpansion of concrete due to sulfate attack close to theCT5 concrete bar and produces the compressive strengthas high as the CT1 concrete at 90 days.

Based on the results of this study, ground POFA (MP orSP) is an excellent pozzolanic material and can be used as acement replacement in concrete to increase the ultimatestrength, as well as to improve the magnesium sulfate resis-tance of concrete. However, the high fineness of POFA isvery important and has to be considered before using thematerial as a substitute for cement.

4. Conclusions

From the results of these experiments, the followingconclusions can be drawn:

1. The use of POFA in replacing Portland cement Type Iresulted in a higher water-to-binder ratio of concreteand caused delay in both the initial and final settingtimes of concrete.

2. The compressive strength of concrete containing OP wasmuch lower than that of the CT1 concrete when thereplacement was more than 20%. Although the expan-sion of concrete bars was reduced by using OP to replacePortland cement Type I at 30% by weight of binder, thecompressive strengths of OP concretes were too low.Therefore, OP is not suitable to be used as a pozzolanicmaterial in concrete.

3. The concretes containing a medium size of POFA (MP-retained on a sieve No. 325 of 19.5%) at the replacementrate of 20% had the compressive strength of 90% of thecontrol concrete at 90 days. The expansion of concretebar mixed with 20% MP was slightly higher than thatof the concrete bar made from Portland cement TypeV and close to the concrete bar made from Portlandcement Type I.

4. The small size of POFA (SP-retained on a sieve No. 325of 1.0%) can be used to replace Portland cement Type I,at rates up to 30%. The 20% SP has sulfate resistance asgood as that of Portland cement Type V and also pro-duces the compressive strength of concrete at 90 daysas high as the control concrete made from Portlandcement Type I.

5. The results encourage the use of POFA, an agrowasteash from the palm oil industry, as a new pozzolan forcement replacement in concrete, which will reduce thecost of concrete, environmental problems, and the land-fill area required for the disposed of POFA.

Acknowledgments

The authors gratefully acknowledge the financial sup-port from the Thailand Research Fund (TRF) under theTRF Advanced Research Scholar and Royal Golden Jubi-lee Ph.D. Program.

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