esnttyheesceisnthe

Effect of Corncob, Wheat Straw, and Plane Leaf Ashesas Mineral Admixtures on Concrete Durability

Hanifi Binici1; Faruk Yucegok2; Orhan Aksogan3; and Hasan Kaplan4

Abstract: In this study, the effects of the use of corncob, wheat straw, and plane leaf ashes �CA, WSA, and PLA� as mineral admixturon concrete durability were investigated. Ten concrete mixtures were produced in three series with control mixes having 400 kg cemecontent. The control mixes were modified with 2, 4, and 6% of CA, WSA, and PLA in place of fine aggregate. To establish the durabiliof concrete, the compressive strengths were measured after 7, 28, 90, 180 days, and 18 months under sodium sulfate solution. In tmeantime, abrasion resistance and water penetration were investigated. Test results indicate that CA, WSA, and PLA addition providgood workability and abrasion resistance compared to conventional concrete. Test results also showed that minimum abrasion resistanis obtained from the control specimen, while maximum abrasion resistance is obtained from CA3 �6%� specimens. Abrasion resistanceincreased as the rate of fine CA, WSA, and PLA is increased. The results indicate that the increase in ash content caused a significaincrease in the sodium sulfate resistance of the concretes. Hence, concrete with CA, WSA, and PLA addition can be recommended for tproduction of durable concrete.

DOI: 10.1061/�ASCE�0899-1561�2008�20:7�478�

CE Database subject headings: Admixtures; Concrete durability; Construction materials; Chemicals.

Introduction

ila

o-datasbeasna

aneresthtss-ty3;

Kajorncheappunngam and Stewart 1992�. Reactive rice husk asho-�.ati-

edstafson-ofin

i-rete

nd�.attyndheic

ase-rsti-

nd1

as

cu

a,

li,

tilalster6;ofE,

Use of pozzolans such as fly ash, calcined kaolin, and palm ofuel ash as partial replacements for cement have been made asresponse to environmental concerns about greenhouse gas prduction �Malhotra 1987; Stroeven and Sabuni 1999; Shi anStegemann 2000; Tay 1990�. One researcher has reported thproperly burnt and ground rice husk ash is also suitable for usea pozzolan �Metha 1979�. New pozzolanic cement material canan interesting area of study. Wheat straw ash has been usedpozzolanic material when there has been excess wheat productio�Biricik et al. 1999�. In Turkey, as in many parts of the world,large amount of corncob and wheat straw could be obtained asagricultural by-product. Wheat straw ashes, and indeed othashes, have high residual silica content. Examples of other ashinclude calcined sunflower ash and calcined tobacco ash, boof which may be useful as pozzolans in extended cemen�Bensted and Munn 2000�. Rice husk ash has been used succesfully in such applications as concrete with controlled permeabiliformwork and roller compacted concrete �Coutinho 200

1Assistant Professor, Dept. of Civil Engineering, KahramanmarSutcu Imam Univ. �K.S.U.�, Kahramanmaras, Turkey.

2MS Student, Dept. of Civil Engineering, Kahramanmaras SutImam Univ. �K.S.U.�, Kahramanmaras, Turkey.

3Professor, Dept. of Civil Engineering, Cukurova Univ., AdanTurkey.

4Professor, Dept. of Civil Engineering, Pamukkale Univ., DenizTurkey.

Note. Associate Editor: Byung Hwan Oh. Discussion open unDecember 1, 2008. Separate discussions must be submitted for individupapers. To extend the closing date by one month, a written request mube filed with the ASCE Managing Editor. The manuscript for this papwas submitted for review and possible publication on October 27, 200approved on December 10, 2007. This paper is part of the JournalMaterials in Civil Engineering, Vol. 20, No. 7, July 1, 2008. ©ASCISSN 0899-1561/2008/7-478–483/$25.00.

478 / JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / JULY

can be used to produce good quality concrete with reduced prosity and reduced Ca�OH�2 content �Zhang and Malhotra 1996

In the Cukurova region of Turkey, a huge quantity of whestraw is produced every summer. Farmers burn it, causing envronmental harm. Instead of being burnt, wheat straw can be usin mud brick production �Binici et al. 2005�. Similarly, vaamounts of waste organic materials from corncob and plane lecan harm the environment. These materials, if burned, could alserve as pozzolanic materials in the production of durable cocretes. Corncob is known to contain a considerable amountsilicium dioxide �SiO2�. Once burned, it leaves an ash very richSiO2 that is pozzolanic in character �Binici et al. 2007�.

Durability of concrete structures exposed to aggressive envronments is a major concern. Many environmental phenomena aknown to significantly affect the durability of reinforced concrestructures �Ihekwaba et al. 1996; Castro et al. 2000; Roper aBaweja 1991; Haque and Kawamura 1992; Tahir and Salih 2007In this study, materials of organic origin, corncob ash, whestraw ash, and plane leaf ash were added. The concrete durabili�subjected to 5% sodium sulfate solution, abrasion resistance awater penetration�, was then tested. According to the results of texperiments, the reliability of the additive materials of organorigination was evaluated.

Materials Used

Aggregate and Cement

An ordinary portland cement �OPC� with 300 Blaine fineness wused for all concrete mixtures. Local Aksu River natural aggrgate was used to make the concretes. The materials were fitaken to the Kahramanmaras Sutcu Imam University, Civil Engneering Department, materials laboratory. The chemical aphysical characteristics of the materials used are given in Tables

2008

Ay-or

dx-g

thte.ofmIners,reg

ntesheof

erorgis.

asas-2toS

he

pashengre4,to

s-o-m

Noftea

ededofhed-I0.htreh.e,

c-edreheh

re

ay

6

Table 3. Terminology for All Specimens

tes

tes

tes

s

s

s

S

Table 1. Chemical Contents of Materials Used, Oxides �%�

I

50

97

97

and 2 and the terminology for all specimens is given in Table 3.maximum aggregate size of 16 mm was used and grading analses were performed according to EN TS 706. The grading data fthe aggregates are given in Table 4.

Ashes

In this study, corncob ash �CA�, wheat straw ash �WSA�, anplane leaf ash �PLA� were used as admixtures. Ten concrete mitures were produced in four series with control mixes havin400 kg cement content. These control mixes were modified wi2, 4, and 6% of CA, WSA, and PLA in place of fine aggregaAll ashes were obtained from open burning of a 23 kg heapeach of corncob, wheat straw, and plane leaf with a maximuburning temperature of 600°C �Chindaprasirt et al. 2007�.burning the organic materials, the temperature needs to be lowthan 700°C in order to obtain reactive amorphous silica. Thuthese materials can be burnt with an incinerator or furnace. Theare quite a lot of burning methods. However, simple open burninis satisfactory where the temperature is controlled by the amouof material in the heap. Burning of wheat straw and plane leavwas initiated by providing the burning source at the bottom of tincinerator for 3 h and was left for 3 days prior to collectionburnt ashes.

The burnt ashes were different in color �see Fig. 1�. Aftcooling, the ashes were ground in a laboratory ball mill f60 min to obtain material under 1 mm particle size before usinas mineral admixture. A grading curve from particle size analysof Aksu river fine sand, CA, WSA, and PLA is given in Fig. 2

Experimental Details

The water used in the production of the concrete specimens wtap water and the cement used to complete the experiments wOPC, produced by Adana Cement Factory. TS 3068 ISO 2736was used for sampling. The mixture was designed accordingthe absolute volume method given by Turkish Standard EN T802. Approximate concrete composition is given in Table 5. T

Table 2. Physical Characteristics of Materials Used

Materials

Specificgravity

�kg /m3�

Vicat timeof setting

�min�Compressive strength

�MPa�

Ordinaryportlandcement

3,150 Initial Final 3 day 7 day 28 d

CA 2,970 115 200 24.2 37.3 48.

WSA 2,890

PLA 2,910

Materials SiO2 Al2O3 Fe2O3 CaO MgO SO3 Na2O K2O L

Ordinaryportlandcement

20.1 5.6 3.8 64.3 1.8 0.8 0.11 0.25 —

CA 37 2.37 1.19 13 7.35 1.32 0.25 15 22.

WSA 4.9 1.15 0.95 24.44 4.63 6.98 1.28 24.72 28.

PLA 9.9 1.11 0.71 21.11 3.19 3.59 0.53 7.7 51.

Note: LI�loss on ignition.

JOURNA

concrete specimens were prepared with the same average slumof 8.5–12 cm and a dosage of 400 kg /m3. The mixing water wkept at a constant temperature of 17°C before mixing and ttemperature of the mixing room was maintained at 20°C durithe mixing process. All ashes used as additives in this study weadded into the concrete mixtures in separate ratios, namely 2,and 6%. The water penetration test was performed accordingEN TS 10967.

Standard specimens of 150 mm3 were cast and the compresive strength of each was measured after immersing in 5% sdium sulfate solution for 18 months. The behavior in sodiusulfate solution was determined according to ASTM 1012.

An abrasion test was performed in accordance with DI52108. In this standard, an abrasion test is applied to specimenssize 75�75�55 mm at 28, 90, and 365 days. First, the concrespecimens were cleaned using a wire brush and kept 24 h inwater tank at 20°C, after which they were taken out and wipwith a wet cloth. The specimens were surface dry saturat�SDS�. Sand blasting pressure was 40 N /mm2. The rate of flowabrasive sand was 500 grams per min. In the present study, ttest was carried out at 20°C temperature and 60% relative humiity. SDS specimens were measured and the length denoted asSand blasting was performed for 60 sec, applied to at least eigdifferent points. At the end of this process, the specimens wekept in 20°C water for 2 h, and then wiped with a wet clotFinally, the specimens were weighted and denoted as I. HencI= I1− I0 was found as the loss of mass.

A water penetration test was performed after 6 months in acordance with EN TS 3455. Concrete cylinders were demoldafter a day and cured in water for 26 days. After that they wesliced at 50 mm thickness and the 50 mm ends discarded. Tsliced cylinders were left to dry in laboratory conditions for 24before the application of epoxy coatings. All specimens we

Specimens System of replacements

C �Control mixture� Aksu River natural aggregates

CA1 2% corncob ash by mass of fine aggregates

CA2 4% corncob ash by mass of fine aggregates

CA3 6% corncob ash by mass of fine aggregates

WSA1 2% wheat straw ash by mass of fine aggrega

WSA2 4% wheat straw ash by mass of fine aggrega

WSA3 6% wheat straw ash by mass of fine aggrega

PLA1 2% plane leaf ash by mass of fine aggregate

PLA2 4% plane leaf ash by mass of fine aggregate

PLA3 6% plane leaf ash by mass of fine aggregate

Table 4. Cumulative Passing for the Aggregate Grades for EN T706�%�

Sieve size�mm� A16

Aksu Riveraggregate C16

16 100 100 100

8 60 70 88

4 36 43 74

2 21 27 62

1 12 18 49

0.5 8 11 33

0.25 3 8 18

L OF MATERIALS IN CIVIL ENGINEERING © ASCE / JULY 2008 / 479

o-

st.le.atvethc-n-of

oflys-ari--

anst

sh7

ysupupn-veanup

ots.s.It

allhere

6.of

3

47

7

2

af

epoxy coated around the cylindrical surface and left in the labratory for testing.

Results and Discussion

Compressive Strengths

Over 300 standard cubic specimens of 150 mm size were caBased on ASTM and TS standards, all results were acceptabMechanical strengths upon compression are the main features thallow assessments of concrete durability. The compressistrength of concrete mixtures versus age and the relative strengof tested concrete specimens are given in Figs. 3 and 4, respetively. It can be seen from these figures that there are clear icreases of compressive strength with increasing percentagesash additions.

From Fig. 3, it can be seen that the compressive strengthsconcrete specimens cured in water for 7 days were approximateequal to those of the control specimens. However, the compresive strength of the CA, WSA, and PLA concretes, in particulthose treated for 365 days, was higher than that the control specmen. The difference was approximately 40%. In general, the compressive strengths of the specimens increased slightly withincrease of the addition of CA, WSA, and PLA. The highe

Table 5. Concrete Mixture Proportions

Properties C CA1 CA2

Cement OPC �kg /m3� 400 400 400

CA �%� 0 2 4

CA �kg /m3� 0 12 24

WSA �%� 0 0 0

WSA �kg /m3� 0 0 0

PLA �%� 0 0 0

PLA �kg /m3� 0 0 0

Water �kg /m3� 200 198 195

W/C 0.50 0.49 0.48

Sand SSD �kg /m3� 600 588 576

Coarse aggregate �kg /m3� 1,200 1,200 1,200 1,

Superplasticizer �l /m3� 3 3.5 3.6

Slump �mm� 120 95 90

Air content �%� 2.4 2.2 2.1

Air temperature �°C� 27 26 26

Concrete temperature �°C� 29 28 29

Unit mass �kg /m3� 2,340 2,329 2,320 2,

Fig. 1. Image of burned corncob ash, wheat straw ash, and plane leash

480 / JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / JULY

compressive strength at all time periods was found in corncob aspecimens after 28 days. However, compressive strength afterdays was almost the same for all specimens. Considering 28 daaverage compressive strength, the compressive strength of groCA3 specimens was found to be 16% higher than that of groWSA specimens and 17% higher than that of group PLA. Cosidering 365 days average compressive strength, the compressistrength of group CA specimens was found to be 23% higher ththat of group WSA specimens and 32% higher than that of groPLA.

The development of strength in the concretes was affected nonly by the ash type, but also in some cases by ash percentageSpecimen CA3 had the highest compressive strength at 365 dayFurthermore, this value was 8% higher for the CA1 specimens.can be observed from Fig. 4 that relative strength values forspecimens were almost equal after 7 days. On the other hand, trelative strengths of all the specimens in the CA group wehigher after 28 days.

Sulfate Resistance of Concretes

The results of the sulfate resistance test are shown in TableThese results show an obvious increase in the sulfate resistance

WSA1 WSA2 WSA2 PLA1 PLA2 PLA

400 400 400 400 400 400

0 0 0 0 0 0

0 0 0 0 0 0

2 4 6 0 0 0

12 24 36 0 0 0

0 0 0 2 4 6

0 0 0 12 24 36

198 196 195 198 196 195

0.49 0.48 0.47 0.49 0.48 0.

588 576 564 588 576 564

1,200 1,200 1,200 1,200 1,200 1,200

3.5 3.6 3.7 3.5 3.6 3.

100 90 85 105 100 90

2.3 2.2 2.1 2.3 2.2 2.

27 27 27 26 27 27

27 28 28 28 27 28

2,322 2,311 2,311 2,324 2,317 2,312

Fig. 2. Grading curve of Aksu river sand, CA, WSA, and PLA

CA3

400

6

36

0

0

0

0

190

0.47

564

200

3.7

85

2

26

28

318

2008

s.edg

thlyatn-adi-

fi-p

ad

ofc-s,s.nto

e-th

cee-is-

thveallo-heof�.d.s-

ndreh.

in

ter

of Co

ve

the concrete with an increase in the percentage of fine aggregateOther researchers have also supported these results. They reportthat both natural and artificial pozzolans contribute to increasinchemical resistance of concrete �Erdogan and Dogulu 1997�.

The positive effects on concretes increased progressively wiincreasing CA, WSA, and PLA contents and were particularevident in the specimens with 6% CA additives. This shows thcompressive strengths under sulfate exposure increase with icreasing ash content. Thus, CA, WSA, and PLA concretes hhigher potential sulfate resistance compared to the control specmens �Table 6�. Increases in the additive content caused signicant increases in sulfate resistance of concrete over a period of uto 18 months of exposure. The CA3 specimen, in particular, hthe highest sulfate resistance among all the specimens.

Compressive strength tests could not be applied to a numberspecimens after the 18-month period due to their unstable strutures. The control concrete specimen showed large expansioncracking, internal fractures, and fractures on whole surfaceHowever, CA, WSA, and PLA concretes showed no significasigns of deterioration. This result is supported by authors whhave reported that up to 40% of portland cement could be rplaced with rice husk ash to make blended cement mortar wi

Fig. 3. Compressive strength of specimens versus time of curingwater

Table 6. Compressive Strengths and Compressive Strength Reduction

Specimens

Compressivestrengths

after 28 days�MPa�

�cured in tap water�

a

�cu

C 26

CA1 29

CA2 32.2

CA3 36.3

WSA1 25.3

WSA2 27.6

WSA3 29.1

PLA1 26.3

PLA2 26.8

PLA3 28.1

JOURNA

reasonable strength development and good sulfate resistan�Chindaprasirt et al. 2007�. It was also mentioned that the servicable life of the mortar had increased by its higher sulfate restance.

Table 6 shows the reduction in relative compressive streng�the ratio of compressive strength in sulfate to compressistrength in tap water�. The relative compressive strengths ofmortars decrease with increasing exposure to sodium sulfate slutions. However, they decrease at different speeds. For C, trelative compressive strength decreases rapidly, whereas thatCA, WSA, and PLA concretes decrease slowly �see Table 6With the additives, the water / �cement+ash� ratio was reduceThat may be the reason for the observed increase in the compresive strength and the sulfate resistance.

Abrasion Resistance

Mass loss at 60 min of abrasion in concretes with CA, WSA, aPLA replacement is given in Fig. 5. This figure shows that thewas little abrasion resistance in C specimens, those without as

Fig. 4. Relative strength of specimens versus time of curing in wa

ncretes

ressivegthsmonths

Pa�tap water�

Compressivestrengths

after 18 months�MPa�

�immersed in5% Na2SO4�

Compressistrength

reduction�%�

.2 18.1 49

.3 40.4 29

.6 45.7 23

.7 51.9 15

.0 32.7 28

.1 37.1 23

.4 42.3 18

.4 26.2 32

.2 27.9 31

.3 32.8 25

Compstren

fter 18�M

red in

35

56

58

60

45

48

51

38

40

43

L OF MATERIALS IN CIVIL ENGINEERING © ASCE / JULY 2008 / 481

ni-esn

e-d

erbea

belen2

threk-

mthed

7.oni-%w

ont-

ve

hed,ont-

r-mhes.p-in.

ng

e-edofA

nt

Specimens with CA as fine aggregate showed greater abrasioresistance than the C, WSA, or PLA specimens. However, specmen PLA3 showed a higher abrasion ratio at 365 days. Concretwhere CA was used as a fine aggregate had the highest abrasioresistance compared to other specimens. The greater abrasion rsistance of the concretes to added fine corncob, wheat straw, anplane leaf ashes were added, is believed to result from a denspore structure of the mortar binder. Furthermore, this mightexplained by the fact that ash allows a good interface withcondensed matrix.

The abrasion ratio of the specimens is given in Fig. 6. It canseen that the control specimens were abraded most quickly, whithe CA3 specimens showed the minimum abrasion rate. Abrasioresistance increases with the amount of ash. However, for theand 4% PLA replacement levels, abrasion ratio and strenglosses were higher than for the 6% PLA specimen. Although thewas no limitation concerning concrete abrasion ratios in the Tur

Fig. 5. Mass loss at 60 min of abrasion versus fine sand replacemewith CA, WSA, and PLA

Fig. 6. Abrasion ratio of specimens versus age

482 / JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / JULY

ish Standard, concretes with abrasion levels lower than 1.2 mwere denoted “highly abrasion resistant concrete” and those wiconcrete abrasion levels higher than 3 mm were consider“poorly abrasion resistant concrete” �Postacıoglu 1987�.

Water Penetration

Depths of water penetration into the mixtures are given in Fig.It can be seen from the figure that the depth of water penetratiinto the CA3 specimen was considerably less than for other specmens. An increase in the percentage of ash additives from 2 to 6reduced water penetration significantly. Control specimens shoconsiderably greater depth of water penetration. Water penetratiwas reduced with an increase in the CA, WSA, and PLA percenage. This can be an explanation of the increase in the compressistrength of the specimens.

In general, all ashes had a profound effect on the depth of twater penetration. As the percentage of corncob ash decreasewater penetration depth increased �see Fig. 7�. Water penetratidepths correlated well with the ash type and replacement percenage of the mixtures.

These additives and by-products may serve as sticky or adheent chemical reagents that combine with other elements to fordenser and homogeneous forms of concretes. The additives fill tgaps within the concrete products, forming less porous structureAll these elements may contribute to enhanced mechanical proerties of concrete. Furthermore, the use of the additives resultexcellent durability, with positive effects on concrete formation

Conclusions

Based on the investigation reported in this paper, the followiconclusions can be drawn:1. Concrete containing CA, WSA, and PLA showed greater r

sistance to sulfate exposure. More resistance was achievwith higher ash additive ratios. Sodium sulfate resistanceCA concrete was greater than that of the WSA, and PL

Fig. 7. Water penetration depth of specimens

2008

specimens. Sulfate resistance of the control cement was poor,ofn

vevey

ery

3e-Ad

c-

r-s.err-hs

w,in

en

ofz,

rer.,

ceng

of

pozzolanic properties of wheat straw ash.” Cem. Concr. Res., 29,

nes.”

T.nd

inm-

ndndnt,

e-er.

oncr.

in

te,

dent,

n-

ndnt.

if-

sted-

on5�,

l.”

tel.”

compared to the CA, WSA, and PLA concretes. At the endan 18-month period, negative effects of sulfate exposure oconcrete specimens increased, which decreased compressistrengths for control specimens by 49%. The compressistrengths of the CA, WSA, and PLA concrete decreases b22, 23, and 29%, respectively.

2. In the CA concrete group, the CA3 specimens had highcompressive strength and greater sulfate resistance than anof the other specimens.

3. Control specimens were abraded most quickly while CAspecimens were abraded most slowly. Generally, abrasion rsistance increased as the amount of fine CA, WSA, and PLwas increased. The CA concrete had an average 71, 38, an31% lower rate of abrasion than C, WSA, and PLA, respetively.

4. Depth of water penetration correlated well with the diffeences between additive type and percentage in the mixtureCA3 specimens were considerably more resistant to watpenetration than the other specimens. An increase in the pecentage of ash affected the water penetration deptmarkedly.

Results of this investigation show that corncob, wheat straand plane leaf ashes could be very conveniently used to obtadurable concrete.

Acknowledgments

The writers wish to acknowledge the invaluable assistance givby Adana Cement Manufacturers Association.

References

Bensted, J., and Munn, J. �2000�. “A discussion of the paper ‘Studypozzolanic properties of wheat straw ash’ by H. Biricik, F. AkoI. Berktay, and A. N. Tulgar.” Cem. Concr. Res., 30, 1507–1508.

Binici, H., Aksogan, O., and Shah, T. �2005�. “Investigation of fibreinforced mud brick as a building material.” Constr. Build. Mate19, 313–318.

Binici, H., Zengin, H., Zengin, G., and Yucegok, Y. �2007�. “Resistanto sodium sulphate attack of plain and blended cement containicorncob ash and ground blast furnace slag.” Mater. Struct.

Biricik, H., Akoz, F., Berktay, I., and Tulgar, A. N. �1999�. “A Study

JOURNA

637–643.Castro, P., Moreno, E. I., and Genesca, J. �2000�. “Influence of mari

micro-climates on carbonation of reinforced concrete buildingCem. Concr. Res., 30, 1565–1571.

Chindaprasirt, P., Kanchanda, P., Sathonsaowaphak, A., and Cao, H.�2007�. “Sulfate resistance of blended cements containing fly ash arice husk ash.” Constr. Build. Mater., 21�6�, 1356–1361.

Coutinho, J. S. �2003�. “The combined benefits of CPF and RHAimproving the durability of concrete structures.” Cem. Concr. Copos., 25, 51–59.

Erdogan, T. Y., and Dogulu, S. �1997�. “Effect of finesses of grougranulated blast furnace slags on their cementitious properties auses.” Proc., First Int. Symp. on Mineral Admixtures in Ceme

1945–1952.Haque, M. N., and Kawamura, M. �1992�. “Carbonation and chlorid

induced corrosion of reinforcement in fly ash concretes.” ACI MatJ., 89, 1112–1121.

Ihekwaba, N. M., Hope, B. B., and Hansson, C. M. �1996�. “Carbonatiand electrochemical chloride extraction from concrete.” Cem. ConRes., 26�7�, 1095–1107.

Kajorncheappunngam, S., and Stewart, D. F. �1992�. “Rice husk ashroller concrete.” Concr. Int., 14, 38–44.

Malhotra, V. M. �1987�. Supplementary cementing materials for concreCANMET, Canadian Government Publishing Centre, 245–253.

Metha, P. K. �1979�. “The chemistry and technology of cement mafrom rice husk ash.” Proc., Workshop on Rice Husk Ash Ceme113–122.

Postacıoglu, B. �1987�. Concrete, Matbaa Teknisyenleri Basímevi, Istabul, Turkey �in Turkish�.

Roper, H., and Baweja, D. �1991�. “Carbonation-chloride interactions atheir influence on corrosion rates of steel in concrete.” Proc., 2nd IConf. on the Durability of Concrete, 236–245.

Shi, C., and Stegemann, J. A. �2000�. “Acid corrosion resistance of dferent cementing materials.” Cem. Concr. Res., 30, 803–808.

Stroeven, P., Bui, D. D., and Sabuni, E. �1999�. “Ash of vegetable waused for economic production of low to high strength hydraulic biners.” Fuel, 78, 153–159.

Tahir, G., and Salih, Y. �2007�. “The influence of compaction poressorptivity and carbonation of concrete.” Constr. Build. Mater., 21�1040–1045.

Tay, J. H. �1990�. “Ash from oil-palm waste as concrete materiaJ. Mater. Civ. Eng., 2, 96–105.

Zhang, M. H., and Malhotra, V. M. �1996�. “High performance concreincorporating rice husk ash as a supplementary cementing materiaACI Mater. J., 93�6�, 629–636.

L OF MATERIALS IN CIVIL ENGINEERING © ASCE / JULY 2008 / 483