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

In this study, the effects of the use of corncob, wheat straw, and plane leaf ashes CA, WSA, and PLA as mineral admixtures on concrete durability were investigated. Ten concrete mixtures were produced in three series with control mixes having 400 kg
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  Effect of Corncob, Wheat Straw, and Plane Leaf Ashesas Mineral Admixtures on Concrete Durability Hanifi Binici 1 ; Faruk Yucegok 2 ; Orhan Aksogan 3 ; and Hasan Kaplan 4 Abstract:  In this study, the effects of the use of corncob, wheat straw, and plane leaf ashes   CA, WSA, and PLA   as mineral admixtureson concrete durability were investigated. Ten concrete mixtures were produced in three series with control mixes having 400 kg cementcontent. The control mixes were modied with 2, 4, and 6% of CA, WSA, and PLA in place of ne aggregate. To establish the durabilityof concrete, the compressive strengths were measured after 7, 28, 90, 180 days, and 18 months under sodium sulfate solution. In themeantime, abrasion resistance and water penetration were investigated. Test results indicate that CA, WSA, and PLA addition providesgood workability and abrasion resistance compared to conventional concrete. Test results also showed that minimum abrasion resistanceis obtained from the control specimen, while maximum abrasion resistance is obtained from CA3   6%   specimens. Abrasion resistance isincreased as the rate of ne CA, WSA, and PLA is increased. The results indicate that the increase in ash content caused a signicantincrease in the sodium sulfate resistance of the concretes. Hence, concrete with CA, WSA, and PLA addition can be recommended for theproduction of durable concrete. DOI:  10.1061/   ASCE  0899-1561  2008  20:7  478  CE Database subject headings:  Admixtures; Concrete durability; Construction materials; Chemicals . Introduction Use of pozzolans such as y ash, calcined kaolin, and palm oilfuel ash as partial replacements for cement have been made as aresponse to environmental concerns about greenhouse gas pro-duction   Malhotra 1987; Stroeven and Sabuni 1999; Shi andStegemann 2000; Tay 1990  . One researcher has reported thatproperly burnt and ground rice husk ash is also suitable for use asa pozzolan   Metha 1979  . New pozzolanic cement material can bean interesting area of study. Wheat straw ash has been used aspozzolanic material when there has been excess wheat production  Biricik et al. 1999  . In Turkey, as in many parts of the world, alarge amount of corncob and wheat straw could be obtained as anagricultural by-product. Wheat straw ashes, and indeed otherashes, have high residual silica content. Examples of other ashesinclude calcined sunower ash and calcined tobacco ash, bothof which may be useful as pozzolans in extended cements  Bensted and Munn 2000  . Rice husk ash has been used success-fully in such applications as concrete with controlled permeabilityformwork and roller compacted concrete   Coutinho 2003;Kajorncheappunngam and Stewart 1992  . Reactive rice husk ashcan be used to produce good quality concrete with reduced po-rosity and reduced Ca  OH  2  content   Zhang and Malhotra 1996  .In the Cukurova region of Turkey, a huge quantity of wheatstraw is produced every summer. Farmers burn it, causing envi-ronmental harm. Instead of being burnt, wheat straw can be usedin mud brick production   Binici et al. 2005  . Similarly, vastamounts of waste organic materials from corncob and plane leaf can harm the environment. These materials, if burned, could alsoserve as pozzolanic materials in the production of durable con-cretes. Corncob is known to contain a considerable amount of silicium dioxide   SiO 2  . Once burned, it leaves an ash very rich inSiO 2  that is pozzolanic in character   Binici et al. 2007  .Durability of concrete structures exposed to aggressive envi-ronments is a major concern. Many environmental phenomena areknown to signicantly affect the durability of reinforced concretestructures   Ihekwaba et al. 1996; Castro et al. 2000; Roper andBaweja 1991; Haque and Kawamura 1992; Tahir and Salih 2007  .In this study, materials of organic srcin, corncob ash, wheatstraw ash, and plane leaf ash were added. The concrete durability  subjected to 5% sodium sulfate solution, abrasion resistance andwater penetration  , was then tested.According to the results of theexperiments, the reliability of the additive materials of organicsrcination was evaluated. Materials Used Aggregate and Cement  An ordinary portland cement   OPC   with 300 Blaine neness wasused for all concrete mixtures. Local Aksu River natural aggre-gate was used to make the concretes. The materials were rsttaken to the Kahramanmaras Sutcu Imam University, Civil Engi-neering Department, materials laboratory. The chemical andphysical characteristics of the materials used are given in Tables 1 1 Assistant Professor, Dept. of Civil Engineering, KahramanmarasSutcu Imam Univ.   K.S.U.  , Kahramanmaras, Turkey. 2 MS Student, Dept. of Civil Engineering, Kahramanmaras SutcuImam Univ.   K.S.U.  , Kahramanmaras, Turkey. 3 Professor, Dept. of Civil Engineering, Cukurova Univ., Adana,Turkey. 4 Professor, Dept. of Civil Engineering, Pamukkale Univ., Denizli,Turkey.Note. Associate Editor: Byung Hwan Oh. Discussion open untilDecember 1, 2008. Separate discussions must be submitted for individualpapers. To extend the closing date by one month, a written request mustbe led with the ASCE Managing Editor. The manuscript for this paperwas submitted for review and possible publication on October 27, 2006;approved on December 10, 2007. This paper is part of the  Journal of  Materials in Civil Engineering , Vol. 20, No. 7, July 1, 2008. ©ASCE,ISSN 0899-1561/2008/7-478483/$25.00. 478  / JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / JULY 2008  and 2 and the terminology for all specimens is given in Table 3. Amaximum aggregate size of 16 mm was used and grading analy-ses were performed according to EN TS 706. The grading data forthe aggregates are given in Table 4. Ashes  In this study, corncob ash   CA  , wheat straw ash   WSA  , andplane leaf ash   PLA   were used as admixtures. Ten concrete mix-tures were produced in four series with control mixes having400 kg cement content. These control mixes were modied with2, 4, and 6% of CA, WSA, and PLA in place of ne aggregate.All ashes were obtained from open burning of a 23 kg heap of each of corncob, wheat straw, and plane leaf with a maximumburning temperature of 600°C   Chindaprasirt et al. 2007  . Inburning the organic materials, the temperature needs to be lowerthan 700°C in order to obtain reactive amorphous silica. Thus,these materials can be burnt with an incinerator or furnace. Thereare quite a lot of burning methods. However, simple open burningis satisfactory where the temperature is controlled by the amountof material in the heap. Burning of wheat straw and plane leaveswas initiated by providing the burning source at the bottom of theincinerator for 3 h and was left for 3 days prior to collection of burnt ashes.The burnt ashes were different in color   see Fig. 1  . Aftercooling, the ashes were ground in a laboratory ball mill for60 min to obtain material under 1 mm particle size before usingas mineral admixture. A grading curve from particle size analysisof Aksu river ne sand, CA, WSA, and PLA is given in Fig. 2. Experimental Details The water used in the production of the concrete specimens wastap water and the cement used to complete the experiments wasOPC, produced by Adana Cement Factory. TS 3068 ISO 2736-2was used for sampling. The mixture was designed according tothe absolute volume method given by Turkish Standard EN TS802. Approximate concrete composition is given in Table 5. Theconcrete specimens were prepared with the same average slumpof 8.512 cm and a dosage of 400 kg / m 3 . The mixing water waskept at a constant temperature of 17°C before mixing and thetemperature of the mixing room was maintained at 20°C duringthe mixing process. All ashes used as additives in this study wereadded into the concrete mixtures in separate ratios, namely 2, 4,and 6%. The water penetration test was performed according toEN TS 10967.Standard specimens of 150 mm 3 were cast and the compres-sive strength of each was measured after immersing in 5% so-dium sulfate solution for 18 months. The behavior in sodiumsulfate solution was determined according to ASTM 1012.An abrasion test was performed in accordance with DIN52108. In this standard, an abrasion test is applied to specimens of size 75  75  55 mm at 28, 90, and 365 days. First, the concretespecimens were cleaned using a wire brush and kept 24 h in awater tank at 20°C, after which they were taken out and wipedwith a wet cloth. The specimens were surface dry saturated  SDS  . Sand blasting pressure was 40 N / mm 2 . The rate of ow of abrasive sand was 500 grams per min. In the present study, thetest was carried out at 20°C temperature and 60% relative humid-ity. SDS specimens were measured and the length denoted as  I  0 .Sand blasting was performed for 60 sec, applied to at least eightdifferent points. At the end of this process, the specimens werekept in 20°C water for 2 h, and then wiped with a wet cloth.Finally, the specimens were weighted and denoted as  I  . Hence,  I  =  I  1 −  I  0  was found as the loss of mass.A water penetration test was performed after 6 months in ac-cordance with EN TS 3455. Concrete cylinders were demoldedafter a day and cured in water for 26 days. After that they weresliced at 50 mm thickness and the 50 mm ends discarded. Thesliced cylinders were left to dry in laboratory conditions for 24 hbefore the application of epoxy coatings. All specimens were Table 2.  Physical Characteristics of Materials UsedMaterialsSpecificgravity  kg / m 3  Vicat timeof setting  min  Compressive strength  MPa  Ordinaryportlandcement3,150 Initial Final 3 day 7 day 28 dayCA 2,970 115 200 24.2 37.3 48.6WSA 2,890PLA 2,910 Table 3.  Terminology for All SpecimensSpecimens System of replacementsC   Control mixture   Aksu River natural aggregatesCA1 2% corncob ash by mass of fine aggregatesCA2 4% corncob ash by mass of fine aggregatesCA3 6% corncob ash by mass of fine aggregatesWSA1 2% wheat straw ash by mass of fine aggregatesWSA2 4% wheat straw ash by mass of fine aggregatesWSA3 6% wheat straw ash by mass of fine aggregatesPLA1 2% plane leaf ash by mass of fine aggregatesPLA2 4% plane leaf ash by mass of fine aggregatesPLA3 6% plane leaf ash by mass of fine aggregates Table 4.  Cumulative Passing for the Aggregate Grades for EN TS706  %  Sieve size  mm   A16Aksu Riveraggregate C1616 100 100 1008 60 70 884 36 43 742 21 27 621 12 18 490.5 8 11 330.25 3 8 18 Table 1.  Chemical Contents of Materials Used, Oxides   %  Materials SiO 2  Al 2 O 3  Fe 2 O 3  CaO MgO SO 3  Na 2 O K 2 O LIOrdinaryportlandcement20.1 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 22.50WSA 4.9 1.15 0.95 24.44 4.63 6.98 1.28 24.72 28.97PLA 9.9 1.11 0.71 21.11 3.19 3.59 0.53 7.7 51.97Note: LI  loss on ignition. JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / JULY 2008 /   479  epoxy coated around the cylindrical surface and left in the labo-ratory for testing. Results and Discussion Compressive Strengths  Over 300 standard cubic specimens of 150 mm size were cast.Based on ASTM and TS standards, all results were acceptable.Mechanical strengths upon compression are the main features thatallow assessments of concrete durability. The compressivestrength of concrete mixtures versus age and the relative strengthof tested concrete specimens are given in Figs. 3 and 4, respec-tively. It can be seen from these figures that there are clear in-creases of compressive strength with increasing percentages of ash additions.From Fig. 3, it can be seen that the compressive strengths of concrete specimens cured in water for 7 days were approximatelyequal to those of the control specimens. However, the compres-sive strength of the CA, WSA, and PLA concretes, in particularthose treated for 365 days, was higher than that the control speci-men. The difference was approximately 40%. In general, the com-pressive strengths of the specimens increased slightly with anincrease of the addition of CA, WSA, and PLA. The highestcompressive strength at all time periods was found in corncob ashspecimens after 28 days. However, compressive strength after 7days was almost the same for all specimens. Considering 28 daysaverage compressive strength, the compressive strength of groupCA3 specimens was found to be 16% higher than that of groupWSA specimens and 17% higher than that of group PLA. Con-sidering 365 days average compressive strength, the compressivestrength of group CA specimens was found to be 23% higher thanthat of group WSA specimens and 32% higher than that of groupPLA.The development of strength in the concretes was affected notonly by the ash type, but also in some cases by ash percentages.Specimen CA3 had the highest compressive strength at 365 days.Furthermore, this value was 8% higher for the CA1 specimens. Itcan be observed from Fig. 4 that relative strength values for allspecimens were almost equal after 7 days. On the other hand, therelative strengths of all the specimens in the CA group werehigher after 28 days. Sulfate Resistance of Concretes  The results of the sulfate resistance test are shown in Table 6.These results show an obvious increase in the sulfate resistance of  Table 5.  Concrete Mixture ProportionsProperties C CA1 CA2 CA3 WSA1 WSA2 WSA2 PLA1 PLA2 PLA3Cement OPC   kg / m 3   400 400 400 400 400 400 400 400 400 400CA   %   0 2 4 6 0 0 0 0 0 0CA   kg / m 3   0 12 24 36 0 0 0 0 0 0WSA   %   0 0 0 0 2 4 6 0 0 0WSA   kg / m 3   0 0 0 0 12 24 36 0 0 0PLA   %   0 0 0 0 0 0 0 2 4 6PLA   kg / m 3   0 0 0 0 0 0 0 12 24 36Water   kg / m 3   200 198 195 190 198 196 195 198 196 195W/C 0.50 0.49 0.48 0.47 0.49 0.48 0.47 0.49 0.48 0.47Sand SSD   kg / m 3   600 588 576 564 588 576 564 588 576 564Coarse aggregate   kg / m 3   1,200 1,200 1,200 1,200 1,200 1,200 1,200 1,200 1,200 1,200Superplasticizer   l / m 3   3 3.5 3.6 3.7 3.5 3.6 3.7 3.5 3.6 3.7Slump   mm   120 95 90 85 100 90 85 105 100 90Air content   %   2.4 2.2 2.1 2 2.3 2.2 2.1 2.3 2.2 2.2Air temperature   C   27 26 26 26 27 27 27 26 27 27Concrete temperature   C   29 28 29 28 27 28 28 28 27 28Unit mass   kg / m 3   2,340 2,329 2,320 2,318 2,322 2,311 2,311 2,324 2,317 2,312 Fig. 1.  Image of burned corncob ash, wheat straw ash, and plane leaf ash Fig. 2.  Grading curve of Aksu river sand, CA, WSA, and PLA 480  / JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / JULY 2008  the concrete with an increase in the percentage of fine aggregates.Other researchers have also supported these results. They reportedthat both natural and artificial pozzolans contribute to increasingchemical resistance of concrete   Erdogan and Dogulu 1997  .The positive effects on concretes increased progressively withincreasing CA, WSA, and PLA contents and were particularlyevident in the specimens with 6% CA additives. This shows thatcompressive strengths under sulfate exposure increase with in-creasing ash content. Thus, CA, WSA, and PLA concretes hadhigher potential sulfate resistance compared to the control speci-mens   Table 6  . Increases in the additive content caused signifi-cant increases in sulfate resistance of concrete over a period of upto 18 months of exposure. The CA3 specimen, in particular, hadthe highest sulfate resistance among all the specimens.Compressive strength tests could not be applied to a number of specimens after the 18-month period due to their unstable struc-tures. The control concrete specimen showed large expansions,cracking, internal fractures, and fractures on whole surfaces.However, CA, WSA, and PLA concretes showed no significantsigns of deterioration. This result is supported by authors whohave reported that up to 40% of portland cement could be re-placed with rice husk ash to make blended cement mortar withreasonable strength development and good sulfate resistance  Chindaprasirt et al. 2007  . It was also mentioned that the service-able life of the mortar had increased by its higher sulfate resis-tance.Table 6 shows the reduction in relative compressive strength  the ratio of compressive strength in sulfate to compressivestrength in tap water  . The relative compressive strengths of allmortars decrease with increasing exposure to sodium sulfate so-lutions. However, they decrease at different speeds. For C, therelative compressive strength decreases rapidly, whereas that of CA, WSA, and PLA concretes decrease slowly   see Table 6  .With the additives, the water /  cement+ash   ratio was reduced.That may be the reason for the observed increase in the compres-sive strength and the sulfate resistance. Abrasion Resistance  Mass loss at 60 min of abrasion in concretes with CA, WSA, andPLA replacement is given in Fig. 5. This figure shows that therewas little abrasion resistance in C specimens, those without ash. Fig. 3.  Compressive strength of specimens versus time of curing inwater Fig. 4.  Relative strength of specimens versus time of curing in water Table 6.  Compressive Strengths and Compressive Strength Reduction of ConcretesSpecimensCompressivestrengthsafter 28 days  MPa  cured in tap water  Compressivestrengthsafter 18 months  MPa  cured in tap water  Compressivestrengthsafter 18 months  MPa  immersed in5% Na 2 SO 4  Compressivestrengthreduction  %  C 26 35.2 18.1 49CA1 29 56.3 40.4 29CA2 32.2 58.6 45.7 23CA3 36.3 60.7 51.9 15WSA1 25.3 45.0 32.7 28WSA2 27.6 48.1 37.1 23WSA3 29.1 51.4 42.3 18PLA1 26.3 38.4 26.2 32PLA2 26.8 40.2 27.9 31PLA3 28.1 43.3 32.8 25 JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / JULY 2008 /   481  Specimens with CA as fine aggregate showed greater abrasionresistance than the C, WSA, or PLA specimens. However, speci-men PLA3 showed a higher abrasion ratio at 365 days. Concreteswhere CA was used as a fine aggregate had the highest abrasionresistance compared to other specimens. The greater abrasion re-sistance of the concretes to added fine corncob, wheat straw, andplane leaf ashes were added, is believed to result from a denserpore structure of the mortar binder. Furthermore, this might beexplained by the fact that ash allows a good interface with acondensed matrix.The abrasion ratio of the specimens is given in Fig. 6. It can beseen that the control specimens were abraded most quickly, whilethe CA3 specimens showed the minimum abrasion rate. Abrasionresistance increases with the amount of ash. However, for the 2and 4% PLA replacement levels, abrasion ratio and strengthlosses were higher than for the 6% PLA specimen. Although therewas no limitation concerning concrete abrasion ratios in the Turk-ish Standard, concretes with abrasion levels lower than 1.2 mmwere denoted “highly abrasion resistant concrete” and those withconcrete abrasion levels higher than 3 mm were considered“poorly abrasion resistant concrete”   Postacıoglu 1987  . Water Penetration  Depths of water penetration into the mixtures are given in Fig. 7.It can be seen from the figure that the depth of water penetrationinto the CA3 specimen was considerably less than for other speci-mens. An increase in the percentage of ash additives from 2 to 6%reduced water penetration significantly. Control specimens showconsiderably greater depth of water penetration. Water penetrationwas reduced with an increase in the CA, WSA, and PLA percent-age. This can be an explanation of the increase in the compressivestrength of the specimens.In general, all ashes had a profound effect on the depth of thewater penetration. As the percentage of corncob ash decreased,water penetration depth increased   see Fig. 7  . Water penetrationdepths correlated well with the ash type and replacement percent-age of the mixtures.These additives and by-products may serve as sticky or adher-ent chemical reagents that combine with other elements to formdenser and homogeneous forms of concretes. The additives fill thegaps within the concrete products, forming less porous structures.All these elements may contribute to enhanced mechanical prop-erties of concrete. Furthermore, the use of the additives result inexcellent durability, with positive effects on concrete formation. Conclusions Based on the investigation reported in this paper, the followingconclusions can be drawn:1. Concrete containing CA, WSA, and PLA showed greater re-sistance to sulfate exposure. More resistance was achievedwith higher ash additive ratios. Sodium sulfate resistance of CA concrete was greater than that of the WSA, and PLA Fig. 5.  Mass loss at 60 min of abrasion versus fine sand replacementwith CA, WSA, and PLA Fig. 6.  Abrasion ratio of specimens versus age Fig. 7.  Water penetration depth of specimens 482  / JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / JULY 2008
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