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  1. 1. L. O. Ettu, U. C. Anya, C. T. G. Awodiji, K. O. Njoku, A. C. Chima / International Journal ofEngineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-June 2013, pp.731-735731 | P a g eStrength Of Ternary Blended Cement Sandcrete ContainingCorn Cob Ash And Pawpaw Leaf AshL. O. Ettu1, U. C. Anya2, C. T. G. Awodiji3, K. O. Njoku4, and A. C. Chima51,2,3,4,5Department of Civil Engineering, Federal University of Technology, Owerri, Nigeria.ABSTRACTThe compressive strength of ternaryblended cement sandcrete containing corn cobash (CCA) and pawpaw leaf ash (PPLA) wasinvestigated in this work. 105 sandcrete cubes of150mm x 150mm x 150mm were produced withOPC-CCA binary blended cement, 105 withOPC-PPLA binary blended cement, and 105 withOPC-CCA-PPLA ternary blended cement, eachat percentage OPC replacement with pozzolan of5%, 10%, 15%, 20%, and 25%. Three cubes foreach percentage replacement of OPC withpozzolan and the control were tested forsaturated surface dry bulk density and crushedto obtain their compressive strengths at 3, 7, 14,21, 28, 50, and 90 days of curing. The 90-daystrengths obtained from ternary blending ofOPC with equal proportions of CCA and PPLAwere 11.30N/mm2for 5% replacement,10.90N/mm2for 10% replacement, 10.60N/mm2for 15% replacement, 10.10N/mm2for 20%replacement, and 9.70N/mm2for 25%replacement, while that of the control was10.00N/mm2. Thus, very high sandcrete strengthvalues suitable for use in various civilengineering and building works could beobtained with OPC-CCA-PPLA ternary blendedcement at longer days of hydration when goodquality control is applied.Key words:Binary blended cement, corn cob ash,pawpaw leaf ash, pozzolan, sandcrete, ternaryblended cement.INTRODUCTIONShortage of accommodation is increasinglybecoming one of the greatestproblems in SouthEastern Nigeria. Since sandcrete is the mostimportant element of low-cost buildings in theregion, reducing the cost of cement used forsandcrete production is considered an essentialcontribution toward solving this problem. In order toachieve this purpose, agricultural by-productsregarded as wastes in technologicallyunderdeveloped societies could be used as partialreplacement of Ordinary Portland Cement (OPC).Ithas already been established thatsupplementarycementitious materials prove to be effective to meetmost of the requirements of durable concrete andblended cements are now used in many parts of theworld (Bakar, Putrajaya, and Abdulaziz, 2010).Incorporating agricultural by-product pozzolanssuch as rice husk ash (RHA) calcined at hightemperatures has been studied with positive resultsin the manufacture and application of blendedcements (Malhotra and Mehta, 2004). Elinwa andAwari (2001) found that groundnut husk ash couldbe suitably used as partial replacement of OPC inconcrete making. Cisse and Laquerbe (2000)reported that sandcrete blocks obtained withunground Senegalese RHA as partial replacement ofOPC had greater mechanical resistance than 100%OPC sandcrete blocks. Their study also revealedthat the use of unground RHA enabled production oflightweight sandcrete block with insulatingproperties at a reduced cost. Agbede and Obam(2008) have also investigated the strength propertiesof OPC-RHA blended sandcreteblocks. Theyreplaced various percentages of OPC with RHA andfound that up to 17.5% of OPC can be replaced withRHA to produce good quality sandcrete blocks.Oyekan and Kamiyo (2011) reported thatsandcreteblocks made with RHA-blended cement had lowerheat storage capacity and lower thermal mass than100% OPC sandcrete blocks. They explained thatthe increased thermal effusivity of the sandcreteblock with RHA content is an advantage over 100%OPC sandcrete block as it enhances human thermalcomfort.Many other researchers have alsoinvestigated the combination of OPC with differentpercentages of a pozzolan in making binary blendedcement composites (Adewuyi and Ola, 2005; DeSensale, 2006; Nair, Jagadish, and Fraaij, 2006;Saraswathy and Song, 2007; Ganesan, Rajagopal,and Thangavel, 2008). Malhotra and Mehta (2004)reported that ground RHA with finer particle sizethan OPC improves concrete properties as highersubstitution amounts result in lower waterabsorption values and the addition of RHA causesan increment in the compressive strength. Mehtaand Pirtz (2000) investigated the use of rice huskash to reduce temperature in high strength massconcrete and concluded that RHA is very effectivein reducing the temperature of mass concretecompared to OPC concrete. Sakr (2006) investigatedthe effects of silica fume and rice husk ash on theproperties of heavy weight concrete and found thatthese pozzolans gave higher concrete strengths thanOPC concrete at curing ages of 28 days and above.Cordeiro, Filho, and Fairbairn (2009) investigatedBrazilian RHA and rice straw ash (RSA) anddemonstrated that grinding increased the
  2. 2. L. O. Ettu, U. C. Anya, C. T. G. Awodiji, K. O. Njoku, A. C. Chima / International Journal ofEngineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-June 2013, pp.731-735732 | P a g epozzolanicity of RHA and that high strength ofRHA, RSA concrete makes production of blockswith good bearing strength in a rural settingpossible. Their study showed that combination ofRHA or RSA with lime produces a weakcementitious material which could however be usedto stabilize laterite and improve the bearing strengthof the material. Habeeb and Fayyadh (2009) alsoinvestigated the influence of RHA average particlesize on the properties of concrete and found that atearly ages the strength was comparable, while at theage of 28 days finer RHA exhibited higher strengththan the sample with coarser RHA. Rukzon,Chindaprasirt, and Mahachai (2009) studied theeffect of grinding on the chemical and physicalproperties of rice husk ash and the effects of RHAfineness on properties of mortar and found thatpozzolans with finer particles had greater pozzolanicreaction. Wada et al. (2000) demonstrated that RHAmortar and concrete exhibited higher compressivestrength than the control mortar and concrete.Cordeiro, Filho, and Fairbairn (2009) furtherinvestigated the influence of different grinding timeson the particle size distribution and pozzolanicactivity of RHA obtained by uncontrolledcombustion in order to improve the performance ofthe RHA. The study revealed the possibility of usingultrafine residual RHA containing high-carboncontent in high-performance concrete. Many otherresearchers have also found sawdust ash a suitableagricultural by-product for use in formulating binaryblended cements with OPC (Elinwa, Ejeh, andMamuda, 2008; Elinwa and Abdulkadir, 2011).A few researchers have also investigatedthe possibility of ternary blended systems wherebyOPC is blended with two different pozzolans. Theternary blended system has the additionalenvironmental and economic advantages that itenables a further reduction of the quantity of OPC inblended cements and also makes it possible for twopozzolans to be combined with OPC even if neitherof them is available in very large quantity. Tyagher,Utsev, and Adagba (2011) found that sawdust ash-lime mixture as partial replacement for OPC issuitable for the production of sandcrete hollowblocks. They reported that 10% replacement of OPCwith SDA-lime gave the maximum strength atwater-cement ratio of 0.55 for 1:8 mix ratio. Elinwa,Ejeh, and Akpabio (2005) had earlier investigatedthe use of sawdust ash in combination withmetakaolin as a ternary blend with 3% added to actas an admixture in concrete. Frı´as et al.(2005)studied the influence of calcining temperatureas well as clay content in the pozzolanic activity ofsugar cane straw-clay ashes-lime systems. Allcalcined samples showed very high pozzolanicactivity and the fixation rate of lime (pozzolanicreaction) varied with calcining temperature and claycontent. Rukzon and Chindaprasirt(2006)investigated the strength development ofmortars made with ternary blends of OPC, groundRHA, and classified fly ash (FA). The resultsshowed that the strength at the age of 28 and 90days of the binary blended cement mortar containing10 and 20% RHA were slightly higher than those ofthe control, but less than those of FA. Ternaryblended cement mixes with 70% OPC and 30% ofcombined FA and RHA produced strengths similarto that of the control. The researchers concluded that30% of OPC could be replaced with the combinedFA and RHA pozzolans without significantlylowering the strength of the mixes. Fadzil et al.(2008) studied the properties of ternary blendedcementitious (TBC) systems containing OPC,ground Malaysian RHA, and fly ash (FA). Theyfound that compressive strength of concretecontaining TBC gave low strength at early ages,even lower than that of OPC, but higher than binaryblended cementitious (BBC) concrete containingFA. Their results suggested the possibility of usingTBC systems in the concrete construction industryand that TBC systems could be particularly useful inreducing the volume of OPC used.Much of the previous works by researcherson ternary blended cements were based on theternary blending of OPC with an industrial by-product pozzolan such as FA or silica fume (SF) andan agricultural by-product pozzolan, especiallyRHA. Tons of agricultural and plant wastes such ascorn cob and pawpaw leaf are generated in manycommunities in South Eastern Nigeria due tointensified food production and local economicventures. Little has been reported on the possibilityof binary combination of these Nigerian agriculturalby-products with OPC in developing blendedcements and no literature exists on the possibility ofternary blending of two of them with OPC. Thiswork is part of a pioneer investigation of thesuitability of using two Nigerian agricultural by-products in ternary blend with OPC for sandcretemaking. The compressive strength of ternaryblended cement sandcrete containing corn cob ashand pawpaw leaf ash was specifically investigated.It is hoped that the successful utilization of corn cobash and pawpaw leaf ash in ternary combinationwith OPC for making sandcrete would further addvalue to these agricultural by-product wastes as wellas reduce the cost of building works and other civilengineering projects that make much use ofsandcrete blocks.METHODOLOGYCorn cob was obtained from Aba district inAbia State and pawpaw leaf from Eziobodo in ImoState, both in South East Nigeria. These materialswere air-dried, pulverized into smaller particles, andcalcined into ashes in a locally fabricated furnace attemperatures generally below 650oC. The corn cobash (CCA) and pawpaw leaf ash (PPLA) weresieved and large particles retained on the 600µm
  3. 3. L. O. Ettu, U. C. Anya, C. T. G. Awodiji, K. O. Njoku, A. C. Chima / International Journal ofEngineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-June 2013, pp.731-735733 | P a g esieve were discarded while those passing the sievewere used for this work. No grinding or any specialtreatment to improve the quality of the ashes andenhance their pozzolanicity was applied because theresearchers wanted to utilize simple processes thatcould be easily replicated by local communitydwellers.The CCA had a bulk density of 810 Kg/m3,specific gravity of 1.95, and fineness modulus of1.98. The PPLA had a bulk density of 790 Kg/m3,specific gravity of 1.83, and fineness modulus of1.36. Other materials used for the work are Ibetobrand of Ordinary Portland Cement (OPC) with abulk density of 1650 Kg/m3and specific gravity of3.13; river sand free from debris and organicmaterials with a bulk density of 1590 Kg/m3,specific gravity of 2.68, and fineness modulus of2.82; and water free from organic impurities.A simple form of pozzolanicity test wascarried out for each of the ashes. It consists ofmixing a given mass of the ash with a given volumeof Calcium hydroxide solution [Ca(OH)2] of knownconcentration and titrating samples of the mixtureagainst H2SO4 solution of known concentration attime intervals of 30, 60, 90, and 120 minutes usingMethyl Orange as indicator at normal temperature.For each of the ashes the titre value was observed toreduce with time, confirming the ash as a pozzolanthat fixed more and more of the calcium hydroxide,thereby reducing the alkalinity of the mixture.A standard mix ratio of 1:6 (blendedcement: sand) was used for the sandcrete. Batchingwas by weight and a constant water/cement ratio of0.6 was used. Mixing was done manually on asmooth concrete pavement. For binary blendingwith OPC, each of the ashes was first thoroughlyblended with OPC at the required proportion and thehomogenous blend was then mixed with the sand,also at the required proportions. For ternaryblending, the two ashes were first blended in equalproportions and subsequently blended with OPC atthe required proportions before mixing with thesand, also at the required proportions. Water wasthen added gradually and the entire sandcrete heapwas mixed thoroughly to ensure homogeneity. Onehundred and five (105) sandcrete cubes of 150mm x150mm x 150mm were produced with OPC-CCAbinary blended cement, one hundred and five (105)with OPC-PPLA binary blended cement, and onehundred and five (105) with OPC-CCA-PPLAternary blended cement, each at percentage OPCreplacement with pozzolan of 5%, 10%, 15%, 20%,and 25%. Twenty one control cubes with 100%OPC or 0% replacement with pozzolan were alsoproduced. This gives a total of 336 sandcrete cubes.All the cubes were cured by water sprinkling twicedaily in a shed. Three cubes for each percentagereplacement of OPC with pozzolan and the controlwere tested for saturated surface dry bulk densityand crushed to obtain their compressive strengths at3, 7, 14, 21, 28, 50, and 90 days of curing.RESULTS AND DISCUSSIONThe particle size analysis showed that boththe CCA and the PPLA were much coarser thanOPC, the reason being that the ashes were notground to finer particles. The pozzolanicity testconfirmed both ashes as pozzolans since they fixedsome quantities of lime over time. The compressivestrengths of the OPC-CCA and OPC-PPLA binaryblended cement sandcrete as well as the OPC-CCA-PPLA ternary blended cement sandcrete are shownin tables 1 and 2 for 3-21 and 28-90 days of curingrespectively.As shown in tables 1 and 2, the variation ofstrength for sandcrete produced from OPC-CCA-PPLA ternary blended cements is similar to those ofsandcrete produced from OPC-CCA and OPC-PPLA binary blended cements for all percentagereplacements and curing ages. Also, sandcreteproduced from ternary blend of OPC with equalproportions of CCA and PPLA have compressivestrength values in between those of binary blends ofOPC and CCA on one hand and OPC and PPLA onthe other hand for all percentage replacements andcuring ages. More significantly for civil engineeringand building construction purposes, the 90-daystrengths obtained from ternary blending of OPCwith equal proportions of CCA and PPLA were11.30N/mm2for 5% replacement, 10.90N/mm2for10% replacement, 10.60N/mm2for 15%replacement, 10.10N/mm2for 20% replacement, and9.70N/mm2for 25% replacement, while that of thecontrol was 10.00N/mm2. Thus, very high sandcretestrength values suitable for use in various civilengineering and building works could be obtainedwith OPC-CCA-PPLA ternary blended cement atlonger days of hydration when good quality controlis applied since the 90-day strength values obtainedin this work for 5-20% replacement are higher thanthose of the control and the strength value for 25%replacement is very close to that of the control.
  4. 4. L. O. Ettu, U. C. Anya, C. T. G. Awodiji, K. O. Njoku, A. C. Chima / International Journal ofEngineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-June 2013, pp.731-735734 | P a g eTable 1. Compressive strength of blended OPC-CCA-PPLA cement sandcrete at 3-21 days of curingOPCPlusCompressive Strength (N/mm2) for0%Poz.5%Poz.10%Poz.15%Poz.20%Poz.25%Poz.Strength at 3 daysCCA 2.80 2.10 2.00 1.90 1.80 1.80PPLA 2.80 2.00 1.90 1.80 1.70 1.60CCA&PPLA2.80 2.00 1.90 1.90 1.80 1.70Strength at 7 daysCCA 4.90 3.20 3.10 2.90 2.80 2.40PPLA 4.90 3.10 2.90 2.70 2.40 2.20CCA&PPLA4.90 3.10 3.00 2.80 2.60 2.30Strength at 14 daysCCA 7.00 4.50 4.30 3.50 3.30 3.00PPLA 7.00 4.40 3.90 3.40 3.10 2.80CCA&PPLA7.00 4.40 4.10 3.40 3.20 2.90Strength at 21 daysCCA 7.90 5.30 5.20 4.90 4.20 3.90PPLA 7.90 4.90 4.70 4.50 4.00 3.60CCA&PPLA7.90 5.10 4.90 4.70 4.00 3.80Table 2. Compressive strength of blended OPC-CCA-PPLA cement sandcrete at 28-90 days of curingOPCPlusCompressive Strength (N/mm2) for0%Poz.5%Poz.10%Poz.15%Poz.20%Poz.25%Poz.Strength at 28 daysCCA 9.20 7.60 6.40 5.90 5.40 4.90PPLA 9.20 6.50 6.20 5.50 5.00 4.50CCA&PPLA9.20 7.20 6.30 5.70 5.30 4.70Strength at 50 daysCCA 9.80 10.00 9.30 8.60 7.70 6.90PPLA 9.80 9.50 8.80 8.30 7.40 6.40CCA&PPLA9.80 9.80 9.10 8.40 7.60 6.70Strength at 90 daysCCA 10.00 11.40 11.00 10.70 10.30 9.80PPLA 10.00 11.20 10.70 10.40 10.00 9.40CCA&PPLA10.00 11.30 10.90 10.60 10.10 9.70It can also be seen in tables 1 and 2 that100% OPC sandcrete (the control) strengthincreased steadily till the age of about 28 days, afterwhich it increased only gradually until the age of 90days. Table 1 further shows that the strength valuesof OPC-CCA-PPLA ternary blended cementsandcrete are very low compared to those of thecontrol sandcrete at early ages of 3 to 21 days ofhydration. The low early strength gets morepronounced with increase in percentage replacementof OPC with CCA-PPLA combination as shown intable 2. The low early strength could be due to thefact that pozzolanic reaction was not yet appreciableat early ages of hydration. The pozzolanic reactionset in after some days and increased with days ofhydration such that the strength of blended cementsandcrete increased more and more with age thanthat of the control. Thus, very high strength could beachieved for OPC-CCA-PPLA ternary blendedcement sandcrete with 5 to 25% replacement ofOPC with pozzolans at 50 to 90 days of curing, assuggested by table 2.Tables 1 and 2 further show that thestrength values of OPC-CCA binary blended cementsandcrete are greater than those of OPC-PPLAbinary blended cement sandcrete at all percentagereplacements of OPC with pozzolan and at allcuring ages. The strength value of OPC-CCA-PPLAternary blended cement sandcrete consistently liesin-between the two for all percentage replacementsand curing ages. This suggests that a greaterproportion of CCA than PPLA should be used foroptimization of the strength of OPC-CCA-PPLAternary blended cement sandcrete.CONCLUSIONSThe variation of strength for OPC-CCA-PPLA ternary blended cement sandcrete is similar tothose of OPC-CCA and OPC-PPLA binary blendedcement sandcrete for all percentage replacementsand curing ages. Also, ternary blended cementsandcrete produced from blending OPC with equalproportions of CCA and PPLA have compressivestrength values in between those of binary blendedOPC-CCA and OPC-PPLA cement sandcrete for allpercentage replacements and curing ages. Moresignificantly, the 90-day strengths of OPC-CCA andOPC-PPLA binary blended cement sandcrete aswell as those of OPC-CCA-PPLA ternary blendedcement sandcrete are higher than the control valuesfor 5-20% replacement of OPC with pozzolans andvery close to the control value for 25% replacement.This suggests that very high values of OPC-CCA-PPLA ternary blended cement sandcrete strengthscould be obtained if high target strength isintentionally designed for and good quality controlis applied. Thus, OPC-CCA-PPLA ternary blendedcement sandcrete could be used for various civilengineering and building works where early strengthis not a major requirement.REFERENCES[1]. Adewuyi, A.P., & Ola, B. F. (2005).Application of waterworks sludge as partialreplacement for cement in concrete
  5. 5. L. O. Ettu, U. C. Anya, C. T. G. Awodiji, K. O. Njoku, A. C. Chima / International Journal ofEngineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-June 2013, pp.731-735735 | P a g eproduction. Science Focus Journal, 10(1):123-130.[2]. Agbede, I. O., &Obam, S. O. (2008).Compressive Strength of Rice Husk Ash-Cement SandcreteBlocks.Global Journal ofEngineering Research, Vol. 7 (1), pp. 43-46.[3]. Bakar, B. H. A., Putrajaya, R. C.,&Abdulaziz, H. (2010).Malaysian Sawdust ash – Improving the Durability andCorrosion Resistance of Concrete: Pre-review. Concrete Research Letters, 1 (1):6-13, March 2010.[4]. Cisse, I. K., &Laquerbe, M.(2000).Mechanical characterization ofsandcretes with rice husk ash additions:study applied to Senegal. Cement andConcrete Research, 30 (1): 13– 18.[5]. Cordeiro, G. C., Filho, R. D. T., &Fairbairn, E. D. R. (2009). Use of ultrafinesaw dust ash with high-carbon content aspozzolan in high performance concrete.Materials and Structures, 42: 983–992.DOI 10.1617/s11527-008-9437-z.[6]. De Sensale, G. R. (2006). Strengthdevelopment of concrete with rice-huskash.Cement&Concrete Composites, 28:158–160.[7]. Elinwa, A. U., &Abdulkadir, S. (2011).Characterizing Sawdust-ash for Use as anInhibitor for Reinforcement Corrosion.New Clues in Sciences, 1: 1-10.[8]. Elinwa, A. U., &Awari, A.(2001).Groundnut husk ashconcrete.Nigerian Journal of EngineeringManagement, 2 (1), 8 - 15.[9]. Elinwa, A. U., Ejeh, S. P., &Akpabio, I. O.(2005). Using metakaolin to improvesawdust-ash concrete. ConcreteInternational, 27 (11), 49 - 52.[10]. Elinwa, A. U., Ejeh, S. P., &Mamuda, M.A. (2008). Assessing of the freshconcreteproperties of self-compactingconcrete containing sawdust ash.Construction and Building MaterialsJournal, 22: 1178 - 1182.[11]. Fadzil, A. M., Azmi, M. J. M., Hisyam, A.B. B., &Azizi, M. A. K. (2008).Engineering Properties of Ternary BlendedCement Containing Rice Husk Ash and FlyAsh as Partial Cement ReplacementMaterials.ICCBT, A (10): 125 – 134.[12]. Frı´as, M., Villar-Cocin˜a, E., Sa´nchez-de-Rojas, M. I., & Valencia-Morales, E.(2005). The effect that different pozzolanicactivity methods has on the kineticconstants of the pozzolanic reaction insugar cane straw-clay ash/lime systems:Application of a kinetic–diffusive model.Cement and Concrete Research, 35: 2137 –2142.[13]. Ganesan, K., Rajagopal, K., andThangavel, K. (2008). Rice husk ashblended cement: assessment of optimallevel of replacement for strength andpermeability properties of concrete. Constr.Build. Mater.,22(8):1675-1683.[14]. Habeeb, G. A., &Fayyadh, M. M.(2009).Saw dust ash Concrete: the Effect ofSDA Average Particle Size on MechanicalProperties and DryingShrinkage.Australian Journal of Basic andApplied Sciences, 3(3): 1616-1622.[15]. Malhotra, V. M., & Mehta, P. K.(2004).Pozzolanic and CementitiousMaterials. London: Taylor & Francis.[16]. Mehta, P. K. &Pirtz, D. (2000). Use of ricehusk ash to reduce temperature in highstrength mass concrete. ACI JournalProceedings, 75:60-63.[17]. Nair, D. G., Jagadish, K. S., and Fraaij, A.(2006). Reactive pozzolanas from rice huskash: An alternative to cement for ruralhousing. CemConcr. Res., 36 (6): 1062-1071.[18]. Oyekan, G. L. and Kamiyo, O. M.(2011).A study on the engineeringproperties of sandcreteblocks producedwith rice husk ash blended cement. Journalof Engineering and Technology Research,3(3): 88-98.[19]. Rukzon, S., &Chindaprasirt, P. (2006).Strength of ternary blended cement mortarcontaining Portland cement, rice husk ashand fly ash.J. Eng. Inst. Thailand, 17: 33-38 (547-551).[20]. Rukzon, S., Chindaprasirt, P., &Mahachai,R. (2009).Effect of grinding on chemicaland physical properties of saw dust ash.International Journal of Minerals,Metallurgy and Materials, 16 (2): 242-247.[21]. Sakr, K. (2006). Effects of Silica Fume andRice Husk Ash on the Properties of HeavyWeight Concrete.Journal of Materials inCivil Engineering, 18(3): 367-376.[22]. Saraswathy, V., & Song, H.(2007).Corrosion performance of rice huskash blended concrete. Construction andBuilding Materials, 21 (8): p.1779–1784.[23]. Tyagher, S. T., Utsev, J. T., and Adagba, T.(2011). Suitability of Sawdust Ash-LimeMixture for Production of SandcreteHollow Blocks.Nigerian Journal ofTechnology, 30 (1): 79-84.[24]. Wada, I., Kawano, T., &Mokotomaeda, N.(2000).Strength properties of concreteincorporating highly reactive rice-husk ash.Transaction of Japan Concrete Institute, 21(1): p. 57–62.