Concrete is a composite material made out of coarseaggregates bonded together with fluid cement that solidifies over the time. Inconcrete, Ordinary Portland cement (OPC) is widely used as the main binder inthe concrete. Globally,an estimated 46 million tonnes of concrete and mortar were consumed in 2013. Productionof OPC is currently topping 2.6 billion tons per year.
Manufacture of 1 kg of OPC emits nearlyequivalent amount of CO2 in to the atmosphere Russell et al., 1999.Therefore OPC production is one of the main contributor to the global warming. Therefore, itwill be much worth, if another material is found instead of cement withequivalent properties or if cement is partly replaced by some othersupplementary cementitious materials (SCMs).
Search of such materials can leadto a sustainable development incorporating a minimum impact on theenvironment. Presently OPC is partlyreplaced with SCMs obtained by industrial by products such as Rice husk ash(RHA), Fly ash, Silica Fume, Ground Furnace Slag, High Reactive Meta kaolinetc. SCMs enhance the concrete properties mainly in two ways.These materials increase the generation of more Calcium Silicate Hydratethrough the pozzolanic reaction and they also contribute in providing denserconcrete due to better packing of particles. Ricehusk contains high amount of organic materials.
However, it has less percentageof inorganic material which is rich in silica. It was made sure through X-Rayfluorescence (XRF) and X-ray Diffraction (XRD) analyses of RHA (discussedlater). Therefore, it can be used as supplementary cementitious materials inconcrete production due to its high pozzolanic property.
Althoughthere are many investigations have been documented in this regards, a properguidelines are not developed yet to perform the mix design of concrete consistof RHA. Therefore it was planned to extend the k-value concept stated in EN206-1: 2013 for the concrete consists of Rice Husk Ash through systematicstatistical approach to use it as a guide for the mix design.Traditionally,the application of concrete recycled coarse aggregate (RCA) is used aslandfill.
Nowadays, the applications of recycled aggregate in the concreteproduction is getting popular around the World due to the higher demand ofnatural aggregate. However, the use of recycled coarse aggregates, which havedifferent characteristics and properties compared to natural coarse aggregates,could modify the concrete properties. However, number of issues associated withRCA are not solved yet.
Thereare many investigations have been documented to examine the behaviour ofconcrete with either RHA or RCA. However, only a few studies have investigatedthe combined use of both RHA and RCA. Therefore, it was planned to investigatethe effect of RHA together with RCA on engineering properties of high strengthconcrete to ensure the sustainable development of concrete industry. Sixteenmix propositions are made by changing percentage of RHA and RCA to investigate engineeringproperties of concrete consists of both RCA and RHA. Thereby, some guidelineswere made to use it as a tool for the mix design of concrete consists of RHAand RCA.
2. Literature ReviewRicemilling industry produces a lot of rice husk during milling of paddy whichoriginates from the fields. Many ways are being practiced for utilising them bymaking commercial use of RHA. RHA can also be used as supplementarycementitious material in the concrete production industry due to its highpozzolanic property Kishore et.
al 2011. Numerous investigations have beenreported in this regards. Various levels of RHA replacement to cement wasexamined on compressive strength characteristics of concrete in previousstudies Makarata et al., 2013; Deepa etal., 2008; Suresh et al., 2006; Sata et al.
,2006. Theresults of the studies made by Makarata et al., 2013 indicated that theconcrete mixed with 20% of ground RHA had a compressive strength at 7 dayshigher than that of concrete without RHA. Sata et al.
, 2006 also reported that the higher fineness ofRHA could be used as a pozzolanic material in making high strength concrete.The maximum compressive strength of 80 MPa was obtained and reported in theirstudy Sata et al., 2006. Furthermore, Deepa et al., 2008 reported that theincorporation of RHA in concretes resulted in improved compressive strength andflexural strength. It can be concluded from the results of these studies thatthe RHA has the high pozzolanic property and could be used as a goodsupplementary cementing material in concrete production.
However, some otherinvestigations showed the results in the other way around Rupali et al.,2017. Moreover, the results made byKhassaf et al.
, 2004 showed that the 10% replacement of cement by RHA givespeak compressive strength. They also revealed that the increment of rice huskash percentage above 10% showed the decline in compressive strength. Tensilestrength of the concrete containing RHA was almost similar as the compressivestrength variation. Marand et al., 2006 found that the addition of RHA inconcrete becomes cohesive and more plastic and thus permits easier placing andfinishing of concrete. In contrast, Rupali et al.
, 2017 and Avinash et al.,2004 revealed that the workability was decreased with the increment of RHA. Furtherinvestigations are necessary to solve the uncertainties associates with theseissues.RCAis obtained mainly by crushing and processing of old concrete structuralelements. RCA may contain bricks, tiles, metals and other miscellaneousmaterials such as glass, wood, paper, plastic and other debris along withcrushed concrete.It has been established in literature that increase in RCAamount at the same w/c ratio leads to decrease in compressive strength,generally up to 10% lower than that of natural aggregate concrete Elhakam etal.
, 2012; Fonseca et al., 2011; Rahal et al., 2007. Kou et al., 2008 reportedthat the compressive strength of RCA added concrete was 20% less than compressivestrength of conventional Concrete. However some other researchers observed thatthe compressive strength of concrete remains unaffected, or increases slightlyfor replacement of Natural aggregate by RCA up to 25% Etxeberria et al.
,2007;Rao et al., 2011; Kwan et al.,2012. Moreover, research conducted by Padminiet al.
,2009 showed that the rate of strength gain in RCA made with 20%, 50% and100% RA was more after 28 days as compared to that of conventional concretePadmini et al.,2009. Thesplit tensile strength of RCA has been observed to be dependent on a variety offactors such as RCA replacement, water-binder ratio, mixing methods, type ofcement, curing age and RA quality Bairagi et al.
,1993. The results of thestudy made by Bairagi et al.,1993 showed that the split tensile strength of RCAwere 6%, 10% and 40% less than that of conventional concrete when RAC was madewith 25%, 50% and 100% RA replacement, respectively. Many studiesshowed that the tensile strength of concrete for replacement ratio of RCA up to30% is same or even exceeds the tensile strength of natural aggregate concretePadmini et al., 2009.
However, only few investigations have beenreported about partial replacement of untreated RHA together with RCA on theengineering properties of HSC. It is worth to find out the influencing factorsand its effects on concrete containing both RHA and RCA to determine thesustainable mix design of designated concrete. Therefore this research studyexamines the engineering properties of concrete containing both RCA and RHA forthe sustainable development of modern concrete industry.