Study on some engineering properties of recycled aggregate concrete with flyash

Abstract

Any landfill in urban India is generally comprised of 45-55%demolished masonry and concrete. In addition, with urbanization, the demand for construction aggregates is increasing year after year and in India, it is estimated to be 5.07 billion metric tons in the year 2020. High quantity of demolition waste in landfill and increasing demand for aggregates can be reduced by extracting aggregates from the demolition waste and utilising the same in construction. Research to evaluate the properties of the aggregates extracted and concrete made there from has been in progress globally. Present study is aimed at studying the load versus deflection behaviour of reinforcedrecycled aggregate concrete (RAC) beams under flexural loading and bond strength of RAC by rebar pullout test. The recycled concrete aggregate (RCA) for this study was obtained by crushing concrete cubes of strength 35-45 MPa, cast at various bridge construction sites and tested in CSIR-CRRI. The properties of RCA produced were studied and an appropriate method for design of RAC mixes was proposed. RAC mixes with 50 and 100%RCA with 20%flyash i.e., R50 and R100, were prepared and their mechanical properties such as compressive strength, split tensile strength, flexural strength and elasticmodulus were evaluated and compared to those of natural aggregate concrete with flyash (NAF). In addition, the bond strength of the above three mixes was investigated byperforming rebar pullout test. For the study of flexural behaviour, 150 × 250 × 2,000 mm reinforced beams were cast and tested under simply supported conditions and one third point loads. The mechanical properties of RAC were comparable to that of NAF. Thebond strength of RAC mixes has been found to be about 35 % lower than that of NAF.Themodulus of elasticity of RAC mix decreased, by up to 34 %, with increase in percentageof RCA. Consequently, the deflections of RAC beams were found to be 10-35 % greater than NAF beam. However, the ultimate loads of the RAC beams were found to be 84-89 % of NAF beam and greater than the theoretical ultimate loads. It has been concluded that the strength properties of RAC are encouraging foruse in new concrete. However, theuse of RAC in structural concrete can be recommended with more confidence whenlow value of elastic modulus and its influence in the flexural behaviour of RAC beamsare suitably addressed.