ABSTRACT

increasing demand of accommodating growing population in urban areas, posed serious problems everywhere. Lesser available space i n most of region of the world lead the planners to plan for sky-scrapers in place of single or short height multistory buildings. As a result demolishing of old structures, hence a huge quantum of demolished waste generated. This waste need to be disposed off properly without creating adverse effects to the surroundings. On the other hand new construction need raw material to be used. Concrete structures make extensive use of aggregates thus natural resources of the aggregate goes on decreasing every day. Both of these problems are interrelated thus the idea of reusing demolished waste was increasingly become popular. It not only saves the natural resources of the aggregates but also provides a good measure of reducing waste management. Therefore this research work proposed the experimental evaluation of flexural behavior of reinforced concrete beams made by partially placing the naturally aggregate with demolished concrete waste. Demolished concrete is collected from the Nawabshah city. Large blocks of demolished concrete are broken into smaller pieces and sieved to maximum of one inch size. Basic properties of these aggregates i.e water absorption and specific gravity are evaluated and compared with properties of natural aggregates to have good insight of the aggregates. Five batches of beams (total 30 beams) reinforced with # 4 bars main bars and #2 bars as stirrups are caste with 0%, 50%, 60%, 70% and 80% replacement of the natural coarse aggregates with demolished waste concrete aggregates. The dimensions of all the beams are kept same (36"x6"x6"). In addition
to beams six cylinders of standard dimensions are also prepared to evaluate and compare the compressive strength. 1:2:4 concrete mix is used for all beams with 0.45 to 0.55 water absorption ratio of demolished concrete aggregates.
Therefore to maintain the slump with higher percentages of recycled aggregates demand higher water cement ratio. After curing all the beams and cylinders for 28 days, beams are tested using central point load for flexural strength and cracking behavior of the beams is observed. The test results of this research work indicated that minimum reduction in flexural strength is 12% in comparison to beams made with 100% natural aggregates. Whereas the maximum reduction in strength recorded is 29.6%. Although the first crack appeared at lesser load than in case of the beams made with 100% natural aggregates, but the behavior and position of crack was same in both cases. Based on the result of this research work it can be concluded that 88% strength can be achieved with 50 % replacement of natural aggregates with demolished waste concrete aggregates. Therefore it can effectively be used in the areas of moderate or low load.