Flexural Behavior of Beam made by Partial Replacement of Natural Aggregates with Coarse Aggregates from Old Concrete.

Increasing demand of accommodation in urban areas, posed serious problems everywhere. Lesser available space in most of region of the world has led the planners to plan for skyscrapers in place of single or short height multistory buildings. This leads to huge quantum of demolished concrete waste. On other hand new construction need raw material thus natural resources of the aggregate goes on decreasing every day. Both of these problems are interrelated. Reusing demolished waste not only saves the natural resources of the aggregates but also provide a good measure of reducing waste management. Therefore in this experimental work evaluation of flexural strength and cracking pattern of RC beam made with coarse aggregates from demolished concrete waste as partial replacement of natural aggregates is carried out. Demolished concrete is collected from the Nawabshah city and processed to maximum of 1" size. Basic properties of these aggregates (water absorption and specific gravity) are evaluated and compared with those of natural aggregates to have good insight of the aggregates. 30 RC beams in five batches with # 4 bars as main bars and #2 bars as stirrups are prepared with 0%, 50%, 60%, 70% and 80% replacement of the natural coarse aggregates. The dimensions of all beams is kept 36"x6"x6" with 1:2:4 concrete mix and 0.45 - 0.55 water cement ratio. After curing for 28 days, beams are tested using central point load for flexural strength and cracking behavior. The test result of this research work shows that minimum and maximum reduction in flexural strength in 12% and 26.6% respectively in comparison to beams made with 100% natural aggregates. Although the first crack appeared at lesser load than reference concrete but the behavior and position of crack is same in both cases. Based on the result of this research work it is concluded that 88% strength can be achieved with 50% replacement of natural aggregates with demolished waste concrete aggregates. Therefore can effectively be used in the areas of moderate or low load.