RECYCLING OF DEMOLISHED CONCRETE WASTE MATERIALS

Abstract

This study investigates the potential re-use of construction waste materials in new construction. It was experimentally substantiated that concrete recycling is an effective technique of sustainably managing construction and demolition waste. The purpose of the work reported here is to encourage the use of recycled and secondary aggregates in low strength concrete applications. Four concrete mixes of different water/cement ratios were made using crushed waste concrete as coarse aggregate. The properties investigated include the physical properties of the recycled aggregate such as specific gravity, aggregate crushing value, aggregate impact value and aggregate water absorption. The compressive strengths of the concrete were equally determined. These properties were compared with those of similar concrete specimens made with conventional natural aggregate. Thus, ninety-six (96) standard concrete cube specimens were cast, cured and crushed. Forty-eight (48) of the cubes were cast from recycled aggregates while forty-eight (48) were from natural aggregates. The results showed that at higher water/cement ratios, the compressive strength of recycled concrete is similar to that of virgin concrete, but at lower water/cement ratios, the compressive strength of recycled concrete is appreciably lower than that of virgin concrete. Thus, at crushing age of 7 days, the variation in the compressive strengths were 5.63 N/mm2, 2.59 N/mm2, 0.88 N/mm2 and 0.44 N/mm2 and at crushing age of 28 days, the variation in the compressive strengths were 3.04N/mm2, 1.85 N/mm2, 0.52 N/mm2 and 0.3 N/mm2 at water/cement ratios of 0.5, 0.55, 0.6 and 0.65 respectively. In addition, the slump and the compacting factor tests revealed that the work-ability of virgin concrete mix is higher than that of recycled concrete. On the basis of this research, higher water/cement ratio such as 0.65 is recommended for concrete produced from recycled aggregate because of its higher water absorption capacity.