EFFICIENCY OF USING RECYCLED FINE AGGREGATE FOR A NEW CONCRETE

Using construction and demolition waste (C&DW) as a source for aggregates draws attention lately due to the large quantities of C&DW accumulating in the modern world. The coarse fraction of this waste was studied extensively in the past as a source for coarse aggregates in the production of new concrete. It is quite acceptable that replacing 10-20% of the virgin coarse aggregate with recycled one will have a minor effect on the properties of the new concrete. However, using the fine fraction of C&DW to replace virgin aggregate is still in question and is restricted in the standards. In the study presented here the fine fraction of C&DW from two sorting plants was used to prepare new mortar and to replace natural sand crushed from natural stone. Two water/cement ratios were studied with three replacement ratios of 0%, 30% and 100%. The results showed that the mortars prepared with the recycled fine aggregates were inferior to the mortar prepared with virgin aggregate. The compressive strength has reduced and the permeability increased. It was found that reducing the water/cement ratio from 0.6 to 0.4 can preserve the compressive strength of the mix while replacing 100% of one of the aggregates studied. Similarly, the equivalent water/cement ratio was evaluated for the other aggregates and replacement ratios. These relationships can be used to evaluate the environmental efficiency of using recycled fine aggregates from C&DW for making new concrete.