Abstract
Waste concrete from prestressed precast hollow cored floor units has been recycled for use as replacement aggregate in concrete (RCA). Waste concrete blocks were crushed to −14 mm using cone, impact and jaw crushers. All produced acceptable physical and mechanical properties, although the impact crusher was best suited in most cases. The water absorption of the RCA was 3 to 4 times greater than natural limestone and river gravel used for control purposes. The fine RCA was at the coarse end of the British Standard limit. Concrete made using zero, 20% and 50% replacement of coarse and fine RCA had increased workability at 20% replacement, but this reduced considerably at 50% replacement. Compressive strength of concrete made with RCA was generally within ±5 N/mm 2 of the control value of 62 N/mm 2 . RCA from the cone crusher produced the highest strengths. The main conclusion is that concrete made with up to 50% replacement of both coarse and fine RCA appears to be comparable with natural aggregate concrete in terms of workability and compressive strength.
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