Replacement of Coarse Aggregate with Construction and Demolition Concrete Waste in Concrete Blocks: An Experimental Study

Rapid urban growth generates large quantities of construction and demolition (C&D) waste and, at the same time, raises the demand for natural aggregate. This paper examines whether hardened concrete waste can replace natural coarse aggregate in concrete blocks. Waste concrete from a demolished government school building was crushed, sieved and used as the coarse aggregate. An M20 mix was designed by IS 10262:2009 with a water–cement ratio of 0.55, and specimens with 100% recycled coarse aggregate were cast and tested at 7, 14 and 21 days. The average compressive strengths were 19.01, 20.68 and 23.52 N/mm², which are 16% and 13% lower than the control values of 22.61 and 27.14 N/mm² at 7 and 21 days. The results indicate that recycled blocks may suit lightly loaded uses such as compound walls and single-storey construction.