UTILIZATION OF CONSTRUCTION AND DEMOLITION WASTE (CDW) IN SUSTAINABLE CONCRETE PRODUCTION IN CONSTRUCTION INDUSTRY OF PAKISTAN

Abstract

Pakistan's escalating solid waste crisis, particularly in Karachi with its annual generation of 49.6 million tons, necessitates the adoption of circular economy principles in construction. This study investigates the feasibility of substituting natural coarse aggregate with Construction and Demolition Waste (CDW) comprising crushed concrete, bricks, and tiles in concrete. Using a 1:2:4 mix design with a constant 0.5 water-cement ratio, six replacement levels (0–100%) were evaluated for compressive strength at 7 and 28 days. Results revealed a nonlinear strength response, with 40% CDW replacement yielding optimal performance (33.12 MPa at 28 days), surpassing the control mix (28.5 MPa). This enhancement is attributed to internal curing from the porous recycled materials. Beyond 60% replacement, however, strength declined due to increased porosity and weakened interfacial transition zones, with 100% replacement achieving only 22.11 MPa. Notably, the 80% replacement mix exhibited the highest strength gain (72.4%) between 7 and 28 days, suggesting potential for non-structural applications. The study concludes that 40% CDW replacement offers an optimal balance between structural integrity and sustainability, providing a viable pathway for waste reduction and resource optimization in Karachi's construction sector.