Effect of the constituents (asphalt, clay materials, floating particles and fines) of construction and demolition waste on the properties of recycled concretes

The present study explores the viability of reusing mixed recycled aggregate from construction and demolition waste as a partial (25 and 50 wt%) replacement for natural coarse aggregate in the manufacture of concretes with a compressive strength of 30 MPa. It further analyses the effect of some of the constituents (asphalt, clay-based materials, floating particles and fines) of these recycled aggregates on the properties of recycled concretes. Despite the high asphalt and floating particle content of the recycled aggregate used, came from waste management plant at Glasgow, it was found to have no adverse effect on the workability of the new concretes. Hardened concrete density and compressive strength were observed to decline with increasing replacement ratios, at a variable rate depending on the components of the recycled aggregate mix and the thickness of their ITZs (the thicker the weaker). While concrete with 25% recycled aggregate exhibited lower sorptivity than the reference concrete, absorption was higher when the replacement ratio was 50%. The findings showed that this type of recycled aggregate can be used in concrete manufactured for housing applications and confirmed the importance of good construction and demolition waste management to deliver high quality recycled aggregate.