Mechanical behaviour of structural concrete with ground recycled concrete cement and mixed recycled aggregate

Abstract

This article analyses the combined effect of valorising ground recycled concrete (GRC) as 10% or 25% cement replacement and 0% or 50% mixed recycled construction and demolition waste aggregate (RA-CDW) in structural concrete. An exhaustive experimental programme was designed to assess the variation in compressive and tensile strength, modulus of elasticity and hardened concrete density. Non-destructive ultrasonic pulse velocity and electrical resistivity tests were also conducted. The concrete mixes prepared with GRC and RA-CDW exhibited lower mechanical performance than those manufactured with natural aggregate and cement only (although the difference was smaller than the respective replacement ratios). These findings were attributed to: a higher water/binder (cement + GRC) ratio, the dilution effect resulting from a lower cement content in the new mixes and the intrinsic properties (water absorption and abrasion resistance) of the new recycled components. The mixes with 10% GRC and 50% RA-CDW, however, showed similar mechanical performance and remained in the same strength class as those with 50% RA-CDW and 100% Portland cement. In terms of the electrical resistivity and ultrasonic pulse velocity tests, the effect of replacing OPC with GRC was below 14%, irrespective of whether natural or recycled aggregates were used. Such promising findings pave the way for more efficient and global C&DW management with a view to steering the construction industry toward the circular economy.