Fracture and flexural behaviors of recycled lump-aggregate concrete

Abstract

Simultaneously reusing demolished concrete lumps (DCLs), recycled coarse aggregates (RCAs) and sand extracted from soil (SEFS) in concrete to form recycled lump-aggregate concrete (RLAC) can effectively improve the recycling ratio of construction and demolition waste. Fracture and flexural behaviors of RLAC were studied experimentally in laboratory tests. To reveal the mechanism of the increasing effect of the DCLs on the fracture energy of RLAC, RLAC plate fracture specimens were tested and their crack propagations were observed using digital image correlation technique. The results show that: (a) the mass DCL replacement ratio can be used in place of the average DCL area replacement ratio in the fracture section of RLAC; (b) when the compressive strength of the source concrete of DCLs is lower than that of the fresh recycled aggregate concrete (RAC), increasing the RCA replacement reduces the flexural strength, compressive strength, initiation fracture toughness and unstable fracture toughness of RLAC; increasing the DCL replacement also reduces the flexural strength, compressive strength, initiation and unstable fracture toughness of RLAC but the values of the reductions of the flexural strength, initiation and unstable fracture toughness are lower than those of the compressive strength; (c) when the fracture energy of the source concrete of DCLs is lower than that of the fresh RAC, increasing the RCA replacement reduces the fracture energy of RLAC, but increasing the DCL replacement increases it markedly by inducing tortuosity and branching of the cracks; and (d) using SEFS (the soil is the Alluvial-Proluvial soil) in place of river sand has hardly any influence on the fracture and flexural properties of RLAC. Finally, formulas are suggested which usefully predict the flexural strength, the initiation and unstable fracture toughness, and the fracture energy of RLAC.