Evaluation of the use of crushed returned concrete as recycled aggregate in ready-mix concrete plant

Abstract

Every year, a significant amount of waste is generated in ready-mix concrete (RMC) plants. Further, the environmental and economic consequences of the disposal of this residue are relevant. Therefore, crushing and sieving the hardened concrete returned to the plant has emerged as a possible and interesting alternative to recycle RMC residue for use as aggregates. This paper presents an experimental study performed by one of the largest producers of RMC in Brazil. The recycled aggregates were evaluated through laboratory analysis and industrial-scale production, to verify their technical impact and applicability in new concrete formulations. The tests demonstrate that recycled aggregate, when used within 48 h after production, has good application potential because no differences in pumpability were found. The standard deviation of the recycled aggregate concrete is slightly higher than that of concrete produced only with natural aggregates, which affects the average compressive strength needed to achieve the same characteristic strength. This condition may increase the production costs of RMC. However, in the case studied, this cost increment was less than the costs associated with disposing of the material in landfills and those related to the purchase of conventional aggregates. Therefore, this study concludes that concretes with recycled aggregates have conditions to be economically viable, especially for classes with a characteristic strength of less than 30 MPa.