Effects of recycled fine aggregates on properties of concrete containing natural or recycled coarse aggregates: A comparative study

Abstract

Most of the past studies related to recycled concrete aggregates (RCA) dealt with only coarse RCA (CRCA), while there were many hesitations regarding incorporation of fine RCA (FRCA) into concrete. Therefore, the present study analyses the compatibility of FRCA with coarse natural aggregates (CNA) and CRCA based on their combined influence on concrete. In this study, the original concrete (produced on-site and tested in the laboratory) was broken down to 50–70 mm with a hand hammer, followed by more size reduction using a jaw crusher (maximum size∼25 mm). Further, they were graded into CRCA and FRCA as per IS 383. FRCA was used directly in concrete, but CRCA was ground further in an abrasion machine. 30%, 60% and 100% FRCA (as a replacement of fine natural aggregates (FNA) by volume) were utilised either with 100% CNA or 100% CRCA to study their effect on fresh properties (workability and density), mechanical properties (compressive, flexural and split tensile strength) and durability properties (water permeability and carbonation) of concrete. The properties of recycled concrete were mostly inferior to conventional concrete at each curing age (except for 90 days compressive strength of concrete incorporated with 30% FRCA). However, the performance gap between conventional and recycled concrete was reduced with an increase in curing age. The recycled concrete containing three different combinations of FRCA and CRCA (0% and 100%, 30% and 0%, 30% and 100%) satisfied IS 10262's target compressive strength criteria for M30 grade concrete. The density of RCA affected the concrete properties more than its water absorption. Also, the water permeability of recycled concrete (followed by its carbonation depth and compressive strength) was most influenced by incorporation of RCA. Conclusively, it was found that FRCA is more compatible with CNA at 30% FNA replacement and with CRCA at 60% and 100% FNA replacement.