Strength, shrinkage and creep and durability aspects of concrete including CO2 treated recycled fine aggregate

Abstract

Strength development and shrinkage and creep behavior of recycled aggregate concrete as well as durability aspects such as carbonation and chloride ion penetration were investigated. Except for Control concrete, natural fine aggregate was replaced by recycled fine aggregate at a rate of 0%, 15%, 30%, or 50% while natural coarse aggregate was completely replaced by recycled coarse aggregate (RCA). Two different recycled fine aggregates were used: Recycled fine aggregate (RFA) and CO2 treated recycled fine aggregate (CRFA). Compressive strength of recycled aggregate concrete at all ages tested was reduced from that of the Control concrete. CO2 treatment of recycled fine aggregate improved not only the aggregate physical properties but also the strength of recycled aggregate concrete. The compressive strength reduction was 19% or less at 100% RCA + 15%–50% RFA replacement level while it was 11% or less at 100% RCA + 15%–50% CRFA replacement level after 28 days. Shrinkage and creep strains were measured for up to 300 days. Shrinkage of concrete with 100% RCA was 12% larger than that of Control concrete, while shrinkage of concretes with 100% RCA + 30% RFA or 30% CRFA replacement increased by about 25%–30%. In the creep test, creep coefficient and specific creep of all recycled aggregate concretes increased by about 20–35% over that of the Control. CO2 treatment of recycled fine aggregate resulted in up to 15% improved strength of recycled aggregate concrete, but showed little improvement on shrinkage and creep. Durability of recycled aggregate concrete evaluated in terms of carbonation and chloride ion penetration was reduced from that of the Control concrete.