Producing Concrete Incorporating Hybrid Cementitious Materials and Recycled Concrete Aggregate with Novel Thermal Treatment Methods

Abstract

Recycled concrete aggregate (RCA), characterized by high porosity and adhered mortar, often impairs the mechanical strength and durability of concrete. This research develops a new integrated treatment method, which combines thermal-mechanical conditioning of RCA with hybrid supplementary cementitious materials (SCMs), including metakaolin (MK) and ground granulated blast-furnace slag (GGBS). Three thermal treatment protocols were applied to enhance RCA quality, and concrete mixes with 50% and 100% RCA replacement were prepared. The study investigated the impact of adding MK up to 30% and GGBS up to 20% on the compressive strength, splitting tensile strength, workability, and water absorption of concrete. Although isolated effects require further investigation, the research found that the integrated use of TT3-treated RCA, where TT3 refers to the stepped thermal treatment protocol and SCMs, showed promising performance under the experimental conditions, producing a 90-day compressive strength greater than that of the control mix and reducing water absorption by more than 30%. The combined application of thermal-mechanical treatment (TT3) on RCA and the use of hybrid supplementary cementitious materials (SCMs), such as metakaolin (MK) and ground granulated blast-furnace slag (GGBS), significantly improved the concrete properties. The integrated use of TT3-treated RCA and SCMs resulted in a 90-day compressive strength that was 5.5% higher than that of the control mix, indicating significant long-term performance improvements.