Performance of recycled aggregate concrete with supplementary cementitious materials (fly ash, GBFS, silica fume, and metakaolin): Mechanical properties, pore structure, and water absorption

Recycled aggregate concrete (RAC) is an eco-friendly material that is increasingly being used in new construc-tions. Nowadays, the application of RAC is mainly limited by lower mechanical properties and durability per-formance. This paper outlines the mechanical properties (i.e., compressive strength, splitting tensile strength, and flexural strength), pore structure, and water absorption of RAC with supplementary cementitious materials (SCMs). In addition, to improve the properties and more sustainability of RAC, utilization of SCMs such as fly ash (FA), granulated blast furnace slag (GBFS), silica fume(SF), and metakaolin(MK) were used as cement replace-ment materials. Thirty-two mixtures were designed with five volume ratios of recycled concrete aggregates (RCA) replacing natural aggregate and containing FA, GBFS, SF, and MK contents as cement replacement (by weight), respectively. The results show that up to 20% FA or 20% SF in binary blends, or 15% SF in ternary blends, the RAC had higher compressive and splitting tensile strength and, thereafter, a gradual reduction in strength with an increase in FA or SF. MK significantly increasingly improved the strengths of RAC with binary or ternary blends, with the rise in the replacement ratio of MK. By characterization of the mineral composition and its relative weight, and the pore structure of RAC with SCMs, the critical influential factors on mechanical properties and water absorption of RAC with binary or ternary blends were the pozzolanic action and filling action of SCMs; however, those of RAC with quaternary or multi-blends was the filling action. It was also found that the water absorptions of RAC with SCMs were positive relative to the total intrusion volume and porosity. A regression model of predicted compressive strength was established.