Effect of sulfate activation of fly ash on mechanical and durability properties of recycled aggregate concrete

•Strength enhancement of high-volume fly ash concrete.•Optimization of fly ash and recycled aggregate levels in concrete manufacturing.•Sulfate activation of fly ash to overcome early age strength issue.•Evaluation of permeability and acid attack resistance of fly ash-recycled aggregate concrete. One of the eco-friendly alternatives for conventional concrete (CON) is the system that incorporates recycled coarse aggregates (RCA) as the replacement of natural coarse aggregates (NCA) and fly ash (FA) as the partial replacement of Portland cement (OPC). The main issue with RCA-FA concrete is the lower early strength (due to FA) and poor overall mechanical and durability performance (mainly due to RCA). Researchers have proposed to use chemical activators to enhance the early age efficiency of hybrid FA-OPC binders. In this study, the mechanical and durability properties of RCA concrete were studied with inactivated FA-OPC and activated FA-OPC binders. Sodium sulfate was used as a chemical activator. Studied parameters include compressive strength, splitting tensile strength, water absorption, sorptivity coefficient, chloride penetration, and acid attack resistance. The results showed that RCA concrete with activated FA-OPC binder had significantly higher mechanical strength than that without activator, especially at an early age. At 50% RCA activated FA-OPC concrete mix showed better or comparable mechanical properties than CON. The positive influence of chemical activation was also noticed on the durability performance of RCA concrete. Both activated and inactivated FA-OPC binders attributed more towards the properties of concrete incorporating RCA. Sulfate activation of FA-OPC can be a useful solution to address the issue of lower strength and durability of high-volume FA-RCA concrete systems.