The study of the freeze-thaw resistance and carbonation resistance of manufactured sand-RAC based on fly ash and slag powder

Abstract To advance the use of industrial solid waste and recycled concrete, this study explores the impact of fly ash and slag powder on the mechanical properties, freeze–thaw resistance, and carbonation resistance of manufactured sand recycled aggregate concrete (MRAC). Different FSMRAC (Fly Ash and Slag Powder MRAC) mixtures were prepared by varying the amounts of fly ash and slag powder. The results show that fly ash and slag powder enhance the splitting tensile strength of MRAC more than its compressive strength. when the contents of fly ash and slag powder are 0% and 30%, respectively, the FSMRAC attains maximum compressive strength of 48.6 MPa and splitting tensile strength of 3.8 MPa, representing increases of 2.96% and 5.6% in compressive and splitting tensile strengths, respectively, compared to MRAC. A total addition of 30% fly ash and slag powder effectively reduces the loss of mechanical properties under freeze–thaw conditions. When the fly ash-to-slag powder ratio (F:S) exceeds 1.5, it improves carbonation resistance and compressive strength; when the ratio is below 1.5, it enhances splitting tensile strength resistance to freeze–thaw cycles. Slag powder promotes hydration and improves mechanical properties, while fly ash densifies the concrete matrix and lowers the carbonation rate. Response Surface Methodology (RSM) analysis indicates that both materials improve MRAC’s properties. Higher fly ash content benefits compressive strength and carbonation resistance, while higher slag powder content improves splitting tensile strength.