Improving the activity of waste concrete recycled powder by a mechanical-microwave combing method

Purpose The efficient utilization of recycled concrete powder (RCP) has attracted much attention. To break through the limitation of single activation technology of RCP, this study investigates the effects of a mechanical-microwave method on the reactivity of RCP. Design/methodology/approach The mechanical properties, hydration products, and pore structure of RCP-incorporated mortar were evaluated. Findings The results demonstrate that the combined activation reduces the median particle size of RCP and induces a low-frequency shift in the Si-O-T FT-IR characteristic peaks, signifying depolymerization of the silicate network and formation of highly reactive broken bond sites. Concurrently, decreased Si2p and Al2p binding energies in XPS spectra confirm enhanced surface reactivity. The 28-day strength activity index (SAI) of RCP mortar improved from 65.7 (untreated) to 82.2% under optimal activation conditions (90-min ball milling followed by 10-min microwave irradiation), outperforming solely mechanical activation by 3.6–6.1%. Furthermore, combined activation increased chemically bound water content from 22.8 to 33.7%, accompanied by a low-wavenumber shift in FT-IR peaks of hydration products. The total porosity of RCP mortar decreased from 17.2 to 14.6%, indicating a denser pore structure. Originality/value This study explores the feasibility and potential mechanism of mechanical-microwave activation of RCP, aiming to provide valuable insights for the sustainable development of materials. Using activated RCP in cement-based materials reduces the demand for cement and substantially cuts carbon emissions, thereby making a critical contribution to the construction industry’s green and low-carbon transition.