<p>Alkali–silica–reaction (ASR) in concrete has always been a significant hidden threat, which could cause the expansion and lead to internal stress, ultimately resulting in extensive damage to infrastructure. This study proposes a novel approach to investigate the potential of waste dolomite powder (WDP) as an inert material in mortar to mitigate ASR. The accelerated mortar bar test demonstrated that incorporating WDP at a constant water-to-cement ratio effectively reduced ASR expansion of mortar by up to 18.17%. Additionally, the results indicated that the mortar prepared by WDP had an evident increase of compressive strength (3.05 – 12.95%), and a decrease of water absorption (3.54 – 22.85%). Pore structure analysis revealed a reduction in porosity by up to 24.55%, attributed to the nucleation and filling effects of WDP during cement hydration. In addition, the dilution effect of WDP in mortar decreased the cement content, reducing the formation of alkaline products and decreasing the pH value of pore solution. X – ray diffraction and thermogravimetry analyses confirmed that the amount of alkaline hydration product (Ca(OH)₂) were reduced by 17.96 – 46.11%. Microstructural analysis was performed by using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy techniques, which further demonstrated that WDP significantly enhanced the compactness of matrix and minimized the formation of cracks, which contributed to the reduced ASR expansion. Notably, the use of WDP significantly reduced the overall embodied CO₂ footprint, energy consumption and economic cost of the mixes. These findings demonstrate the potential of WDP in improving the performance and sustainability of cement-based materials, providing valuable insights for future development of emerging low-carbon and durable building materials.</p>