<p>Concrete production relies heavily on Portland cement, which contributes substantially to global carbon dioxide emissions. To address the environmental impact of cement manufacturing, researchers have increasingly focused on sustainable materials that can partially replace cement while maintaining or improving the performance of cementitious composites. Waste glass powder (WGP) is one such material, offering both environmental benefits and the potential to enhance the mechanical properties of mortar and concrete. Despite these advantages, uncertainties remain regarding its influence on key durability characteristics, particularly alkali-silica reaction (ASR) expansion. This study evaluates the feasibility of incorporating WGP as a partial cement replacement in mortar mixtures by examining its effects on physical, mechanical and microstructural properties. Mortar and paste samples were produced with WGP replacement levels of 0, 5, 10, 15, 20, 25 and 30 percent by weight of cement. The experimental program included measurements of bulk and dry densities, setting time, compressive strength, capillary absorption and ASR expansion. Microstructural analysis was conducted using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The findings show that using 5 percent WGP results in a modest increase in compressive strength of approximately 2 to 5 percent compared with the control mixture. At this replacement level, the microstructure becomes denser and contains less portlandite, indicating beneficial pozzolanic activity. However, increasing the WGP content leads to higher ASR expansion, which highlights the importance of limiting its dosage. Overall, the study demonstrates that incorporating a small amount of WGP, particularly around 5 percent, can improve the mechanical performance and microstructural quality of mortar while supporting the sustainable reuse of waste glass in construction materials.</p>