<p>This study investigates the effects of using different sand-to-cement ratios on the workability, mechanical and durability properties of cement mortars with recycled sand derived from construction and demolition waste. In addition, carbon footprints and cost analysis were conducted to evaluate the environmental and economic performance of the mortar mixes. With constant water-to-cement ratio across all mixes, the results demonstrate that increasing recycled sand content reduces compressive strength, water absorption, and flowability, leading to stiffer mixes. The construction and demolition waste mortar with a sand-to-cement ratio of 1.2 achieved the optimal balance between workability and strength, reaching a 28-day compressive strength of 48.9&#xa0;MPa while meeting flow requirements. Construction demolition waste mortar is more cost-effective than natural sand mortar, and while the total carbon footprint remains unchanged, it will reduce landfill waste and conserve natural resources, promoting sustainable construction.</p>