Effect of Recycled Fine Aggregate Replacement Ratio on the Fresh State, Mechanical, and Water Absorption Properties of Self- Compacting Mortar

<title>Abstract</title> <p>The growing volume of construction and demolition waste, coupled with the depletion of natural resources, has spurred interest in recycled aggregates as a sustainable alternative in cement-based materials. Yet their effect on the rheological and mechanical behavior of self-compacting mortar remains incompletely understood. This study examines how replacing natural fine aggregates with recycled aggregates affects the fresh and hardened properties of self-compacting mortar. Five mortar mixtures were prepared, with recycled aggregate replacement levels of 0%, 25%, 50%, 75%, and 100%. Flow spread, flow time, 28-day compressive strength, and water absorption tests were carried out to assess the performance of each mixture. The results showed that as recycled aggregate content increased, flowability decreased and flow time increased. This behavior is largely explained by the rougher surface texture, higher porosity, and greater water absorption capacity of the recycled aggregates. Higher replacement levels also led to a gradual decline in compressive strength and a corresponding rise in water absorption, reflecting increased pore volume and a weakened interfacial transition zone between the cement paste and the aggregates. Despite this progressive drop in mechanical performance, mixtures with moderate replacement levels particularly between 25% and 50%achieved a favorable balance of workability, strength, and relative durability. Taken together, these findings suggest that the controlled use of recycled aggregates can help reduce the consumption of natural resources and support more effective management of construction waste. It offers a practical, environmentally sound approach to producing self-compacting mortar.</p>