Sustainable Mortar for Non-Structural Applications Using Alkali Bypass Dust

This study investigates the potential of alkali bypass dust (ABD) as a supplementary material to partially replace cement in paste and mortar formulations. The selection of ABD is motivated by the dual objectives of utilizing an industrial waste product to promote sustainable construction and reducing the carbon footprint associated with cement production. The chemical and mineralogical composition of ABD was characterized using X-ray fluorescence (XRF) and X-ray diffraction (XRD), revealing a composition similar to Portland cement but with a notably lower CaO content (44.32%) and the presence of calcite, portlandite, quartz, and free lime. The incorporation of ABD as a cement replacement significantly influenced the fresh and hardened properties of the mixtures. In paste mixtures, results demonstrated a proportional increase in water demand and setting times with higher ABD content, attributed to its lower reactivity and higher water absorption. Mechanical properties were adversely affected; compressive and flexure strengths in paste mixtures decreased substantially, with a 40% reduction observed at just 10% replacement. This was corroborated by a decrease in density, an increase in water absorption, and a significant drop in ultrasonic pulse velocity (UPV), indicating a more porous and less dense microstructure. In mortar mixtures, a 30% cement replacement with ABD yielded compressive and flexure strengths that remained within acceptable ranges for plastering and masonry applications, despite a reduction in workability. The findings suggest that while high-volume ABD replacement negatively impacts performance, a 30% replacement level presents a viable, sustainable alternative for specific non-structural applications, contingent upon further durability assessments.