Volcanic scoria as a sustainable alternative to sand in structural lightweight concrete.

This study investigates the potential of using scoria, a lightweight volcanic aggregate, as a sustainable replacement for natural sand in the production of structural lightweight concrete, addressing the challenges posed by sand scarcity in Ethiopia. The concrete mixtures were proportioned to achieve a minimum compressive strength of 25 MPa, with natural sand partially or fully replaced by scoria at volumetric substitution levels of 35%, 50%, 70%, and 100%. Key concrete properties were assessed at curing ages of 7, 28, and 56 days. The experimental program included slump, compressive strength, split tensile strength, flexural strength, water penetration, and ultrasonic pulse velocity (UPV) tests. The 35% replacement mix achieved the highest compressive strength at 43.6 MPa, surpassing the control sample (39.6 MPa), while the 50% replacement yielded optimal flexural (4.88 MPa) and tensile strengths (3.36 MPa). Workability decreased with increasing scoria content, and densities dropped from 2405 kg/m³ (control) to 2164 kg/m³ (100% scoria). Scoria's microstructural properties, observed via SEM and XRD, confirmed its glassy, porous structure, contributing to enhanced water resistance, with penetration depths decreasing to 20 mm at 35% scoria replacement. These findings suggest that scoria, at optimal levels, can improve concrete's mechanical and durability properties, offering a viable, eco-friendly sand alternative.