Sustainable Utilization of Waste Pumice Powder in Slag-Based Geopolymer Concretes: Fresh and Mechanical Properties

In societies worldwide, there is significant pressure on the construction industry to employ waste/recycled materials instead of natural-sourced materials to develop infrastructures to mitigate negative environmental consequences. This study investigated the feasibility of using waste pumice powder as a binder in place of granular blast-furnace slag to manufacture geopolymer concrete. Three sets of GC mixes were developed with three ratios of alkaline activator/binder (A/B) of 0.45, 0.5, and 0.55. Eight GC mixes were prepared for each set, with eight replacement ratios of GGBFS with WPP (0%, 30%, 50%, 60%, 70%, 80%, 90%, and 100%). The influence of WPP addition as a substitute source of aluminosilicate precursors on the fresh (workability and setting time), mechanical (compressive strength and flexural strength), physical characteristics (density and water absorption), and microstructure morphology of WPP/slag-based geopolymers were studied. A linear correlation between UPV and compressive strength was found. The results revealed that setting times and workability are affected by the A/B ratio and content of WPP. WPP reduces the workability and increases setting time (both initial and final). There was a drop in compressive and flexural strengths as the percentage of WPP in the GC increased. The maximum compressive (60 MPa) and flexural strength (4.96 MPa) at an A/B ratio of 0.45 for a 100% slag content mix were obtained. However, a GC mix containing 50% WPP and 50% slag with a compressive strength of 28 MPa after 28 days of curing at ambient temperature was achieved, which is acceptable for structural applications.