Concrete expansive agents produced from two sludges and calcium sulfate: Development and performance evaluation

This study explores the feasibility of producing expansive agents using freshwater sludge and carbide sludge, supplemented with calcium sulfate, to achieve chemical properties and expansion performance comparable to commercial expansive agents. Freshwater sludge alone does not provide sufficient sulfur, limiting the expansion effectiveness of expansive agents derived from these two sludges. Additional calcium sulfate is advantageous in balancing the calcium-aluminium-sulfur compositions in expansive agent production. Systematic experiments were conducted in this study to evaluate the characteristics, expansion behavior, and mechanical performance of the synthesized expansive agents, as well as the hydration products and microstructure of cement blended with these expansive agents. The results demonstrated that adding calcium sulfate optimized the chemical composition of synthesized expansive agents, making them comparable to commercial products. Cement blended with these agents showed expansion peaks of 0.04 %-0.16 % in the autogenous deformation test and 0.025 %-0.053 % in the restrained expansion test, similar to those of commercial products. The expansion in expansive agent-cement systems was mainly attributed to the increased formation of ettringite and portlandite. Furthermore, both commercial and synthesized expansive agents exhibited similar effects on strength development, with strength losses of less than 10 % compared to plain cement mortar. The newly developed synthesized expansive agents meet commercial performance requirements, enhance economic value, and offer suitability for sustainable development applications. • Use freshwater sludge, carbide sludge & calcium sulfate to produce expansive agents. • CaO-SO 3 -Al 2 O 3 ratios in expansive agents can be adjusted. • Produced expansive agents and commercial products have similar chemical composition. • Produced expansive agents and commercial products achieve comparable performance.