Properties of dredged sludge solidified with alkali-activated slag-based materials and blended with copper slag as fine aggregates of mortars

Dredged sludge (DS), a waste with high annual output, is widely distributed in rivers and lakes worldwide. Although the application of DS as construction materials has been studied, it only focuses on cement-based solidification, accompanied by low strength and high energy consumption. In this paper, to maximize waste reuse and reduce carbon emissions, various industrial by-products (fly ash (FA), steel slag (SS) and ground granulated blast-furnace slag (GGBS)) were utilized to solidify DS to develop a novel construction material with relatively higher strength. Copper slag (CS), an industrial waste, was reused to replace natural sand (NS) as fine aggregates of mortars. The properties of setting time, workability, rheological performance, hydration heat, mechanical properties and water absorption were explored. The results show that the obtained 28d-compressive strength is above 3.9 MPa, which reveals excellent cementitious effect of the binder. Compared with low strength (LS, 50 wt% FA + 50 wt% GGBS) and middle strength (MS, 50 wt% SS + 50 wt% GGBS) group, high strength (HS, 100 wt% GGBS) group presents faster setting time, lower spread, higher cumulative hydration heat, higher strength and lower water absorption. The increase of replacement ratio of NS by CS improves workability, decreases yield stress and lowers water absorption. When 50% CS was used to replace NS, the strength increases because more hydration products formed. But when the replacement ratio increases from 50% to 100%, the 28d-strength variation is not obvious. Hence, CS can be recommended as a complete substitution for NS to maximize solid waste utilization.