Dual admixtures for cement-based composites comprising steel slag powder and residual lignin-based liquor

Abstract

Steel slag is a by-product of the steel industry that can be used as an aggregate and/or mineral admixture, conferring physical and mechanical benefits to cement-based composites. In parallel, sugarcane bagasse is a by-product of the sugar/alcohol industry used in biorefineries to produce bioethanol. The delignification processes, employed as a pretreatment in biorefineries, generate residual liquors that contain lignin. Lignin is a natural polymer with plasticizing properties when incorporated into cement mixtures. Given this scenario, this work sought to produce and evaluate dual admixtures containing a residual lignin-based liquor and a steel slag powder. The proposed dual admixtures were prepared from two strategies and incorporated in cement pastes and mortars at different dosages. Mixtures containing a commercial silica suspension and a reference mixture (without admixtures) were also evaluated. The flow test showed that the dual admixtures promoted higher spreading than the silica suspension in all the proposed dosages. Also, the mortars containing the dual admixtures had significantly higher compressive strengths and more refined pore structures than the reference mortar. The residual lignin-based liquor enhanced the workability of the composites and favored the dispersion of the steel slag powder into the matrix. The liquor's plasticizing and set-retarding capacities were attributed to its anionic functional groups and sugar content, respectively. Additionally, the high-efficiency grinding of the steel slag powder contributed to improving its specific surface area and fineness parameters, justifying its performance as a filler and a supplementary cementitious material. This study presents a new route for developing more eco-efficient cement-based composites. It also complies with the principles of circular economy by offering a feasible strategy for valorizing large-scale industrial wastes in civil construction.