Influence of a LAS-based modifying admixture on cement-based composites containing steel slag powder

Abstract

The incorporation of industrial waste and by-products in cement-based composites has been widely studied and has a high potential for use, contributing to reducing environmental impacts. Also, the use of biodegradable, low-cost, and sustainable admixtures can provide considerable physical and economic advantages to cementitious materials. This work presents a study on the interactions of a modifying admixture based on Linear Alkyl Benzene Sodium Sulfonate (LAS) and steel slag powder (SSP) in the properties of cement-based composites. A two-level two-factor face-centered composite design (CCD) has been employed with response surface methodology (RSM) for modeling. The effect of the studied parameters (0–1.0% LAS and 0–50% SSP) on mortars' consistency and mechanical strength was evaluated. The separated and combined effects of SSP and LAS on hydration kinetics and the formation of hydrated products were investigated through ultrasonic pulse velocity (UPV) variations and X-ray diffraction (XRD) analyses. Also, fragments of mortar specimens were observed using scanning electron microscopy (SEM). For the studied ranges, increasing SSP and LAS contents increased the spread up to 22% and reduced the mechanical strength up to 57%. Both LAS-based admixture and SSP delayed the setting time, influencing the hydration kinetics. Mortars produced with the LAS-based admixture showed air incorporation, evidenced by the appearance of pores with spherical shapes. Results of RSM did not indicate interactions between the effects of SSP and LAS, and the SSP was the component that led to the most significant impacts.