Potential of industrial waste as alternative alkaline activator for development of eco-efficient mortars

Abstract

The alkali-activated materials (AAMs) design can be viewed as one of the most investigated fields in building materials engineering. However, despite numerous studies aimed at the utilization of various precursors, very limited attention is paid to the utilization of waste alkali sources as an alternative to commercial activators. In this regard, this study provides a novel approach to the utilization of industrial waste alkalis as a replacement for commercial alkali activators to reduce costs and reduce the environmental burden. The main innovation consists in the utilization of a waste-cleaning solution (SWCA) as an alternative alkaline activator for blast furnace slag to improve the environmental and economic efficiency and preserve functional properties. The functional properties of designed alkali-activated mortars are described by the setting time, pore size distribution, and mechanical strength. To comply with sustainable measures, the carbon dioxide emissions and costs analysis associated with the material production are carried out. The obtained results reveal the great potential of waste alkaline sources as a replacement for commercial activators. The increase in the applied SWCA concentration induced a shortening in the initial setting time from 240 to 120 min and the final setting time from 480 to 245 min. The designed mixtures reached a satisfactory level of mechanical strength (25 MPa) in comparison to low-grade cement mortars together with a substantial reduction in environmental burden excluding the avoided production. Specifically, a carbon footprint of 75 kg/m3 CO2 equivalent was achieved which represents 5 times lower values compared to low-grade concrete and even better value than AAMs based on a commercially-produced activator. Significant improvements were achieved also in cost efficiency per cubic meter as it was dropped to approx 40 €/m3, thus designed alkali-activated mortars provide better cost efficiency per cubic meter over traditional binders. The findings show that AAMs based on waste alkaline activator should of particular attention to materials science as lowers the consumption of energy-intensive sources and represent a valuable step toward a circular economy.