Geopolymer materials made from fly ash, blast furnace, and incinerator slags in Vietnam: a study on their mechanical and physical properties

Abstract

This work examined geopolymers made from blast furnace and incinerator slags, as well as blast furnace slag and fly ash, with and without nano-silica additives. The materials were characterized using x-ray diffraction, scanning electron microscopy, and energy-dispersive x-ray mapping. For the incorporation of incinerator and blast furnace slags, the optimum parameters based on compressive strength were as follows: the NaOH concentration was 14M, and the mass ratios of incinerator/blast furnace slag to water glass/NaOH were 4:6 and 7:3, respectively. The leaching of heavy metals (Cr, Zn, Cu, Cd, Pb, As, Ni, and Hg) from the resulting geopolymer was environmentally acceptable. For geopolymers based on fly ash and blast furnace slags, a fly ash/blast furnace slag ratio of 60/40 yielded the highest compressive strength of 57.4 MPa. Adding 1.5% nano-silica to the fly ash/blast furnace-based geopolymer increased the compressive strength by up to 11.5% compared to the control sample. This concrete attained waterproofing grades from W10 to W14 and could protect steel reinforcement against corrosion in water environments containing Cl- and SO₄^2- ions. These results demonstrate that geopolymer concrete, made from industrial waste, contributes to reducing environmental pollution and the consumption of natural resources and energy.