Investigation on the effects of desulfurization gypsum on the engineering properties of ternary geopolymers: Improving the utilization of industrial wastes

Abstract

Geopolymer as a low-carbon binder can effectively reduce carbon emissions and improve industrial waste utilization. To optimize the performance of GGBS-FA binary geopolymer, a ternary geopolymer was designed by the addition of desulfurization gypsum (DG). The engineering properties of GGBS-FA-DG ternary geopolymers were investigated by laboratory tests. Moreover, microstructure tests were performed to reveal the improvement mechanism of the engineering properties of the ternary geopolymers. Results show that the compressive strength of ternary geopolymer with 60% GGBS was higher than that with 70% GGBS. With the increase in addition amount of DG, the strength first increased and then decreased, and the optimal DG content was 6%. However, the strength of ternary geopolymers with 50% GGBS was barely improved and remained the lowest. Initial and final setting times were prolonged with the increase in DG content, and the initial setting time reached 34 min for the optimal ternary geopolymers (i.e., 60% GGBS, 6% DG). Drying shrinkage was reduced by 15.8% as the DG content increased to 8%. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results revealed that gel products and needle-like ettringite (AFt) crystals were generated in the ternary geopolymers. AFt can fill the pores and further improve the strength based on the gel strength. AFt wrapped on the surface of early-formed aluminosilicate can prevent it from further polycondensation into three-dimensional network gels, thus retarding the setting at the early curing stage. In addition, the beneficial expansion of AFt can inhibit the drying shrinkage for the ternary geopolymers with the optimal DG content.