Effect of additional Al sources on early-age strength of fly ash-based geopolymer containing calcium carbide residue and Glauber’s salt as activators

Abstract

Alkali-activated materials are more environmentally friendly than cementitious composites and are used in the construction and building sector. However, their intrinsic low early strength under ambient temperatures hinders their practical applicability. More research is needed on the possibilities of increasing early strength at ambient temperatures. In this study, aluminum sulfate (AS) was used as an additional aluminum source to improve the early-age properties of fly ash (FA)-based geopolymers incorporating calcium carbide residue (CCR) and Glauber’s salt (GS) as activators. XRD, TG, SEM, ICP and isothermal calorimetry analyses were carried out to characterize the phase composition, microstructure and hydration process of the prepared materials. The results showed that the 1d strength of AS1-CCR10 was increased by 260.7 % compared with the control material, and the effect on the late strength was negligible. The relative content of AFt increased by 2.97 %, creating a more compact microstructure. During the extraction process, insufficient dissolved Al3+ in the composite led to a decrease in initial strength. In the hydration process, the induction period of AS1-CCR10 was advanced by 40.92 % and that of t50 was advanced by 57.74 %, which accelerated the early reaction rate. However, the Krstulovic-Dabic model could not accurately describe the initial stage of the hydration reaction of composite materials. This study is helpful to broaden the utilization of geopolymer composites and provide a theoretical basis for the preparation and reaction mechanism of alkali-activated materials.