Influence of size effect on the properties of slag and waste glass-based geopolymer paste

A large amount of solid waste is produced due to the simultaneous production and consumption activities of an increasing population in the world. Solid wastes-based geopolymer as a green alternative has the potential to replace traditional cement concrete to lower CO₂ emissions. In this study, the sample size effects of waste glass powder (WGP) and ground blast furnace slag (GBFS)-based geopolymer pastes cured at different conditions and ages on its physical properties and micro-characteristics were systematically investigated, including the mass loss, compressive strength, microstructures, and reaction products at different geopolymerization stages. The results show that the sample size effect was significant in the geopolymer pastes, and the compressive strength decreased with the increasing sample size. A higher reaction degree was observed in the smaller-sized geopolymer specimens based on the microstructural investigation. The higher curing temperature and higher relative humidity (RH) could contribute to the generation of C–S-Hs and lead to better mechanical performance. The analysis of coring and cutting samples reveals that the alkaline concentration gradient was formed during the reaction process, and the precipitation of alkali reagents was more obvious in the larger-sized geopolymer sample. In addition, the XRD, TGA/DSC, mass loss, and carbonation test results indicate that the moisture distribution was vital and had different functions during the geopolymerization process at different reaction stages.