Calcium carbide residue and Glauber's salt as composite activators for fly ash-based geopolymer

Geopolymers are promising green binding materials with little carbon dioxide emissions during the production process. In this study, two waste by-products, namely, calcium carbide residue (CCR) and Glauber's salt (GS) were used to prepare fly ash (FA)-based geopolymer. The effects of parameters including the proportion and content of CCR and GS, water-solid ratio, and material fineness were systematically investigated. The reaction mechanism of activation was examined based on thermal behavior and phase transformation. The microstructure of the samples was evaluated by scanning electron microscopy and mercury intrusion porosimetry. Optimization of the parameters resulted in a maximum flexural strength of 6.0 MPa and compressive strength of 37.9 MPa. The results reveal that CCR and GS can react to form sodium hydroxide and calcium sulfate, which function as ac-tivators for geopolymers. As an important contribution, this study addresses the usage of the industrial waste products, namely, FA, CCR, and GS from economic and environmental perspectives.