Limestone impact on properties, microstructure and CO2 emissions of waste glass-activated blast furnace slag cements

Utilizing industrial and urban solid wastes is crucial for developing low-carbon cements. This study proposes a novel method to integrate recycled glass and blast furnace slag (BFS) into alkali-activated cements. It also investigates the influence of pulverized limestone (LSP), as a readily available cost-efficient partial replacement for BFS. The activators were alternative solid sodium silicates (SSWG), prepared by thermochemical treatment of soda lime silica waste glass in NaOH solutions. SSWG had moduli (Ms) SiO₂/Na₂O = 1 and 1.5 and were added at 6 and 8%wt. Na₂O relative to the mass of BFS + LSP. After 3 years, pastes of 100% BFS at 20 °C yielded the highest compressive strength of 78 MPa, while incorporating 50–75% LSP resulted in 61–42 MPa, depending on the Ms and %Na₂O. Microstructural analysis via XRD, thermal analysis, SEM, and ²⁷Al and ²⁹Si NMR, indicated the formation of cementitious products like C–S–H, C–(A)–S–H, hydrotalcite, natron, gaylussite and pyrssonite. LSP increased the chain length in C–(A)–S–H-type products and affected the Al uptake by a seeding effect. The eco-efficiency analysis showed that the studied cements emit 45–74% less kgCO₂.eq per ton than Portland cement.