Alkali‐activated waste glass (AA‐WG) has received much attention because to its high mechanical properties achieved with low energy demand. However, AA‐WG exhibits low stability, including volume expansion, porosity increment, and a reduction in compressive strength. Enhancing the stability of AA‐WG could improve its commercial viability and expand its range of applications. Therefore, this study aims to evaluate the role of calcite CaCO3 (CC) and magnesite MgCO3 (MC) in enhancing the physicomechanical properties and phase composition of AA‐WG at elevated temperatures. The proposed strategy includes replacing WG with different contents of CC and MC, followed by activation with a 4 M NaOH solution and curing at 100°C for 24 h. The hardened samples were then exposed to 800°C for a 2 h holding time to evaluate the thermal stability of the AA‐WG, AA‐WG‐CC, and AA‐WG‐MC mixtures. The results demonstrated that increasing the CC content up to 50 wt.% significantly enhanced the compressive strength of the AA‐WG when cured at 100°C, while the incorporation of MC caused a negative effect. Surprisingly, an opposite trend was observed at a higher temperature of 800°C, where the samples containing MC exhibit better mechanical and physical performance compared to those with CC. The variation in the type, composition, and weight loss upon ignition of the carbonate‐based minerals significantly influenced the stability and phase composition of the thermally exposed AA‐WG. Although the sample with 50 wt.% MC showed higher volume shrinkage, it demonstrated higher compressive strength (~82 MPa) at 800°C than the sample with 50 wt.% CC (~7 MPa). This difference can be attributed to the formation of diopside CaMgSi2O6 and forsterite Mg2SiO4, which have higher crystallinity, specific gravity, and hardness compared to wollastonite CaSiO3 and the tri‐calcium silicate phases Ca3SiO4.
