Developing　high-performance,　low-carbon　fire-resistant　construction　materials　is　critical　for　enhancing　building　safety　against　fire　hazards　while　reducing　environmental　impact.　This　study　investigates　the　role　of　silicate　modulus　(Ms=SiO₂/Na₂O　molar　ratio,　0.75–1.75)　in　improving　the　thermal　stability　of　alkali-activated　slag　paste　(ASB)　incorporating　12　%　municipal　solid　waste　incineration　bottom　ash　(MSWI-BA)—a　context　rarely　addressed　in　prior　Ms　optimization　research　on　alkali-activated　binders.　Comprehensive　experimental　(macroscopic　properties:　workability,　thermal　performance　at　25–1000　°C;　microstructural　characterization:　XRD,　TG,　FTIR,　SEM-EDS,　MIP)　and　molecular　dynamics　simulation　methods　were　employed.　Results　show　Ms=　1.5　is　optimal,　yielding　the　highest　residual　compressive　strength　at　400　°C.　Unlike　prior　studies　focusing　on　ambient　properties　of　pure　slag/fly　ash　systems,　this　work　links　Ms　to　high-temperature　performance　in　MSWI-BA-based　ASB:　elevating　Ms　leverages　MSWI-BA＇s　Al-containing　components　to　promote　C-A-S-H　polymerization　(lower　Ca/Si,　higher　Al/Si　than　conventional　slag　systems),　densifying　the　matrix　and　enhancing　thermal　stability.　Molecular　dynamics　simulations　further　clarify　atomic-scale　mechanisms—balanced　Al/Si　ratios　mitigate　thermal　deformation　and　boost　elastic　modulus,　directly　correlating　with　residual　strength.　This　study　advances　beyond　existing　research　by　targeting　MSWI-BA-based　systems,　focusing　on　high-temperature　performance,　and　providing　multiscale　insights,　establishing　Ms　optimization　as　a　design　approach　for　fire-resistant　alkali-activated　composites.　©　2025　Elsevier　Ltd