Alkali-activated ultra-high performance concrete, Alkali content, Silicate modulus, Mechanical properties, Elevated temperature, Materials of engineering and construction. Mechanics of materials, TA401-492

This study comprehensively examines the combined effects of alkali content and silicate modulus on the mechanical properties, moisture transport behavior, and microstructural evolution of alkali-activated ultra-high performance concrete (A-UHPC) under both ambient and elevated temperatures. Unlike previous studies that focused separately on ambient or high-temperature performance, this research offers a holistic evaluation of the manner in which these parameters influence A-UHPC across varying thermal conditions. Experimental evaluations, including mechanical strength tests, moisture transport analysis, and microstructural characterization (SEM, TGA, XRD, FTIR), demonstrate that the optimal synergy of 6 % alkali content and a 1.6 M silicate modulus results in superior compressive strength (132.60 MPa), reduced porosity, and enhanced durability. At elevated temperatures, this formulation retains structural integrity up to 400℃ but experiences substantial deterioration at 800℃ due to phase transformations and microstructural degradation. These findings contribute critical insights for optimizing A-UHPC to achieve enhanced mechanical performance and fire resistance, laying a foundation for its broader application in extreme environments.