Alkali-activated materials are difficult to maintain strength under very high temperatures in the fire. But results are not available for those materials when subjected to sustained moderate temperature range (i.e. 60 °C–250 °C) which is a more common thermal condition in many engineering applications. In this paper, the mechanical and microscopic properties of alkali-activated fly ash-slag (AAFS) materials under sustained moderate temperature effects are studied. The microscopic properties are characterized by XRD, FT-IR, ²⁹Si NMR-MAS, MIP and SEM-EDS. The results show that AAFS is able to maintain the compressive strength even being treated under 250 °C for 28d. The microscopic characterizations indicate that N-A-S-H gel exhibits greater thermal stability than C-A-S-H and C-S-H gels. However, after the gel loses water under sustained temperature effect, N-A-S-H is hard to reorganize. In other words, when more N-A-S-H is produced due to the addition of more slag, the AAFS becomes more porous with looser microscopic morphology leading to lower compressive strength. It is also found that, after sustained moderate temperature treatment, the gel reorganizes and agglomerates into cluster-like particles, while the matrix becomes more uniform and compact. The sustained temperature helps refine the pore size and improve the volume of connected pores and super-macropores which is helpful to maintain the compressive strength of AASF. This study provides experimental and theoretical basis for the application of alkali-activated materials subjected to sustained moderate temperature effects.

碱活化材料在火灾中的极高温度下难以保持强度。但是，当这些材料处于持续的中等温度范围（即 60°C–250°C）时，这些材料无法获得结果，这是许多工程应用中更常见的热条件。本文研究了碱活化飞灰渣（AAFS）材料在持续中等温度作用下的力学和微观性能。通过XRD、FT-IR、²⁹ Si NMR-MAS、MIP和SEM-EDS对微观性质进行表征。结果表明，AAFS能够保持抗压强度甚至在 250 °C 下处理 28 天。微观表征表明 NASH 凝胶表现出比 CASH 和 CSH 凝胶更高的热稳定性。然而，凝胶在持续温度作用下失水后，NASH很难重组。换句话说，当由于添加更多的炉渣而产生更多的 NASH 时，AAFS 变得更加多孔，微观形态更松散，导致抗压强度降低。还发现，在持续的中温处理后，凝胶重新组织并聚集成簇状颗粒，而基质变得更加均匀和致密。持续的温度有助于细化孔径，提高连通孔和超大孔的体积，有助于保持 AASF 的抗压强度。