This paper studies the evolution of elastic and thermal properties of cementitious composites containing micro-size lightweight fillers after exposure to elevated temperatures (up to 800 °C). A multiscale investigation is carried out to study the thermal degradation of cementitious composite materials at multiple scale levels: at cement past level, the dehydration kinetics of cement hydrates (i.e., C–S–H, CH and aluminate hydrates) and development of microcracks are studied as functions of exposure temperatures. The damage mechanism of the inclusion phases and damages within the interfacial transition zone (ITZ) under elevated temperature are also investigated. In addition, the change of mechanical (i.e., elastic moduli, compressive strengths) and thermal (thermal conductivities) properties are measured as functions of the exposure temperature. Based on the experimental studies, a multiscale thermal degradation model is developed where the thermal degradations of cement paste (including water composition, porosity, and solid phase changes), inclusion phases, and the interfaces are captured through a multiscale sub-stepping homogenization scheme. The thermal degradation model is validated through multiple sets of experimental data. Finally, the influence of key parameters including the particle size distribution of the inclusions, the chemical composition, as well as the effects of ITZ damage are studied.

本文研究了含有微型轻质填料的水泥复合材料在高温（高达800°C）下的弹性和热性能的演变。进行了多尺度研究以研究水泥复合材料在多个尺度上的热降解：在水泥过去的水平下，水泥水合物（即C–S–H，CH和铝酸盐水合物）的脱水动力学以及微裂纹的发展是作为暴露温度的函数进行研究。还研究了高温下夹杂物相的破坏机理和界面过渡区（ITZ）内的破坏。另外，测量机械（即，弹性模量，抗压强度）和热（导热率）性质随暴露温度的变化。基于实验研究，开发了一种多尺度热降解模型，其中通过多尺度亚步均化方案捕获水泥浆的热降解（包括水成分，孔隙率和固相变化），夹杂物相和界面。通过多组实验数据验证了热降解模型。最后，研究了关键参数的影响，包括夹杂物的粒度分布，化学成分以及ITZ损伤的影响。并通过多尺度子步均化方案捕获接口。通过多组实验数据验证了热降解模型。最后，研究了关键参数的影响，包括夹杂物的粒度分布，化学成分以及ITZ损伤的影响。并通过多尺度子步均化方案捕获接口。通过多组实验数据验证了热降解模型。最后，研究了关键参数的影响，包括夹杂物的粒度分布，化学成分以及ITZ损伤的影响。