Thermal damage assessment of cementitious composites is essential for evaluating post-fire health conditions of the engineering structures, as well as the basis for reinforcement and repair after fires. Fibers and fly ash are widely used in cementitious composites due to their excellent properties. However, quantifying and predicting the thermal damage of hybrid fibers reinforced cementitious composites blended with fly ash at high temperatures is still inexplicit. Hence, this study aims to realize multiscale prediction of thermal damage for hybrid fibers reinforced cementitious composites blended with fly ash at high temperatures. First, the volumes of the phase compositions during hydration and dehydration are calculated by the hydration of cement and fly ash and the dehydration of hydration products. Then, a multiscale model is established to predict the thermal damage of hybrid fibers reinforced cementitious composites and verified by the experimental data. At last, the temperature field of tunnel lining structure in fires is obtained by numerical modeling and employing it to predict thermal damage at different thicknesses and moments. Results show that the heating rate determines the dehydration degree of hydration products and the volumes of the phase composites at high temperatures. The proposed multiscale model can reflect the thermal microcracking of cement paste, the interfacial thermal damage between aggregates and the cement paste, and the deterioration of elastic modulus of fibers. After three hours of exposure to fires, serious damage appears at the surface and the thickness of 2 cm and 5 cm of the lining, while there is nearly no damage at a thickness of 30 cm or more.

中文翻译：

---

高温下掺有粉煤灰的混合纤维增强水泥基复合材料热损伤的多尺度预测

水泥基复合材料的热损伤评估对于评估工程结构火灾后的健康状况至关重要，也是火灾后加固和修复的基础。纤维和粉煤灰因其优异的性能而广泛应用于水泥基复合材料中。然而，量化和预测混合纤维增强水泥基复合材料在高温下的热损伤仍然不明确。因此，本研究旨在实现混合纤维增强水泥基复合材料在高温下的热损伤的多尺度预测。首先，通过水泥和粉煤灰的水化以及水化产物的脱水计算水化和脱水过程中相组成的体积。然后，建立了多尺度模型来预测混合纤维增强水泥基复合材料的热损伤，并通过实验数据进行了验证。最后，通过数值模拟得到火灾时隧道衬砌结构的温度场，并利用其预测不同厚度和时刻的热损伤。结果表明，加热速率决定了高温下水化产物的脱水程度和相复合物的体积。所提出的多尺度模型可以反映水泥浆体的热微裂、骨料与水泥浆体之间的界面热损伤以及纤维弹性模量的恶化。受火3小时后，表面及2厘米、5厘米厚度的内衬出现严重损坏，而30厘米及以上厚度几乎没有损坏。