Thermohydraulic spalling mechanisms in concretes with different binders without and with PP fibers exposed to fire: An experimental and numerical analysis

目前的研究表明，粘结剂体系的类型对混凝土的火灾剥落行为有重要影响。例如，研究表明，与波特兰和波特兰石灰石水泥的混凝土相比，波特兰高炉水泥的混凝土更容易剥落。由于建筑业有针对性地减少二氧化碳排放，以及与之相关的含有惰性和活性水泥成分的波特兰复合水泥的使用增加，在这种情况下，热液压过程所起的作用的问题就提出了。因此，研究项目的目的是深入了解硬化水泥膏体的粘合剂特异性脱水机制，混凝土热暴露过程中形成的微裂缝网络及其变化，以及由此产生的热液输送过程。为此目的计划的实验室测试范围从小型部件的着火测试到对不含PP纤维和含PP纤维的不同类型混凝土的干燥行为和裂缝形成过程的深入分析。数值模拟的目标是描述热致微裂纹的形成，同时考虑到初始裂纹的形成和相互作用的输运过程。为此，设想了用于预测所研究混凝土的水热力学行为的多物理模型与用于表征几个空间尺度上的损伤和运输过程的子模型的组合。在试验结果和验证模型的基础上，特别参考热液机制，对高炉水泥和精选波特兰复合水泥混凝土的剥落行为进行了评价和预测。对于易剥落的混凝土，还对裂缝诱导效果和添加pp纤维降低剥落倾向的有效性进行了评价，并作为所使用水泥类型的函数。

Current investigations show that the type of binder system has a major influence on the fire-induced spalling behavior of concrete. For example, investigations show that concretes with Portland blastfurnace cements tend to spall more strongly as compared to concretes with Portland and Portland limestone cements. Due to the targeted reduction of CO2 emissions in the construction industry and the associated increased use of Portland composite cements with inert and reactive cement constituents, the question of the role played by thermohydraulic processes raises in this context. The aim of the research project is therefore to gain insights into the interaction of binder-specific dehydration mechanisms of the hardened cement paste, the microcrack network that forms and its changes during thermal exposure of the concrete, and the resulting thermohydraulic transport processes. The spectrum of laboratory tests planned for this purpose ranges from fire tests on small-format components to in-depth analysis of the drying behavior and the crack formation processes in the different types of concrete without and with PP fibers. The numerical simulations pursue the goal of describing the thermally induced microcrack formation, taking into account the initial crack formation and the interacting transport processes. For this purpose, a combination of multiphysical models for predicting the hydro-thermo-mechanical behavior of the investigated concretes with submodels for characterizing the damage and transport processes on several spatial scales is envisaged. Based on the experimental results and the validated models, the spalling behavior of concretes with blast-furnace and selected Portland-composite cements is evaluated and predicted with special reference to the thermohydraulic mechanisms. For the spalling-prone concretes, the crack-inducing effect and the effectiveness of adding PP-fibers to reduce the spalling tendency are additionally evaluated as a function of the cement type used.