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

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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.