Abstract
Concrete exposure to high temperatures induces thermo-hygral phenomena, causing water phase changes, buildup of pore pressure and vulnerability to spalling. In order to predict these phenomena under various conditions, a three-phase transport model is proposed. The model is validated on X-ray CT data up to 320 °C, showing good agreement of the temperature profiles and moisture changes. A dehydration description, traditionally derived from thermogravimetric analysis, was replaced by a formulation based on data from neutron radiography. In addition, treating porosity and dehydration evolution as independent processes, previous approaches do not fulfil the solid mass balance. As a consequence, a new formulation is proposed that introduces the porosity as an independent variable, ensuring the latter condition.
Highlights
Exposing concrete structures to fire can lead to spalling, a process where material violently breaks off of the surface
When concrete is exposed to high temperatures, dehydration and free water evaporation often exceed the rate of vapour migration, resulting in rising pore pressures
Data from thermogravimetric analysis, which is performed on ground up concrete in artificial atmospheres, are not suitable for deriving a constitutive equation of dehydration for compact specimens under high heating rates
Summary
Exposing concrete structures to fire can lead to spalling, a process where material violently breaks off of the surface. The novelty in this work is that the skeleton mass balance is solved along with the other balance equations, avoiding this error and resulting in one fewer constitutive equation This allows for dehydration descriptions that depend on the pore state, e.g., liquid water saturation or pore pressure, a significant extension compared to previous models. When using TGA data to model dehydration, the assumption that mass loss equates to water release only holds for aggregate types that are chemically and physically stable at high temperatures, such as quartzite or basalt. Noting that factors such as dehydration, chemical decomposition of aggregates, thermal strains and microcracking contribute to its increase Their actual description assumes the porosity to stay constant below 100 °C, three times the initial porosity above 800 °C and a cubic polynomial in the range between T ∈ [100 °C, 800 °C]:.
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call