Towards a single-phase mixed formulation of refractory castables and structural concrete at high temperatures

TL;DR

This paper develops a numerical mixed formulation model for high-temperature behavior of refractory castables and structural concrete, focusing on stability, sensitivity, and applicability to complex scenarios, validated by 2D mesoscale simulations.

Contribution

It introduces a simple, adaptable mixed formulation model for high-temperature concrete behavior, including sensitivity analysis and validation against experimental data.

Findings

Permeability and thermal conductivity are key parameters affecting simulation results.

Unidimensional models are insensitive to sorption isotherm interpolation choices.

2D mesoscale simulations align well with experimental observations.

Abstract

Structural materials are broadly used in applications such as nuclear vessels, high-temperature processes, and civil construction. Usually, during their placing and lifespan, they may present free or chemically bonded liquid phases in their structure, demanding careful attention when exposed to high heating rates. Their behavior in such conditions is a challenging problem as it comprises numerous highly nonlinear properties (not easily measured via experimental tests), strongly coupled equations and unreliable experimental benchmarks. Nonetheless, such simulations are of great interest. This work aims to provide a numerical study, checking whether its solution indeed converges and yields reliable results. Additionally, as the model needs several input parameters, this work conducts a sensitivity analysis and also assesses its applicability to more complex scenarios, as such issues remain open in the literature. In order to do that, a simple model that can be easily adapted for mixed formulations and complex geometries was proposed. It was found out that when considering unidimensional models the choices regarding the interpolation of the sorption isotherms are not essential to the numerical stability of the system. Besides that, the permeability and thermal conductivity of the material are the most important parameters that affect the simulation results of pressure, temperature and evaporable water content profiles. Finally, the 2D mesoscale simulation of concrete with polymeric fibers (based on the mixed formulation of the problem) yielded results that agreed with experimental observations. Thus, the model proposed herein can provide a solid base for future works and also important insights towards simpler methodologies.