Modeling of carbonation, de-carbonation and re-carbonation processes of structural concrete subjected to high temperature heating

Abstract

When structural concrete is exposed to a fire, various changes in chemical and mechanical properties proceed. The concentration of carbon dioxide CO2 rises to about 15% depending on the situation of fire accidents accompanying combustion of carbide. The self-healing of damaged concrete is expected by absorbing CO2 after fire. Thus, consideration of high temperature heating for carbonation is indispensable for performance assessment of structural concrete. This paper proposes a multi-scale thermo-chemo-physics model for carbonation, de-carbonation and re-carbonation processes during and after high-temperature heating. The proposed integrated model is experimentally validated by using the thermo-gravimetry experiments of cement paste and the strength of mortar composites immediately after high-temperature heating and after post-fire-curing. The CO2 concentration and the humidity are experimentally changed as the thermodynamic boundary conditions for wide-range verification and validation. The compressive strength is treated not as the material property but the computed structural capacity of a cylindrical solid in which the temperature, hydration degree and carbonation develop non-uniformly. The proposed model can capture the tendency of experimental results and allows practically reasonable assessment of fire-damaged and moist-cured concrete as a multi-scale composite.