Vapor Pressure Modeling of High-Strength Concrete at High Temperatures

High-strength concrete (HSC) is susceptible to spalling at high temperatures. One reason for this is that vapor pressure builds up in concrete and plays a key role in spalling under certain conditions. However, vapor pressure modeling is still insufficient so far. Steam tables, which bear the actual states of water steam, have never been applied in vapor pressure modeling. In this paper, a meso-scale vapor pressure modeling approach using steam tables is presented. The effects of the thermal decomposition of the cement paste matrix and the vapor phase transfer driven by the gradient of vapor pressure are considered. By applying the theory of poromechanics, the Biot modulus is deduced and the mechanical effect of vapor pressure is modeled. Finally, the distribution and mechanical effect of vapor pressure in a 100 mm (3.94 in.) HSC cube specimen exposed to fre are modeled, and the applicability and effectiveness of the model are presented. Keywords: high-strength concrete; high temperature; modeling; spalling; vapor pressure.