Modeling Moisture Transport from a Portland Cement-Based Material During Storage in Reactive and Inert Atmospheres

Abstract

Monolithic samples of a cement mortar were stored in reactive (100% CO₂) and inert (100% N₂) atmospheres at three levels of relative humidity (23, 48, and 98%). Atmospheric conditions were monitored and the mass of each sample was measured periodically over a period of 88 days. Carbonation depth of split samples was delineated using 1% phenolphthalein solution. In addition, a solid–liquid isotherm was developed by drying smaller monoliths over eight hygroscopic salt solutions in 100% N₂ until a constant mass was obtained. Isotherm experimental data was used to parameterize a two-regime moisture transport model based on previously developed drying approaches. This first-order model accounts for both funicular moisture transport and isothermally controlled drying in a fixed porous matrix. Kinetic drying data for the cement mortar was described adequately by simulation of mean relative saturation as a function of drying time and external relative humidity. Comparison of moisture transport in the inert atmosphere to that in the reactive atmosphere indicates that matrix drying had a substantial effect on the carbonation depth; however, drying was seemingly independent of the carbonation process.

Keywords:

• Moisture transport
• Modeling
• Portland cement
• Drying
• Carbonation

Notes

^aIn some literature,[6] this state is referred to as “irreducible saturation.” However, the term “irreducible saturation” has also been used to describe the point where the liquid phase becomes discontinuous.[30]

^bMolar volume.[35]