Direct monitoring of drying kinetics of building limestones using cavity ring-down spectroscopy

Enchanced understanding of the drying kinetics of building materials is important to explain durability and improve conservation. Cavity ring-down spectroscopy has been demonstrated to be an effective method to investigate drying kinetics, and is here applied to investigate the drying behaviour of five commonly used building limestones, and one sandstone. Although the time period for phase I drying increases with increasing porosity, the constant mass flux remains essentially unchanged. This is not so for phase II drying diffusivities which are reported for Portland Whit Bed limestone, Portland Base Bed limestone, Clipsham limestone, Bath limestone, Savonnières limestone and Stoke Hall sandstone, and are found to be in the range 3.0 – 6.5 ×10−9 m2 s−1 at 25 ℃. Differences in the phase II diffusivity do not appear to be solely controlled by porosity. Activation energies associated with phase II drying for Clipsham limestone, Portland Base Bed limestone and Stoke Hall sandstone, are determined to be 31.9±1.8, 29.4±1.4 and 27.1±2.2 kJ mol−1, respectively.