Effect of Water Sorption on Carbonate Rock Expansivity

Abstract

Length change experiments on carbonate rock samples indicate that the thermal coefficient of expansion (contraction) from normal room temperature to below freezing is a function of the sorptive characteristic of the rock. The highly adsorptive rocks, i.e. those adsorbing more than 40% of their water from near 100% humidity atmosphere, show an increased thermal contraction coefficient in the saturated state over their dry state. The low adsorptive rocks have the same thermal expansion coefficients either in a dry or saturated state.The highly adsorptive rocks expand isothermally upon saturation. The average isothermal expansion of a group of nine rocks was equivalent to the dry thermal expansion of a 78 °C temperature change. The low adsorptive rocks showed a small net isothermal contraction upon wetting.The results indicate that the thermal coefficients of expansion obtained below the 100 °C range must specify the saturation conditions of the rock, and may differ for dry and saturated rock. A mechanism of weathering of highly adsorptive rocks is suggested, based on isothermal expansion and contraction of these rocks in dry and saturated states respectively. If confined, as in concrete, such rocks may generate destructive expansive forces upon wetting.