A microdestructive method using dye-coated-probe to visualize capillary, diffusion and evaporation zones in porous materials

Abstract

The vaporization plane, a narrow zone of subsurface evaporation often present in porous rocks, separates the region where water flows due to capillary forces from the dry zone where moisture moves in gas phase only. The knowledge of its depth and geometry is critical for estimating water flux in rock-atmosphere interphase, for understanding moisture distribution and for localization of damaging salt crystallization. Yet, an easy-to-use method applicable in the exterior has been missing. This strongly limits interpretation of moisture-related measurements as moisture content differences in the above-mentioned zones are often immeasurable by currently used field techniques. We have introduced a new micro-destructive method to measure the vaporization plane depth using an instrument consisting of a rod, adhesive, and dye powder, reacting with moisture, that is inserted into porous materials in 2 mm diameter holes. We tested different rods, adhesives, and dyes, and the best combination of these has been used in >500 experiments to determine the vaporization plane depth in porous rocks and building materials. The knowledge of vaporization plane depth enables more reliably to interpret the moisture and suction data obtained from numerous existing techniques. This new uranine-probe method should be thus of interest to many scientific disciplines: evaporation, unsaturated hydrology, weathering, or geobiology.