Microscopic Localisation of Hydrophilically Oriented Pore Bodies and Throats in Hydrophobised Porous Materials

Abstract

Internal insulation of the building envelope is a prime topic in building physics, due to the risk of moisture problems that this technique entails. As a remedy to these problems, the application of a water-repellent agent, which reduces the amount of absorbed wind-driven rain, has become popular in recent years. When such an agent is applied on a building material, it penetrates the pore network of the material, hereby attaching itself to the pore surfaces and rendering them hydrophobic. It is generally believed that some smaller pores can remain hydrophilic due to the inability of the agent to enter. An in-depth microscopic investigation towards these hydrophilic pores, however, has never been performed. Since direct visualisation of the polymer chains was proven impossible, this paper locates the hydrophilic (parts of) pores in a material, hydrophobised with 3 different water-repellent agents, by imaging the moisture storage at pore level using X-ray computed tomography images at different stages of the desaturation process. While completely hydrophilic pore bodies and throats are not found in the studied material, water storage remains possible in hydrophilic corners of hydrophobised pore bodies and throats. These corner islands are less present than in hydrophilic media and do not form a continuous liquid flow path. Therefore, they provide possible locations for little moisture storage but do not contribute notably to moisture flow.