Laser scanning confocal microscopy characterization of water repellent distribution in a sandstone pore network

Abstract

In the present work, we propose the use of the Laser Scanning Confocal Microscopy (LSCM) to determine the effect of water repellents on rock's pore-network configuration and interconnection. The rocks studied are sandstones of Miocene age, a building material that is commonly found in the architectural heritage of Tunisia. The porosity quantitative data of treated and untreated samples, obtained by mercury porosimetry tests, were compared. The results show a slight decrease in total porosity with the water repellent treatment, which reduced both microporosity and macroporosity. This reduction produced a modification in pore size distribution and a shift of the pore access size mode interval toward smaller pore diameters (from the 30-40 microm to the 20-30 microm intervals). The water repellent was observed in SEM images as a continuous film coating grain surfaces; moreover, it was easily visualized in LSCM, by staining the water repellent with Epodye fluorochrome, and the coating thickness was straightforwardly measured (1.5-2 microm). In fact, the combination of mercury intrusion porosimetry data and LSCM observations suggests that the porosity reduction and the shift of the pore diameter mode were mainly due to the general reduction of pore diameters, but also to the plugging of the smallest pores (less than 3-4 microm in diameter) by the water repellent film. Finally, the LSCM technique enabled the reconstruction of 3D views of the water repellent coating film in the pore network, indicating that its distribution was uniform and continuous over the 100 microm thick sample. The LSCM imaging facilitates the integration and interpretation of mercury porosimetry and SEM data.

Background-Free Deep Fluorescent Imaging of a Pore Architecture in Geomaterials Based on Magnetic Upconversion Nanoprobes

“…In LSCM imaging, the vertical depth of the optical section is in excess of 30 μm, and it can even reach ∼150 μm in some quartz sandstones. A bunch of geological materials such as sandstone, carbonates, − mudstones (shales), marble, and even many engineering materials such as polymer membrane, concretes, , and catalysts have been visualized by LSCM. Additionally, many geological applications, including fluid transport in geological materials and brittle failure processes as well as stress-induced damage in rocks, have been studied based on the LSCM imaging data of the pore architecture.…”