**2. Material and Sample Preparation**

Concrete cylinders (around 140 mm diameter) cored from tunnel voussoirs of the HADES URL (the Belgian Underground research laboratory) were provided by ON-

**Citation:** Lamouchi, T.; Levasseur, S.; Potier, L.; Dubois, T.; Skoczylas, F. About Gas Permeability and Diffusion through Concrete. *Mater. Proc.* **2023**, *13*, 42. https://doi.org/ 10.3390/materproc2023013042

Academic Editors: Katarzyna Mróz, Tomasz Tracz, Tomasz Zdeb and Izabela Hager

Published: 7 March 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

DRAF/NIRAS. They were then re-cored into small rectified cylinders with a diameter of 65 mm and height of 50 mm. Such a height was considered to be enough for permeability and diffusion measurements, as it is more than three times the maximum aggregate size (14 mm). The concrete composition as provided by ONDRAF/NIRAS is presented in Table 1 below.

**Table 1.** Concrete composition.


Four samples were prepared, and their porosity was measured with the classical vacuum and weighing techniques [1]. The samples were dried at a temperature of 105 ◦C until the mass was constant. The results gave a mean porosity of 12.5%.

#### **3. Experimental Setup and Experimental Conditions**

Two different setups were used: one for permeability measurements and one for gas diffusion. Gas-permeability measurements are quite usual in our lab, and they did not require any new design. This was not the case with diffusion tests, which required the performance of a new design.
