PSI - Issue 64

Laurena De Brabandere et al. / Procedia Structural Integrity 64 (2024) 97–104 Laurena De Brabandere et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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3.3. Gas permeability (CEMBUREAU method) Gas permeability was tested based on a RILEM recommendation (Andrade et al., 1999) using the CEMBUREAU permeameter. In order to do this, cores with a diameter of 150 mm were drilled from the concrete slabs and a disc with a height of 50 mm was cut from the center of the core. Since the presence of moisture in the pores will have an effect on the measured permeability, the specimens were preconditioned with a procedure based on the work of Carcassès (2002) and tested at 3 different saturation degrees. First of all, the specimens were dried at 60 °C until a constant mass (< 0.1 m% over 24 h) was achieved. To limit the damage to the microstructure, it was chosen to initially dry the specimens at 60 °C instead of 80 °C, which was used in the research of Boel (2007) and Gruyaert (2011). Once the specimens were dry, they were vacuum saturated. Then, the specimens were weighed under water (m w ) and saturated (m sat ). After weighing, the circumference of the discs was sealed with aluminium foil to prevent radial moisture transport and they were dried in the oven at 60 °C for 24 hours. After 24 hours, the samples were wrapped in aluminium foil and again placed in the oven at 60 °C for 24 hours to facilitate a homogeneous moisture distribution in the sample. Then, the covered specimens were placed in a climate-controlled room at 20 °C and 60 % RH to cool down for 24 hours before removing the foil and performing the permeability measurements. After the first measurement, the specimens are dried again following the same procedure at 60 °C before performing the second permeability measurement and then again at 105 °C before the last permeability measurement. This protocol makes it possible to do permeability measurements at 3 different saturation degrees. The mass of the specimens was determined before each of the three permeability measurements and denoted as m 1 , m 2 and m 3 . For the measurements of the gas permeability, the specimens were placed in the permeameter cells (Fig. 2) and the rubber tubes surrounding the specimens were pressurized to avoid leakage of the oxygen gas. Subsequently, a pressure of 3 bars was applied using oxygen gas and this was maintained for 30 minutes to establish a steady-state regime. After 30 minutes, the flow rate was measured through the flow meters containing soap water (see Fig. 2). This procedure was repeated at pressure levels of 4 and 5 bar. For each mix, 4 specimens were tested. Therefore, two cells, instead of 3, were connected to the device, so two specimens could be tested at the same time. The flow measured in the flow meters is therefore a mean flow through the two specimens.

Fig. 2. Test setup gas permeability (CEMBUREAU method).

The different saturation degrees were calculated using formula (1). = − 3 − 3 The gas permeability coefficient, k a in m

(1)

2 , was calculated using formula (2), where Q is the flow rate [in ml/s], L is the height of the specimen [in m], P 2 is the applied pressure [in bar], P 1 is the atmospheric pressure ( ≈ 1 bar) and A is the cross-sectional area of the specimen [in m 2 ].