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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with an epoxy resin. Then, the cylinders were submerged in water for 72 h. After submersion, the cylinders were dried in an oven at 40 °C until the mass loss was lower than 0.1% over a 24 h period. The dry specimens were placed on spacers in a container with water, so that the water level was 10 mm higher than the bottom of the specimens. The samples were weighed after 0.5, 1, 2, 3, 4, 5, 6 and 24 hours and then every 24 hours during the first week of the experiment. After one week, the samples were weighed weekly for a total duration of 1 month. Before every measurement, the excess water on the bottom of the specimen was removed with a damp cloth. For every mix, 3 cylinders were tested. 3.2. Water vapour diffusion Water vapour diffusion was measured using the cup method (Alderete et al., 2018; Feng et al., 2015), which is an adaptation of the standard NBN EN ISO 12572 (Standardization, 2016). In order to do this, cores with a diameter of 53 mm were drilled from the concrete slabs and cut into slices with a height of approximately 10 mm. After cutting, the thickness of the slices was measured and they were placed in a climate-controlled room with a temperature of 20 °C and a RH of 60 % for 1 month to have a similar RH in all samples. After 1 month of conditioning, the circumference of the slices was coated with an epoxy resin so that no moisture exchange with the environment was possible through the circumference, ensuring an unidirectional moisture flow through the sample. Subsequently, the slice was glued on a cup so that the concrete slice acted as a barrier between the environment and the air inside the cup. The RH inside the cup was maintained constant using a hygroscopic salt. A saturated salt solution (a solution with excess of salt) is able to keep a constant RH by absorbing and releasing water into the environment. In this research, two hygroscopic salts were used, sodium chloride (NaCl) and lithium chloride (LiCl). The corresponding RH for both salts at a temperature of 20 °C is given in Table 2, according to the standard NBN EN ISO 12571 (Standardisation, 2021). The cups were placed in a climate-controlled room at 20 °C and > 95% RH, creating a moisture gradient (MG) between the environment (RH out ) and the air inside the cup (RH in ). The obtained moisture gradient for each salt is given in Table 2.

Table 2. Relative humidity (RH) and moisture gradient (MG) of saturated salt solutions. Salt RH [%] MG [%] Sodium chloride (NaCl) 75.5 19.5 Lithium chloride (LiCl) 11.3 83.7

A schematic overview of the setup is shown in Fig. 1. For each mix and each saturated salt solution, 5 concrete slices were tested. The mass of the cups was weighed at regular time intervals for a duration of 6 months.

Fig. 1. Schematic overview of the cup method for water vapour diffusion.