PSI - Issue 64

Sothyrak Rath et al. / Procedia Structural Integrity 64 (2024) 122–129 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

125

4

2.3. Core sample preparation and porosity evaluation The concrete core was extracted using a 5-mm coring bit. The coring location was selected based on the same criteria used for powder extraction. Two approximately cylindrical cores measuring 5 × 10 mm (diameter × height) were extracted from each specimen, as shown in Fig. 1(b). Some cores were inevitably smaller than the specified size owing to the challenges associated with the coring process. After extraction, the samples were D-dried for 24 h and their porosities were measured through the vacuum saturation method using the following process (ASTM C1202 22e1 (2022)). First, the cores were oven-dried at 105 °C for 48 h and then their dry mass m d (g) was recorded after cooling to 20 °C (normal condition) in a desiccator. Subsequently, the cores were vacuumized in a chamber under 90 kPa pressure for 3 h. Next, the water was pumped into the chamber, without removing the lid, until the samples were completely submerged. The vacuum process was employed again under the same pressure for 1 h. After that, air was allowed to enter the chamber, and the samples were soaked for 20 h. Finally, their saturated mass, m s (g), was recorded, and their porosities (ml/ml) were calculated as follows:

(2)

where ρ w (1 g/cm

3 ) is the water density and V (cm 3 ) is the sample volume calculated using the average of the three

heights and diameters of the cylindrical core.

2.4. F – T tests The prism specimens were subjected to F – T tests, following the JIS A1148 standard (method A) (JIS A1148 (2015)). The experimental setup and exposure conditions are shown in Fig. 2(a and b), respectively. The samples were placed in a rubber container containing tap water as the freezing solution, with the water level maintained 3 mm above their tops. Additionally, the tops and bottoms of the samples in the rubber container were interchanged after each measurement. During the exposure condition, the temperature was cycled between 7 and − 18 °C at a rate of 0.5 °C/min for a total duration of 240 min per cycle. After every 10 cycles, the durability factors of the samples were evaluated as follows (JIS A1148 (2015)):

(3)

where DF (%) is the durability factor, P n = ( f n / f 0 ) 2 × 100 (%) is the relative dynamic elastic modulus at the N th cycle. N is the number of cycles where P n falls below 60% or 300 cycles, whichever is lower. f n and f 0 (Hz) are the primary resonance frequencies of the deflection oscillation, measured using the JIS A1127 standard (JIS A 1127:2010 (2010)), at the N th and 0 th cycle, respectively, and M is the total number of cycles, which was 300. The F – T exposure of each specimen ended when P n dropped under 60% or N reached 300. Two specimens were used to obtain the average durability factor of each concrete sample.

a

b

5 mm

5 mm

Fig. 1. (a) Powder sample used for the MIP test; (b) Concrete core.