PSI - Issue 42

E. Tziviloglou et al. / Procedia Structural Integrity 42 (2022) 1700–1707 Tziviloglou et al. / Structural Integrity Procedia 00 (2022) 000 – 000

1703

4

f ( ) = 3 ( ) 1/2 (1.99 − ∙(1− )∙(2.15−3.93 +2.7 ( ) 2 ) (2+4∙ )∙(1− ) 3 2

(2)

Where P max is the ultimate mechanical load, S is the span of the specimen, B is the width of the specimen, W is the height of the specimen, and α is the depth of the notch. 2.2.2. Electrical impedance measurements EIS measurements were used to evaluate the resistivity changes of cementitious matrices reinforced with GnPs. The tests were performed on triplicates. To avoid significant moisture changes in the inner mass of the examined specimens that could significantly affect the experimental results, the specimens used for the EIS measurements were tested in saturated surface dry condition. By this means, the saturation was kept to a constant level, and the distraction of the conductivity caused by moisture variations during the EIS measurements was prevented. Each measurement lasted approximately 3 minutes. EIS measurements were conducted using Dielectric Thermal Analysis System (DETA-SCOPE ® , ADVISE), as shown in Fig. 2, by applying an alternate signal (amplitude 1 V, and frequency range 1 Hz - 0.391 MHz). The magnitude of impedance and the phase angle were recorded by the data acquisition software of the system. Out of the ten scans that were recorded per specimen, only the fifth scan was considered for the further investigation of the electrochemical features of the mixtures.

Fig. 2. Experimental set-up for EIS measurements.

3. Results and discussion 3.1. Fracture toughness

Fig. 3 shows the average fracture toughness of 28-days-old cement nanocomposites. Overall, fracture toughness tends to increase for the nano-reinforced specimens compared to the reference ones. The maximum increase was shown by the two mixtures with the lowest GnPs concentrations (M-0.05 and M-0.10) and it ranged between 24 % and 29 %, with M-0.05 exhibiting the highest value. Then, the average K Ic values tends to decrease for the mixtures with higher GnPs contents, i.e., 0.2 wt% and 0.4 wt%, although without reaching the reference mixture value. The observed mechanical response, which demonstrates an initial improvement for mixtures with lower GnPs concentrations, and then a gradual decrease as the content of the nanoparticles increases, has been previously reported in studies with similar GnPs contents, such as Baomin et al. (2019), Chougan et al. (2019) and Tao et al. (2019). The