PSI - Issue 28

Angeliki-Eirini Dimou et al. / Procedia Structural Integrity 28 (2020) 1694–1701 A.-E. Dimou et al. / Structural Integrity Procedia 00 (2019) 000–000

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in width, and 20 mm in height (Fig. 1). Six specimens for the mechanical tests were prepared per each specimen type (cylindrical or prismatic). After 24 h, all specimens were de-moulded and placed in water tanks, where they were kept for 28 days. To study the electrical properties of the pastes, six prismatic specimens were produced having the same dimensions with the specimens from flexural testing with the addition of four metallic surfaces with dimensions 15 mm width x 30 mm height were placed vertically in the specimen as shown in Fig. 1.

Table 1. Mix recipes for the pastes in wt% and for constant ratio W/B = 0.55 Materials Blank paste

rGO reinforced paste

MWCNTsCOOH reinforced paste

NHL5

80 20

80 20

80 20

MK rGO

- -

0.15

-

MWCNTsCOOH

-

0.15

Fig. 1. Sample specimen for the electrical resistance tests

2.2. Methods 2.2.1. Mechanical tests

The monotonic compression tests were performed at a 300 kN Instron SATEC loading frame (Fig. 2 (left)). The crosshead displacement rate was kept constant and equal to 300 μm/min to achieve quasi-static conditions. The four point bending (flexural) tests were performed at a 10 kN MTS Insight testing machine (Fig.2 Errore. L'origine riferimento non è stata trovata. (right)). The loading span was 1/2 of the support span and the crosshead displacement rate was kept constant and equal to 0.001 mm/sec in order to achieve quasi-static conditions.

Fig. 2. Experimental setup for the compression (left) and the flexural (right) tests.

2.2.2. Electrical resistance measurements The electrical resistance was measured with the four-wire method and the specimens were dried in an oven for moisture removal (T = 60 o C for three days) before testing. In this method, the resistance measurement takes place by applying voltage to the specimen via the metallic probes. By passing a current through two outer probes and measuring