PSI - Issue 28

Dimos Triantis et al. / Procedia Structural Integrity 28 (2020) 502–510 D. Triantis, I. Stavrakas, A. Kyriazopoulos, E. D. Pasiou, S. K. Kourkoulis / Structural Integrity Procedia 00 (2019) 000–000 7

508

2020b). From this point on the rate of increase of PSC becomes gradually lower until its maximum value (point E) is attained, almost 2 s before the macroscopic fracture of the specimen. Then the intensity of the PSC starts decreasing designating the onset of macroscopic crack propagation. The as above described time evolution of the PSC was systematically observed in all experiments of the present protocol. The data for characteristic specimens of the other three classes tested are shown in Fig.6. which is plotted exactly according to the manner adopted for Fig.5.

3000

4.8E-3

3 days

2000

3.2E-3

Axial strain

1000 PSC [pA]

1.6E-3

0

0.0E+0

1

10

100

1000

t f - t [s]

(a)

3.6E-3

3.6E-3

360

360

28 days

90 days

2.4E-3

2.4E-3

240

Axial strain 240

Axial strain

120 PSC [pA]

120 PSC [pA]

1.2E-3

1.2E-3

0.0E+0

0.0E+0

0

0

1

10

100

1000

1

10

100

1000

t f - t [s]

t f - t [s]

(b) (c) Fig. 6. The PSC for a typical specimen of the “3 days”- (a), the “28 days”- (b) and the “90 days” (c) -class, plotted versus the “time-to-failure” parameter, along a logarithmic scale. 5. Conclusions The electric activity in cement-mortar specimens under uniaxial compression was studied as a function of their age (time after settlement), in juxtaposition to the respective mechanical response of the specimens. For the latter one, and as it was expected, it was concluded that both the ultimate compressive strength (UCS) and the respective elastic modulus E, increase up to an age of about 28 days and then they remain almost constant. This is quantitatively depicted in Fig. 7a in which the average values of UCS and E, of the four classes of specimens tested, are plotted versus the age of the specimens. In fact, the differences for both UCS and E between the class of specimens of age 28 days and that of specimens of age 90 days are negligible. Concerning the electric activity, quantified in terms of either the maximum value of the PSC recorded or of the overall electric load (i.e., the PSC’s time integral) it was definitely concluded that for the specimens of early age (3 and