Table 2.

NT analysis results for the AE and electrical resistance time series of mortar enriched with iron oxide and Luserna stone specimens tested (cf. Figure 3).

Specimen (cf. Figure 3)	Material †	Time of Approach to Criticality (s)
		$\mathbf{NT}\mathbf{Analysis}\mathbf{of}\mathbf{AE}\left({\mathit{A}}_{\mathbf{m}\mathbf{a}\mathbf{x},\mathit{k}}{}^2\right)$	$\mathbf{NT}\mathbf{Analysis}\mathbf{of}\mathbf{Resistance}\left(\left|{\mathit{W}}_{\mathit{k}}\right|\right)$
(a)	CM	655–665	232–272
(b)	CM	934.83	328–580 ††
(c)	LS	964.25	844
(d)	LS	790.32 & 900.65 ‡	884 ‡‡
(e)	LS	866.54	508

^† CM: Cement mortar/LS: Luserna stone. ^†† No approach to criticality was found for the dissipated energy (W) of specimen (b). However, the reported approach to criticality was identified after the NT analysis of power ($\frac{dW}{dt}$). ^‡ NT analysis of specimen’s (d) AE yielded two times of approach to criticality: 790.32 s and 900.65 s, for low and high threshold, ${\left(A_{\max }{}^2\right)}_{Th}$, values, respectively. Note that the later approach to criticality (on 900.65 s) is more important as a possible precursor. ^‡‡ The same time of approach to criticality was also identified after the NT analysis of power ($\frac{dW}{dt}$).