Acoustic Emission Waves Propagation in Rubberized Concrete under Special Monitoring Conditions

This study investigates the change in the acoustic emission (AE) parameters emitted in rubberized concrete under abrasion action at a sub-freezing temperature ($-20°\mathrm{C}$). Seven concrete mixtures were developed with two coarse-to-fine aggregate ratios (C/F) (2.0 and 0.7), various crumb rubber (CR) content (0%, 10%, 20%, and 30%), and different rubber particle sizes [4.5 mm CR and 0.4 mm powder rubber (PR)]. Rotating cutter tests were conducted on three 100 mm cubic samples from each mixture at $-20°\mathrm{C}$ and 25°C while monitored via an AE system. AE parameters such as amplitude, number of hits, and signal strength were collected and underwent two parameter-based analyses: $b$-value and intensity analysis approaches, resulting in three additional parameters: $b$-value, severity ($S_r$), and the historic index [$H(t)$]. Results showed that testing concrete samples under abrasion at cold temperature,$-20°\mathrm{C}$, resulted in a decrease in the emitted number of hits, cumulative signal strength (CSS), $S_r$, $H(t)$, and an increase in $b$-values compared to testing at 25°C. Furthermore, incorporating rubber particles was found to decrease the AE signals’ amplitudes significantly at 25°C and slightly at $-20°\mathrm{C}$, which manifested the higher wave attenuation occurrence at ambient temperature compared to cold temperature. AE analysis also showed a decrease in the abrasion resistance for mixtures with higher C/F, higher CR content, and larger rubber particle size. These decreases were more noticeable at 25°C compared to $-20°\mathrm{C}$. Finally, the study developed two damage classification charts to estimate the ranges of abrasion mass loss percentage and wear depth in terms of the intensity analysis parameters: $S_r$ and $H(t)$.