Evaluation of freeze–thaw effect on concrete using sideband peakcount-based non-linear ultrasonic NDT&E techniques

Concrete is susceptible to cracking and damage under repeated freeze–thaw conditions. Ultrasonic techniques have been widely used as non-destructive testing and evaluation techniques to assess concrete integrity under various damage mechanisms; however, commonly adopted linear ultrasonic (LU) techniques are less effective for identifying microscale damage. Nowadays, non-linear ultrasonic (NLU) techniques are favoured for detecting microscale damage due to their high sensitivity to microcracks. Recently, sideband peak count (SPC)-based NLU techniques have emerged as a robust alternative to traditional NLU methods. In this study, both LU and SPC-based NLU techniques were conducted to assess the damage of mortar specimens that were subjected to different freeze–thaw cycles. The freeze–thaw damage was also evaluated with conventional resonant frequency and compressive strength tests. Results indicate that LU-based technique – ultrasonic pulse velocity (UPV) – performs the worst correlation with the changes in compressive strength of the mortar specimens. The other LU parameter – signal attenuation – shows better result than UPV, exhibiting a similar trend with relative dynamic modulus of elasticity (RDME) from resonant frequency test. The two SPC-based techniques sideband peak count-index (SPC-I) and sideband peak intensity (SPI) are more sensitive to different degrees of frost damage. Specifically, the SPC-I technique correlates well with the change in RDME throughout the testing period. In terms of the mechanical property, SPI performs the best among the three techniques (resonant frequency, SPC-I and SPI), especially for assessing the damage at the early stages when the accumulative damage did not change compressive strength significantly. At later stages as the damage progressed, all three techniques produced reliable results.