Crack monitoring and damage assessment of BFRP-jacketed concrete cylinders under compression load based on acoustic emission techniques

Fiber reinforced polymer (FRP) composites have been widely used in strengthening of existing concrete columns. However, the concrete cracks inside the FRP-strengthened columns caused by external loading cannot be observed by traditional field inspection techniques due to the coverage of FRP composites. In the present study, axial compression loading tests were performed on two unjacketed concrete and six BFRP-jacketed concrete cylinders. Acoustic emission (AE) techniques were utilized to monitor the cracking process of concrete specimens. The conventional AE hit and AE amplitude analysis were effective in detecting the first occurrence of concrete crack. The first noticeable concrete crack and final major crack can be detected by the crack intensity analysis. Then, five stages of cracking process of unjacketed concrete and BFRP-jacketed concrete specimens can be determined by a combination of the AE hit analysis and crack intensity analysis. AE analysis revealed that the cracking process of BFRP-jacketed concrete differed from that of unjacketed concrete, due to the presence of BFRP composites: (1) the time range of AE stable developing stage of BFRP-jacketed concrete was longer than that of the unjacketed concrete and the time range increased with an increase in FRP layers; (2) the crack intensity analysis parameters, which are based on AE signal strength, (i.e., severity index (S_r) and historic index (H_s)) of BFRP-jacketed specimens presented noticeable higher values at the final failure stage; (3) the RA value-average frequency (RA-AF) analysis revealed that the occurrence of shear cracks was delayed in the BFRP-jacketed concrete. The present study demonstrated that AE monitoring can effectively capture the characteristics of the cracking process of FRP-jacketed concrete.