Crack detection and classification of repaired concrete beams by acoustic emission monitoring.

In this study, acoustic emission (AE) monitoring was used to investigate the cracking behavior of normal concrete beams repaired with fiber-reinforced cementitious composites (FRCC). The investigated beams were strengthened at two locations: tension side and compression side of the beam. Two different fibers were used in FRCC strengthening material: steel fibers and polyvinyl alcohol fibers. One normal concrete beam and two fully cast FRCC beams were also tested for comparison. All beams were tested under four-point loading until failure. The investigation considered the variations in several AE parameters such as number of hits, cumulative signal strength, signal amplitude, peak frequency, absolute energy, and b-value analysis. In addition, rise time/amplitude analysis was successfully utilized in this study to classify the failure modes (flexural or shear/debonding failure between the repair layer and existing beam) for all beams. The impact of the fiber type, strengthening location, and sensor location on the aforementioned parameters was clearly highlighted. Varying the fiber type of the FRCC or changing the repair location of the beam seemed to have a significant impact on the resulting AE parameters. A good correlation was found in repaired and unrepaired beams between AE parameters and the progression of cracks beyond the first crack until failure. The results also indicated that the AE analysis carried out in this study led to the identification of the first crack in repaired and unrepaired beams.