Preliminary results on acoustic emission and vibration-based monitoring of locally corroded reinforced concrete beams

Abstract

The current tendency to increase the lifetime of reinforced concrete (RC) structures creates concerns about their serviceability and safety. Reinforcement corrosion is the most common deterioration process in RC, which can severely decrease the structural capacity. Corrosion causes a reduction of the rebar’s cross section, cracking and spalling of the concrete cover due to the expansion of the corrosion product and a decrease of the bond strength at the reinforcement-concrete interface. Assessing the structural capacity of corroded existing structures remains an important issue to maintain good safety and to achieve more targeted repairs. On-site quantification of structural reliability requires advanced non-destructive techniques to evaluate the damage and efficient methods for structural health monitoring. This paper presents the initial results of an experimental campaign on corroding RC beams. Beams with a length of 3 m are subjected to local accelerated corrosion while being monitored with the acoustic emission (AE) technique and dynamic vibration testing (DVT). AE investigates the damage progress and underlying causes of the cracks. When cracks are formed, the stress redistribution in the material causes elastic waves, which can be recorded by piezoelectric transducers placed on the surface of the beam. Examination of the waveforms allows for a localization and characterization of the damage source. Additionally, DVT observes the change in modal parameters of the beams, measured by accelerometers. These changes can be related to a loss of stiffness in the structure, resulting in a perception of the decrease in structural capacity. The combination of local (AE) and global (DVT) monitoring techniques improves the damage inspection as both the damage process and the loss of stiffness are observed. The results of AE provides information when the cracks have not yet reached the surface, while DVT is most relevant when severe damage already occurred. After corrosion, a four-point bending test is performed to evaluate the remaining structural capacity.