Detection and evaluation of failures in high-strength tendon of prestressed concrete bridges by acoustic emission

Failures in high-strength steel tendons of prestressed concrete structures are becoming a serious problem, as the deterioration of structures progresses due to aging. The failure is mainly attributed to the corrosion induced in severe environment as salt attack. Intensive studies were made in a laboratory and fields to investigate an applicability of acoustic emission (AE) technique to detect and locate the corrosion-induced failure. Three types of beams post-tensioned by steel bar, strand, and parallel wire cable with three different grout conditions (unbonded, partially grouted and fully grouted) were prepared in the laboratory tests. Failure was introduced by artificial corrosion, charging anodic current to the tendon. It was found that significant AE signals with extremely high amplitudes were produced by failures of steel wires and bars. Linear source location of the events was performed by three AE sensors placed in the center and the two ends of the beams. Reliability was shown to be 82–86% in terms of delectability of the failures. Continuous AE monitoring was carried out in two high-way bridges in service for 24 days. Eighteen AE sensors were placed at strategically selected positions on the post-tensioned beams of these bridges. Artificial AE signals were indirectly detected from the beams due to artificial failures by corrosion in small post-tensioned specimens bonded to the beams. Intensive analysis of the detected AE signals showed that meaningful AE events from the failures are clearly discernable from other sources as traffic noises and hammering. It has been proven that AE is a very useful technique to detect and evaluate failures of high-strength steel tendons in prestressed concrete bridges.