Concrete structures could suffer from the corrosion of reinforcing steel bars (rebars) because of the penetration of chloride ions. For crack detection and damage evaluation in concrete, acoustic emission (AE) techniques have been extensively applied to concrete and concrete structures. In the corrosion process of reinforced concrete, it is demonstrated that continuous AE monitoring is available to identify the onset of corrosion and the nucleation of concrete cracking because of the expansion of corrosion products. At the latter stage, the expansion of corrosion products generates corrosion-induced cracks in concrete. The generating mechanisms of these cracks are studied in accelerated corrosion tests of reinforced concrete beams. Kinematics of microcracks are identified by SiGMA (Simplified Green's functions for Moment tensor Analysis) analysis of AE. It is demonstrated that AE activity at the onset of corrosion and at the nucleation of corrosion-induced cracks is in remarkable agreement with the phenomenological model of the corrosion process in steel. Then, mechanisms of corrosion-induced cracks are visually and quantitatively investigated by the SiGMA analysis.
Cellular lightweight concrete (CLC) is increasingly used for low strength non-structural and structural applications. The effects of synthetic fiber reinforcement on the fracture behavior of CLC is investigated. In particular, acoustic emission (AE) technique is employed to study the influence of macro (structural), micro polyolefin synthetic fibers and their combinations on the fracture behavior of CLC beams. Notched fiber reinforced CLC beams were tested to study the crack initiation and propagation characteristics using AE sensors. Different AE parameters are correlated with the crack growth and damage accumulation. An attempt has been made to correlate the crack mouth opening displacement (CMOD) with the number of AE hits. The variation of cumulative acoustic energy release of the cracks is studied with respect to applied load and CMOD. Three dimensional source location of cracks is carried out based on the AE events picked by the sensors bonded to the CLC specimens. The analysis of AE results indicates that the crack source location identification from AE is consistent with the actual crack development. Analysis of AE signals reveal that the CLC matrix cracking produces signals with less number of hits that lie in the notched plane in bending. Moreover, the signals from the post peak regime correspond to more number of hits which tend to be scattered around the plane of notch due to the fiber pull out.
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