Determination of crack location, type and orientation ina concrete structures by acoustic emission

Abstract

Elastic waves emitted by microfracturing are called acoustic emission (AE). Recently AE techniques have been extensively applied to concrete engineering as a non–destructive testing (NDT) method. A key aspect of AE is that the nucleation of internal cracks is directly detected by a surface observation. In conventional AE techniques, such AE parameters as event count (activity), amplitude, energy and spectra are correlated with the failure process of materials. Thus, AE characteristics are utilized for NDT. The AE source (crack) is also located by employing a multichannel (more than 5) AE detecting and recording system. In this Paper an advanced AE analysis procedure is proposed. In addition to crack locations, crack types and crack orientations are determined from AE relative amplitudes of the first motions. The procedure classifies cracks into tensile cracks and shear cracks. Based on information of the crack type, the crack orientation is determined; this is the direction of crack opening in the case of tensile cracks, and the direction of sliding motion in the case of shear cracks. The proposed procedure is applied to a pull-out test of an anchor–bolt from a concrete block and a cylinder–tensile test. In the pull out test the opening directions of the tensile cracks is perpendicular to the failure surface, while the directions of sliding motion of the shear cracks are parallel to the failure surface. In the cylinder–tensile test the opening directions of the tensile cracks are perpendicular to the loading direction and all sources are located near the final plane. The proposed procedure is therefore able to determine the microcrack kinematics generated in concrete.