Studies on the Mechanisms of Fracture Evolution of Microcracks and Size Effect in Concrete through Acoustic Emission Analysis

Abstract

The mechanics of fracture evolution in heterogeneous material like concrete is a distinct and complex phenomenon and still stands as an open problem after decades of research. A cluster of multi-scale cracks ahead of the crack tip is known as a fracture process zone in concrete. The fracture process zone reduces stress singularity ahead of the crack tip by stress redistribution and contains several toughening mechanisms. Therefore, understanding of fracture behaviour of the concrete builds around the fracture process zone evolution. Moreover, fracture process zone also originates the well know size-effect phenomena in concrete. The energy dissipated by cracks in fracture process zone travels throughout the material as a stress wave, which is known as acoustic emission. The acquisition of acoustic emissions by piezoelectric sensors for understanding fracture phenomenon is a recently developed modus operandi for fracture studies in concrete. In this research an attempt is made to develop new paradigms of AE analysis and explore as many as possible aspects of AE information. In this dissertation, the acoustic emission technique is used and a thematic styled scientific inquiry for fracture process evolution in concrete as well as damage inference is presented. The acoustic emission waveforms carry information regarding the source, its mechanism, and the propagation media. Therefore, deciphering the information carried by waveforms is a crucial task. The individual spectra of waveforms as well as the collective population of AE events are explored. The level of information sets the theme of the study in which waveform spectra, magnitude distribution, cumulative AE energy, and non-extensive entropy is investigated consecutively. The wavelet transform for the multiresolution spectral study gives an estimator called wavelet entropy to distinguish signal based on spectral energy distribution...