MICRO-STRUCTURAL CHARACTERISTICS OF CONCRETE IN RELATION TO ITS STRUCTURAL INTEGRITY, WITH APPLICATION IN ACOUSTIC EMISSION

Abstract

Over the past 30 or so years, studies on acoustic emission from loaded concrete material have yielded only limited useful information to relate the general acoustic emission characteristics to the overall responses of concrete material to applied loading. No significant advancement has been achieved in research to establish the intrinsic relationships that should exist between the observed acoustic emission characteristics to the inherent micro-structural behaviour of the bulk concrete material. Reasons which are attributed to this current state of research development include the very high cost of the acoustic emission monitoring equipment, many technical difficulties associated with the application of the acoustic emission monitoring technique on concrete material and the lack of rigorous analytical theories to identify the dominant role and close interaction of micro-structural material inhomogeneity in deriving the global responses of the bulk heterogeneous concrete material to applied loading. Whilst nothing much can be done with regards to the high cost of the acoustic emission equipment, the research needs point towards addressing the difficult but requisite task to resolve the cause and effect of the observed acoustic emission phenomena in relation to the complex behaviour of concrete at increasing load application. The research work reported in this PhD thesis presents an innovative and experimentally simple approach to translate the global stress and strain data of a uniaxial compression test to quantify the observed acoustic emission phenomena in terms of the characteristic micro-structural responses of the bulk heterogeneous concrete material at increasing applied load. The scope of this research work covers the complete, characterisation of the progressive aicro crack growth process in concrete at increasing externally applied load through qualitative analysis by the principles of micro-fracture mechanics theory, the formulation of the statistical modelling to simulate the corresponding progressive micro cracking process, the derivation of the constitutive stress-strain equations for concrete at monotonic and cyclic loading in uniaxial compression to ultimate failure to facilitate the definitive evaluation of the structural integrity of the concrete material, the establishment of systematic correlation of various acoustic emission characteristics to the constitutive micro-structural responses of concrete to increasing external load application, and the development of an alternative technique to replace the ineffective Kaiser effect of acoustic emission to reliably identify the various levels of previously induced strain history due to multiple cycles of loading at increasing maximum global compressive strain onto a body of concrete material. The most significant contribution from the manifold outcomes of this research is the better insight of the relation between the internal localised micro-material damage and the global specimen responses of concrete.