A quantitative assessment of damage sustained in concrete during compressive loading

Abstract

Synopsis A new technique is described which gives a quantitative assessment of the damage that occurs during the loading of materials. The technique is based upon the behaviour of an ideal material in which energy is dissipated by two processes. The first is taken to correspond to damage and energy is dissipated only during the first loading over a given strain range. The second process is analogous to damping and energy is dissipated whenever straining occurs. It is shown that, in many respects, concrete behaves similarly to the ideal material. Acoustic emission measurements show, over a wide strain range, that concrete is damaged only during the first loading. The assessment of energy dissipated in damage correlates well with the change in initial elastic modulus which is used as another indicator of structural degradation. Measurements indicate that the process offracture in concrete in uniaxial compression is continuous and begins at very low applied strains. No evidence to support the existence of ‘critical’ or ‘discontinuity’ stress levels has been found.