Identification of damage mechanisms in concrete under high level creep by the acoustic emission technique

Many researchers have proposed hypotheses concerning the physical mechanisms that govern creep and among them the development of microcracks is well recognized. For high load levels, microcracking may initiates at the moment of load application and begins to grow to form a time-dependent crack path. An experimental investigation is proposed here in order to provide interesting insight into the coupling between creep and damage with specimens loaded in flexure. The acoustic emission (AE) technique is used as a tool to provide information on the pertinence of the physical hypothesis that microcracks appear during creep. An original test is performed to accelerate the creep phenomenon by submitting concrete beams to desiccation after a basic creep period. The results show a good proportionality between the creep deformation and the AE activity and thus the efficiency of acoustic measurements for the estimation of the state of damage. In addition, an unsupervised pattern recognition analysis is used as a tool for the classification of the monitored AE signatures. The cluster analysis shows two clusters during basic creep and three clusters during desiccation creep indicating different damage mechanisms.