Abstract
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.
Highlights
The results show a good proportionality between the creep deformation and the acoustic emission (AE) activity and the efficiency of acoustic measurements for the estimation of the state of damage
Concrete structures are susceptible to degradation due to delayed strains which has an impact on their safety margin and life time, especially when they are subjected to high loading level
At the moment of load application, the AE activity is important with AE signals of high amplitude corresponding to microcracks in the beam and to noises at the contact between the beam and the jack. This part was removed and the AE activity was followed during the three distinct phases of creep corresponding to the evolution of creep displacement into three regimes: primary creep, which corresponds to a fast decrease of strain kinetic under the initial load, followed by secondary creep, which corresponds to a quasiconstant strain kinetic, and tertiary creep in which the strain kinetic increases quickly leading to the global failure of the beams
Summary
Concrete structures are susceptible to degradation due to delayed strains which has an impact on their safety margin and life time, especially when they are subjected to high loading level. The principal mechanism of tensile creep is due to the microcracks development which could be responsible of the decrease of the residual strength and the modification of concrete properties [6, 7]. An experimental investigation is proposed on beams loaded with flexural creep at high stress levels. Damage evolution under creep is assessed by using the AE technique This non-destructive technique proves to be very effective, especially to check and measure micro-cracking that takes place inside a structure under mechanical loading and it is recommended to detecting and localizing cracks in concrete [14,15,16,17,18]. The characterization of the damage evolution during basic and desiccation creep is suggested by using the AE method
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