Monitoring of the fracture mechanisms induced by pull-out and compression in concrete

• First time acoustic emission (AE) monitoring during LOK (pull out) test in concrete.
• Determination of the AE waveform characteristics of the different fracture modes.
• Determination of the actual stress field by FEM.

In-situ characterization of strength is of paramount importance for concrete engineers. To get an estimation of the compressive strength, slightly destructive tests are conducted on the surface of the material. One is the LOK test (pull-out) which offers a reliable estimation of compressive strength. The developed stress field is quite complicated and researchers have argued about the nature of the fracture mechanism. In the present paper, acoustic emission (AE) is applied during both compression and pull-out experiments on concrete cubes. Results show that the two damage modes emit different AE signatures, with compression leading to higher frequencies and pull-out to longer signal durations, while the finite element method (FEM) is used to analyze the stress field. Identification of the active damage mode in real time, is beneficial in order to assess the condition of integrity of concrete in structures by nondestructive monitoring.