Healing performance on concrete under mode I fracture by ultrasonic testing using embedded transducers, acoustic emission and digital image correlation method

摘要

Crack formation is the main cause of concrete mechanical properties degradation. Autonomous self-healing (i.e.SH) encapsulation systems promise material recovery by filling the cracks with healing agent (providing healing and sealing). The cracking of concrete elements is experimentally investigated by mode-I failure tests in small-dimensioned concrete beams subjected to three-point bending tests. The perplexing fracture process phenomena require an advanced monitoring system. In this study, an optical method (i.e. Digital Image Correlation- DIC), Acoustic Emission (i.e. AE) and an ultrasonic wave propagation technique based on embedded piezoelectric transducers, are combined in order to evaluate the crack formation and opening of three concrete beams in which embedded SH encapsulated system is applied. The loading is applied in two stages. The initial loading is responsible for the crack initiation and formation as well as for the SH capsules breakage. After the healing agent is released and dried, the concrete samples are reloaded. The DIC technique calculates the crack opening and visualizes the crack formation and propagation path. In parallel, the features extracted by the AE technique quantify the fracture process at different loading stages and detect the regions in which healing occurs by indicating the SH capsule breakage. Finally, a few couples of low-cost PZT transducers based on the concept of Smart Aggregates (i.e. SMAGs) are embedded in the concrete beams for the estimation of the state of damage. Incorporation of the aforementioned fracture analysis provides a full-field view of concrete failure performance and is the keystone to characterize healing performance.