Reservoir-Vascular Tubes Network for Self-Healing Concrete: Performance Analysis by Acoustic Emission, Digital Image Correlation and Ultrasound Velocity

A novel linear reservoir-vascular tubes network is presented in this work and the design efficacy is explored by testing concrete beams loaded on bending and by assessing their damage healing and mechanical recovery. The healing system is composed of additively manufactured polymer components that appear equally effective compared to conventional ceramic tubes since the 3D printed polymer-tubes instantly break upon cracking. It is shown that bulk reservoirs embedded into concrete can deviate cracks and detrimentally affect the concrete's resistance to failure. The crack formation and re-opening is monitored by acoustic emission (AE) and digital image correlation (DIC) concluding that initial brittle cracking is shifted after healing to a pseudo-ductile crack re-opening with extended post-softening. The sealed cracks show significant strength and toughness recovery (i.e., above 80% of the original value) escorted also by an ultrasound pulse velocity (UPV) increase (up to 126% relative to the damage state) after a healing intervention. The work critically reports on obstructions of the current design: (i) the network tubes are clogged although the agent was flushed out of the network after healing and as a result re-healing is unattainable; and (ii) vacuum spaces are formed during casting underneath the network tubes, due to limited vibration aiming on the tubes' tightness, but also due to inefficient aggregates settlement, leading to a strength decrease. This work calls attention to the impact of vascular networks design and performance on a complex cracks network and fracture zone development.