Advanced 3D printed mini-vascular network for self-healing concrete

Recently, the development of 3D mini-vascular networks has demonstrated their ability to facilitate selfhealing in concrete structures. These 3D printed polylactide (PLA) hollow ligament tetrahedral shaped units (TETs) can heal multiple occurrences of damage by releasing a single-component healing agent stored within. To improve the healing efficacy of the concrete-TET system whilst overcoming the potentially short shelf life of single-component healing agents, the TETs design was modified. TETs with coaxial hollow ligaments (d-TETs) suitable for storing bi-component healing agents were manufactured. Different healing agents, including epoxy resin (i.e. cycloaliphatic epoxy resin plus hardener) and sodium silicate in isolation or in combination with either nanosilica or nanolime solution were explored. The d- TETs were effective in storing these bi-component healing agents without them undergoing premature mixing and curing. Moreover, the d-TETs successfully ruptured and released healing agents at a crack width of 0.35 mm. After one damage-healing cycle, significant strength and stiffness recovery was achieved: d-TETs hosting sodium silicate and nano-lime yielded the best strength recovery (25%), whilst most other sodium silicate-based healing agent combinations demonstrated stiffness recoveries of approximately 40%. This demonstrates the efficiency of the d-TETs concept as a system, which allows strength and stiffness recovery despite the limited volume of healing agent.