3D printed capsules for self-healing concrete applications

This study focuses on the use of additive manufacturing techniques as a possible way to produce novel types of macro-capsules, suitable to be filled with different healing agents and subsequently embedded in cementitious materials to introduce self-healing properties and deal with the sensitivity of these materials to crack formation. Specifically, tubular macro-capsules were produced by 3D printing and filled either with an expansive polyurethane resin or with a liquid sodium silicate. The 3D-printed capsules were first characterized in terms of water tightness and shell continuity, to evaluate the eventual need for additional protective layers. Then, they were inserted into cement mortar prisms and subjected to controlled cracking by three-point-bending to experimentally investigate their bonding with the cement matrix and the ability to release their content at the crack site to promote self-healing. The actual self-healing effect was expressed in terms of recovery of load-carrying capacity under mechanical tests. Positive results were achieved, showing a good potential of the proposed capsule-based system for structural applications. Further improvements can be envisaged through the optimization of the capsule shape, for which the 3D printing technology offers virtually unlimited possibilities.