Recent advances on self-healing in cement-based materials through the addition of cementitious macro-capsules

Recently, increasing attention has been directed toward developing technological solutions that introduce self-healing properties into cement-based materials. This approach aims to mitigate the intrinsic sen-sitivity of these materials to crack formation, thereby preserving their load-carrying capacity, enhancing dur-ability, and reducing overall maintenance costs. Among the various strategies explored to achieve self-healing, the incorporation of capsules stands out as one of the most promising due to its versatility. This study presents recent advances in self-healing cement-based materials through the use of tubular macro-capsules with a cementitious shell, developed by the authors. The responsiveness of the capsules to cracking was demonstrated under realistic flexural conditions. Their influence on the intrinsic material strength was evaluated in comparison to reference materials without capsules. The capsules' ability to store and release various healing agents was studied, focusing on organic (polyurethane-based), inorganic (sodium silicate and silane-based), and biological (bacteria-based) agents. Optimization of the capsule shell formulation, coating, and manufacturing procedures was conducted accordingly. The self-healing effect was evaluated in terms of the restoration of mechanical properties, using static reloading tests up to failure, and the improvement in water-tightness, assessed through various permeability and sorptivity tests. The stability of the self-healing performance over time was also studied under the effect of repeated mechanical and thermal actions, specifically for the polyurethane-based healing agents. The results demonstrate the significant potential of cementitious macro-capsules for self-healing concrete applications.