Investigation of polyurethane-shelled microcapsules for self-sealing concrete applications exposed to aggressive environments

This study evaluates polyurethane-shelled microcapsules containing a commercial water-repellent agent as an autonomous self-sealing system for concrete in aggressive environments. Microcapsules were synthesized via membrane emulsification and interfacial polymerization, yielding a D50 of 77 μm and sufficient integrity for concrete incorporation. An optimization study identified 2 by weight of cement (bwoc) % as the optimal dosage, balancing hydrophobic performance and mechanical properties. Cracked (100 and 300 μm) and uncracked specimens were exposed to freeze–thaw cycles with de-icing salts, artificial seawater, and a chloride-rich solution. Capsule rupture upon cracking hydrophobized the crack walls, resulting in sealing efficiencies of up to 96% for 300 μm cracks. Freeze–thaw exposure reduced scaling by up to 74%, while marine exposure lowered chloride ingress through cracks by up to 37%. Limited effects were observed under chloride-only conditions, highlighting exposure-specific performance. Overall, polyurethane microcapsules act as an effective self-sealing system, enhancing concrete durability in an environment-dependent manner.