Development of polyurethane-shelled microcapsules using membrane emulsification for self-sealing cementitious applications

The ingress of water into cementitious materials through cracks and other defects can lead to corrosion and decay. Numerous self-sealing methodologies have been implemented to combat the degradation. One such method is the use of capsule-based self-sealing methodologies, designed to be triggered when there is microcracking and, subsequently, release their cargo. However, challenges remain in ensuring consistent capsule stability, reliable distribution and triggering, and a scalable, cost-effective production method. In this study, polyurethane-shelled microcapsules containing Sikagard®-705L, a commercially available water repellent agent, were synthesised via membrane emulsification and interfacial polymerisation. By adjusting production flow rates, stabiliser concentrations, and shell formulations, the capsule size and size distribution were regulated and optimised. This enhanced the understanding of formulation-specific relationships between parameter changes and the resulting capsules. Further characterisation of the capsules was caried out, investigating the shell morphology via optical microscopy and scanning electron microscopy (SEM), thermal stability via thermogravimetric analysis, and stability over time via optical microscopy. The self-sealing effectiveness was then validated via water absorption tests, contact angle measurements of a cracked or cut cementitious surface containing microcapsules, and sufficient rupture and homogenous distribution throughout a specimen via SEM and micro computed tomography. It was seen that cracked mortar specimens (crack width of 300 μm on average) were successfully sealed after the microcapsules were integrated into the mortar and mechanically ruptured. To conclude, the optimised microcapsules were produced on a platform that facilitates size control and monodisperse distributions and successfully facilitated self-sealing within the cementitious matrix.