Design of a Hydrophobic Nano-SiO2-modified ER@EC Microcapsule: Improving Rheology, Regulating Hydration while Preserving Self-Healing in Cementitious Materials

Microcapsule-based self-healing concrete chronically suffers from rheology deterioration and hydration stagnation due to the hydrophilic and hygroscopic nature of microcapsules, limiting its efficacy and broader application. To address these issues, a novel hydrophobic nano-SiO2-modified epoxy resin (ER)@ethyl cellulose (EC) microcapsule was developed and characterized. Examinations revealed that both 5% and 7% SiO2-modified ER@EC microcapsules displayed favorable fundamental properties for cement-based materials, featuring high core contents (53.08% and 48.04%) and water contact angles over 90°. Compared to the unmodified capsules, the incorporation of 7% SiO2-modified capsules prominently enhanced the rheology and hydration exotherm of fresh cement pastes, attributed to floc disassembly caused by electrostatic repulsion and increased water volume induced by replacement and ball-bearing effects. Moreover, incorporating a 4% dosage of 5% SiO2-modified capsules exhibited prominent healing efficiencies of 6.14% for compressive strength and 35.11% for chloride diffusion resistance. The hydrophobic nano-SiO2-modified ER@EC microcapsules actively improved rheology and hydration exotherm while preserving the ability to self-heal cracks in cement-based materials.