High-strength cement-based repair and grouting compositions modified with nanodispersed silica

Introduction. The development of high-strength repair and grouting compositions for restoring concrete structures is a relevant task. The aim of the research is to study the effect of long-term stored nanodispersed silica (NS) on cement stone properties. Methods and Materials. Portland cement CEM I 42.5 N and sol-gel NS (storage: 1 day – 1.5 years) were used. Surface acid-base properties – indicator method; hydration kinetics – non-isothermal calorimetry. Four compositions: control, NS, NS + PC type S, NS + PFM. Compressive strength – up to 28 days; SEM, XRD, DTA. Results. NS surface has a polyfunctional acid-base spectrum. Long-term storage does not degrade activity: strong acid centers (pKa = –4.4) increase from 7.42 to 260–265 mg eq/g; strong basic centers (pKa = 8.8) remain at 515–628 mg eq/g. NS stored for 1.5 years intensifies heat release (max ~25.5 °C). Compressive strength increase by day 28: NS – 14.5%; NS + PFM – 16.7%; NS + PC type S – 18% vs control. SEM, XRD, DTA confirm portlandite binding and dense low-basic C–S–H matrix formation (min. weight loss on heating – 9.1% for NS+PFM). Discussion. Bifunctional NS surface provides a synergistic effect: basic centers adsorb Ca²+ ions, initiating nucleation; Lewis acid centers coordinate OH– and H2O, activating them. Complex NS + surfactants improve nanoparticle distribution and intensifying pozzolanic reaction. Conclusion. NS activity remains after 1.5 years of storage. Complex NS+plasticizers provide a synergistic effect. Developed compositions are recommended as class R3 (B35) repair compounds and grouting mixtures for critical structures, including collector repair, equipment grouting and anchor bolt installation.