New Insights into Topical and Integral Crystalline Waterproofing Cementitious Coatings: Permeability Testing and Microstructural Investigation

Crystalline waterproofing admixtures are commonly used as permeability-reducing admixtures to improve concrete durability and minimize water ingress in civil infrastructures. Understanding the role of crystalline waterproofing admixtures on the chemical and molecular structure of hydrating phases is essential for developing engineered crystalline waterproofing admixtures. The effect of integral crystalline waterproofing admixture and topical crystalline coatings was examined for water penetration and water permeability as per modified DIN (Deutsches Institut für Normung) 1048 and CRD-C 48, respectively. The resulting microstructure was evaluated with X-ray diffraction, Al 27 and Si 29 magic angle spinning, nuclear magnetic resonance, Fourier transform infrared spectroscopy, scanning electron microscopy/energy dispersive spectrum analysis. Hydration kinetics and pore structure were examined via isothermal calorimetry and mercury intrusion porosimetry. Benefits in terms of water penetration were observed even with lower cement content and a higher water-to-cement ratio with the integral crystalline waterproofing admixture. Concrete with the integral admixture showed an 89% reduction in permeability, while concrete with a topical crystalline coating showed a 99% reduction, as compared to the control. Reduction in water penetration was attributed to a densification effect from the formation of calcium-silicate-hydrate and calcium-aluminum-silicate-hydrate gels in both integral and topical waterproofing coatings. The formation of the calcite/aragonite phase in the integral waterproofing further assisted in this densification, which helped to lower water ingress compared to the control. Scanning electron microscopy analysis showed nanoscale crystals below 100 nm that helped to densify between the gel and capillary pore network. These findings provide insights into waterproofing effects influenced by active silicate and carbonate ingredients of the crystalline waterproofing materials. Finally, sustainable materials in crystalline admixtures initiated the nano-building blocks that provided a durable, waterproofing treatment.