Multifunctional silane-based superhydrophobic/impregnation treatments for concrete producing C-S-H gel: Validation on mockup specimens from European heritage structures

Many of the concrete structures that conform our modern cultural heritage are in need of repair and protective interventions. Silane-based impregnation treatments can be used to repair onset cracks and reinforce the surface due to their ability to produce silica and C-S-H gels, and can be modified by incorporating hydrophobic precursors to create multifunctional treatments that also protect from water ingress. Since the effectiveness of impregnation treatments is dependent on substrate properties and chemical-physical changes it may have experienced over time, validation using standard materials may not always be representative of on-site application. In this work, the effectiveness of three innovative silane-based impregnation treatments developed by our group (two of them combining superhydrophobic properties) was evaluated on mockup specimens, which simulate the properties of the cementitious materials from six different heritage structures across Europe, artificially aged to simulate weathering by three methods: carbonation, chloride ingress and physical damages (freeze-thaw and thermal cycles). The characterization of the treatments showed they are compatible in terms of chemical interaction, applicability and minimal aesthetical alterations. Surface resistance and ultrasound pulse measurements have been used to assess the improvement in mechanical properties. The incorporation of hydrophobic components and fumed silica has a relatively low impact over the mechanical properties while it significantly reduces water absorption and grants water repellent properties to the surface, giving rise to a superhydrophobic performance.

Automated summary

Many concrete structures in need of repair and protection can be treated using silane-based impregnation treatments, which produce silica and C-S-H gels and can be modified to create multifunctional treatments that also protect from water ingress. However, standard material validation may not always be representative of on-site application due to substrate properties and changes over time. In this study, three innovative silane-based impregnation treatments, two of which have superhydrophobic properties, were evaluated on mockup specimens that simulate the properties of cementitious materials from different heritage structures in Europe. The treatments showed compatibility, minimal aesthetic alterations, and improved mechanical properties.