Conservation of Modernism Movement Concrete: Tackling the Compatibility Issue of Retrofit Solutions with the Degraded Substrate

The conservation of Modernism heritage is of utmost importance today since the concrete heritage of the 20th century is now aged and faces severe durability issues. However, due to restrictions introduced considering their architectural identity and aesthetics, the repair and conservation interventions should be performed only if the reversibility of actions is ensured. The design of repair patches and retrofit layers should be based on this principle and at the same time performed in long-term and often in aggressive environments, indicatively sea exposure. This work report on recent experimental tests evaluating the compatibility criteria that should be established in order to ensure durability and the optimal mechanical performance of cement-based fiber-reinforced repair patches for degraded concrete. The adhesion to the degraded substrate is of utmost importance since bonding should lead to efficient interaction among materials, however should not alter the substrate consistency and response to service loads. The deterioration mechanism of chloride-ions exposure leading to concrete carbonation and rebars corrosion is tested by evaluating large open cracks as formed after bending of small-scale concrete slabs. The retrofit layering is applied after the accelerated exposure of the slabs to the chloride environment and evaluated by cyclic bending tests that follow. The compatibility of the materials under flexural stresses is monitored using an integrated inspection methodology: acoustic emission and digital image correlation, whereas the adhesion of the retrofit to the substrate is inspected using microscopy scanning and ultrasound pulse velocity. It is demonstrated that premature interfacial debonding can be linked to the incompatibility of materials due to different stiffness and lack of interlocking. This phenomenon can be catastrophic for future rehabilitation projects.