Synergy between crystalline admixtures and nano-constituents in enhancing autogenous healing capacity of cementitious composites under cracking and healing cycles in aggressive waters

More than one century after its massive introduction in the building industry, concrete is still the most popular building material. Nevertheless, several critical infrastructures show severe signs of distress. This fact fostered, in recent years, the need of rethinking the design process of concrete structures, in view of reducing maintenance costs and extending their service life. This work has been performed in the framework of the H2020 project ReSHEALience (GA760824). The main idea behind the project is that the long-term behaviour of structures under extremely aggressive exposure conditions can highly benefit from the use of high performance materials, in the framework of durability-based design approaches. The project will tailor the composition of Ultra High Durability Concrete (UHDC), by upgrading the High-Performance Cementitious Composite/High-Performance Fibre Reinforced Cementitious Composite (HPCC/HPFRCC) concept through the incorporation of tailored nanoscale constituents focusing, among the others, on stimulating the autogenous self-healing capacity. This work shows the effectiveness of the aforementioned concept achieved through the incorporation in a reference HPFRCC of three types of nano-constituents: alumina nanofibers (0.25% by weight of cement), cellulose nanocrystals (0.15% by weight of cement) and cellulose nano-fibrils (0.15% by weight of cement). The influence of the nano-constituents has been analysed in terms of mechanical properties, such as flexural and compressive strength and on shrinkage and durability properties, analysed by means of sorptivity tests on un-cracked, cracked and self-healed specimens with reference to selected aggressive exposure scenarios representative of intended engineering applications of the investigated materials.