Mechanical properties and self-healing capacity of ultra high performance Fibre Reinforced Concrete with alumina nano-fibres: Tailoring Ultra High Durability Concrete for aggressive exposure scenarios

The effects of alumina nano-fibres are investigated in this paper on the mechanical performance of Ultra High Performance Fibre Reinforced Cementitious Concrete and their efficacy in enhancing the durability of the cementitious composite when exposed to extremely aggressive conditions, with main reference to the stimulated autogenous crack sealing and self-healing capacity. A tailored characterization of the flexural and tensile behaviour of the composite has been first of all performed, also with the purpose of validating an experimental and analytical approach for the identification of the tensile stress vs. strain/crack opening constitutive relationship, which makes use of a purposely conceived indirect tensile test methodology, called Double Edge Wedge Splitting test. Secondly the crack sealing and self-healing capacity have been investigated, considering the recovery of both mechanical flexural performance and durability properties (water permeability) and cross analysing the results for a thorough validation. Microstructural investigations have complemented the aforementioned experimental programme to confirm the efficacy of alumina nano-fibres in enhancing the durability performance of the investigated composites. Superior performance of the mix with alumina nano-fibres with respect to parent companion ones has been highlighted and explained through both a nano-scale reinforcing effects which helps in controlling the cracking process since its very onset as well as through their hydrophilic nature which is likely to foster cement and binder hydration reactions, which can usefully stimulate crack sealing and performance healing recovery at both the macroscopic and mesoscopic fibre-matrix interface) level.