Self-healing characterization of UHPFRCC with crystalline admixture: Experimental assessment via multi-test/multi-parameter approach

• The adoption of strain-hardening cement composites significantly promotes self-healing. • Multi-test approach for self-healing assessment appeared to be robust in durability monitoring. • Self-healing is very effective already after 1 month of curing for the UHDC studied. • The mixes showed sizable self-healing with even almost full crack-sealing after 6 months. • Re-cracking has a detrimental effect in self-healing for all the considered parameters. Within the framework of the Research Project ReSHEALience, new advanced Ultra High-Performance Fibre-Reinforced Cement Composites with enhanced durability, hereafter denoted as Ultra High Durability Concretes, are under investigation to characterize their tensile behaviour and durability performance in aggressive conditions, devoting particular attention to the phenomenon of self-healing. Three different mixes are under scrutiny, based on the combination of cement (CEM I or CEM III), slag, small aggregates (sand with a maximum size of 2 mm), and steel or metallic-alloy amorphous fibre. Self-healing capability has been investigated in aggressive environment (namely, under immersion in geothermal water) via 3 different test setups: (1) water permeability test on pre-cracked concrete disks, (2) 4-Point Bending Test – 4PBT on 100 × 100 × 500mm 3 prismatic beam specimens and (3) on 25 × 100 × 500mm 3 thin beams. In the case of beams, self-healing has been assessed via visual inspection of cracks trough digital microscope and via mechanical re-loading, so to investigate both crack-sealing capability and mechanical recovery. The results of this assessment aim at providing the starting point for a data base finalized at defining a design approach explicitly taking into account self-healing in the evaluation of structural durability. In particular, it has been observed as the adoption of strain-hardening cement composites significantly promotes self-healing phenomenon, thanks to smeared cracking in the tensile region and to consequent low values of crack opening. Self-healing proved to be very effective already after 1 month of curing.