A methodology to assess the evolution of mechanical performance of UHPC as affected by autogenous healing under sustained loadings and aggressive exposure conditions

This study investigates the evolution of the performance of an Ultra-High Performance Concrete (UHPC) under simultaneous action of sustained loading and aggressive environmental exposure. UHPC mixes were investigated containing different functionalizing micro- and nano-scale components to promote autogenous self-healing. In order to assess the healing capabilities in the different multi-action scenarios and the evolution of the mechanical response of the material over time, a tailored methodology was implemented, including non-destructive and destructive tests performed all along the scheduled exposure/healing times up to 12 months. In particular, an innovative set-up was designed to reproduce on the specimens the sustained flexural loading conditions a structure undergoes during its service life; the load was applied simultaneously with each of the three selected different exposures, to simulate the chloride and sulphate aggressive environments, besides a reference one. Multiple indices were defined to quantify the self-healing efficiency, which were further calibrated against experimental microscope crack observation as well as cross correlated with each other, as a further proof of the reliability of the proposed methodology. The results confirmed the material durability, especially in the cracked state, through its capacity of sealing the cracks and restoring original properties in short periods and preserving its load bearing capacity, thus providing solid argument for UHPC as the ideal candidate material for highly durable and sustainable structural applications in aggressive scenarios.