How Does Self-healing Under Sustained Loadings in Aggressive Water Affect the Constitutive Response of a UHPFRC?

In the present study, the effects of sustained load combined with aggressive exposure on the long term performance of UHPFRC has been investigated. Three different materials have been tested: a reference one, containing a crystalline admixture as promoter of the autogenous self-healing and two further matrices, additionally enhanced with alumina nano-fibers and cellulose nano-crystals. The aim of adding these functionalizing nano-constituents is to work on the micro- and nano-structure of the matrix and enhance the durability in the cracked state. For this reason, specimens (100 × 30 × 500 mm) were pre cracked to a target crack width level. A couple of specimens was self-contained in suitable 4PBT setup to exert a constant flexural sustained load while being exposed to different exposure conditions of tap water, 3.3% chloride aqueous solution, and geothermal water. The study is proposed to elaborate different nondestructive and destructive measurements to evaluate the self-healing efficiency and its impact on the mechanical performance of the specimens, specifically the tensile constitutive response. Direct tensile test, and 4PBT have been used to assess healing efficiency by testing the conditions of the specimens before damage, after damage and after simultaneous mechanical and chemical exposure. Inverse analysis has been applied to the 4PB curves to obtain the tensile constitutive laws before and after crack localization. The obtained results proved that the autogenous self-healing of UHPFRC, as an active process, not only allows to recover the pristine condition of the cracked specimens, but also to achieve higher tensile capacity, attributed to the healing particles precipitating in the distributed cracks in the damaged area.