Effects of self-healing on tensile behavior and air permeability of high strain hardening UHPC

Abstract High strain hardening UHPC was expected to be self-healing due to its multiple micro-cracks in tension and the low water-to-binder ratio. The direct tensile tests with the acoustic emission (AE) analysis method and air permeability tests were carried out on high strain hardening UHPC in order to investigate the self-healing behavior under three re-curing conditions (water, 80%RH and 45%RH). Moreover, the cyclic tensile loading was applied to create more severe damage and two re-curing schemes (water and steam) were used to evaluate the self-healing effects. Experimental results show that the direct tensile stress-strain curves of high strain hardening UHPC re-cured in water and 80%RH conditions have the recovery of first cracking strain. New crystals were observed in the micro-cracks after self-healing, whose strength was proved to be lower than that of the intact part. The high strain hardening UHPC can recover 40%-47% of the first cracking strain after 28 days of water re-curing, where new damages characterized by AE sources number were found to generate inside the UHPC matrix. Air permeability test shows a sensitive response to the damage created by the tensile deformation. Steam re-curing method shows more effective and less time consuming for self-healing than water re-curing method.