A “fracture testing” based approach to assess crack healing of concrete with and without crystalline admixtures

•Effects of crystalline admixtures on the self healing of concrete have been investigated.•Effects of self healing on the recovery of mechanical properties have been evaluated.•Under water concrete autogeneously heals; crystalline admixtures promote self healing in air.•Self healing was quantified through indices load and damage recovery.•A crack closure above 70–80% is necessary to start recovery of stiffness and load bearing capacity. In this paper a methodology of characterization of both autogenic and engineered self-healing of ordinary concrete, with or without a crystalline admixture, has been assessed. The employed crystalline admixture consists of a mix of cement, sand and active silica and is added to the raw concrete constituents before mixing. The effects of the self healing phenomena on the recovery of stiffness and load-bearing capacity have been evaluated by means of 3-point bending tests performed up to controlled crack opening and up to failure, respectively before and after conditioning. Different exposure conditions have been considered, such as water immersion, air exposure and accelerated temperature cycles. Moreover, Ultrasonic Pulse Velocity tests and microstructural observations have been carried out. On the basis of the results, self-healing related indices have been also defined.