Evolution of self-healing performance of UHPC exposed to aggressive environments and cracking/healing cycles

This paper investigates the resilience of UHPC's self-healing capabilities under aggressive environmental conditions and cracking/healing cycles. UHPC specimens ‘with a double-edged wedge splitting geometry were made, incorporating a commercial crystalline admixture (Penetron Admix®). The evaluation of UHPC's healing capacity involved subjecting pre-cracked samples to three different water immersion conditions: tap water, saltwater, and geothermal water. The closure of cracks during different curing periods was meticulously recorded using optical microscopy. Furthermore, specialized tests, including ultrasonic pulse velocity (UPV) measurements and splitting tensile tests, were conducted to quantify the recovery of mechanical properties. The results reveal that extended exposure results in a gradual closure of cracks, where salt water and geothermal water exhibit lower self-healing capabilities. Self-healing improves after the 1st crack/self-healing cycle but decline rapidly after the 2nd cycle. Mechanical property is strongly correlated with the extent of self-healing, and all samples display varying degrees of stiffness recovery, with the most pronounced recovery occurring after the 1st cycle. However, following the 2nd cycle, the stiffness recovery values decrease due to repeated loading, resulting in increased damage and a reduced number of reactive particles, thereby compromising self-healing and stiffness recovery. Despite enduring multiple instances of crack damage, UHPC samples still exhibit notable toughness recovery, underscoring the enduring efficacy of the self-healing mechanism even in challenging conditions.