Self-healing performance of engineered cementitious composites under natural environmental exposure

The self-healing performance of an engineered cementitious composite (ECC) exposed to the natural environment is presented.  Fifteen dog-bone shaped ECC samples were preloaded after 14 days of curing and then placed outside in an open area at Heriot-Watt University (Edinburgh campus).  Ultrasonic pulse velocity measurements were used to determine the rate and extent of the self-healing capabilities of the ECC in the natural environment.  The results showed that, while the more highly damaged samples displayed the greatest decrease in ultrasonic velocity, they also displayed initial accelerated healing, which implies an increased quantity of individual cracks in the more damaged samples rather than an increase in individual crack widths.  It was also found that the self-healing of microcracks in the ECC was robust.  Narrow hairline cracks (< 10 μm width) healed in less than 6 d, while 20–30 μm wide cracks either partially or fully healed after 6 days of intermittent rainfall.  Wider microcracks (40–75 μm) partially healed after 3 weeks of outdoor exposure.