Self-Healing of Microcracks in High-Volume Fly-Ash-Incorporated Engineered Cementitious Composites

This paper presents the self-healing ability of engineered cementitious composites (ECCs) containing high-volume fly ash (HVFA). Composites containing two different contents of FA (55 and 70% by weight of total cementitious material) are examined. A splitting tensile strength test was applied to generate microcracks in ECC mixtures, where cylindrical specimens were preloaded up to their 85% maximum deformation capacity at 28 days. These specimens were then exposed to further continuous wet (CW), continuous air (CA), and wet/dry (W/D) cycle curing regimes up to 60 days. The extent of damage was determined by using the rapid chloride permeability test (RCPT), splitting tensile tests, and microscopic observation. In terms of permeation properties, microcracks induced by mechanical preloading significantly increase the RCPT values of ECC mixtures. Moreover, increasing FA content is shown to have a negative effect, especially on the permeation properties of virgin ECC specimens at an early age. Without self-healing, however, the effect of mechanical preloading on the chloride-ion penetration resistance of ECC with 70% FA is lower compared to ECC with 55% FA. The test results also indicate that CW and W/D cycle curing contribute and speed up the healing process of the cracks, significantly improve mechanical properties, and drastically decrease the RCPT of ECC. The use of HVFA in ECC production is likely to promote self-healing behavior due to tighter crack width and a higher amount of unhydrated cementitious material available for further hydration. Therefore, it appears that the curing conditions and ECC composition significantly influence self-healing ability.