Medium-term self-healing evaluation of Engineered Cementitious Composites with varying amounts of fly ash and exposure durations

•The medium-term healing allowed ECCs to effectively regain strength and stiffness.•High-fly-ash ECCs continued moderate healing beyond the age of 270days.•The major components of the medium-term precipitation were CaCO3 and C-S-H.•The recovered strain capacity of ECCs increased along with the amount of fly ash. Extensive studies have shown that young Engineering Cementitious Composites (ECCs) have the potential to achieve effective self-healing. The present study investigates the medium-term self-healing performance of cracks in ECCs that are relevant in the medium and long-term stages of the material service life. For this purpose, the prepared ECC specimens are pre-cracked at an age of 180days. The major experimental variables are the weight fraction of fly ash in ECCs (a fly ash to cement ratio of 1.2, 1.6, or 2.0) and the healing duration (7, 28, or 90days). The medium-term self-healing performance is quantified using a resonant frequency test followed by a uniaxial tensile test. In addition, scanning electron microscopy and energy dispersive X-ray analyses are employed to observe the micro-structure of the healed crack and identify the medium-term healing product, respectively. The results suggest that as long as water is present in the environment, ECCs have moderate medium-term self-healing ability, and can partially recover their tensile mechanical properties. In particular, effective medium-term self-healing performance can be achieved within 90days of conditioning for ECCs with a pre-strain of less than 1%.