Effects of different admixtures on the self-healing behaviour of engineered cementitious composites

Engineered cementitious composites (ECC) still face the issue of limited self-healing ability, even with their superior crack control capability. In this work, in an attempt to improve the self-healing properties of ECC, superabsorbent polymer (SAP), light-burned magnesia and calcium sulfoaluminate (CSA) were added to ECC. The healing effect and mechanism were studied using various means, including crack closure tests, scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction. The results showed that the composite additive significantly enhanced the self-healing efficiency with a synergistic action. The SAP–CSA combination exhibited the most pronounced effect. Cracks with an initial width of 0.18 mm were completely sealed within 30 days and the compressive strength recovery rate reached up to 116%. SAP continuously releases water, facilitating the rehydration of unhydrated cementitious materials and accelerating the formation of calcium silicate hydrate gel and calcium carbonate. CSA efficiently healed cracks by rapidly reacting with water to generate ettringite, which directly obstructed the cracks. This study offers a theoretical and practical foundation for enhancing the self-healing performance of ECC.