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This paper investigates damage and healing of cementitious materials based on fly ash (FA) with a special focus on the effect of repeated loading on the self-healing performance. In total, 90 prism specimens and 33 cylinder specimens were prepared and tested. Variables including the FA replacement ratio and preloading level were considered. Different methods were adopted to evaluate the self-healing performance, i.e., mechanical tests, acoustic emission (AE) analysis, water absorption measurement, and scanning electron microscope (SEM) observation. Test results revealed that an appropriate amount of cement replaced by FA was beneficial to the self-healing performance of the specimens subjected to a high level of repeated preloading, where the strength increased by 11% and the water absorption rate decreased by 12%, in comparison with that of the undamaged specimens. This was attributed to the active hydration of FA, which was confirmed by an energy dispersive X-ray spectroscopy (EDS) analysis. This study extends understanding of the self-healing performance when subjected to repeated loading and provides some useful suggestions for the self-healing technique based on mineral additives. [ABSTRACT FROM AUTHOR]

The effective mechanical properties of matrices healed by embedded microcapsules were investigated using Eshelby theory based on the microscale healing mechanisms, referring to the mechanical properties of the adhesive and the proportion of cracks that could be healed. This was determined by measuring the water absorption and vacuum saturation of precracked matrices. The microcapsules or cracks should not exceed 4 vol.% to ensure that approx. 90% of the modulus is retained even if the cracks cannot be reattached at all. Both the healed cracks and unhealed cracks contribute to the anisotropy, with a greater contribution from the unhealed cracks. The elastic modulus of the adhesive has a more significant influence on the anisotropy as the applied load increases. The measured stiffness recovery indicates that the cracks were only partially healed. This value corresponds to a healing efficiency index of 0.2–0.4 for the present conditions. [ABSTRACT FROM AUTHOR]