Cracking is known as the main challenge for the life-cycle performance of concrete. However, the difficulty and cost of repair and maintenance would significantly increase when the cracks are invisible to the raw eyes or inaccessible for human. Therefore, utilizing a self-healing system seems to be an innovative and promising alternative. This work studied the healing performances and influences of two types of abiotic self-healing systems, i.e. urea-formaldehyde (UF) microcapsules and encapsulated impregnated lightweight aggregates (LWAs).We hypothesized that UF microcapsules should have the potential of mitigating the early-age shrinkage and enhancing the freeze-thaw resistance of cement mortar and cement concrete, respectively. Moreover, the LWAs impregnated with saturated Ca(OH)2 solution should be capable of healing the cracks of cement mortar due to bending. Thus, we conducted a series of tests and characterizations to validate our hypotheses and realize the potential of these two self-healing systems.The UF microcapsules exhibit good performance in mitigating the total shrinkage of cement mortar during the 35-day curing period. With the aid of polyvinyl alcohol (PVA) microfibers, the mitigating performance could be further improved. Moreover, this self-healing system could reduce the gas permeability of cement mortar. The scanning electron microscopic observation confirms the healing behavior and validates the chemical composition of healing products. Besides, the UF microcapsules could significantly enhance the durability of cement concrete subjected to freeze-thaw cycles. The 3-D X-ray microcomputed tomography (CT) reveals the enhancing mechanism. We developed a probabilistic damage model based on Weibull distribution and the predicted service life of such self-healing concrete is extended 10 times.Based on the response surface method, the LWAs impregnated with saturated Ca(OH)2 solution are encapsulated by modified PVA films with the optimal designs. The mechanical regain of cement mortar with/without LWAs is determined through three-point bending test. According to the experimental results, the relationship between the mechanical regain and healing period is proposed based on fracture mechanics.To fully validate these models, the test of relative dynamic modulus of elasticity till the failure of concrete and mechanical regain after a longer healing period will be conducted in the future
