Effect of mineral microcapsules on self-healing properties of cement mortar

Cement-based composites are prone to cracking under the influence of many physical and chemical factors, which affects their durability. Improving the crack self-healing performance of cement-based composites is the key to improve their durability and reduce the maintenance cost throughout their life cycle. Therefore, based on the three functional characteristics of crystal expansion, water storage and release, and auxiliary reinforcement, this paper developed an all-inorganic microcapsule cement-based crack self-healing material integrating repair and reinforcement, with three minerals, namely composite expansion agent, Na-bentonite and talc powder, as the core material, and alkali exciting material (water glass stimulated metakaolin) as the wall material. Based on the study of intrinsic mechanical properties, with strength recovery rate, crack width healing rate and crack area healing rate as evaluation indexes, the influence of microcapsule on the crack self-healing effect of cement mortar specimens was explored, and the self-healing mechanisms were analyzed through microscopic testing. The results show that the strength of mortar increases first and then decreases with the increase of microcapsule content. When the dosage is 10%, the 28d flexural and compressive strengths of mortar are the highest, which are 6.17% and 4.39% higher than that of blank group, respectively. With the same dosage, the strength recovery rate reaches 115.5% after secondary cured in water for 28 days, and both the average and normalized crack area healing rates are 100% and 72.3%, respectively, at 35d, which are much higher than 55.3% and 37.7% of the blank group. The XRD and SEM analysis show that under the condition of secondary curing, a large number of hydration products such as Ca(OH)₂, AFt, CaCO_3, Mg₃Ca(CO₃)₄ and C-S-H gel with micro-expansion, high strength and good cementitious properties are generated at the crack, so as to realize rapid filling, repairing and reinforcing of cracks.