Abstract
Self-healing cementitious materials containing a microencapsulated healing agent are appealing due to their great application potential in improving the serviceability and durability of concrete structures. In this study, poly(phenol–formaldehyde) (PF) microcapsules that aim to provide a self-healing function for cementitious materials were prepared by an in situ polymerization reaction. Size gradation of the synthesized microcapsules was achieved through a series of sieving processes. The shell thickness and the diameter of single microcapsules was accurately measured under environmental scanning electron microscopy (ESEM). The relationship between the physical properties of the synthesized microcapsules and their micromechanical properties were investigated using nanoindentation. The results of the mechanical tests show that, with the increase of the mean size of microcapsules and the decrease of shell thickness, the mechanical force required to trigger the self-healing function of microcapsules increased correspondingly from 68.5 ± 41.6 mN to 198.5 ± 31.6 mN, featuring a multi-sensitive trigger function. Finally, the rupture behavior and crack surface of cement paste with embedded microcapsules were observed and analyzed using X-ray computed tomography (XCT). The synthesized PF microcapsules may find potential application in self-healing cementitious materials.
Highlights
Crack-induced deterioration is one of the severest threats to the safety and durability of cementitious structures, which gives rise to large amounts of rehabilitation work, associated costs and waste of resources every year
Thanks to its excellent water and chemical resistance as well as a low flammability and toxicity, phenol–formaldehyde (PF) resin has been suggested as a promising component of the polymer–cement composites to be used in the civil engineering field [8,9]
It can be clearly seen from the images that the shell of the microcapsules is homogeneous with pores in it
Summary
Crack-induced deterioration is one of the severest threats to the safety and durability of cementitious structures, which gives rise to large amounts of rehabilitation work, associated costs and waste of resources every year. In recent years, inspired by the phenomenon of tissue regeneration in biology, microcapsule-based self-healing cementitious composite has gained a great popularity in the civil engineering field [1,2,3,4,5,6,7]. These mechanically triggered capsules are placed in the cementitious structure during the process of concrete mixing. Research has focused on developing a practical container for the healing agent This resulted in a series of mechanical trigger microcapsules, which yield promising application potential. The healing agent with a PF resin shell has higher stability in cementitious materials and the possibility to be triggered by crack propagation
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