## 1 Introduction  
Based on the principle of bionics, the intelligent integrated concrete materials and structures with self-healing ability are prepared. They can automatically locate and repair the micro-damaged parts in the concrete structure and improve the performance of the concrete materials. Bionic self-healing of concrete material refers to imitating the damage healing function of biological tissue, whereby the special components that are embedded in the cementitious matrix form an intelligent self-healing system. When cracks initiate due to damage, the healing system that is embedded in the matrix is triggered by the force, heat, or chemical damage and releases a healing agent to bond the cracks and prevent further extension of the crack, with the purpose of achieving the repair. When compared with the traditional repair technology, a self-healing system has the advantages of low cost, no need to rely on external operations, good renewability, etc. For self-healing, a relatively rapid response is required to reconstruct the structural integrity or to prevent to a certain extent further propagation of the crack [1; 2; 3; 4; 5; 6; 7]. In recent years, various studies have been conducted using microcapsule technology to achieve self-healing functionality in cementitious materials [8; 9; 10; 11; 12; 13; 14; 15; 16]. [PERSON] et al. [17; 18; 19] fabricated microcapsules using rejuvenator diphenylsilane (DPS) as the core material and analyzed the diffusion behavior of microencapsulated rejuvenator in aged bitumen by Fourier-transform infrared spectroscopy (FTIR). They also investigated the self-healing performance of bitumen by a modified fracture healing-refracture method through a repetitive tension test using microcapsules containing rejuvenator. Later, they employed a modified beam on elastic foundation (BOEF) method to investigate the mechanical properties of bitumen/microcapsule materials, in which microcapsules of different sizes and shell thickness were evaluated. [PERSON] and [PERSON] et al. (20,21) developed a type of polymeric microcapsule for the self-healing of microcracks in cementitious materials, while using phenol-formaldehyde resin for the shell and dicyclopentadiene as the healing agent. They examined and analyzed the rupture behavior and crack surface of cement paste with embedded microcapsules by X-ray computed tomography (XCT). In addition, the chemical stability of the microcapsules and the trigger performance were verified in a simulated concrete pore solution and hardened cement paste specimens. Additionally, the relationship between the physical properties of the microcapsules and their micromechanical properties were investigated using nanoindentation. They found that the mechanical force that is required to trigger the self-healing function of microcapsules increased with the increase of the mean size of microcapsules and the decrease of shell thickness. [PERSON]'s group (20, 21, 22) used encapsulated bacterial spores for self-healing concrete. They investigated the applicability of encapsulated spores and the influence of microcapsules on mortar specimens. The crack healing ratio and the water permeability were evaluated to determine the self-healing capacity. They also studied the microstructure of the capsules containing self-healing materials by micro-computed tomography analysis. The results of this analysis revealed the three-dimensional distribution and de-bonding of the microcapsules in their native state in a polymer system with self-healing properties. They also studied the rupturing capability of microcapsules when crossed by a crack in concrete of a typical size. The suitability of five types of polymeric capsules was assessed by using a numerical model to screen the best performing capsules and verifying their suitability by experimental methods. Capsules that were made of a specific type of poly(methyl methacrylate) (PMMA) were evaluated. They determined that thick walls were unsuitable as the microcapsules ruptured for larger crack sizes.