A 2D lattice model was constructed to simulate crack process of in shell-interlayer-cement paste zone. The simulated tensile strength was validated by an experimental uniaxial tensile test and used as the input for a 3D lattice model, which was constructed to perform mechanical analysis based on a series of 2D X-ray microtomography images. The fracture behaviour of the 3D lattice model with assigned mechanical properties gave a similar crack pattern and tensile strength as the real structure. This study is expected to provide a feasible approach for investigating the fracture and trigger behaviour miccrocapsules embedded in a self-healing cementitious system.

Two modified Mg-Al hydrotalcites (MHTs), (MHT-pAB and MHT-NO₂) were incorporated into mortar (with different w/c ratios) in two different ways: (1) as one of the mixing components in bulk mortar; (2) as part of cement paste coating of the reinforcing steel. Accelerated chloride migration, cyclic wetting-drying and diffusion tests were performed to investigate their effect on reinforcement corrosion. The results indicated that MHTs could be promising alternatives for preventing chloride-induced corrosion when an appropriate dosage is adopted and applied in a proper way, particularly, replacing 5% mass of cement by MHT-pAB in bulk mortar or as a coating of reinforcing steel (MHT-pAB/MHT-NO₂ to replace 20% mass of cement). The effect of MHT-pAB on time-to-corrosion initiation (TTC) of reinforcing steel was estimated using the DuraCrete model. It was found that the incorporation of 5% MHT-pAB in bulk mortar led to a more than double TTC relative to reference mortar without MHTs.

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.