Constitutive relations, mechanical behaviour, and failure criterion of microcapsule-based self-healing concrete under uniaxial and triaxial compression

Microcapsule-based self-healing concrete can autonomously release repairing agents to bond and seal cracks when the material is damaged. It is seen as a promising construction material from the perspective of a sustainable society. In addition, it is important to study mechanical behaviour under complex stress conditions to promote the application of self-healing concrete in engineering structures. This study investigated the constitutive relations, strength and deformation, and failure criterion of the epoxy/urea-formaldehyde microcapsule-based self-healing concrete through uniaxial compression, conventional triaxial compression and true triaxial compression tests, in which the influence of different microcapsule dosages, confinement pressures and the principal stress ratios on the mechanical behaviours was considered. The results showed that the ultimate strength of the specimen decreased with increasing microcapsule dosage under all loading conditions. The lateral pressure significantly promoted the ultimate strength and deformation capacity of the specimen, and this increase mainly depended on the maximum principal stress (σ1) rather than the intermediate principal stress (σ2). By visual checking the failure modes of the specimens, more cracks were observed under the conventional triaxial compression than those under the true triaxial compression. This multi-crack failure mode allowed more core material of microcapsules to enter the microcracks, which accordingly increased the strength of the microcapsule-based concrete.