Application of self-healing engineering materials: Mechanical problems and research progress

Abstract

In order to meet the needs of future infrastructure and industrial construction, namely building new advanced infrastructures with intelligent capabilities, the optimization of the structure and material composition design in traditional civil engineering has aroused general interest in both industrial and academic fields. The damage resistance of engineering structure has a direct impact on the social and economic cost to a country. To considerably reduce the maintenance cost and improve the service life of engineering structures, a feasible scheme is to build a life-like system with the capability of self-healing. In recent years, techniques like microcapsule self-healing, electrodeposition self-healing, induction heating self-healing and microbial self-healing have been widely used in civil engineering and road engineering, which are expected to improve the durability and stability of engineering structures, thus prolonging their service life to the maximum extent. However, the improvement of the performance of self-healing engineering materials and the accurate prediction of the crack propagating trajectory and the service life of the materials require a better understanding of the self-healing mechanism. In this review, the development and the advancement of the application of self-healing materials in civil engineering are firstly summarized. The self-healing mechanisms of cement concrete and asphalt, the two most used materials in civil engineering, are concluded, respectively. However, due to the low efficiency of the materials’ natural self-healing capability, some enhancement technologies are proposed and applied to improve the self-healing performance of those engineering materials, which are summarized in the later introduction. In the second part, the mechanical analysis for the explanation and prediction of the self-healing behaviors is introduced in detail based on damage and fracture mechanics. Besides, there are still some mechanical problems that remain unsolved, such as decoupling of elastic effect and self-healing effect on macro performance recovery and establishing a fatigue model considering damage evolution, crack propagation and self-healing effect, which are also summarized and analyzed. In the third part, the existing constitutive models considering self-healing effects and the relevant numerical algorithms are reviewed. Based on the three basic hypotheses, namely the strain equivalent hypothesis, the strain energy equivalent hypothesis and the power equivalent hypothesis, the effective configuration considering damage-healing effect is described. Additionally, relatively detailed review is given on the numerical algorithms considering self-healing mechanism with the aid of molecular dynamics (MD) and finite element method (FEM). Finally, the unsolved problems and challenges are proposed for further researches, where the coupling effects of the internal and external factors on the damage-fracture-healing process will be studied from a mechanical point of view. Therefore, the deep understanding of the healing and damage behavior of materials needs sufficient multi-scale analysis involving nano-scale, micro-scale, meso-scale and macro-scale. To sum up, self-healing materials play an important role in improving the durability and reliability of engineering structures. Therefore, the improvement of the self-healing efficiency is the key point to realize the wide and high efficient application of self-healing materials in civil engineering, which needs not only an essential understanding of the mechanical mechanisms but also fast numerical algorithms to accurately evaluate and predict the self-healing behavior.