Modelling Of Repairing Efficiency Of Microcapsule-based Self-repairing Cementitious Material

Cementitious composites are inevitably to crack in engineering structures due to their inherent brittleness and low tensile strength.Cracks and the network can cause the deterioration of the performance of the matrix material,aggravate the degradations processes and reduce the service life of the structure.The capsule-based self-repairing system provides a feasible way to repair the cracks and effectively delays the potential damages in cementitious material matrix.Based on the size information and spatial distribution pattern of cracks in cementitious materials under service,as well as the amount and morphology of microcapsules,the efficiency model of capsules embedded in microcapsule-based self-repairing cementitious materials was developed in the paper from the perspective of interdisciplinary.The study will enrich the design theory of capsule-based self-repairing cementitious materials and be helpful for the application in practical engineering.Based on the theory of "homogenization theory" and "composite material theory",the microstructure of microcapsule-based self-repairing cementitious composites was characterized.According to the theory of homogenization theory and periodically multiscale modeling,a representative volume element(RVE)with representative microstructure was developed for microcapsule-based self-repairing cementitious materials.From the perspective of the probability that the crack forces the capsule to break,the theory of quantitative stereology and geometric probability was employed to investigate the self-repairing efficiency of the capsule-based cementitious material and an analytical model was developed where the amount of repairing agent released per unit crack area was taken as the efficiency parameter.The effects of capsule dosage,size and morphology(spherical and spherocylindrical)on self-repairing efficiency were studied.The results showed that the self-repairing efficiency increased with the increase of capsule dosage and size.In the case of the same amount,the self-repairing efficiency of the spherocylindrical capsule was not necessarily higher than that of the spherical capsule,and the efficiency value was also related to the aspect ratio of the spherocylindrical capsule and the size of the spherical capsule.The accuracy of the established model results was verified via a published data.Based on the extended finite element method(XFEM),the crack propagation in the two-dimensional self-repairing cement-based material under uniaxial tensile loading was simulated.In the three-dimensional case,the occurring,spreading and fracturing process of micro-cracks in the self-repairing model material were simulated where microcapsules with different shapes,sizes and dosages were embedded,and then the volume fraction of microcapsules on the fracture surface was obtained.The repairing efficiency was characterized by the change of elastic modulus before and after self-repairing working.The effects of volume fraction,size and morphology characteristics on the elastic modulus of microcapsule-based self-repairing cement-based materials were simulated before and after self-repairing.It was found that,when the capsule content was 3% the self-repairing efficiency for both the spherocylindrical and spherical capsules reached the maximum and the efficiency of the spherocylindrical capsule was higher than that of the spherical one.At the same time,when the microcapsule diameter was 400 ?m,the repairing efficiency get higher for spherical microcapsule-based self-repairing cementitious materials.