Prediction Of Repairing Efficiency In Microcapsules Based Self-repairing Cementitious Materials Via XFEM Method

Cracks in cementitious composites are inevitable due to the defects such as high brittleness,weak tensile strength and early shrinkage.The cracks and crack network in the material not only reduce its mechanical properties,but also provide a channel for the invasion of harmful substances,which in turn causes the deterioration of the performance of the cementitious material and reduces the service life of the structure.The emergence of self-repairing technology in cementitious material overcomes the shortcomings of traditional repairing mode,such as passive repairing and high cost,and provides a possibility for the intelligent repairing of cementitious materials in engineering.The theory and technology of microcapsules based self-repairing has become a hot issue in the field of self-repairing cementitious material.In this paper,the mechanical property changes of cementitious materials were analyzed before and after the action of the embedded microcapsules by the extended finite element method(XFEM).The effects of different microcapsules shapes,sizes and crack sizes on the repairing efficiency of microcapsules were calculated and compared with the results of experimental studies from the literature.The prediction information of the repairing efficiency of microcapsules based self-healing cementitious materials was performed by modeling.Generally,the mechanical properties of cementitious materials will be affected once the microcapsules embedded.For a certain amount of spherical or spherical cylindrical microcapsules randomly dispersed into the cementitious matrix,this paper applies the Halpin-Tsai model and the Modified Mori-Tanaka method in composite material theory to calculate the effective elastic modulus of the composite material before repairing.Calculations prove that under the same shape,the elastic modulus of the self-healing system before repairing calculated by the two theoretical calculation models are almost the same.However,the negative effect of spherical cylindrical microcapsules on the elastic modulus of the matrix is less than that of spherical microcapsules.Also,compare the theoretical calculation value with the published articles’ experimental data before the microcapsules goes into working.The results show that the value of theoretical model are consistent with the experimental data,which indicates that the Halpin-Tsai model and Modified Mori-Tanaka methods can be used to calculate the elastic modulus of the composite before repairing.By applying extended finite element(XFEM)and writing Python scripts,the geometrical structure model of microcapsule based self-repairing cementitious composite material can be established under different shapes(spherical and cylindrical),sizes(500 μm-700 μm),contents(1%-5%),and different pre-crack depth,.The occurring,spreading and fracturing process of micro-cracks and microcapsule fracture behavior in the self-repairing model material were simulated and the geometric probability of crack forcing capsule rupture under randomly distributed conditions of the matrix capsule is verified.When the crack grows,the capsule ruptures and the repairing agent penetrates into the crack to complete the repair.Generally speaking,it can be considered that for this process self-repairing cementitious composites are transformed from two-phase composites with the addition of a one-phase cured repairing agent to a three-phase material consisting of a cement matrix,a microcapsule,and a cured repairing agent.After the repairing,the theoretical value of the elastic modulus of the three-phase composite was calculated by applying the Modified Mori-Tanaka theoretical formula,and the ratio of the elastic modulus of the composite before and after the repairing was used to characterize the efficiency of the self-healing effect.The results showed that the repairing efficiency of the microcapsule self-healing system decreases as the amount increases at low amount(1%-5%).The elasticity modulus of the microcapsule based self-repairing system was not affected by the change of microcapsule size at the same amount(3%).The optimal strategy could be found when the amount of microcapsules were doped at 3%,the crack length was 3 mm.