Cause Analysis and Influence Evaluation of Cracks in Thick Slab Construction

Cracks were found in the slab of a nuclear power plant when the formwork was removed. By means of ultrasonic testing, water storage test and crack width detection, the fracture distribution, depth and width characteristics are determined. On this basis, the numerical simulation analysis of hydration heat in the maintenance process is carried out to simulate the possible crack generation and distribution of the floor slab in the maintenance process. The simulation result shows that cracks under the combined action of temperature and shrinkage are consistent with the cracking characteristics of floor slab. Through numerical simulation of the cracked floor and intact floor, the change of the out of plane bearing capacity (bending and shear) of the cracked floor is compared and analyzed. In the model, considering the reduction of the bearing capacity at the crack section and the change of load transfer effect at the crack interface, the concrete model is disconnected according to the known opening situation, and the contact relationship is set on the crack interface to simulate the crack. Through comparative analysis, the mechanical properties of the cracked floor are evaluated, and the refined numerical simulation method of the working components with cracks is proposed. This paper can provide guidance for the cause analysis and influence evaluation of similar thick plate cracking phenomenon.

Effect of Microcapsule Content on Diels-Alder Room Temperature Self-Healing Thermosets

A furan functionalized epoxy-amine thermoset with an embedded microcapsule healing system that utilizes reversible Diels-Alder healing chemistry was used to investigate the influence of microcapsule loading on healing efficiency. A urea-formaldehyde encapsulation technique was used to create capsules with an average diameter of 150 µm that were filled with a reactive solution of bismaleimide in phenyl acetate. It was found that optimum healing of the thermoset occurred at 10 wt% microcapsule content for the compositions investigated. The diffusion of solvent through the crack interface and within fractured samples was investigated using analytical diffusion models. The decrease in healing efficiency at higher microcapsule loading was attributed partially to solvent-induced plasticization at the interface. The diffusion analysis also showed that the 10% optimum microcapsule concentration occurs for systems with the same interfacial solvent concentration. This suggests that additional physical and chemical phenomena are also responsible for the observed optimum. Such phenomena could include a reduction in surface area available for healing and the saturation of interfacial furan moieties by reaction with increasing amounts of maleimide. Both would result from increased microcapsule loading.