Two-component polyurethane healing system: Effect of different accelerators and capsules on the healing efficiency of dynamic concrete cracks

The application of an autonomous healing system to concrete structures includes the encapsulation of a polyurethane (PU)-based healing agent in the concrete, with the system being triggered when a crack forms and propagates through the concrete. This concrete repair technology enables the extension of the operational service life of structures. In the present study, three novel types of healing agent encapsulation systems were considered, namely, body-contact double capsule, parallel-style double capsule, and concentric-style capsule. The compatibility of the PU healing agent with a dynamic crack was examined using different accelerants. The adhesion area of the crack was also investigated for different healing systems with respect to the capsule type, capsule spacing, accelerant, and crack width. Three-point bending tests were conducted to evaluate the strength contribution of the healing agent after concrete repair. The strain capacity of the healing agent was further evaluated qualitatively and quantitatively by both visualization and water absorption tests. It was found that the healing system that utilized a parallel-style double capsule with a spacing of 0.8 cm and a composite accelerant enabled 61% recovery of the concrete strength after the healing of a 150 mu m wide crack. The system also enabled concrete samples with wider cracks to recover 50-100% of their original strain capacity. These observations confirmed the potential of the healing system for use in enhancing the durability of concrete structures exposed to water absorption tests. Furthermore, the results of mechanical performance tests revealed that the degree of strength recovery is proportional to the adhesion area of the healing agent within the crack. (C) 2019 Elsevier Ltd. All rights reserved.