Dynamic response and blast resistance mechanism of polyurea coating on RC slab during contact explosions

Polyurea (PU) coated reinforced concrete (RC) has been widely studied in structural strengthening under contact explosion, however, experimental investigations on dynamic response and failure mechanism of the coating during explosion remain scarce. In this paper, four contact explosion experiments are conducted on uncoated and rear side coated RC slabs. Dynamic strains and dynamic deformation of the coating are obtained by large-range strain gauges and a proposed measurement method based on a high-speed camera. Dynamic response characteristics of the coating are discussed and the blast resistance mechanism is further analyzed. Additionally, the effect of coating rebounding on the RC substrate and the effect of explosive placement on the coating are discussed. The results show that PU coating dissipates the blast energy through elastic deformation, plastic deformation, rupture and debonding. Glass transition at high strain rate may cause the rupture of the coating, and coating thickening significantly reduces the tensile strain rate under the same contact explosion conditions. With the development of breach and spalling of the RC substrate, PU coating on the rear side can be divided into four zones, and the blast resistance mechanism of the coating varies in different zones. Additionally, the elastic potential energy release of the coating may produce a secondary impact on the RC substrate. Coatings are more severely damaged when contact explosives are placed in locations that avoid rebars and should be considered as the most unfavorable load for the retrofitting of RC structures.