The effect of polyurea coatings on spalling and breach of reinforced concrete slabs under contact explosion

Polyurea-coated reinforced concrete (RC) has been extensively studied both experimentally and numerically for structural strengthening against contact explosion; however, theoretical investigations remain limited. This paper proposes an analytical model based on stress wave propagation theory to (a) investigate the reflection of compression waves at the backside of the RC substrate slab and (b) predict the spalling depth. Utilizing this analytical model, the effects of polyurea coating on the critical spalling and critical breach of RC slabs are discussed in further detail. Furthermore, the feasibility of applying the empirical breach prediction, originally developed for uncoated RC slabs, to predict the breach of polyurea-coated RC slabs is validated through existing experiments. The results indicate that the polyurea coating influences the spalling process of the RC substrate slabs. Specifically, the net stress wave adjacent to the concrete-polyurea interface is a compression wave, while in the deeper concrete, it transitions to a tensile wave. The polyurea coating primarily affects the first spall of the RC substrate slab; subsequent spalling processes after the first spall align with those observed in uncoated RC slabs. Upon the occurrence of critical spalling, the polyurea coating enhances the critical spalling resistance of RC slabs, although it significantly increases the spalling depth. Conversely, when a critical breach occurs, the polyurea coating reduces the number of spalling but has a minimal effect on the total spalling depth. Based on these findings, it is proposed that the empirical method for predicting breaches in uncoated RC slabs can be applied to predict breach damage in sprayed polyurea-coated RC slabs, and existing experimental results validate this extrapolation.