A novel debonding failure test method for polyurea-composite anti-seepage coatings in water conveyance tunnels

Polyurea composites are widely used as anti-seepage materials in hydraulic structures. Although the pull-off adhesion test is commonly employed to evaluate their performance, it may not accurately predict their impermeability under field conditions. To address this limitation, a new testing device was developed to directly assess the impermeability of polyurea composites under both forward and reverse hydraulic pressure, thereby circumventing the effects of adhesive bond strength and material cohesive strength. Concrete surface coating tests using traditional pull-off adhesion and new hydraulic adhesion methods revealed that polyurea composites exhibited excellent anti-seepage performance under forward hydraulic action but weaker debonding resistance under reverse hydraulic action. The bonding area and substrate smoothness significantly affected the resistance of the coating to water pressure. Increasing the bonding area by 7.5% improved bond strength under hydraulic action by 80% and 86% for concrete and sandstone substrates, respectively. The traditional pull-off adhesion test overestimated the anti-seepage performance under reverse pressure, yielding average peel strength values being 106% higher than those obtained from the new water pressure test. Under cyclic water pressure, the resistance of the material improved, and the coating demonstrated self-healing properties. This study provides valuable insights for assessing polyurea performance in water conveyance tunnels and enhancing the durability of anti-seepage coatings.