The performance of surfacing overlaying bridge deck waterproofing systems

Information on the specification and performance of the surfacing overlaying concrete bridge decks owned by the Highways Agency is described. The main factors that affect the performance of surfacing of total thickness less than 100 mm, and the possible causes of the premature failures that have occurred on some bridges with liquid-applied waterproofing systems are identified. The results from laboratory tests that were carried out (i) to identify factors that affect the bond of surfacing to two bridge deck waterproofing systems, including wheel loading, (ii) to investigate the flow of sub-surface water through surfacing, and (iii) to measure the stiffness modulus of four waterproofing systems are presented. The local strains inducing by wheel loading in surfacing overlaying waterproofing systems that were calculated using the finite element method are reported. Recommendations are proposed to improve the durability of the surfacing on bridges that concern the provision of sub-surface drainage, the characteristics of the waterproofing system, the void content of the surfacing directly overlaying the system, and the bond of the surfacing to the system. The role of the red sand asphalt layer that is currently specified as an additional protective layer to the waterproofing system and is intended to act an indicator layer during resurfacing works is discussed, and its replacement is recommended.