Research on anti-shear performance of waterproof adhesive layer (WAL) in polyurethane-mixture steel-bridge pavement structure

Polyurethane-mixture pavement materials for steel bridges have excellent overall road performance and are expected to solve the durability and short service life problems of traditional asphalt-based steel-bridge pavement materials under harsh bridge usage environments. A waterproof adhesive layer (WAL) with good shear resistance is essential to fully exploit the outstanding performance of polyurethane pavement materials. However, research in this area is currently limited. This study applied polyurethane, which has good bonding performance with polyurethane pavement materials, as WAL. The impact of the coating amount of WAL, amount of crushed stone, and curing time on its shear performance were analyzed by conducting anti-shear strength tests and shear-fatigue tests. The results were then compared with those of epoxy resin WAL. The results indicate that the shear performance of polyurethane WAL is significantly better than that of epoxy resin WAL. At a crushed stone amount at 50%, coating amount of WAL in the range of 0.2-0.7k g/m2, and curing time of 60 min, the shear strength of the polyurethane WAL was 2.35-2.41 times that of epoxy resin, and the shear fatigue of polyurethane WAL was 1.14-1.28 times that of epoxy resin under the same conditions. The shear strength initially increases and then decreases with the increase in the WAL coating amount. However, the shear-fatigue life continues to increase with the increase in the WAL coating amount. The optimal coating amounts for polyurethane and epoxy resin WALs are 0.5 kg/m2 and 0.6 kg/m2, respectively. The anti-shear strength and shear-fatigue life decrease continuously with the increase in the amount of crushed stone. The addition of crushed stone reduces the anti-shear performance between the WAL and polyurethane-mixture pavement layer. Therefore, the recommended amount of crushed stone is 50%. During construction, a minimal amount should be applied while meeting the non-sticking requirement of construction-machinery rollers. The shear strength of the polyurethane-mixture pavement layer laid using both types of WALs in a dry-to-touch status is significantly higher than that laid using liquid or dry-hard WALs. The optimal curing times for the polyurethane and epoxy resin WALs are 60 min and 90 min, respectively.