Cracking of wearing courses on steel orthotropic bridge decks

Asphalt surfacing on steel orthotropic decks act compositely with the steel deck plate and must be regarded as an integral part of the structural deck system. It should be watertight, develop no cracks and well bonded to steel deck plate, besides providing a smooth riding surface with high skid resistance for the driver. Cracking of the asphalt surfacing on steel decks will do great harm not only to the surfacing itself but also to the steel structure. This paper reported in-site crack survey on wearing surfaces of more than ten bridges, including gussasphalt, SMA with polymer modified asphalt and epoxy asphalt. It is found that all cracks are top-down cracking. The cracks were classified into four types according to its characters of geometry and location, with the names of regular cracks, short hair cracks, bubble cracks and slippage cracks. Causes of the cracking of asphalt surfacing on steel orthotropic decks were discussed. Regular cracking is believed to be a fatigue matter according to 3-D Finite Element Analysis. Short hair cracking and bubble cracking are mainly related to construction defects, while slippage cracking is primarily due to the interlayer lack of bonding strength and shear resistance.