MECHANISM OF LONGITUDINAL SURFACE CRACKING IN PAVEMENTS ON STEEL BRIDGE DECKS

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Longitudinal surface cracks (LSC) are often observed in asphalt pavements on steel bridge deck. The cracks appear longitudinally on pavement surface in wheel paths and their spacing coincides with a half of spacing of longitudinal ribs. The objective of this study is to find the causes and mechanism of the LSC. A condition survey was conducted on more than 50 steel deck bridges to investigate actual conditions of pavements on the bridges. The survey revealed that LSC actually starts from pavement surface but does not reach its bottom, and that they appear not only above the webs of main girder or longitudinal ribs but also between the webs. Behaviors of asphalt mixtures at high temperature were investigated. It was observed that at high temperature small cracks really occurred around aggregates and grew further. The reason of the cracking was that the aggregates vertically moved by wheel load and broke thin films of aged asphalt binder around the aggregates. A computer simulation was performed using a newly developed FE model, in which a steel deck structure is modelled with a strip element and the pavement on it is modelled with a prism element. To take into account viscosity of asphalt materials, the Burger model was incorporated. In the simulation, axle loads traveled over a pavement and variations of stresses and strains in the pavement with time were calculated. The dissipated energy in the pavement was estimated. The simulation results suggested that high dissipated energy at the pavement surface between webs might cause the LSC there, which was not able to be explained with fatigue analysis based on the tensile strain fatigue criterion.