Creating a connection between asphalt wearing surface and timber bridge decks

Timber bridges are increasingly popular again in infrastructure networks nowadays. Protection of timber structural elements from direct exposure to rain and sun is essential to prevent biological degradation of the wood material when using softwoods. In case of a timber deck, the asphalt wearing surface must be water-tight. Creating connected layups has advantages over layups where the asphalt is not connected as traffic loads are transmitted directly to the bridge deck: asphalt surfaces can be loaded with heavier traffic, slopes of bridges can be higher, breaking and acceleration loads are directly transmitted to the bridge deck, and fatigue life of the asphalt is improved. The Swiss standard VSS 40 451 standardized an unconnected mastic asphalt surfacing on timber bridges. Research project VSS 2016/326 was performed to investigate road layups where asphalt wearing surfaces were connected to the bridge deck. This work presents only a part of the results, focused on the bonding issues. Results show that such a layup proves to deliver satisfactory performances, and that shear capacity is comparable to that of concrete and steel decks. Good surface qual-ity of the timber deck is important before application of the bonding agent to avoid short term blistering of the asphalt.