Surfacing on bridge structures is not, and should not be, like that of a standard pavement on a soil subgrade. The essential difference lies in a different mode of operation. There are special circumstances that must be considered, including the following:
• The cooling and warming effect developing from underneath the bridge deck pavement caused by changes in air temperature under the steel structure and faster changes of the pavement temperature due to wind action, which occurs faster and more intensely than in case of a pavement on grade
• Structural deflections of a bridge’s deck caused by passing vehicles
• The amplitude of bridge deck vibration, which is much higher than that of conventional road pavement
• Much more intensive applications of deicers, leading to the quick degradation of asphalt mixes applied on bridges
For all these reasons, asphalt pavements on bridge decks are subjected to faster deterioration than their soil subgrade equivalents. Therefore, when designing a combination of bridge pavement courses, some additional points have to be observed as follows:
• The critical element influencing the pavement service life is the durable bonding of all the layers together (asphalt courses with a protection layer and the deck).
• The more flexible the structure, the more elastic the asphalt layers should be.
• Good compaction of the layers should be taken into consideration because it results in low-water permeability, although rolling on a low-stiffness bridge is challenging.
The deflections of orthotropic plate structures are usually higher than structures with cement concrete deck slabs. Consequently, when asphalt mixes are constructed on steel orthotropic structures, the most frequently applied asphalt mixes are those with the highest fatigue strengths (e. g., mastic asphalt with a highly modified binder) (Damm and Harders, 2000). In some countries, fine-graded SMA has been also used (see Section 13.2.1). Some interesting concepts and analyses can be found in several papers dealing with this subject (Huurman et al., 2003; Medani, 2001a; Medani, 2001b).
