## 1 Conventional Asphalt Pavements Used on Bridges  
Bridge pavements behave differently from typical pavements placed on the ground. There are a number of design criteria that can be used to design road pavements with optimum dimensions [1; 2; 3] yet these criteria are not applicable to bridge pavements. In the latter case, there are no unequivocal design criteria [4; 5] and conventional design methods turn out to be inadequate for bridge pavements [6]. The actual life of bridge pavements turns out to be shorter [7] than the life of ground-supported pavements. In addition, bridge designers, focusing primarily on the structural aspects and the load capacity of the bridge itself, fail to approach the problem of bridge pavement durability in a correct manner. On bridges we deal with specific loading conditions [8; 9], different from those found in the case of ground-supported structures. These specific conditions include, without limitation, the possibility of high amplitudes of vertical deflections (imposed by vehicles) and horizontal displacements (due to temperature variation) and vibration of the supporting structure. Bridge pavements have the following main functions [10; 11]:  
* Spread the loads over the bridge deck;
* Dampen the dynamic effects caused by traffic loading;
* Accommodate strains of the bridge deck caused by temperature variation in the range \(-30\)\({}^{\circ}\)C to \(+70\)\({}^{\circ}\)C;
* Ensure the required interlayer bond, including bond between the waterproofing layers and the deck;
* Ensure the required evenness, tightness, surface roughness and resistance to abrasion, rheological effects and rutting;
* Reduce sensitivity of the asphalt mixtures to both low and high temperatures. Different designs were applied in Poland and other European countries for bridge pavements [12; 13]. At present, bitumen-bound materials [4; 9; 13; 14] are used most often on bridges. The conventional surfacing systems used on bridge decks comprise the waterproofing layer, protective (binder) course and wearing course (Figure 1). The waterproofing layer is an important part of the bridge surfacing system and should [15; 16; 17]:  
* Be impervious to water, water vapor and gases;
* Be resistant to the action of chemicals related to operation and maintenance of roads;
* Have smooth surface to facilitate drainage of water from the surface and reinforcing fleece embedded in the binder (if designed);
* Be made of materials whose coefficient of thermal expansion is similar to that of the bridge deck,
* Be elastic over a wide temperature range (-30 \({}^{\circ}\)C to +70 \({}^{\circ}\)C);
* Adhere well to base and ensure good bond with the protective or wearing courses (in the case of one-layer surfacing systems);
* Be resistant to mechanical damage and the working temperatures of asphalt mixture used for the protective layer (at least 160-240 \({}^{\circ}\)C). The waterproofing layer should be at least 5 mm thick in the case of sheet materials and at least 2 mm thick in the case of coatings. Torch-on membranes are the most popular deck waterproofing material used on the bridges in Poland [18]. However, torch-on membranes involve certain risks, related, inter alia to their application (bonding to the base in particular) and the process of placing of mastic asphalt to the protective course. These risks include [19; 20; 21]:  
* Burning through the membrane during application (the temperature of burned gasses during heating up the underside of the membrane with a gas torch can reach from about 700 \({}^{\circ}\)C to as much as 1400 \({}^{\circ}\)C) (Figure 2). Figure 1: Typical arrangement of pavement layers on the bridge deck. Figure 2: Application of a torch-on membrane—heating up the material with gas torches. * Forming of bulges during placement of the protective layer due to local lack of adhesion between the membrane and substrate and the increase in partial pressure of air in the voids. * Destruction of membrane (structural degradation).