– driving comfort (inclusive bikes and motor cycles);

– noise reduction;

– easy application and maintenance;

– economically competitive。

Due to the fact that BEJs are critical elements in asphalt bridge deck pavements that must meet high multifunctional requirements for avoiding failure, the Swiss Federal Road Office has issued guidelines in 2005 [7] based on different research projects performed by Empa which led to a considerable improvement of quality and performance of this type of plug joints [2, 3]。 This work together with activities and experience in other European countries will soon lead to the European Technical Approval Guideline ETAG n° 032 for Expan- sion Joints for Road Bridges, Part 3: Flexible Expansion Joints。

Figure 1。 Damage of BEJ (from left to right): material transport。 & displacement & run out in summer; aggregate loss & surplus of binder; cohesion cracks & adhesion cracks along BEJ site in winter; cracks from too large BEJ movement > 30 mm

2 Flexible bituminous plug expansion joint systems

2。1 Structural elements and Materials

Bituminous plug joint systems (BEJ) for bridges are defined as in-situ poured flexible plug expansion joints comprising a band of specially formulated flexible joint filling material which is filled in a trench flush to the surface of the asphalt bridge deck pavement as schematically shown in Figure 2。

Abutment  Construction

Gap Opening 10。。。60mm

-10。0。。。+20mm =30mm

Figure 2。 Elements of flexible bituminous plug expansion joint systems for small (b ≤ 500 mm) and large (500 mm) joint movements (schematic); PBM = Polymerbitumen sheet; MA= Mastic as- phalt

The trench of BEJs for small movements is typically 500 mm wide and 70&pide;160 mm thick。 BEJs for large movements may have a width of 1000 mm。 The maximum acceptable slope in any direction is 6% and the horizontal angle between bridge axis and the longitudinal axis of the BEJ should not be less than 65° [7]。

Bituminous joint filling material may be a mixture composed of gap graded aggregates serving as mechanical skeleton for carrying the traffic loads and an elastomeric polymer- modified bituminous binder typically of a Styrene-Butadiene-Styrene (SBS) type。  However,

different other bituminous filling materials are possible and, in fact, under continuous de- velopment。 The filling material forms the surfacing and is topped by a chip surface dressing for skid resistance purposes。 It is supported across the bridge deck joint gap by thin metal plates or other suitable components with some sliding capability which prevent the filling material to be squeezed into the gap by traffic loads。 The gap normally has a width of 10&pide;60 mm。 In order to avoid stress concentrations and cracks, friction between the steel plate and the joint material should be reduced to a minimum。 This may be achieved by a fabric layer serving as a separation between the filling material and the steel plate。

2。2 BEJ for small joint movements

According to the ASTRA guidelines [7], plug joint systems are required to work within a temperature range from -10 °C to +40 °C and, in case of BEJs for small joint movements, BEJs are expected to take repeated gap closing and opening between -10 mm and 20 mm (assuming zero-opening at 10 °C)。 With respect to bridge bearing replacements, plug joints should also be able to endure vertical gap movements to a maximum of 5 mm。