Damage may occur in summer time when BEJs may be too soft and the filling material may be squeezed out by the tires, e。g。 in case of breaking。 In winter time, damage may show up as cracks, or, even worse, as debonding between BEJ and pavement (Fig。 3)。

In order to obtain a fully functional and waterproof system, the interface between the asphalt pavement and the bituminous plug joint materials deserves special attention [4]。 This is particularly true during the construction phase which requires careful pre-treatment and activation of the BEJ-tanking sides and should only be carried out on dry material and in dry atmosphere (no rain)。 In addition, these pavements must have an air void content of less than 6 Vol-% otherwise a 1。0 m wide pavement patch of dense pavement, such as MA, should be placed on both sides of the BEJ in order to avoid lateral water infiltration during construction and under service conditions because of the water barrier effect of the BEJ。

2。3 BEJ for large joint movements

In case of BEJs for large joint movements (b 500 mm), most of the basic principles and requirements remain, of course。 However, the system may contain additional mechanical moving aids that are surrounded by the BEJ filling and mechanically anchored to the con- crete of the bridge deck on both sides of the joint。 This makes the system more complex and deserves additional consideration。 In Figure 2, half of such a system with a row of springs embedded in the filling is depicted schematically。

The steel plate may be replaced in these BEJs by a more sophisticated sliding plate kit with one-sided fixation。 The construction of these sliding plate kits is special and may lead to premature failure。

Figure 3 shows an example of a sliding plate kit where failure at -20 °C was observed in a joint movement test with a joint opening velocity of 10 mm/h (see below) after two ten- sion compression cycles reaching only about 35% of the intended joint opening capacity [1]。 Also shown is the linear elastic 3D Finite Element calculation of the normal stresses in the gap opening direction with Abaqus which clearly reveals a stress concentration around the bolts for the case shown left of the figure。 This stress could be reduced by countersunk bolt heads as shown to the right of the figure。 With this improved configuration the BEJ survived 20 cycles at -20 °C。

Figure 3。 Top: Failure in tension at -20 °C (left), normal stresses in gap opening direction (right) - arrows mark the critical bolts; Bottom: Different fixations of the sliding plates, with protruding bolt heads (left) and countersunk bolt heads (right)

Depending on the type and construction of the mechanical movement aids, BEJs for large deformations may have some advantages with respect to the adhesion stress situation at the interface between the filling material and the adjacent pavement material。 As shown in Fig- ure 4, most of the stresses are taken over by the mechanical fixation of the movement aids。 This does not prevent from a good pre-treatment of the BEJ-tanking side and a careful fill- ing to assure waterproofing, of course。 It also means that the distance between the fixation and the tanking side should be large enough to allow proper filling。

Figure 4。 Von Mises stresses concentrating at the fixation of the moving aids of a BEJ for large joint movements

3 Testing of flexible bituminous plug expansion joint systems

3。1 General test methods

BEJs are special multifunctional bridge deck pavement elements that may have high impact on traffic safety (skid resistance, evenness, potholes from material loss) and durability of the bridge structure。 Hence, they must be carefully evaluated and tested in type and quality testing as well as self-control testing during construction and placing。 Testing of BEJs for small joint movements comprises testing of binder, aggregate and BEJ filling as well as test- ing of the BEJ system。 Most of these tests are well known and related to European Stan- dards。 All tests are explained in detail in the guidelines [7] and are therefore not described here。