L-profile-substitutes for adjoining pavement

Figure 14。 Test results of S7 at –20 °C and 9。2 h/cycle (left); horizontal expansion in S9 at joint openings after 30 mm and 65 mm at –20 °C (right)。

The maximum force for S9 and S7 at –20 °C was approx。 80 kN and 60 kN respectively。 After the first cycle, the force decreased by about 20% to 30% (Fig。 14) showing clearly that the maximum loading capacity during gap opening has been reached before the gap closing movement was activated。 This gap closing movement started at the inflection point。 During the gap opening of the next cycle, the load could not exceed the load value in this inflection point, of course。 Reaching the maximum loading capacity during the first cycle is a clear indication that significant damage in the BEJ occurred。

During joint opening of S9 up to 65 mm at –20 °C, strains between the adjoining asphalt pavement and the L-shaped steel anchors of the springs remained minimal and most de- formations were distributed in the zone between the two L-shaped steel anchors。 The part of the asphaltic plug joint above the sliding steel plate suffered the most significant local expansion (Fig。 14)。 In JMS tests, S9 showed significant lateral contraction of about 16 mm and a thickness reduction of 7 mm。文献综述

Neither crack formation nor lateral debonding was observed in S9 after 20 test cycles。

One of three S7 specimens suffered a crack after 18 cycles。

Investigations of the in-situ performance of S9 and S7 BEJs on bridges after about 1&pide;6 years took place together with different experts, comprising visual assessment of cracking in the asphaltic joint filling material, lateral debonding, debonding between joint and pave- ment, blistering, material dislocation, local deepening of the surface, water tightness, etc。 (Fig。 15)。

Generally, the different plug joints were in good condition。 However, it has to be kept in mind that the assessment was not conducted at minimum temperatures (important for cracking) for practical reasons。 Apart from a few defects, such as lateral debonding at the bridge parapet and in the centre line of the motorway in case of two relatively new sites, the condition of the inspected BEJs for large joint movements was rated as satisfactory。 Based on visual assessment, all BEJs fulfilled their functionality as joint sealing。 Hence, it could be concluded that the new type of BEJ for large movements showed promising per- formance in the laboratory and on site。 The springs embedded in the BEJ material fulfilled their function to enforce a homogeneous longitudinal strain distribution within the plug joint during joint movements。

Figure 15。 Edge debonding between asphaltic joint filling material and lateral metal plate (left); ac- cumulation of binder at the surface edging。

6 Conclusions

Various investigations on bituminous plug joint systems (BEJ) for concrete bridges were presented。 These investigations served as basis for guidelines by the Swiss Federal Road Office [7] and have certainly promoted the development of BEJ systems for small and large joint movements with good performance in moderate, alpine and Mediterranean climate。 They also helped to eliminate poor systems, thus narrowing down the market to carefully engineered innovative products and reducing risks of BEJ failure for the last 10 years。 This

is promising news, since the advantage of noise reduction with systems for total joint movements up to 100 mm together with the advantage of easy replacement and repair makes this type of plug expansion joints an attractive option in densely populated urban areas。

Most BEJs on inspected bridges in Switzerland showed good performance under traffic over several years。 Cracking and debonding were the most common defects detected dur- ing visual inspections。 Field survey and performance evaluation showed that long term be- havior of BEJ joints in terms of rutting and cracking is generally still not at the same level as for asphalt pavements。 On the other hand, MMLS3 testing demonstrated that rutting behavior in the BEJ filling similar to the adjacent MA pavement can be achieved。 However, further research and development is certainly needed。