Strengthening of a bridge slab - Bridge B8 - Sulzbach, Germany

In the scope of the planned rehabilitation of a bridge on the B8 federal highway, partially corroded pre-stressing cables of the transversely pre-stressed bridge slab were detected. The design of the slab revealed a lack of load-bearing capacity, which required strengthening. In this case, the planners decided to reinforce the slab with S&P CFRP laminates glued into slots (NSM laminates). The NSM laminates were the more economical choice here due to the bond strengths and the local conditions.

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Topic
Strengthening of a bridge slab
Object
Bridge B8
City
Sulzbach
State
Hessen
Country
Germany
Date

Situation

The difficulty of this reinforcement project was that access to the shopping center with cinema etc. had to be made possible despite the rehabilitation work. Due to the simultaneous rehabilitation of another bridge in this area, the traffic was diverted or could be led over the two bridges in one lane. Accordingly, the rehabilitation and reinforcement had to be carried out on one half of the lane at a time. 

Refurbishment in two stages

The FRP laminates were dimensioned in such a way that a joint with a corresponding overlap was calculated in the middle of the bridge deck. In this overlap area, the slots for the FRP laminates were made wider so that two laminates including adhesive could be bonded into one slot at a time. The work of FRP reinforcement in lane 1 was carried out in October 2022. Due to the rehabilitation of the other bridge and traffic planning, the FRP reinforcement in lane 2 could not be carried out directly afterwards. Due to weather conditions, this work was scheduled for spring 2023. 

The asphalt surface course was already applied in the completed and reinforced area. However, the overlap area had to remain free in order to be able to connect the laminates in lane 2. In order to be able to ensure a later clean bonding of the strips in the joint area, no adhesive was applied in this area yet. However, the slot had to remain free of dirt for the entire period, as this could no longer have been removed. The contractor provided an appropriate planking, which was sealed and bonded to the substrate. This also allowed the asphalt surface course to be applied without any problems. 

In March 2023, the reinforcement was scheduled to be connected in lane 2. The protective planking of the overlap was opened and the overlap area was in good condition as planned. This meant that the FRP laminates could be overlapped,  and installed without any problems.  

Solution

Gluing two laminates in one slot in the overlap area is a special solution, but it could be realized here without any problems. The laminates were each enclosed with adhesive and the butt joint could be kept clean over the entire period. This was supported by close coordination between the contractor, the planners and the team from S&P and StoCretec GmbH. 

No problems with temperature fluctuations

The overlay with asphalt does not cause any problems here. According to the research project of Empa (Switzerland) [1][2][3], the full load-bearing capacity of the FRP laminates or the adhesive, respectively, after the cooling phase to below 50 °C, is given without any restrictions. Solar radiation and seasonal temperature fluctuations are also harmless in terms of durability and load-bearing capacity according to the research report.

[1] Czaderski, C./ Gallego, J.M./ Michels, J. (2017): Temperature stability and durability of Externally Bonded CFRP strips in bridge construction (Forschungsprojekt AGB 2012/001). Zürich, Schweiz. Eidgenössische Materialprüfungs- und Forschungsanstalt
[2] Breveglieri, M./ Czaderski, C. (2022): Reinforced concrete slabs strengthened with externally bonded carbon fibre-reinforced polymer strips under long-term environmental exposure and sustained loading. Part 1: Outdoor experiments. Zürich, Schweiz. Eidgenössische Materialprüfungs- und Forschungsanstalt
[3] Breveglieri, M./ Czaderski, C. (2021): RC slabs strengthened with externally bonded CFRP strips under long-term environmental exposure and sustained loading. Part 2: Laboratory experiments. Zürich, Schweiz. Eidgenössische Materialprüfungs- und Forschungsanstalt

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