Replacement of ceiling in Sonnenberg tunnel, Cityring Lucerne

Initial Situation

As part of the complete renovation of the Lucerne Cityring, several challenging construction tasks had to be executed. The ongoing works significantly impacted traffic flow through the city, making it a high priority to minimise closure durations. One key objective was the construction of a new intermediate deck in the Sonnenberg Tunnel within a single weekend closure.
This included formwork, reinforcement, concreting, and stripping – all within a very limited timeframe. From concrete production to achieving a compressive strength of 40 N/mm², the time window was restricted to just 10 hours. At the same time, the concrete required a workability time of 3 hours to allow for pumping and placing.

Solution and assessment

This ambitious goal was achieved using a customised formulation of Concretum^® Q-FLASH 2/20. The construction schedule was meticulously aligned with the concreting process. Outstanding planning and seamless coordination between the concrete producer, pumping service, and contractor were key to the project's success.
The concrete could be pumped and placed for a full 3 hours without any loss of consistency. Once the setting process began, rapid strength development was triggered. As a result, the formwork could be removed as planned, and the tunnel was reopened to traffic on Monday morning, right on schedule.