A job for specialists: a 1,500-m long road tunnel under downtown Essen, Germany, needed to have its walls and ceilings refurbished. A job in which time was of the essence, which had to be completed within a timeframe of two weeks. And it was, thanks to the smooth and successful interaction of a team of specialists from ThyssenKrupp Xervon's building preservation unit.
Over 140,000 motor vehicles pass daily through the two tubes of this tunnel built in 1970. The tunnel is the city section of Germany's renowned A40 that passes through the Ruhr region at speeds, originally intended to be fast, but now mostly snailpace. So it was not surprising that the contract awarder (North Rhine-Westphalia's Roadworks department, Krefeld branch for motorways) wanted to limit the working time to a few days in order to keep as short as possible the necessary shutoff time and hence the daily traffic chaos.
Within this tight time schedule, 25,000 m² of concrete walls and ceiling as well as 20,000 m² of wall tiles were in need of professional refurbishment.
Additional jobs included minor structural steel and sealing work. For these jobs, the timescale of a mere week was available for each of the tunnel tubes. During these few days, first of all the concrete wall and ceiling surfaces were closely "tapped" in order to detect any damage. Crumbling concrete was dislodged, cracks were marked, hollow sections prized apart. Meter-wise the concrete refurbishers on their mobile platforms proceeded through the tunnel sections. The next step: dry sandblasting of the exposed surfaces so that the accessible reinforcing bars could be freed from rust (cleaning standard SA 2.5) and then given an initial corrosion-protection coating. In two shifts, the maintenance men worked on the tunnel, with up to 14 employed per shift.
So that the individual steps could be completed as quickly as possible, teams were assembled consisting in each case of four mobile platforms with up to six specialists. From the first of the platforms, the wall and ceiling surfaces were tapped and, where necessary, broken apart. The team at their tails then sandblasted and recoated the exposed steel bars. This allowed the workers within a short time to get an impression of the extent of the damage. And it turned out that the damage was much more extensive than originally supposed; added personnel were therefore delegated to the site as soon as possible in order to prevent any time schedule overrun.
"Thanks to the well-trained workers and the two project managers Heike Koitsch und Markus Lessmann, we really had an ace up our sleeve," adds Daniel Debbelt, in charge of concrete refurbishment at Xervon's Langenfeld branch. His team of qualified engineers, white- and blue-collar workers, 17 in all, each possessed the necessary qualifications endorsing their concrete skills. Qualifications also reflected in the professional concrete surface reprofiling following the application of a second corrosion coating.
The same professionalism was applied to the tile works done simultaneously as the concrete refurbishment. Several hundred square meters of hollow and damaged wall tiles were removed and replaced as the project proceeded. A closing team of professionals then plugged and filled the sealing joints. At certain points, a rapidly reacting injection gel was applied to the concrete in order to provide sustained water repellent properties.
All in all: the tunnel works were completed to the customer's full satisfaction, both as regards quality and punctuality. In fact, earlier than planned. At the moment, the last of altogether 87 ventilation shafts are being cleaned and repaired.