Concrete structure 'encased' with aluminum pre-walls and slat cladding 

The concrete construction of the ramps to the Rottemer Tunnel will be completely hidden from view by specially formed acoustic pre-walls with aluminum panels by Aldowa. The anti-glare louvers in the ramps will also be covered with a unique cladding in diamond-shaped flashing. A mega job for the specialist in metal and composite cladding, which also includes part of the cladding in the tunnel and on the center tunnel channel.

Aldowa has provided cladding in tunnels and other engineering structures before and, thanks to that experience, was asked by construction consortium De Groene Boog to quote for the pre-walls, the slat cladding and a piece of cladding in the Rottemer Tunnel. "In the end we won the tender, mainly because the 'feeling' was right," knows Martien Trouborst, project manager at Aldowa. "Given the high time pressure in which everything had to be started up, we took the initiative to organize a number of scrum sessions (read: pressure cooker design sessions) together with the technical people of the construction consortium and the architect. In this way, we were able to go through the design process very efficiently and find a suitable solution for all the complexities."

Many thousands of panels

All parties experienced the scrum process as very positive, Martien says. "Because you are physically sitting together, all challenges are discussed openly and honestly with each other and you see that actually everything is possible. As a result, we were soon able to determine the standard panel size (1375 by 833 millimeters) of the pre-walls and put them into production. This was also necessary because we are talking about many thousands of perforated panels. And if you know that one panel spends 15 minutes on the punch, you can probably imagine the lead time. So we scaled up production considerably to make the panels." They are not exactly standard panels. "Because of a kink diagonally across the panel, in the flat view not all the angles are 90 degrees. The bottom left corner and top right corner are spaced apart, so to speak. So on the punch, the panel is not perpendicular, which makes it a specific project solution with as many as 15,000 holes per panel."

Ready-made elements

Aldowa then set up an assembly line in which elements were made of three panels wide (2.50 meters) and varying in height from 2.50 meters to 8.50 meters with acoustic insulation behind them to absorb road noise. Martien: "In this way we created a large buffer to prevent stagnation during assembly. The elements were tilted a quarter turn and placed on the trailers. One truck per three trailers was available to shuttle between our intermediate storage and the construction site. So in that sense, the project is also a logistical challenge." In total, Aldowa installs about 600 elements, which means it has in-house engineering, production, assembly and erection. "On the south side, the ramp to the tunnel has been completely lined, on the north side we have just started," says Aldowa.

Diamond-shaped typesetting

In both ramps to the Rottemer Tunnel, there are 24 anti-glare lamellae to soften the transition from daylight to the dark tunnel. "They are substantial concrete beams across the road. The aluminum cladding around the concrete beams follows the road surface downward. The front lamella is the smallest at 1.7 meters high, the lamella closest to the tunnel is no less than 2.7 meters high," Martien explains. "For this too we engineer, supply and install the aluminum flashing, in this case in a diamond-shaped motif after a design by QWA architects. Because of the adjacent residential buildings on the south side, the slat cladding here is also perforated and provided with acoustic insulation. On the north side, they are all closed." Meanwhile, Aldowa has started assembly here as well, as with the tunnel lining of the first 40 meters of the tunnel on both sides.