Renovation project: Gotthard Tunnel, Switzerland

On average, more than 6.3 million vehicles, including over 770,000 trucks, pass through the tunnel at 1,100 meters above sea level every year. It goes without saying that the tunnel walls have to withstand a lot of wear and tear. After more than 40 years of operation, the walls in the entrance and exit areas of the first tube are to be clad with new ceramic tiles in 2022. Following a tender by the Federal Roads Office (ASTRA), Plattenleger-Team GmbH from Triengen was awarded the contract for the renovation work by the general contractor PORR.

Plattenleger-Team GmbH kicked off the project in February 2022 at the north portal near Göschenen. The tiling work for the entire project in the entrance area of the north and south portals covers a total area of 2,500 m² and a total length of 500 meters.

The repair work had to adhere to a strict schedule and overcome the weather-related challenges for installers and materials caused by wet and cold conditions. The demands on the materials used were correspondingly high. The products had to be highly resilient, flexible, and optimally coordinated with each other. “It is precisely for such increased requirements that we at codex have developed products that not only withstand the extreme stresses of some locations, but are also optimally coordinated with each other in combination.” “This enabled us to offer product solutions for the renovation work in the Gotthard Tunnel, from the primer and waterproofing to the thin-bed mortar and grout,” says Dursum Hotic, Sales Manager at codex at Uzin Utz Schweiz AG.

The tunnel tubes are exposed to high levels of stress due to increased humidity and temperature fluctuations. In addition, the vehicles passing through every day carry contaminants into the tunnel. To prevent corrosion and thus ensure additional traffic and infrastructure safety, the walls in the entrance area are being retiled. A key factor here is the durability of the system structure and the tiles themselves. The substrate in the Gotthard Road Tunnel, made of young reinforced concrete, is only ready for covering after six months. In addition, expansion joints and cable ducts interrupt the surface. The products used therefore had to be crack-bridging and also compensate for possible shrinkage of the concrete.

Before the actual tile laying work could begin, the reinforced concrete tunnel walls were roughened by hand to create a textured surface. The surface was first primed with codex FG 300 dispersion primer for absorbent substrates. Its high penetration capacity offers greater reliability, especially on concrete or aerated concrete. To reliably seal the moisture-stressed substrate, the tiling team then applied the flexible 1-component sealing slurry codex AX 230. It is suitable for surfaces that are particularly exposed to moisture and wet conditions. This polymer-modified flexible sealing slurry is fiber-reinforced and creates a crack-bridging seal when bonded. Due to its high flexibility, the sealing layer reduces tension. This is particularly important in an area such as the tunnel entrance, as it is exposed to severe weather conditions, which cause more movement in this layer.  To further stabilize the sealing layer in the long term, codex UX 410 glass fiber fabric was then used. The alkali-resistant reinforced fabric with glass fibers for reinforcing fillers and thin-bed mortars was embedded in codex AX 230. codex UX 410 is characterized by its high tear resistance and improves the load-bearing capacity of the substrate for risk-free subsequent installation.

Over 1,600 ceramic tiles from Agrob Aruba measuring 40 x 40 cm were used in the entrance and exit areas of the north portal. The ceramic tiles used are traditionally designed in the colors of the canton of Uri: white, yellow, and black. As part of the specified safety measures for tunnel accidents, the harder-fired tiles are significantly more break-resistant. Project managers Marin and Marko Milicevic played it safe when it came to laying them, working together with codex. The codex Power RX 11 Outdoor thin-bed mortar, specially developed for demanding cementitious laying, combined speed and safety in a single cementitious product. The new flagship product in the codex product family is a two-component, highly flexible S2 thin-bed mortar for safe installation in outdoor areas. Thanks to its S2 classification, it also compensates for strong shear forces from the substrate. Splash water and moisture (frost and vapor pressure) place heavy demands on the tiles on the side walls at the tunnel entrance. codex Power RX 11 Outdoor was used there not least because of its waterproof mortar matrix, which blocks water from penetrating the mortar bed. “It easily withstands the demanding weather conditions on site. We also had no problems with skin formation despite drafts, nor were there any difficulties in processing due to the low temperatures,” reports Marko Milicevic.

The 2-component epoxy grout codex X-Tensive is ideally suited to the requirements of the final grouting. The high-performance joint is resistant to mechanical and thermal stresses. Nevertheless, it is easy to work with, which ensured rapid progress on this tightly scheduled large-scale construction site.

The team of tilers from Triengen mastered the demanding requirements for installation and the logistical challenges of working on one of the busiest highways in Switzerland and Europe without disrupting traffic using codex products. In collaboration with codex application engineers, the project was completed within the specified renovation period of 8 weeks. “In fact, thanks to our trained and motivated employees, the expert advice of codex application engineers Daniel Gisler and Hans-Dieter Ziech, and the reliable product solutions, we were even able to complete the construction site before the end of the renovation period,” says Milicevic.

In a second stage, the same work will also be carried out on the south portal of the Gotthard Tunnel near Airolo. Here, too, Swiss tilers can once again count on the proven quality and versatility of the codex product range.