Some 90 years ago Sika celebrated its first successes with the challenge of waterproofing the old Gotthard railway tunnel for impending electrification. In the present Gotthard Base Tunnel, at 57 kilometers the longest tunnel in the world, challenges comparable to those of 90 years ago have emerged, while entirely new ones have also come to light. Sika solutions position the company at the fore.

The Gotthard Base Tunnel will be something special, an innovation in tunnel construction. The tunnel burrows through one of the highest alpine mountain ranges, the Gotthard. Beneath the highest mountain peaks the tunnel courses some 2,000 meters below the rock and at its crown will lie only about 550 meters above sea level. In this it revolutionizes railway traffic between the North and the South in Europe.

The new route can be utilized by both massive freight trains and modern high speed passenger trains, such that the journey time for passenger trains between Zurich and Milan shortens by an hour. But it is not only the dimensions that present great challenges for the tunnel builders; above all the climatic conditions and the structural specifications make this the structure of the century:

  • Service life of the concrete of 100 years
  • High temperatures below ground (30 – 40°C)
  • High humidity (above 80%)
  • Long transport distances for fresh concrete (up to 30 km)
  • Long workability for fresh concrete (up to 6 hours)
  • Prevalent mountain water, corrosive for concrete


With Sika admixtures the concrete in the Gotthard Tunnel can be adapted continuously to the respective requirements. In particular for shotcrete the tunnel builders need highly specific formulae. Water reducers such as Sika ViscoCrete, set retarders such as SikaTard and pumping agents such as SikaPump must be added to the concrete so that it can be transported over the long distances in the tunnel and thereby constantly remain workable.

In general concrete begins stiffening after roughly half an hour. In the Gotthard Tunnel however, the concrete needs to remain fluid for up to six hours, since the concrete producers first load the concrete from the production works outside the tunnel onto trains, with which it is transported to the borehole location, where the tunnel builders must then still process it onsite.

Upon arrival at the borehole, Sigunit is added. The set accelerator ensures that the freshly applied concrete rapidly stabilizes the newly excavated tunnel cavity. Deep within the mountain the tunnel boring machine drills into the stone around the clock.

Directly behind the emerging cavity, the machine has a steel ring which supports the overlying stone for a distance of a few meters. After this, high-grade shotcrete must be applied immediately, because as the miners penetrate into the mountain meter for meter, they are protected against the collapse of the overlying stone only by the layer of shotcrete of a mere few centimeters.


The quantities of admixtures required for the concrete compositions can vary at any time; these quantities are dependent on a number of external factors. The construction workers use only processed excavation material from the rock for the concrete in the Gotthard Tunnel. The quality of the aggregates thereby changes almost constantly depending on the composition of the stone.

Therefore the technical building site advisors are continuously taking samples of both freshly mixed as well as newly sprayed concrete. Daniel Kalbermatter, Technical Building Site Advisor of the tunnel segment Faido-Bodio, says that since the start of construction they have already measured the flow diameter of the fresh concrete more than 15,000 times. “Due to altered allowances in the material from the mountain, variances continually come up, so that the concrete formula needs new adjustment.”

Continuous testing should guarantee that the tunnel will in fact hold for 100 years without major renovation work. At the same time this enables the use of excavated material from the tunnel, despite varying quality, for production of concrete without influencing the quality of the end product. This ecological husbandry of materials is important on one hand to reduce the landfill quantities from the mountain, and on the other to be able to manufacture the concrete more sustainably, that is with fewer delivery transports of raw materials.

Fruitful cooperation in the tunnel

This major order for Sika was preceded by an exceptional phase of investment: due to the size and complexity of the project, a comprehensive qualification process was carried out that lasted from 1996 to 2002. For this purpose concrete and admixture suppliers had to join forces and have concrete formulae tested together. Sika teamed up with Holcim, investing more than three million Swiss francs as well as numerous hours of work in advance.

Jürg Schlumpf, Sika Concrete Technologist, remarks: “I’ve been participating in this project since the very first concrete trial, at the time as a product engineer. I have to say, it is THE project above all others – for me and for Sika. We’ve invested in concrete formulae improvements like we never have before. Today the Gotthard Project is the Sika reference par excellence, and will hopefully help us secure additional major project orders.”

The investment then has proven well worth it for Sika now. For one, an order was received for three of five contract sections on the Gotthard Range, and in addition, the cornerstone was laid for highly beneficial cooperation with Holcim. This Sika key customer is active worldwide. Good cooperation in Switzerland is intended for export to other countries, so that a great many growth chances present themselves to Sika – also throughout the next hundred years.