Concrete admixtures BASF has successfully coped with the problems of underground construction
Refractory mortars and cement injections have provided increased safety
Plasticizer MasterEase UG 3904: innovation from BASF for underground construction
June 1, almost 20 years after the start of construction, the official opening of the Gotthard base tunnel in Switzerland. Its construction was made possible, in part due to BASF chemical products for the construction activities. “We are proud to have been able to offer innovative solutions and” know-how “, which helped our customers overcome the many difficulties in the implementation of this ambitious project,” – Ralph Shpettmann said Head of BASF Construction division in the world.
During the construction of 57-kilometer Gotthard tunnel it was spent about 4 million metric tons of concrete -. It is about 40 times more than in the construction of the tower “Burj Khalifa”, which is the tallest building on the planet. BASF supplied concrete admixtures, injectable formulations based on mineral water inflows to stop and fireproof mortar.
Long distances and high temperatures inside the tunnel
On the 20-kilometer stretch between settlements Erstfeld and Sedrun builders of two parallel tunnels and connecting galleries located every 300 meters, used concrete admixtures from BASF. “Underground work presents conflicting demands on the concrete. On one hand, when transporting a few kilometers into the mountain it does not solidify and remain suitable for stacking in for several hours. On the other hand, after the sprayed concrete tunnel wall of his grasp should happen almost immediately. This is what has become one of the most difficult problems encountered when installing the Gotthard base tunnel, “- said Rene Bolliger, head of the regional division BASF products for underground construction (Germany, Austria, Switzerland). The solution was found thanks to the selection of the right combination of additives into the concrete of the BASF range. So, gave concrete superplasticizers MasterGlenium required rheological properties and workability, while the accelerators of the line MasterRoc SA provided its curing and hardening within a few seconds after application to the tunnel walls. In addition, experts of BASF completed the line MasterSet new supplement designed specifically to work on the construction of the Gotthard base tunnel. Its function is to significantly slowing the cement hydration process. This approach, coupled with the use of superplasticizers BASF, allow concrete to make optimal use – even after long distance transport inside the tunnel, and at high subterranean temperatures. In addition, the production of BASF additives (retarders, superplasticizers and concrete setting) involved in order to ensure safety after the rock excavation, as well as in the process of concreting the inner lining of the tunnel. “We are constantly engaged in the introduction of innovations that make our customers’ business even more successful. The most recent example of innovations designed for underground construction works, is our plasticizer MasterEase UG 3904. Its advantage is to facilitate the mixing and pumping of the solution, of which – together with the plasticizer – enters free of alkalis setting accelerator “- added Mr. Bolliger.
Solutions for deep shafts
Two vertical shafts lead from the ground near the mountain village of Sedrun to a depth of over 800 meters, which is one of the two multi-function stations provided in the tunnel project. It is intended for train stops in an emergency, as well as for ventilation and other technical infrastructure. And here the builders are not without solutions offered by BASF. The fact that the sinking of vertical shafts (just as the laying of the tunnel) is first carried sprayed, and then laying the concrete mix was made. “Transporting concrete on vertical pipeline proved to be particularly challenging; we had to exclude the possibility of segregation of the concrete component during its movement down the mine shaft “, – said Mr. Bollinger. Picking a suitable superplasticizer of MasterGlenium line, and determine its optimal dosage for the appropriate conditions, of BASF experts provide a complete concrete suitability for subsequent installation after its free fall for a few hundred meters. In order to prevent the penetration of water, cracks and voids in the rock were filled with finely ground cement MasterRoc MP 650.
Fire safety
Fires in tunnels pose a serious threat, and so there are very strict fire regulations. If the concrete is heated to temperatures above 1.000 ° C, then it will lose its load-bearing capacity, which will lead to the destruction of the tunnel. On the wall of the Gotthard base tunnel near its southern portal was coated with a product included in the range of BASF – special refractory mortar MasterRoc FP 1350. «Thanks to this product the wall of the tunnel will be able to withstand temperatures up to 1.400 ° C for at least 90 minutes. This time will be enough to ensure that firefighters have done their work “, – said Frank Clement, of BASF specialist in fire protection measures in underground construction.
Swiss construction megaproject
Gotthard Base Tunnel is the Length of the railway tunnel in the world. Its construction has been spent a total of about 9 billion. Euro. This route passes through the Alps, the duration of the trip from Zurich to Milan will be shortened by about one hour. Designers have significantly reduced the slope of the tunnel; so its highest point (550 meters above sea level) is located only 90 meters higher than the north portal in Erstfeld. As a consequence, the tunnel can pass twice heavier freight trains at a rate twice as high. For comparison: in the first Gotthard tunnel, which was opened for train traffic in 1882, height difference between the lowest point and portal in Erstfeld was approximately 700 meters.