The Heartbeat of Hydropower

It is an ice-cold morning in the Fremri-Kárahnjúkar mountains. Shift workers are entering an access tunnel that leads to the underground Kárahnjúkar Hydropower Station. Deep within the main cavern, water from surrounding reservoirs and rivers thunders through six turbines, generating 690 megawatts of power for a new aluminum smelting plant built by Alcoa in the town of Reyðarfjörður.

This is the beating heart of Iceland’s largest-ever industrial development: a € 1.1 billion hydropower plant which, during its five-year construction period, required 70 km of tunneling and the construction of five dams, and is now one of the largest concrete-faced, rock-filled dams in the world.

Highest Environmental Award

The project won praise in Iceland for setting an exceptionally high standard of safety. It also carried off the country's highest environmental award, the Conch, for its policy of generating no waste to landfill and avoiding any wastewater discharge into the neighboring fjord. Diversification and the availability of clean energy from hydro- and geothermal power plants has made Iceland a key aluminum-producing country, with a planned production capacity of 1.5 million tons in 2010. Aluminum is manufactured by an electrolytic process that uses bauxite as the basic raw material.

Emission-free energy

Electric power represents about 20% to 40% of the cost of producing aluminum. Smelters tend to be situated at harbors (most of the bauxite comes from Australia) and where electric power is inexpensive. For Iceland, the renewable and emission-free energy supply created by the Kárahnjúkar Hydropower project is a ticket to economic diversity and a step toward a unique future as a forerunner in the use of such energy for power-intensive industries.

Shotcrete was the solution

As workers file past the gray-rock arch leading to the power station, they can still see some of the hoses that were used to pump the shotcrete, a special concrete for lining tunnel walls and stabilizing rock. During excavation and construction, this material offered the civil engineers a solution to some of the project’s most serious challenges, including water seepage, frost and the long transport distances.

Modified by admixtures, the shotcrete was pumped hundreds of meters into the mountain, where it was sprayed onto the surrounding rock to stop water inflows and secure the walls. The Fremri-Kárahnjúkar mountains are now the site of Iceland’s largest-ever industrial development, a 690-megawatt hydropower plant.

Admixtures for pumpability

The Icelandic climate presented harsh conditions for concreting and Sika's admixtures were put to the ultimate test during the five-year project. Products such as SikaViscoCrete®-SC305 were successfully used to maintain the pumpability of the shotcrete. “Other Sika admixtures, such as accelerators, made the mix stick to the wall, which it wouldn’t do otherwise,” explains Sika engineer Gustav Bracher.

Tests in Prequalification Phases

Not only did engineers and workers have to deal with excessive water seepage, long stretches of rock also needed steel-fiber-reinforced shotcrete, ground injections, and foam and steel ribs support behind the cutter heads of the giant tunnel boring machines. “It was good that we participated actively in the prequalification phases and implemented ductility tests for the steel fiber-reinforced concrete,” said Bracher. “A smooth logistics operation was also essential for the client at such a remote site.”

Reliable raw material flow

To meet the demands, Sika flew in raw material from the U.S. and set up production equipment for liquid accelerators at two sites. In the course of the project, the contractor produced more than 200,000 m3 of shotcrete with 6,000 tons of alkali-free accelerator and 8,000 tons of Sika®Fiber steel fibers. Sika supplied not only all the admixtures for the 170,000 m3 of concrete, but also the epoxy flooring systems. As Bracher put it, “This underscored the comprehensive nature of Sika's product range on a major project.”

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