Special Concrete for Artificial Coral Reefs in Kosterhavet

This week several concrete reefs were placed in the Swedish Kosterfjord to give the endangered cold water coral 'Ögonkorall'a chance to regrow. Thomas Concrete Group's research laboratory has developed a unique concrete mix that not only maintains an optimal pH value but also withstands the harsh marine environment, ensuring durability for up to 150 years.

A project to restore the reefs for the endangered coral, locally known as Ögonkorallen (Desmophyllum pertusum), was initiated by the County Administrative Board of Västra Götaland and the University of Gothenburg in 2019. Thomas Concrete Group’s research laboratory C-lab and the Swedish subsidiary Thomas Betong are behind the development of this unique concrete.

“For this specific coral and other organisms to thrive and colonize the area, the concrete needs to have a low pH value. For this project, we tested five different compositions to determine which recipe works best,” says Ingemar Löfgren, Research and Development Manager at Thomas Concrete Group.

Photo taken by Anita Tullrot

Using concrete in marine environments is not new

Archaeologists have found piers from Roman times that have existed for 2000 years. Then, volcanic ash and slaked lime was used as a binder in the concrete. In this project, a low carbon concrete, with a low cement content and the addition of blast furnace slag and silica dust, has been developed, which ensures the reef’s durability in a marine environment. This special concrete recipe has reduced the pH value to 11.5, making the artificial reefs a place where the larvae of the coral can thrive and attach, leading to new natural reefs.
The concrete was delivered by Thomas Betong, and the concrete reefs were manufactured by Svensk Armering & Betong Byggen. The plan is to place a total of 132 concrete reefs at selected locations in Kosterfjorden. The 600 kilos heavy concrete blocks are shaped like a six-armed octopus, with clusters of hollow concrete on the surface. They function as artificial reefs and are placed where water flows faster and where coral larvae can settle.

This project is close to our hearts

Previously, there were reefs for the coral in six locations in Kosterfjorden. However, bottom trawling and other human activities have reduced this to only two remaining reefs. Giving the coral reefs a chance to regrow is also crucial for the survival of other species. Over 1,300 different species have been observed at these reefs, including commercially important fish species like cod.

“This project is close to our hearts. We are very happy to contribute with our technical expertise to a more vibrant marine environment. The project demonstrates the enormous potential of concrete as a building material not only on land but also in water,” says Hans Karlander, CEO of Thomas Concrete Group.

The project is co-financed by the EU LIFE program and the Swedish Agency for Marine and Water Management. It will continue until 2025. In addition to researchers from the University of Gothenburg, the County Administrative Board of Västra Götaland is also a part of the project.

Ingemar Löfgren, R&D Manager Thomas Concrete Group
Ingemar Löfgren

Ingemar Löfgren

R&D Manager

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