How aluminium can help solve concrete's sustainability challenge

A Hydro led research project using aluminium as reinforcement enables the use of concrete mixes where more than 50% of the cement can be substituted with sustainable binders. The result is concrete that requires far less energy and CO2 emissions to produce slimmer, lighter concrete structures with long service life.

The project is called DARE2C – Durable Aluminium Reinforced Environmentally-friendly Concrete Construction. The backdrop is the world's most used material, concrete, and has two main challenges: climate footprint and durability.

"Aluminium corrodes in the highly alkaline environment in today's concretes. On the other hand, in the development of more environmentally friendly clay-substituted cement, the steel reinforcement is not protected due to the low pH. The idea behind the research project is to hit two birds with one stone by combining low-carbon aluminium reinforcement with an extraordinary low-carbon concrete," says Grete Hjetland, DARE2C Project Manager and Chief Engineer at Hydro.

DARE2C is a research and development project led by Hydro and supported by the Norwegian Research Council. The consortium comprises the Norwegian University of Science and Technology (NTNU), SINTEF and eight business partners.

"In the DARE2C project, we have found using aluminium as reinforcement enables the use of concrete mixes where more than 50% of the cement can be substituted with sustainable binders, such as clay and volcanic pozzolan from Iceland. This results in concrete requiring far less energy and CO2 emissions to produce," says Hjetland.

 Most aluminium alloys are stable in corrosive environments, meaning the concrete structure can be designed with respect to strength class rather than environment class. Since the reinforcement does not have to be protected by concrete, the cover can be reduced or omitted. The use of aluminium reinforcement, therefore, results in slimmer and lighter structures, and thereby also, less use of aggregates and cement. The lighter concrete elements reduce emissions related to transport as well.

 The new Ro-Ro ramp was built at Hydro's primary aluminium plant in Sunndal, Norway. Parts of the ramp use concrete and aluminium composite elements to demonstrate the concept's functionality.

"Presence of salt in water and sands used in traditional concrete will strongly reduce the durability as well as the lifetime of buildings and structures made from ordinary steel reinforcement. Revolutionary results from the DARE2C project show that seawater can be used as mixing water providing huge opportunities for green and durable buildings in countries with a shortage of fresh water. Additionally, the concept allows for the use of aggregates coated with salt," says Hjetland.

The low-carbon concrete mix developed in the research project provides durable concrete constructions with respect to carbonation, chlorides, sulphate and alkali aggregate reactions. One challenge that remains is that the concrete does not pass the standardized test for salt on top of the concrete, for example, when exposed to road salt. This is a challenge for all low-carbon concretes. However, the standardized freeze and thaw test is solved by adding air to the concrete mix in the usual way.

Two pilots demonstrating the DARE2C concept, combining aluminium and concrete, have already begun, with more exciting pilots and projects also in the pipeline:

 A walkway made of aluminium-reinforced prefabricated concrete elements at Geitbåtmuseet, Heim Municipality in Norway. The possibility of leaving the structural reinforcement exposed and visible gives the designer an additional layer of expression.

At the new Ro-Ro ramp built at Hydro’s primary aluminium plant in Sunndal, Norway, the DARE2C project has had the possibility to integrate a concrete and aluminium composite element in the traditionally built ramp to demonstrate the functionality of the concept in a heavily exposed structure in a corrosive environment.

“There is a growing focus on the climate challenge in the construction industry. Architects and engineers are looking for more sustainable materials with longer service life. Aluminium-reinforced concrete constitutes a more sustainable concrete. In that context, we are happy to be noticed,” Hjetland says.