It is considered a given that steel is what is used as reinforcement in concrete, not aluminum. The reason is that the pH of ordinary concrete is so basic (high pH) that aluminum corrodes.
But imagine if it was not the aluminum’s “fault”, but rather the cement, a creative researcher dared to ask – and decided to invent a new concrete that is not so alkaline.
A few years later, it turns out that the new concrete – in addition to being suitable for aluminum reinforcement – has many and surprisingly significant benefits related to environment and quality, which can revolutionize the concrete industry:
- The new concrete requires far less energy and CO2 emissions to produce
- It enables slimmer concrete structures (smaller volumes of concrete)
- The concrete becomes maintenance-free
- It can even absorb and store CO2 from its surroundings during the use phase
A recipe for everlasting concrete
What is the reason why reinforcement with aluminum instead of steel can provide such significant benefits?
Except for the fact that steel is strong and thus an intuitive choice for reinforcement, steel also has some inherent weaknesses. Steel corrodes when in contact with seawater and CO2 from the air. In fact, steel reinforcement must be covered by denser and thicker concrete, to protect the steel reinforcement itself from contact with air and water!
If air and water reach the steel and the steel corrodes, the concrete will crack. Therefore, today's common concrete structures only last as long as the concrete can shield the steel from external influences.
With aluminum this is different. Aluminum has a natural "membrane" of oxide that protects the metal against corrosion, so it can resist and endure air and seawater far better than steel. That is why you do not need to use such dense concrete to protect the reinforcement, nor thick covering. The concrete structures can be given less weight and a wider variety of design possibilities, a longer life and less maintenance.
Less CO2 emissions
Aluminum reinforcement allows the use of binders (which steel cannot withstand) that result in far less CO2 emissions compared with traditional cement clinker. A lot of the cement (about 55%) is replaced by ordinary clay and other binders that do not decompose CO2 like the cement clinker does, and is burned (produced) at lower temperatures. Yes, actually at 850 degrees instead of 1,450 degrees. This, of course, saves huge amounts of energy and emissions.
The new concrete has additional environmental benefits. If desired, the concrete can even be blended by using seawater, which is a huge advantage in places with limited access to freshwater.
A creative professor – and a team of experts
It was Professor Harald Justnes at SINTEF in Trondheim who asked the unlikely question of whether it would be possible to compose a new and less basic concrete that makes it possible to reinforce concrete with aluminum instead of with steel.
Along with him, he got an entire research project, DARE2C, with the aluminum company Hydro as project manager, and with NTNU, SINTEF, the cement producer Norcem (Heidelberg) and the contractors Veidekke and Overhalla Betongbygg on the team – and indispensable support from the Norwegian Research Council.
Two years later, the new concrete recipe has been fine-tuned and tested with aluminum reinforcement – with such promising results that already, halfway through the research project, it is assumed that the new concrete will actually become a reality.
In addition to sounding good and implying courage, DARE2C (read "dare-to-see") stands for "Durable Aluminum Reinforced Environmentally-friendly Concrete Construction" – and aluminum is crucial in enabling a whole range of benefits.
During some hectic summer weeks, the concrete bench was designed, the aluminium reinforcement produced and other components provided with great effort from all the participants in the project. The result was this beautiful aluminum-reinforced concrete bench, cast by Overhalla Betongbygg and first exhibited at the AquaNOR fair in Trondheim in August 2019.
Although the bench was made of primary aluminum, an important goal with the research project is to enable use of recycled aluminum – and preferably aluminum that has been reused so many times in various consumer products, and so mixed with other metals, that it no longer has so many suitable alternative applications.
Aluminum engine blocks for cars is one application where it does not matter that used aluminum has been "contaminated" with many other metals. But as the world will need fewer engine blocks for cars with internal combustion engines in the future, the use of recycled aluminum scrap as reinforcing metal in concrete may be a suitable alternative – and even further improve the climate footprint of the new concrete structures. The use of recycled aluminum is one of the major advantages of the DARE2C concept.
"Durable aluminum-reinforced environmentally-friendly concrete" is still under development – however it is now very likely that such concrete structures may soon be on their way to markets and applications near you.