SINTEF researchers claim aluminium reinforcement can reduce concrete’s carbon footprint

A novel approach to address the corrosion concerns associated with steel-reinforced concrete involves using blue clay to impart a certain amount of acidity, which is compatible with aluminium. This innovative aluminium-reinforced concrete has been claimed to resolve the aforementioned corrosion difficulties effectively. Researchers at SINTEF, a scientific institution in Norway, have successfully shown their ability to substitute a minimum of 50 per cent of the carbon-intensive Ordinary Portland Cement with calcined clay and calcium chloride. This substitution method effectively mitigates carbon emissions associated with the production process.

Professor Harald Justnes, Chief Scientist at SINTEF Community, said, “Less concrete cover over reinforcement (not for durability, but mechanical grip only) means thinner wall elements, etc. and thereby less concrete.”

The emission reductions are achieved through various means, including the removal of cement content, the burning of clay at lower temperatures (850°C) compared to limestone calcination (1,450°C), the decrease in materials consumption due to the use of aluminium reinforcements, the utilisation of recycled aluminium to reduce energy consumption, and the enhancement of construction longevity while minimising maintenance requirements.

According to the researchers, the reinforced material exhibits a reduction of 80 per cent in CO₂ emissions throughout its lifespan. Professor Harald Justnes, Chief Scientist at SINTEF Community, believes that the material in question can be used in many contexts where the strength of C35 concrete is deemed satisfactory for building purposes. Given that the need for a low water-to-cement ratio to ensure longevity and exceed strength is not applicable in the case of conventional steel-reinforced concrete, it is possible to build the concrete structure to meet the desired strength criteria.

 "A fast pozzolan is needed that consumes calcium hydroxide fast when the cement component starts producing it after setting. The clay we use today is kaolinitic with 50 per cent clay mineral and the rest being feldspar particles (inert). The beauty of using ordinary blue clay, as it is dug out of the ground, is that organic stuff is burnt away and any fine mineral particles are accepted by the concrete as filler," added Harald Justnes.

Furthermore, it can be seen that the typical deteriorations experienced by conventional steel-reinforced concrete are no longer applicable in this context. The user posits that introducing carbonation does not pose a significant issue in aluminium-reinforced concrete. The binder without carbonation exhibits a pH level of 9 but may also undergo carbonation at a reduced pH of 8. According to the speaker, aluminium is deemed suitable in this context due to its ability to live in conditions characterised by a moderate pH level.

The resilience of the aluminium alloy renders chloride intrusion inconsequential. The author observes that salt water may be a viable alternative for mixing water, and sand extracted from the sea can be utilised without cleaning. The individual asserts that sulphate attack is considered outdated due to the absence of calcium hydroxide necessary for the first reaction with gypsum. This assertion is supported by evidence from a four-year storage experiment conducted at a temperature of 5°C using a 5 per cent Na2SO4 solution.

Alkali aggregation reactions (AAR) have become primarily obsolete due to the low pH levels and the presence of alkalis in the form of silicates and aluminates. According to reports, this phenomenon results in improved utilisation of resources because of the ability to utilise aggregates prone to AAR.

To showcase the capabilities of the technology, the research team has developed a compact bridge that has been engineered as a composite structure capable of supporting a weight of 10 metric tonnes. This bridge incorporates prefabricated aluminium profiles upon which a layer of concrete has been poured. Additionally, a sandwich wall element has been developed, in which the concrete serves as the outside ornamental shell while the aluminium is exposed on the surface. A stairway system is now being planned for implementation at the university campus in Trondheim. As part of this project, saltwater as mixing water will be used in some precast parts, aiming to validate this approach's feasibility.