Fri. Apr 12th, 2024

Ongoing research reveals that Quebec's subsoil offers interesting resources for limiting greenhouse gas (GHG) emissions from the most widely used construction material in the world.

Solutions to reduce the carbon footprint of concrete

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On the left in the photo, a concrete slab containing 25% aluminosilicates and, on the right, a traditional concrete slab.

  • Vincent Rességuier (View profile)Vincent Rességuier

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There is excitement on the Nemaska ​​Lithium construction site in Bécancour, in Center-du-Québec. The processing plant is starting to take shape. Ultimately, it must produce 34,000 tonnes of lithium hydroxide annually.

However, a tiny quantity of the ore will be used to make batteries for electric vehicles. There will therefore remain mountains of residue, and the company hopes to recycle a good part of it.

A pilot project is underway with the aim of marketing concrete made with aluminosilicate residues produced on site and which have pozzolanic properties. It’s a powder that has binding properties and that’s why it can be used to replace cement, explains Dan Fournier, head of by-product valorization. /p>

With the help of a local company, Nemaska ​​Lithium manufactured an experimental concrete, the main elements of which are aluminosilicates and calcined limestone (clinker). This recipe contains 25% aluminosilicates, which significantly reduces the proportion of clinker which generally makes up nearly 80% of standard cement in North America (Portland cement).

The goal of Nemaska ​​Lithium is to create a circular economy .

A quote from Dan Fournier, head of by-product valorization at Nemaska ​​Lithium

The manufacturing of clinker results in significant GHG emissions. For one ton of finished product, approximately one ton of carbon dioxide escapes into the atmosphere.

By using these mining residues, the carbon bill would therefore tend to decrease. The plant has the capacity to produce 220,000 tonnes per year of aluminosilicates which can be used to make cement.

According to Nemaska ​​Lithium, using this resource could reduce CO2 emissions by around 200,000 tonnes compared to the Portland cement recipe.

It now remains to prove that this new product competes in quality with its competitors already on the market.

For this, two witness slabs were poured last November; one with traditional concrete, the other with experimental concrete. They are exposed to the comings and goings of construction trucks as well as the spreading of abrasives.

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Dan Fournier, head of by-product valorization, Nemaska Lithium

Nemaska ​​Lithium is accompanied in this adventure by the Concrete Infrastructure Research Center at the University of Sherbrooke, which is evaluating the durability of this new mixture.

Tests have already been carried out by our colleagues at the National Research Council. We are currently carrying out tests on a larger scale and it works very well, assures the director of the laboratory, Professor Arezki Tagnit-Hamou.

With solid expertise in the field, he collaborates with industry, the Quebec government and other researchers to explore low-carbon cement options.

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Canada's Greenhouse Gas Reporting Program has listed 11.2 megatons of CO2 in 2019 for the cement manufacturing industry.

The prospect of mining residues seems promising, especially as projects for the exploitation of critical materials tend to multiply. Ultimately, he anticipates interesting volumes, which remains the sine qua non condition for the adoption of new materials.

To complete the offer, he is testing another avenue in Val-des-Sources, in Estrie. Tailings from the Jeffrey asbestos mine contain silica with pozzolanic properties.

There are about 800 million tonnes of the material, some of which could be used to make cement. However, treatment should be carried out, in particular to eliminate possible traces of asbestos. A major project whose outlines still need to be clarified.

Professor Tagnit-Hamou identified another avenue, that of calcined clays which can also replace, in part, calcined limestone.

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Professor Arezki Tagnit-Hamou, director of the Concrete Infrastructure Research Center at the University of Sherbrooke.

Limestone must be heated to more of 1400 degrees Celsius to become reactive, while clay only needs to be heated to near 750 degrees. This allows a saving on fossil fuels, the most used being oil or coal.

But, above all, clay does not emit C02 when heated to high temperatures. For one ton of calcined limestone, emissions of around 800 kilograms of carbon dioxide are expected.

Mr. Tagnit-Hamou advises the company Clayson Écominéral, which plans to open a clay quarry in Gaspésie, in the Matane sector.

Its founding president, Joël Fournier, ensures that calcined clays can be used in the composition of cement up to 40%. In this case, he says, it is possible to reduce GHG emissions almost in half compared to Portland cement.

According to Mr. Fournier's estimates, the deposit would have the capacity to provide one million tons of calcined clay per year for more than 100 years.

Significant volumes as the Cement Association of Canada calculated that total clinker production amounted to 11.4 million tonnes in country in 2020.

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Joël Fournier wants to open a clay quarry in Gaspésie

Joël Fournier believes that production costs would be competitive upon marketing. As proof, he cites the fact that this resource is already used in many countries in Europe, China, India and Cuba.

He is currently in discussions with several industry players. Two options are available to him. Either sell the clay directly to the cement factories which would be responsible for transforming it. Or build a factory on site, a project estimated at $150 million and which could raise questions of social acceptability.

If all goes well, he estimates that production could begin within a year.

Whatever happens, most innovations will have to be reviewed by government institutions. They must ensure the conformity of products by testing their resistance and durability. It is also necessary to measure the possible risks for health and the environment.

Steps which tend to stretch over time, according to Professor Arezki Tagnit-Hamou, burned by his previous experiences. For example, he piloted a method for integrating glass powder obtained from recycled bottles into cement. More than a decade passed between the first experiments, in 2004, and the adoption of the standards.

That's where the problem lies, he says. It's really too long a road. We must work to accelerate the adoption of standards.

It also encourages industry representatives, who are sometimes cautious, to be open to new practices, as well as ministries and municipalities to support businesses by purchasing low-carbon concrete.

At the current rate, Professor Tagnit-Hamou believes that changes in practices are not fast enough to achieve the objectives of reducing gas emissions at greenhouse effect.

On the other hand, haste is not always well received, as we saw in the Northvolt case.

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