Blue planet, green ideas | Small victories to green the cement

(Saint-Basile) Despite appearances, the roadways, bridges and sidewalks on which we walk are in no way harmless to the environment. On the contrary. Cement – ​​like the glue used to make concrete – is one of the biggest polluters on the planet.

In cement plants in Quebec, as elsewhere in the world, efforts are increasing to modify processes in order to produce “greener” concrete. A huge headache since, to make cement, you have to heat rock to volcanic temperatures, an essential step that generates a lot of carbon dioxide (CO₂).

But now in San Francisco, American engineers have been boasting since January of having captured CO₂ rejected during the manufacture of cement to reinject it into a fresh concrete casting. In order to achieve this, two firms, Heirloom Carbon Technologies and CarbonCure, chemically treated a pile of limestone stones to then saturate it with greenhouse gases. Residual dioxide stored in a few barrels.

Admittedly, CarbonCure’s top executive, Rob Niven, called the success “a drop in the ocean.” Still, the experiment sparked curiosity in the industry.

A chemical engineering researcher at Polytechnique Montréal, and particularly interested in green and clean technologies, Mohammad Latifi speaks first of all of a “good publicity stunt” on the part of the two American companies.

“These solutions are not sustainable because they do not respond to environmental and social risks, and because it is very expensive, he specifies. It’s a good idea on paper, but difficult to achieve in practice. In fact, about 0.005% of the CO₂ emitted during the experiment was reinjected into the concrete,” he adds.

New fuels

At Ciment Québec, located in the municipality of Saint-Basile, near Quebec City, President and CEO Luc Papillon claims to have reduced the CO2 footprint by 10%.₂ per ton of cement for 20 years. It aims for reductions of the same magnitude in the coming years. On one visit, he drove The Press to a pile of old railway sleepers (wooden sleepers) from Western Canada. They will be used as fuel to heat the rock to a temperature of approximately 1450°C.

“Instead of using gas or coal to heat the stone, today we use a host of residual materials, anything that cannot be buried. There are these frames, but we also use the ends of the recycling line of building materials. We have already burned the scraps used to design our showers. We therefore use resin scraps, but also missed rolls of aluminized plastic. »

Engineer at Ciment Québec, Guillaume Lemieux explains that the next step is to reduce CO emissions at the source.₂. A “factory within a factory” is also under construction on the site, he explains.

“There are also works to reduce the amount of clinker [constituant du ciment] for each ton of cement. »

Except that there is a limit to the technology because of the costs, believes Mr. Papillon. He cites as an example a Norwegian oil giant which has undertaken to build a 1,000 kilometer gas pipeline to bury CO₂ offshore, at the bottom of the ocean.

“We are talking about a hundred million dollars, easily. And you have to ask yourself questions about the different risks and impacts, the costs and benefits. »

At Polytechnique Montréal, chemistry professor and specialist in carbon capture technologies Louis Fradette led an industrial ecology study for Montréal-Est. Concerned for a long time by the question, he believes that the challenge is to succeed one day in capturing the CO₂ fully, and on a large scale.

“Concrete is the finest building material mankind has ever found. It’s easy to produce, flexible, it’s strong, we know how to reinforce it. Everyone knows how to work concrete. But it’s hard to let go. It’s as if we were a bit prisoners of the cement. »

According to him, there is not a single avenue, but several “small victories”, a “bouquet of solutions” to reduce the quantity of polluting gases.