Ciment sans clinker : la solution d’avenir ?

The world of cement is experiencing a revolution which is currently happening in Vendée. This material, which has become essential in the construction sector, can now be manufactured without clinker[1] thanks to a technological breakthrough brought by the company Hoffmann Green Cement. Not content with creating a product five times less carbon-intensive than traditional Portland cement, it has also completely rethought the industrial model, with a vertical factory itself supplying 50% of its energy consumption.

The story of the industrial start-up began more than ten years ago with an innovation from David Hoffmann that he tested alone. It is possible to replace the clinker with a cold mixture of blast furnace slag (molten silicate liquid, in the form of sand after cooling) and activators in order to obtain hydraulic binders which can react with water to make cement. The proportion is approximately 85% powder waste (blast furnace slag or clays from washing quarry sands or desulfogypsums) and 15% activators, also in powder form. The approach was too innovative at the time for cement manufacturers and bankers, who refused to support him in his work. The meeting in 2014 with Julien Blanchard and the microcosm of Vendée entrepreneurs will change everything: they raise around a hundred million euros to build a pilot factory. “It took nine months to be able to reproduce industrially what had until then only been done in the laboratory. With 6,000 m² on the ground, no combustion therefore no chimney, little waste, this first factory can already produce 50,000 tonnes of cement per year »says François Simon, Île-de-France prescriber for the cement manufacturer Hoffmann.

A sector that needs to decarbonize

This first step is a drop in the bucket compared to French cement production, which was 16.5 million tonnes in 2018. But it shows a very promising new direction. The cement sector actually emits around 10 Mt CO₂eq each year, or 12.5% ​​of greenhouse gas emissions from industry in France. It must therefore make a significant effort to achieve decarbonization. It plans to do this by modernizing its factories, greening the thermal mix of its kilns, reducing the clinker rate, and incrementally applying other decarbonization technologies. But, as Ademe showed in its sector transition planthese reference solutions would still lead to the emission of 6 Mt CO₂eq in 2050, when they should be reduced to 2 Mt CO₂eq. Even using technology carbon capture and storage (CSC), emissions from cement manufacturers would still be nearly 5 Mt CO₂eq. To achieve the right result, Ademe modeled two other scenarios, one pushing the sobriety cursor more strongly, and the other maximizing technological solutions, in particular CCS.

The solution proposed by Hoffmann, by eliminating the clinker manufacturing step, makes the prospect much more affordable. This is why it has gradually been recognized, and recently received the Low Carbon Cement prize awarded by the World Cement Association, while Julien Blanchard was distinguished by the Academy of Architecture. It should be noted, however, that this recognition took time. “As traditional cement manufacturers locked in regulations by imposing a minimum clinker content of 5% in cement, the Hoffmann solution had to fight to obtain approvals. After more than four years and 6 million euros spent to carry out physical, chemical and mechanical tests with the CSTB, our H-UKR cement notably obtained an ATEx A technical assessment.[2] » explains François Simon. By validating a useful life of 100 years, and qualifying it as a common technique for insurers and technical inspectors, this cement will be able to be used for concrete used in engineering structures and more generally for any superstructure (posts, beams , sails, slabs).

A vertical factory 4.0

Hoffmann was also the winner of the Factory Prize RSE during the 2023 Usine Trophies, to salute its second production unit. This factory, inaugurated on May 12 in Vendée and named H2, has the particularity of being the first vertical cement plant in the world ! It was built with Hoffmann Green concrete to demonstrate its effectiveness in creating a tower 70 m high and approximately 25 m wide. The upper part of the tower contains 19 vertical cells filled with raw materials and chemicals – up to a dozen activators, sometimes dosed in very small quantities – necessary for the production of cement. They are assembled cold by gravity in the lower part of the tower, thus minimizing the need for energy and maintenance. A choice that strengthens the company’s resilience in the face of an energy crisis: energy only accounts for 2% of its structural costs, or ten times less than traditional cement manufacturers. Twelve solar trackers and photovoltaic panels on the roof of the annex buildings will provide half of the electricity consumption required for the site.

With this second factory, Hoffmann increases its production capacity to 250,000 tonnes of cement per year. Other factories should emerge in the coming years. Because demand will inevitably increase, and certain large buyers, such as Spie Batignolles, are starting to secure the volumes that Hoffmann will be able to deliver to them. Even if Hoffmann cements are currently more expensive than their competitors, it is likely that this will not last. By increasing its production volume, the company should reduce its costs, while traditional cement manufacturers will inexorably see theirs increase: Ademe’s assessments show that, without decarbonization efforts, the traditional sector would see a tripling of the cost of production (with a ton of CO₂ at only 180 euros), but that the implementation of efforts – by keeping the clinker – will still lead to a doubling of costs…

[1] As a reminder, for 200 years, clinker has been the main active ingredient in cement. It is obtained by firing a mixture of limestone (80%) and clay (20%) at 1,450°C in a rotary kiln. This stage represents almost all of the greenhouse gas emissions from cement manufacturers: they are due both to the consumption of thermal energy (a third of emissions) for cooking, and to the chemical reaction of calcination which transforms limestone in lime and CO₂ (two thirds of emissions).

[2] Technical Experimentation Appreciation