2023-06-02 09:41:32
IMT Nord Europe has built a semi-industrial flash calcination treatment demonstrator. This process makes it possible to manufacture chemically active materials, which are then used to improve the performance of cementitious matrices. The institute is testing the recovery of new materials, in particular dredged sediments.
Flash calcination treatment is a process invented in 1992 and initially used to transform kaolin clays into metakaolin, that is to say into a chemically active material with pozzolanic properties. Clearly, this material can behave as a binder in a cementitious matrix to improve its performance. Argeco is the only manufacturer in France to use this process at its Fumel site in New Aquitaine. Convinced of the potential of this technology, IMT Nord Europe built a semi-industrial demonstrator with the aim of transforming new materials, in particular dredged sediments.
“To manufacture a pozzolanic material, the conventional method consists in heating the product for at least one hour, at a temperature which depends on the product and which varies between 900 degrees and can go up to 1450 degrees in the case of a cement, explains Mouhamadou Amar, teacher-researcher at IMT Nord Europe. The advantage of flash calcination is that it is heated for less than a second, at a temperature between 600 and 800 degrees. The speed of the process and the fact that less heating is required allows energy savings, which ultimately results in economic and environmental gains. »
The process is divided into four steps. The sediments are first dried and then ground to obtain particles with a diameter of less than 40 micrometers. They are then introduced into the doser of the calcination unit, then transported by an endless screw to the entrance of the combustion chamber where they are propelled inside by compressed air. The particles are then subjected to a heat flux which ensures calcination at the targeted temperature for less than one second.
These particles then fall into a calcination column, where the destructuring of the material takes place through dehydroxylation. All OH bonds will somehow be cleaved and become potentially reactive sites. The material becomes chemically active and pozzolanic. The final step is to recover the product in a cyclone unit where approximately 95% of the processed material is recoverable, and the rest is filtered to ensure that micro and nanoparticles do not escape into the environment.
Reducing the carbon footprint of concrete thanks to flash calcination
The material obtained is called a mineral addition and is able to react with portlandite, a compound produced by cement when it is hydrated. “The mixture of these two products brings greater strength to a cementitious matrix, improves its porosity, its durability and its long-term performance.completes the teacher-researcher. Mineral additions are commonly used in construction and can be made from kaolin. What sets us apart is upgrading a different starting material, i.e. dredged sediment or soil, and then using flash calcination technology to manufacture it. For the past three to four years, cement manufacturers have been interested in this process because they need to find solutions to reduce their carbon footprint. One of the ways is to use less cement and partly substitute it with a mineral addition, which has less environmental impact, in particular that produced by flash calcination. »
The other advantage of this technology is that it can be used on a wide range of materials. IMT Nord Europe has successfully tested it on dredged sediments and is exploring the possibility of recovering excavated earth (backfill) as well as washing fines from the treatment of cuttings and deconstruction materials. “Today, all these materials are considered waste and we are studying how to recover them to consider them as a resource by bringing them value”, add Mouhamadou Amar.
Scientists are also exploring another avenue for enhancing the flash calcination process by developing a new category of materials, namely geopolymers. Unlike a mineral addition, the objective here is that they replace 100% Portland cement, and that they are used in the manufacture of concrete structures, with the same level of performance as constructions made of concrete. ordinary. This research work is currently in progress.
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