There is a new theory coming up that puts forth the fact that zero-carbon cement, which happens to be made by way of feeding the concrete construction waste within the present steel recycling process, can go on to potentially cut carbon emissions in terms of both cement and steel sectors.
This approach happens to be the first cement recycling method that has been proposed to date and can also offer solutions to one of the most pressing decarbonization issues in the world. There are estimates In addition to this, steel production is thought to be contributing a minimum of 6%. suggest that almost 8% of the present anthropogenic carbon dioxide emissions are derived from the production of cement. In addition to this, steel production is thought to be contributing a minimum of 6%. Driving such kind of emissions happens to be dependent on the lime to make these materials.
It is well to be noted that Portland cement happens to need clinker, which gets made by way of heating the limestone as well as minerals in a kiln. The process results in releasing carbon dioxide from the limestone-calcium carbonate when it gets converted to lime-calcium oxide. Clinker then gets combined along with silica-rich clays on a surface in order to make cement. Apart from this, steel production needs lime as a flux material so as to mop up the impurities coming from the molten metal all throughout the manufacturing process.
A group at the University of Cambridge in the UK has gone on to come up with a process that happens to recycle cement from the waste demolition concrete, which has sand, cement, aggregates, and water through using it as a lime supplement in order to eradicate impurities when it comes to steel recycling. The cement gets re-clinkered in this process, thereby helping it to be reused in the new concrete, whereas it is less lime that is needed so as to recycle the steel.
Cyrille Dunant, who was the one behind developing this new process went on to state that they had noted that steel decarbonization was very much possible due to the fact that steel recycling was very well established; however, the emissions that happened to be associated with lime were indeed a big problem and that when it had occurred to him that the cement paste could very well go on to replace the flux.
Cementing the place of electricity
When we talk of the new process, the old cement powder happens to be first extracted from the waste concrete by way of heating or mechanically. The old cement then gets fed into the recycling process for scrap steel, which then makes use of the electric arc furnace so as to melt the material. After this, the cement then goes on to become a flux so as to soak up the impurities, which then go on to form a liquid slag that tends to float on the surface of the liquid steel. As and when the molten steel gets eradicated, the slag goes on to quickly cool in the air and then is ground up into powder.
It is worth noting that the pilot-scale trials by Cambridge Electric Cement have gone on to give out the combined recycling process, thereby revealing that the recycled cement slag happens to have an almost identical chemical mix to that of conventional clinker.
One of the experts in infrastructure materials at the University of Leeds in the UK, Leon Black, says that this is indeed a very interesting development that happens to have great potential. The group has indeed been able to go beyond a major barrier when it comes to the development of new cements in the fact that they have stuck with Portland cement but, at the same time, have been able to find a much more efficient way so as to produce it.
As per Dunant, the recycled cement can also be zero carbon since the emissions have already gone on to occur by way of the decarbonization of lime when it got manufactured originally.
The fact is that recycling the cement only happens to have emissions that are associated with heat, and it is electric. Critically, since this happens to be a substitute lime part that is used in steel recycling, the mixed emissions of recycling steel as well as the cement together can be much lower than recycling steel only, thereby depending on the scrap grade.
But Black does note certain issues. The big problem is indeed going to be sourcing a sufficient number of concrete waste quantities. As a matter of fact, this is what has gone on to stop the cement sector from doing it as per their process. One more challenge is the temperature that is needed to produce the cement. This happens to be much higher as compared to what is used in a cement kiln, and hence the overall decarbonization of the entire production process is completely dependent on decarbonizing the generation of electricity.
The fact is that the researchers are indeed confident that these issues can very well be overcome, however, they do acknowledge that more work is needed. One needs to gauge as to how to go ahead and modify the operations when it comes to presenting large-scale industrial equipment so as to manufacture cement, which, by the way, it was not designed for. One has to qualify the new clinker in terms of durability as well as consistency in the quality of production.
It is worth noting that the researchers have already gone on to file for a patent as far as the process is concerned and now happen to be working on the industrial trials along with the construction sector collaborators.
There is an anticipation that the process could very well go on to produce 1 billion tonnes of cement every year by 2050, which, by the way, represents almost a quarter of the present annual production of cement. They indeed happen to hope that it will only grow so as to cover a significant proportion in terms of the cement needs, thereby decreasing the impact when it comes to this very critical material, says Dunant.
