CarbiCrete Creates Negative Emission Concrete by Using Steel Slag Instead of Cement

Concrete is one the most abundantly used man-made material on Earth. Nearly 70 per cent of the world’s population resides in buildings made out of concrete. And with that, concrete gets produced more and more as each year passes by. However, concrete is catastrophic to the environment. As per the data from the United Nations Environment Programme, concrete production alone is responsible for 8 per cent of humanity’s carbon dioxide emissions; where if the world’s concrete industry were a country, it would have been the third-largest carbon dioxide emitter, surpassing China and America.

Where we stand today, it is not possible to eliminate the use of concrete entirely. Hence, to mitigate the problem, Canadian technology company CarbiCrete has produced an alternative to regular concrete that absorbs CO₂ instead of releasing it into the atmosphere. For this, elimination of cement is a must as most of concrete’s CO₂ emissions come from manufacturing its binding agent – cement. When limestone is heated up to 1,400^o C, generally by using a fossil fuel source, the heat causes the limestone to break down and release CO_2.

CarbiCrete technology, on the other hand, uses steel slag – a waste material formed during the steel-making process – to replace cement as a binding agent. The first step involves mixing cement with aggregate and water. With CarbiCrete, cement is replaced with steel slag, which is mixed with the other materials using standard equipment. Steel slag is sourced by CarbiCrete through a global supply agreement with Harsco, the steel industry’s largest materials processor. This mixture is then poured into a conventional block-making machine where CMUs are formed. During the curing process, CO₂ captured from industrial plants is injected into the slag, where CO₂ gets converted into a mineral. The curing process takes 24 hours and stores 3 kg of CO₂ per CMU by converting them into a stable mineral, alongside an additional kg of CO₂ that is pulled from the surrounding air during the curing process. Additionally, its production process requires no heat. CarbiCrete technology, thus, eliminates cement, slag and CO₂ all at once.

Reportedly, CarbiCrete – the negative emission concrete – is 30 per cent stronger than conventional concrete. CarbiCrete CMUs have the same water absorption properties and display better freeze/thaw resistance. Currently, CarbiCrete is licensing its process to companies that produce pavers, CMUs, retaining walls and other masonry products.

Image credits: CarbiCrete