Cement-based concrete is the most-used manmade material on the planet, but it is responsible for 8% of annual greenhouse gas (GHG) emissions each year. Over 90% of these emissions are due to the use of cement, a key binding agent in concrete. Innovative technologies that replace cement are crucial for reducing the impact of our built environment.
One approach to reducing concrete’s emissions is the partial replacement of cement with supplementary cementitious materials (SCMs). Mixing alternative binders with cement can partially reduce concrete’s carbon footprint. Slag cement is one such SCM that allows concrete producers to replace some cement content in the concrete mix with blast furnace (BF) slag.
CarbiCrete’s technology replaces 100% of cement in the concrete mix with steel slag, a byproduct of the basic oxygen furnace (BOF) or electric arc furnace (EAF) steelmaking process. Combined with carbonation curing, CarbiCrete technology can reduce concrete’s carbon footprint by over 20 times compared to a conventional cement-based process.
With so many similarities in the language we use to discuss slag cement and CarbiCrete’s steel slag binder, here’s four major differences that set CarbiCrete apart:
1. Absolutely no cement
Slag cement requires the use of ordinary Portland cement (OPC) to create a suitable binder in the concrete mix— according to the Slag Cement Association, slag cement can replace no more than 50% of cement in the concrete mix, or 80% in specific applications. CarbiCrete’s steel slag binder enables 100% cement replacement. Without cement, the global warming potential of end products made with CarbiCrete technology is significantly reduced.
2. Carbon mineralization curing
Concrete products manufactured using slag cement are cured with water and conventional curing methods. CarbiCrete’s steel slag binder reacts with CO2 gas in our patented curing chambers instead of water. Through carbon mineralization, the CO2 and slag react to form the calcium carbonate that gives concrete its strength.
Carbon mineralization not only reduces the products’ curing time from 28 days to 24 hours, it also permanently sequesters CO2 emissions within the concrete products. This means that even after the concrete has been destroyed, emissions stay permanently trapped within the chemical structure of CarbiCrete products.
3. Available supply and green steel compatibility
Slag cement makes use of ground granulated blast furnace slag (GGBFS), which is produced during the reduction of iron ore to iron in a blast furnace. Blast furnaces are extremely carbon-intensive, often relying on fossil fuel and a decreasing supply of virgin material. Hatch posits that by 2040, low-emission technologies like electric arc furnaces will encompass a significant portion of steel production.
The steel slag utilized in the CarbiCrete process is a waste material generated when iron is processed into steel. It has limited uses and often ends up in a landfill. The EAF steelmaking process is considered the frontier of green steelmaking technology; it utilizes scrap metal that is expected to maintain a steady supply in coming years.
4. Cost
Due to a decreasing supply and a significant demand for GGBFS, the North American market is increasingly served through overseas imports. As a consequence, slag cement is not only more emissions-intensive than the CarbiCrete process, it’s also more costly. Additionally, cement prices are expected to steadily increase in coming years due to increased demand for new buildings, and a rise in raw material prices, making steel slag an attractive replacement: less expensive and easier to acquire, steady supply and ability to replace 100% of cement in masonry and hardscape application.
CarbiCrete’s unique steel slag binder shows crucial improvements in cost, environmental performance, and long-term feasibility when compared to slag cement. As the construction industry moves toward decarbonization, the elimination of cement and the incorporation of permanent CO2 storage via mineralization are major benefits to CarbiCrete’s technology that make it an excellent long-term solution for the transformation of the sector.
