CarbiCrete, a Canada-based clean tech company founded in 2016, develops an innovative method for producing cement-free, carbon-negative concrete from steel slag byproducts and captured CO₂ gas. In addition to reducing CO₂ emissions, CarbiCrete’s technology sequesters CO₂, resulting in carbon-negative concrete production.
Challenges: concrete CO₂ emissions and low carbon concrete
Concrete CO₂ emissions
Traditional concrete is composed of cement, aggregates, water, and admixtures. Cement production, particularly Portland cement, is responsible for a significant portion of carbon dioxide (CO₂) emissions in the construction industry, accounting for around 8% of global CO₂ emissions. This is because the production of cement involves a chemical reaction called calcination, in which limestone (CaCO₃) is heated to over 1,400 ºC in a kiln to produce lime (CaO). This process releases carbon dioxide according to the following reaction:
CaCO₃ + heat → CaO + CO₂
Additionally, the cement production also requires large amounts of energy to heat the kiln and grind the raw materials into the fine powder that is used to make cement. The energy required for cement production comes mainly from burning fossil fuels such as coal, oil, and natural gas, which also releases CO₂ into the atmosphere.
It is estimated that 75% of the infrastructure that will exist in 2050 has not yet been built, which will lead to a massive increase in demand for cement, which necessitates new approaches to producing low-carbon cement.
Low carbon concrete
Low carbon concrete, also known as green concrete or sustainable concrete, aims to reduce the carbon footprint associated with the production of traditional concrete. It is created using alternative materials, innovative production methods, and optimized mix designs.
Low carbon concrete reduces carbon emissions by replacing a portion of cement with supplementary cementitious materials (SCMs) such as fly ash, slag, or natural pozzolans. Additionally, low carbon concrete can be produced using alternative binders, such as geopolymers or calcium sulfoaluminate cement.
This book Making Better Concrete provides guidelines for designing and building with high fly ash concrete for higher-quality, lower carbon structures.
Low carbon concrete has diverse applications in the construction industry, including the production of precast concrete elements and building blocks for residential, commercial and industrial buildings, as well as pavements, parking lots, and sidewalks, which makes it a promising solution for sustainable development.
While low carbon concrete offers many benefits, there are also some challenges that need to be addressed to accelerate its adoption in the construction industry. These challenges include higher costs, lack of standardization, limited availability of alternative materials, concerns regarding durability, resistance to change, and energy consumption.
CarbiCrete has developed a process for producing carbon-negative concrete by using steel slag and captured CO₂ gas. To create cement-free concrete, steel slag and filler material are first mixed with water in a manner comparable to conventional concrete production. Concrete blocks are created via compression. Steel slag is used as a binder. The CO₂ curving (or carbonation) of the concrete blocks is the core technology of CarbiCrete. In a sealed chamber, concrete blocks are cured in CO₂ gas. The calcium in the steel slag reacts with CO₂ to form calcium carbonate (CaCO₃), which binds the concrete together and improves the ultimate strength and durability.
CarbiCrete concrete production
The flowchart below depicts the steps for producing cement-free concrete blocks from steel slag and CO₂ gas.
- Refine steel slag
As a byproduct of the steelmaking process, steel slag is received and refined.
The steel slag contains coarse and fine slag particles. The received steel slag is refined by filtering it to separate coarse slag particles from fine slag particles. This fine slag powder is used to replace cement in the concrete mixture as a binder.
The estimated global production of steel slag is between 190 million and 280 million tons. Global slag production is expected to grow by about 8% by 2026 and 10.5% by 2031. CarbiCrete obtains steel slag from Harsco, the largest materials processor in the steel industry. This ensures a steady supply of high-quality steel slag for CarbiCrete’s production process.
- Prepare concrete mix
A filler material is mixed with the steel slag. The filler material is a granular material, and the refined steel slag serves as the binder. The mixture of steel slag and granular material is further combined with water to create a cement-free concrete mixture.
- Mold concrete
The mixture of steel slag and granular material is molded via compacting. A larger amount of pressure can contribute to a building product’s higher compressive strength, but it also results in less CO₂ uptake during the subsequent carbonation process, which limits the compressive strength achieved. Therefore, a pressure of less than 20 MPa can be applied to allow satisfactory carbon uptake.
- Reduce water amount
Air flow is applied to the concrete blocks to reduce the amount of water in the concrete. This increases the porosity of the concrete blocks, which results in increased carbon uptake in the subsequent carbonation process.
- Carbonate concrete
The concrete blocks are placed in a sealed chamber and exposed to CO₂ gas. Calcium in the steel slag reacts with CO₂ to form calcium carbonate (CaCO₃), which binds the concrete together and improves its ultimate strength and durability. The carbonated concrete is left to cure, during which time it gains strength and durability. This process is called carbonation. The carbonation results in CO₂ sequestration.
- Hydrate curved concrete
The curved concrete blocks are placed within a sealed hydrating environment for a predetermined amount of time. The duration of the hydrating process may vary based on the building product to be made.
CarbiCrete concrete carbonation
The diagram below depicts the CarbiCrete’s system of concrete carbonation.
The concrete blocks to be cured are placed within a sealed carbonation chamber. Pure CO₂ gas from a cylinder is warmed by a heater to ambient temperature before injecting it under pressure into the chamber. A regulator regulates the pressure and maintains a constant pressure to ensure that CO₂ consumed by the concrete blocks is continually replenished.
A balance and data logger are further provided to calculate the CO₂ uptake.
The curing of the concrete blocks with CO₂ occurs after two hours and continues thereafter. 24 hours may be spent curing the concrete blocks with carbon dioxide.
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Global concrete market
The global concrete market is vast, with a market size of approximately $700 billion in 2022. This market is expected to reach a value of nearly $1 trillion by 2028. This growth is driven by the rising demand for sustainable and environmentally friendly construction materials, such as Carbicrete’s cement-free, carbon-negative concrete.
CarbiCrete produces precast concrete products using their patented technology that replaces cement with ground steel slag and cures it with CO₂. Carbicrete’s technology is applicable to various industries that utilize concrete, including:
Residential, commercial, and industrial construction projects can benefit from Carbicrete’s carbon-negative concrete, as it offers a more sustainable alternative to traditional cement-based concrete.
Public infrastructure projects, such as roads, bridges, and transportation systems, can also utilize Carbicrete’s technology to reduce their carbon footprint and promote sustainable development.
- Precast concrete products
Manufacturers of precast concrete products, such as concrete blocks, pipes, and panels, can adopt Carbicrete’s technology to produce more environmentally friendly products.
- Green building
The green building sector, which focuses on constructing energy-efficient and environmentally friendly buildings, is a natural fit for Carbicrete’s technology. Green building certifications, such as LEED and BREEAM, may award points for using carbon-negative concrete in construction projects.
CarbiCrete has raised a total of $22.3M in funding over 7 rounds, including
Their latest funding was raised on March 24, 2022 from a Series A round.
CarbiCrete is funded by 10 investors, including
- Government of Canada
- Ministère de l’Énergie et des Ressources Naturelles
- Harsco Environmental
- Sustainable Development Technology Canada
- New Climate Ventures
- FS Investors
- SQN Venture Partners
- Arc Energy Fund 9
- Something Good Ventures
Chris Stern is CEO.
CarbiCrete Board Member and Advisor
Kevin Rahill is Board Member.