CarbiCrete, a Canadian cleantech 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 COâ‚‚Â emissions and low carbon concrete
Concrete COâ‚‚ 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 COâ‚‚ 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.
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 Technology
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 COâ‚‚ gas.