Montreal company Carbicrete has developed a method for sequestering carbon in concrete, claiming its product captures more carbon than it emits. The technology cuts out the need for calcium-based cement, a key ingredient in traditional concrete that is responsible for around eight per cent of all global CO2 emissions. "It's negative emissions," Carbicrete CEO Chris Stern told Dezeen. "We're taking CO2 out of the system every time we make a block." Concrete locks carbon away "forever" The company is one of many that is racing to find low-carbon or carbon-free alternatives to traditional concrete but is one of the only ones claiming to have achieved negative carbon. However, the process relies on emissions produced by other industries, so it is helping to reduce the amount of additional CO2 going into the atmosphere rather than actively removing it from the atmosphere. But as CO2 captured from the sky via direct air capture (DAC) companies such as Climeworks becomes more affordable, concrete could start to play a part in lowering concentrations of atmospheric carbon. "We'd love to get it from a direct air capture unit," Stern said. "We're not there yet just because the industry is not there yet but it's certainly well-positioned for us." Technology could eliminate hundreds of megatons of emissions Carbicrete, which was founded in 2016, licenses its technology to concrete manufacturers who can integrate it into their existing production processes for concrete masonry units (CMUs) and precast panels. In collaboration with Quebec manufacturer Patio Drummond, the company is building up its production capabilities to 25,000 CMUs per day while the first building using material is set to be built in Canada at the start of next year. Instead of cement, Carbicrete's system combines waste slag from the steel industry plus carbon captured from industrial plants that would otherwise have gone into the atmosphere. "We're taking it from there and then injecting it into concrete and getting rid of it forever," Stern said. More carbon is captured during the production process than is emitted during the manufacture of the concrete, making the resulting concrete carbon-negative according to Stern. Once scaled up, Stern believes the technology can help to reduce the 2.2 billion tonnes of carbon emissions that are generated by the cement industry every year. "We can take care of megatonnes on a yearly basis, [capturing] anywhere between 100 and 300 [million tonnes of CO2]," Stern explained. "So it's definitely going to make a dent." Process works without cement Carbicrete's technology cuts out the need for cement, the binding agent that makes up around 12 per cent of traditional concrete but is responsible for half of the material's carbon footprint. To make cement, calcium carbonate (usually in the form of limestone) is heated to around 1,480 degrees Celsius to extract calcium oxide. This process releases carbon dioxide, which accounts for 40 per cent of limestone's mass, into the atmosphere. The energy-intensive process is usually powered by fossil fuels, creating additional emissions. Carbicrete's method circumvents these emissions, cutting out approximately two kilograms of CO2 for every concrete masonry unit. As a substitute, the company uses a waste byproduct from the steel-making process called slag, which contains calcium oxide. In traditional concrete production, cement is cured with water, causing the calcium to react with the CO2 in the surrounding air and turning it back into strengthened calcium carbonate. Read more: https://www.dezeen.com/2021/06/15/carbon-capturing-concrete-carbicrete/