Carbon Upcycling’s thrifty solution for low-carbon concrete

Using industrial waste and recycled carbon dioxide helps to shrink concrete’s hefty carbon footprint.

The grey mountains of slag piled high by Hamilton’s hulking steel mills are a salient reminder of the vast amount of by-products created in the production of industrial materials. The infernally hot process of transforming pig iron and scrap metal into goods like steel wire or beams produce two types of material: iron slag, the chunky mineral residue created by firing iron ore and coke, and then something called “basic oxygen furnace slag,” a cast-off produced during the process to remove impurities. While there’s a robust market for the former, there’s less demand for the latter, apart from low-end applications like aggregate for road construction. Steel mills generate hundreds of thousands of tonnes of it each year, and the bulk of it ends up in landfills.

Heavy industries like steel, coal-fired power plants and cement production are energy and resource intensive, and they release enormous amounts of greenhouse gas into the atmosphere. To shrink the carbon footprint of some of the most widely used materials on the planet, we need to think about not only greening the energy that drives these sectors but also finding new ways to make the best use of the wastes they leave behind.

Steel mills produce about half a million tonnes of basic oxygen furnace slag a year, notes Apoorv Sinha, CEO of a Calgary-based Carbon Upcycling, a startup that’s developing methods to capture and recycle carbon emissions from industrial waste and turn it into low-carbon cement and other materials. “That product currently does not have a great use case.”

That’s something Sinha is working to fix.

A decade ago, Sinha set out to leverage chemistry to create new materials from upcycled industrial waste. It is, he acknowledges, a complicated proposition. Whatever he builds needs to work seamlessly with gigantic plants that have finely calibrated processes and specialized equipment that can’t be radically modified.

While the company works with a range of materials, Carbon Upcycling’s most promising technology involves capturing waste carbon and combining it with the by-products from steel plants and coal-fired generating stations to produce a cement additive. This fall, the company is starting construction on a facility at Ash Grove, a sprawling cement plant in Mississauga that’s owned by building products multinational CRH. Once it’s built, the company will start upcycling low-value industrial waste and carbon dioxide captured from Ash Grove’s own flue gas to concoct a low-carbon ingredient to the firm’s cement products — an elegant circular economy solution. By this time next year, the company aims to produce 100 tonnes of low-carbon cement a day, using slag from nearby steel plants or landfill sites.

The proximity, in fact, is key: “Our thesis is that we need to provide a hyper-local solution that works at the cement plant level,” says Sinha.

Decarbonizing the world’s most abundant construction material

Carbon Upcycling is part of a rapidly growing industry of startups working on ways to decarbonize cement and concrete. It’s a goal shared by the global industry, says Sarah Petrevan, the vice president of industrial decarbonization and sustainability at the Cement Association of Canada. “It is imperative for our industry to find a way to achieve net-zero emissions in a real, transparent and credible way,” she says.

It is, however, a massive challenge. Worldwide, concrete production is responsible for a whopping 8 per cent of greenhouse gas emissions. In Canada, because of the country’s relatively small cement-making capacity and the fact that the energy used by cement plants in this country is cleaner, the figure is somewhat lower; in 2019 it accounted for 1.5 percent of the country’s emissions, roughly equivalent to the carbon emitted by 2.4 million vehicles.

The main culprit behind those emissions is Portland cement, the powdery substance that literally serves as the glue holding together most of the world’s buildings and roads. It’s made by heating up mined and crushed limestone — a.k.a. “clinker” — to extremely high temperatures. The process yields huge quantities of carbon dioxide, both from the chemical transformation of limestone and the energy used to generate the heat. Additional carbon is released by combining cement with sand, gravel and water to make concrete, and then shipping it from plants like Ash Grove to construction sites.

R. Douglas Hooton, a professor emeritus in the department of civil and mineral engineering at the University of Toronto and the NSERC/CAC Industrial Research Chair in Concrete Durability and Sustainability, notes that many cement companies are focusing decarbonization efforts in two key areas: energy and alternatives for clinker. To reduce their use of coal, many firms are using biofuels and waste fuels as well as natural gas for energy, he says. And to reduce the industry’s reliance on limestone, there are numerous startups and researchers pushing to find alternatives to limestone as a raw material as well as replacing part of the Portland cement with ground up glass, fly ash or basic oxygen furnace slag. While the use of cement replacement materials is common, many of these solutions are still at the pilot stage. But as Hooton notes, they’re “really valuable in moving the industry toward different low-carbon concrete solutions.”

Carbon Upcycling, which raised U.S.$26 million last year, including an equity stake from Ash Grove’s parent company CRH, has emerged as one of the firms closing in on large-scale solutions. Its new facility is expected to reduce the entire plant’s carbon intensity by 12,000 tonnes annually, says Richard Sluce, Ash Grove’s director of customer solutions. The low-carbon cement will be cost competitive with conventional cement, and the goal is to scale up the plant once this small-scale commercial run is working well. According to Apoorv, the facility will sequester 3,000 tonnes of CO2 each year, making it one of the world’s first commercial-scale carbon capture and utilization cement plants.

While the new facility is technically still a pilot project, it will generate commercial-scale quantities sufficient for large infrastructure projects, says Sluce. And, he adds, “there is always an opportunity to increase production with further investment.”

There are two elements to the Carbon Upcycling process that hold particular promise for investors and strategic partners. One is that it doesn’t involve water. (Whenever cement comes in contact with water or steam, it begins to harden, rendering the component materials difficult to process.) Plus, Carbon Upcycling’s equipment — a carbonation reactor — can be incorporated into Ash Grove’s facility without significant changes. “We can make use of a lot of existing infrastructure, which lowers the difficulty of bringing the technology online, as well as the cost,” says Sluce. “One of the goals is to prove the technology and the material, gain market acceptance, and look at ways to scale the process further.”

Local solutions are lower carbon solutions

One of the challenges for Carbon Upcycling and other low-carbon cement firms is that a successful product is the result of a confluence of factors, including a low-carbon energy system. (Much depends, for instance, on whether the cement plants are using coal-generated electricity or cleaner power.) Another critical variable: the availability of limestone alternatives within a local market. In most of Canada, for example, fly ash from coal plants is no longer available because coal has been phased out. Some cement scientists have promoted the use of a calcium-rich clay and raw limestone combination as a lower-carbon alternative to limestone, but it’s not widely available in Eastern Canada.

In some markets, cement makers can use ground-up glass as an additive, or, as in Greater Toronto, basic oxygen furnace slag. But even with this material, there’s a wrinkle. As the steel industry shifts to electric-arc furnaces, which generate about a third of the emissions per metric ton of steel as compared to conventional blast furnaces, less reusable slag will be created.

Sinha says Carbon Upcycling’s edge is that its technological process allows it to use the kind of slag cast off by electric arc furnaces as well as basic oxidation furnaces.

Perhaps the most important ingredient in this complex industrial recipe involves location: increasingly, cement and clinker are being shipped all over the world, a development that torques the environmental cost of a commodity.

To that end, Carbon Upcycling is developing three types of feedstock — fly ash, steel slag and clay materials — since every cement plant across the globe has local access to at least one of them. Sinha says three of the world’s 20 largest cement producers have invested in Carbon Upcycling out of a recognition that ever longer global supply chains make little sense when emergent technologies can upcycle local waste materials and a cement plant’s own emissions.

“In these hard-to-abate sectors,” he says, “change is going to have to happen at facilities that already have local supply chains, local labour and local practices.”

 
Carbon Upcycling is one of six companies in Mission from MaRS: Carbon Management, a special initiative that aims to help Canada achieve its net-zero goals by accelerating the adoption of carbon removal solutions.

 
Illustration: Stephen Gregory; photos: Unsplash and Flickr