'Concrete revolution' takes aim at construction’s worst polluter

From building blocks that capture and store CO₂ emissions to rubble recycling and low-carbon concrete mixes, Canada’s construction sector is changing how it thinks about its go-to material. Some believe it could be the start of a “concrete revolution”.

Solving the carbon conundrum presented by a material responsible for up to 8 per cent of global greenhouse gas emissions is critical for an industry under pressure to reduce its emissions to help Canada meet its 2050 net-zero commitments.

Companies ranging from startups to multinationals are investing an increasing amount of time and money in new processes and technologies to decarbonize a concrete and cement sector worth $76 billion to the economy.

"The first emissions in the construction building cycle are in the manufacture of the materials being used. People tend to forget that,” said Mark Hutchinson, vice president for innovation at Canada’s Green Building Council, an industry advocacy body.

"We need to think innovatively about concrete — and steel, glass and other materials — and how we can reduce the embodied carbon in these.”
 

“No shortage of ideas”

Concrete has been used in construction for millennia, from the dome of the Pantheon in ancient Rome to the world’s biggest hydropower project, China’s Three Gorges Dam – and closer to home in the iconic contour base of Toronto’s CN Tower.

Cement makes up only 10-15 per cent of a typical concrete mix, but because it’s manufactured using fossil-fuel fired kilns, it accounts for up to 80 per cent of concrete’s emissions.

The cement industry has set a 2030 target to cut emissions by 40 per cent from 2020 levels and reach net zero by 2050. To do that, it’s delving into carbon-sequestering concrete concepts, alternative concrete mixes, and using low-carbon fuels and clean hydrogen to power concrete manufacturing processes.

While low or zero-carbon products and technologies are starting to find a niche in the $6 billion building materials market, the challenge is scaling up to meet the huge commercial, residential and infrastructural demand — without adding to Canada’s carbon emissions.

“I like to say there’s no shortage of good ideas,” David Redfern, CEO of Lafarge Eastern Canada, said on a recent industry podcast. “But the heavy lift is operationalizing these ideas, putting them into practice.”

“Concrete revolution”

LafargeHolcim, the world’s biggest cement maker, was an early entrant in the green concrete race, investing in its own low-carbon technology as well as working with pioneering cleantech startups.

"We have been making cement and concrete the same way for many centuries,” said Robert Cumming, Lafarge’s head of sustainability and environment for Eastern Canada.

We are in the first years of a concrete revolution.

Robert Cumming, Lafarge Canada

In recent years, however, the industrial giant has developed concrete mixes with between 30 to 90 per cent lower CO₂ emissions than Ordinary Portland Cement, the industry standard used on most construction sites today.

”By changing certain mixtures and processes we see the potential for even further emissions reductions,” he said.

The company is changing over some of its Canadian plants to produce OneCem, a cement that uses less clinker – a mix of limestone and other materials heated in carbon-emitting kilns at high temperatures – to reduce emissions by five to 10 per cent per tonne. The conversion of Lafarge’s huge Saint Constant, P.Q. plant is expected to slash emissions by 60,000 tonnes a year.

Despite the clear benefit in greenhouse gas reductions, Cumming said it took a decade for Canada’s standards regulators to approve OneCem “even though the same mix has been in use in Europe for a long time.”

“The industry is onboard to go green. We and our construction partners understand that carbon is a liability and so we are 'walking toward each other' on this,” he said.

Lafarge is also seeking to capitalize on new thinking outside the company.

"We are in the first years of a concrete revolution. The innovators and researchers in this space are amazing," Cumming said of the growing number of startups focused on the concrete decarbonization challenge.

The search for novel approaches includes a carbon-recycling pilot project with Ottawa-based Hyperion Global Energy that could cut cement plant emissions by up to 1,000 tonnes a year, and an investment in EXACT Technology, a Toronto-based outfit that designs monitoring and control software to make concrete production more efficient.

“Game changer”

But Lafarge sees particular market-disrupting potential in a “carbon negative” concrete building block developed by CarbiCrete, a spin-off from Montreal’s McGill University.

The ash-gray blocks look like any found on a construction site but are stronger and already competitive on price-per-unit, according to the company. However, CarbiCrete has gone a step further than other “sustainable” concrete blocks.

By substituting steel slag, a waste product from steelmaking that usually ends up in landfills, for the cement traditionally used as a binding agent, CarbiCrete greatly reduced the carbon impact of their blocks.

CarbiCrete’s key advantage lies in the fact that the blocks are strengthened in a curing process involving injected CO₂ that is permanently captured in the process, making the blocks “carbon negative”.

“That was the game changer,” said Gary Belisle, chief operating officer at CarbiCrete.

“Once I saw that there was a way to go beyond carbon-neutral — beyond simply removing the cement — and get to carbon-negative by sequestering CO₂ in the curing process, I was sold,” he added.

So was Lafarge. It agreed last year to supply steel slag to CarbiCrete in a deal the two companies said aimed to “re-shape the construction industry by reducing embodied carbon in the built environment.”

The CarbiCrete Process

A typical recipe for concrete includes sand, gravel and rock held together by cement and mixed with water. But making cement is energy and carbon intensive, generating up to 80 per cent of the CO2 emissions in concrete.

CarbiCrete substitutes cement with steel slag - the waste material from steelmaking - in a process called Carbonation Activation. It needs less energy, captures carbon and takes less time to manufacture, the company says.

Here's how it works:

Steel slag is produced when impurities are separated from molten steel in a steel mill furnace. The slag often ends up in landfills. CarbiCrete sources its slag from local steel mills.

The steel slag is mixed with water and aggregates and formed into pre-cast products using standard industry moulds and block-making equipment.

Instead of using heat and steam, the concrete blocks are then cured, or hardened, using CO2 in a special absorption chamber. The CO2 reacts with the steel slag to form calcium carbonates which gives the concrete its strength.

The curing process also removes up to 1 kg of CO2 in a standard-sized masonry block. That adds up to a 20,000-tonne reduction in annual carbon emissions for a carbonates which gives typical North American the concrete its plant, CarbiCrete says.

After 24 hours, the blocks are ready to use at a building site, compared to 28 days for curing regular concrete. Tests show the cement-free blocks are up to 30 per cent stronger than traditional masonry units, the company says, and more durable in Canada's freeze-and-thaw climate.

Source: CarbiCrete

The years-long quest for zero-carbon concrete is now nearing “a commercial tipping point” as it becomes price competitive with traditional masonry products, Belisle said.

Using steel slag as a binder in its concrete mix can reduce costs by 10 to 20 per cent per block, by CarbiCrete’s calculations. The blocks are also faster to manufacture – potentially reducing project times and costs – and shown in tests to be 30 per cent stronger than standard units.

"We are currently equivalent in price with conventional concrete blocks, around $2.50 to $3.00 a block,” Belisle said, adding that the economics will get better in the next five years “as the price of cement continues to rise and we improve our technology and process.”

Quebec-based Patio Drummond, a large maker of concrete products in North America, has been an important partner in CarbiCrete’s efforts to build a market for its carbon-negative concept. Patio Drummond began selling the new-model concrete blocks a year ago and is ramping up production to 3,600 a day by retooling its Drummondville factory.

Earlier this year, CarbiCrete landed $3 million in support from NGen, a Canadian advanced manufacturing innovation cluster, to renovate a masonry plant in Port Colborne, Ont. to produce one million carbon-negative concrete blocks a year.

The company is also considering setting up a block-manufacturing facility next to a steel mill to gain direct access to both waste slag and the CO₂-rich flue gas used in the curing process. Belisle said his company is on the hunt for a partner to expand into product lines beyond building blocks.

"The goal is to produce concrete paving, retaining walls, all sorts of industrial concrete products that are much higher price, higher margin [than blocks]," Belisle said. "And we believe we can carve another 25 to 30 per cent out of the cost in the process.”

'Circular economy' concrete

Recycling is also in the mix as a low-tech, low-cost option to shrink concrete’s carbon footprint. Lafarge is exploring a “circular economy-style” strategy that would repurpose rubble from demolished buildings as raw material for manufacturing concrete onsite as a new building goes up.  

With an eye on the four million tonnes of construction and demolition waste generated in Canada each year, Lafarge is testing a process at its Saint Constant, P.Q. plant that mixes recycled material into ready-to-use, industrial-grade concrete.

"You could have a quarry that is 100 km away from a city [building project] and have to consider the emissions associated with trucking all that material in, or you can look at a demolition site as a temporary 'mini quarry' and reuse that material where it is," said Cumming.

“Lower emissions, greater productivity, and construction waste becomes a raw material: better for us, better for the developers," he said.

While industry efforts to decarbonize concrete are gaining pace, governments will nonetheless have a leading role to play in accelerating the transition to greener building materials, sustainable building advocates believe.

The Pembina Institute, a Calgary-based think tank, said in a July report the most effective policy tools to promote sustainable concrete would be a predictable carbon price on emissions, financing to offset the higher cost of producing low-carbon cement, and a government procurement strategy focused on using greener construction products.

Ottawa’s new Green Buildings Strategy, published in July, included a “buy clean” pledge to use low-carbon materials in government projects, but advocacy groups said a procurement plan should span all levels of government to be effective. 

"We have many of the solutions available, but it has to start with the materials themselves,” said CAGBC's Hutchinson.

Next week, Canada's National Observer will explore how timber, one of the world’s oldest building materials, is poised for a comeback as Canada’s construction industry steps up its green transition. Sign up for free notifications when the next installment of our Big Green Build special report is online.