Cutting-edge concrete products are easier on the environment and the budget
by Zena Ryder
- New technologies allow the absorption of CO2 from industrial processes into concrete as a curing agent
- Waste CO2 and bacteria are being used to make new types of concrete aggregate
- Some companies replace the cement in concrete with other materials, with no loss in strength or durability
- Reported costs are equal to, or less than, standard concrete
Every builder — on-site or off-site — needs concrete. But ordinary concrete is very harmful to the environment, largely because of how cement is made. Cement kilns are heated with fossil fuels to around 2,500 F, which releases large quantities of carbon dioxide into the atmosphere.
Here, we’ll look at four companies — CarbonCure, CarbiCrete, Biomason and Blue Planet Systems — that are working to reduce concrete’s carbon footprint. These companies have also found ways to improve various properties of concrete and even reduce its cost.
CarbonCure
CarbonCure in Halifax, Nova Scotia was founded in 2012. Its technology cures concrete with waste CO2 from industrial processes such as fertilizer and ethanol production.
The CO2 is transported to CarbonCure’s customers — producers of ready-mix, masonry blocks, precast panels and pavers, etc. — and stored in tanks.
CarbonCure’s software syncs with the manufacturer’s existing batching software to control the amount of CO2 injected into the concrete. “The CO2 injection happens at the same time as other processes in the batching sequence,” says Allison Palmer, Senior Manager of Market Development at CarbonCure. “There’s no impact on cycle times, and therefore no impact on construction schedules.”
Once injected into the concrete, the CO2 reacts with calcium in the cement forming a calcium carbonate mineral. The CO2 never escapes into the atmosphere, even when the concrete is demolished.
CarbonCure has sold 500 systems worldwide and over 15 million cubic yards of CarbonCure concrete have already been poured, Palmer says. (There’s a “Find a Producer” tab on their website.)
Concrete made with CarbonCure can be used in the same applications as regular concrete and meets all the same regulatory standards. The CO2 curing process makes the concrete stronger. A 2019 research paper in the journal Materials, reported that carbonation-cured concrete had more than 10% higher compressive strength than moisture-cured concrete at the same age.
This enhanced strength means that producers can reduce cement in their mixes by an average of 4% to 6% (some up to 10%) while maintaining the same compressive strength, Palmer says.
Less cement means less cost. Even after factoring in the added expense of CarbonCure’s technology, Palmer says, “most of our producers can provide their concrete products with no additional cost to the end-user.”
CarbiCrete
Cement-free concrete? Canada’s CarbiCrete, a Montreal-based company founded in 2016, says that its technology allows precast concrete manufacturers to use ground steel slag, a by-product of steel manufacturing, to completely replace cement in their concrete products.
Steel slag is much cheaper than cement. So, even factoring in the costs of new equipment and licensing technology from CarbiCrete, the resulting concrete products cost the same, or less than, ordinary concrete, according to CEO Chris Stern. The company claims savings as high as 20%.
The slag is mixed with sand, aggregates and water— just as cement usually would be — using concrete product manufacturers’ existing equipment. The mixture is formed into blocks or pavers, which are placed into special absorption chambers and cured with captured waste CO2.
The CO2 reacts with calcium silicates and calcium ions in the slag to form calcium carbonate, a stable mineral that doesn’t turn back into carbon dioxide.
According to research published in the Journal of Cleaner Production in 2016, blocks made with steel slag are as strong as ordinary concrete blocks and are more durable when subjected to repeated freeze-thaw cycles. The researchers also concluded that concrete blocks made with slag and cured with CO2 were carbon-negative. That is, the manufacturing process removes more CO2 from the atmosphere than it emits.
CarbiCrete licenses its technology to precast concrete manufacturers and manages the installation of the CO2 tank and the absorption chamber at each manufacturer’s plant. Once set up, the gas supplier handles tank maintenance and refills. CarbiCrete’s agreement with an international materials processing company ensures that their customers can always get whatever quantity of slag they need.
At the moment, CarbiCrete is focused on the masonry and precast market, rather than on ready-mix. “We have a pathway to get to ready-mix, but the margins on ready-mix are lower compared to higher-cost items like masonry and precast,” Stern says.
Concrete products made using CarbiCrete’s technology should be available in Quebec at the end of this year, Stern says.
Biomason
Another company that completely eliminates the need for cement is Biomason in Durham, North Carolina, which was founded in 2012. They call their product “biocement” because it’s produced through a biological, rather than a chemical, process.
Their process is similar to the one involved in coral formation. In nature, coral polyps take calcium and carbonate ions from seawater and make an exoskeleton of limestone (calcium carbonate), which is what hard coral structures are made of.
In ordinary ambient temperatures, Biomason’s bacteria use calcium and carbonate ions to produce calcium carbonate. The calcium carbonate bonds loose aggregate particles (sand and gravel) together, just as ordinary cement does.
Biomason’s precast concrete tiles go by the name of bioLITH. To make them, the company mixes bacteria, nutrients and water with loose aggregate and presses the mixture into precast shapes. Additional calcium and carbonate are provided in liquid form after pressing. It takes less than 60 hours for the tiles to reach full strength of 4000 to 6000 psi. according to Katie Bailey, Brand Communications Manager.
BioLITH tiles can be used in vertical and horizontal applications, indoors and outside, and are installed in the same way. They’ve been used throughout Europe and the US. “The concrete BioLITH tiles are made from is four times stronger than ordinary concrete, so the tiles can be much thinner. That makes them lighter and cheaper to ship,” says Bailey.
She says that Biomason is really a biotech company, even though they are currently manufacturing and selling concrete tiles. They recently partnered with IBF, Denmark’s biggest concrete manufacturer, which will incorporate biocement technology into all their concrete products.
Biomason eventually wants to license its technology to other concrete manufacturers.
Blue Planet Systems
Ordinary concrete is 60% to 80% aggregate. Blue Planet Systems, a Los Gatos, California company founded in 2013, makes aggregate with sequestered waste CO2. To do this, it combines CO2 and calcium (from recycled concrete, for example) to produce calcium carbonate, or limestone.
Blue Planet’s aggregate sequesters so much CO2, that concrete made from it and ordinary cement is carbon negative. That is, manufacturing the concrete permanently captures more CO2 than it emits.
San Francisco Bay Aggregates, a company owned by Blue Planet Systems, began making the aggregate in mid-2021. They use waste flue gas from a natural gas-fired power plant.
To capture the CO2, Blue Planet uses a gas-liquid contactor, which uses very little energy. Flue gas rises from the bottom and a ‘capture solution’ trickles down from the top. As they pass one another, CO2 dissolves into the capture solution and becomes carbonate and bicarbonate ions.
When the carbonate/bicarbonate solution is combined with calcium, synthetic limestone is formed. Blue Planet’s website says that concrete made with their aggregate meets or exceeds all ASTM strength tests.
For building codes, “the primary test for aggregate is for abrasion,” Dr. Brent Constantz, Blue Planet’s Founder and CEO, explains. “It’s put in a drum with steel shot and rolled around. Then it’s screened. If too much breaks down and goes through the screen, it fails the test. If it’s hard enough that it doesn’t break down much, and not much fine material goes through the screen, it passes.”
The company plans to deliver its aggregate to projects in the San Francisco Bay Area this year.
Conclusion
It’s good to see companies tackling the carbon footprint of concrete, especially given that some of their techniques are compatible and can be used together.
Even buildings that are built mostly off-site rely on concrete for foundations and podiums. By switching to concrete with a smaller carbon footprint, the offsite construction industry has huge potential to greatly reduce CO2 emissions. These innovative concrete products also offer other beneficial properties — such as being cheaper, stronger and lighter than ordinary concrete.
Zena Ryder is a freelance writer who writes about construction for businesses, magazines, and websites. Find her at zenafreelancewriter.com
Hemp-Based Rebar?
Hemp is made from a variety of the cannabis plant—related to, but different from, the variety grown for its psychoactive properties. Historically, hemp has been used for many purposes, from rope and clothing to ink and lamp oil.
When you learn that Porsche has used hemp in race car bodies, the idea of hemp-based rebar becomes less shocking. Just as fiberglass is made with polyester resin and glass fibers, the doors and rear wing of Porsche’s race cars are made of a composite material that includes hemp fibers.
Earlier this year, researchers at Rensselaer Polytechnic Institute in New York announced they’d developed hemp fiber-reinforced thermoplastic rebar. The hemp fibers come from the woody core of the plant. (Thermoplastics become pliable when heated and harden when cooled — and can repeatedly withstand these processes.)
Compared to steel rebar, the researchers say that preliminary results show “a significant reduction in carbon footprint, as well as strength characteristics comparable to steel.”
With thanks to Mandi Kerr, Founder and CEO of the Global Hemp Association.
