Each year, over 4.4 billion tons of concrete are poured globally, making concrete the most-used building material in the world. With such a large volume of production, it’s no surprise that concrete accounts for 8% of worldwide annual embodied carbon. And needless to say, solutions to address this issue will have profound positive effects on climate change.
The concrete industry is not sitting idle. Over the past few years, several new technologies have started to reshape concrete into a greener product. Below, we’ll walk you through some of the most innovative approaches to reducing the embodied carbon in concrete. Please note that these solutions are “stackable”, meaning they can all be used simultaneously to reduce concrete’s embodied carbon content as much as possible.
Leading Sustainability Initiatives in the Concrete Industry
Replace Portland Cement With Fly Ash, Slag, or Portland Limestone Cement
To reduce the embodied carbon content of concrete, use fly ash and slag cement instead of the usual Portland cement.
Here’s why it matters:
According to the National Ready Mix Association, 20 Mpa concrete contains 345 kg of CO2 per cubic meter when Portland cement is used in the mix. The amount of embodied CO2 is primarily determined by the type and quantity of Supplementary Cementitious Materials (SCMs) used in the concrete mix. So, the real culprit behind concrete’s CO2 footprint is Portland Cement.
Meanwhile, using slag cement or fly ash in the concrete mix can get you the same 20 Mpa concrete, but with as little as only 214 kg of CO2 per cubic yard.
Another alternative to the regular Portland cement — one with a lower Global Warming Potential — is Portland Limestone Cement (PLC). This type of SCM comprises finely ground uncalcified limestone with regular, calcified limestone. Thanks to this unique composition, PLC contains about 10% less embodied carbon than ordinary Portland cement.
Blue Planet Systems — Permanent Carbon Capture
Blue Planet Systems has designed a process that captures waste CO2 and turns it into aggregate that can be used in concrete.
Here’s how it works.
Blue Planet Systems captures and mineralizes waste CO2 from various industrial processes. Next, this mineralized CO2 is combined with so-called “geomass” calcium. The latter is also sourced from waste and includes steel slag, kiln dust, fly ash, and other manufacturing byproducts.
Together, the mineralized CO2 and the calcium geomass produce synthetic limestone aggregate, ready for use in concrete mixes. For each ton of this synthesized limestone aggregate, Blue Planet Systems mineralizes 440kg of CO2.
This means by simply switching coarse and fine aggregate to the Blue Planet synthetic limestone aggregate, you can store 1120 lb of CO2 in a cubic yard of concrete. This takes its embodied carbon from +600 pounds of CO2 to -494 pounds!
The recapture and mineralization processes being championed by Blue Planet Systems offers an excellent way to store waste CO2 (and actually put it to use) in countries with higher CO2 emissions and a rapid pace of development, such as China, India, and Southeast Asia.
At the moment, Blue Planet Systems operates out of a plant in Pittsburg, California. However, the company plans to increase the current facility by 2024 and broaden its reach domestically and globally by expanding to Houston, TX, Canada, the UK, and Singapore in the next 5 years.
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Carbon Cure — Injects Waste CO2 Into Fresh Concrete During Mixing
Carbon Cure offers another direct way to offset concrete’s embodied carbon content — by injecting it with CO2 that would otherwise be released into the atmosphere.
The company’s approach is straightforward — they capture waste CO2 from big emitters, like petroleum and cement manufacturers. This captured carbon is stored in tanks, which get refilled with the CO2 and delivered to plants by industrial gas companies, such as Praxair.
At the batch plants, the CO2 then gets added to concrete mixes, where it mineralizes and turns into Calcium Carbonate.
Thanks to this recycling process, every cubic yard (4,050 pounds) of Carbon Cure’s concrete saves approximately 25 pounds of CO2, which amounts to roughly a 5% reduction in embodied carbon.
Carbon Cure’s business model is also simple — concrete producers using the company’s technology can achieve substantial savings by relying less on Portland cement. For instance, Carbon Cure charges $1 per cubic yard of concrete, but using this approach lets you save $1.50/cubic yard on Portland Cement.
Intuit Dome, the new LA Clippers arena in Inglewood, CA, is being constructed using Carbon Cure’s concrete.
CarbonBuilt — A Sustainable Way to Produce Concrete Masonry Units
CarbonBuilt offsets the carbon emissions associated with CMU production with its proprietary Reversa technology.
Reversa uses captured CO2 from industrial processes to create a chemical reaction in the CMU concrete while it’s curing. Thanks to this reaction, which sequesters ¾ of a pound of CO2 from every CMU block, the blocks can be manufactured with 85% less embodied carbon.
So far, CarbonBuilt’s Reversa has undergone successful field testing on 2 different projects and will see its first commercial use in the Southeastern USA in the fall of 2022.
Wrapping It Up
Because of its widespread, global use, concrete is responsible for a large share of the world’s embodied carbon. But this doesn’t mean that the industry is accepting the status quo; on the contrary, recent years have seen the launch of several new technologies that can offset concrete’s carbon footprint.
From recapturing and recycling CO2 to opting for more sustainable SCMs, the industry is rapidly pivoting to a greener future. Best of all, these solutions don’t compete with each other — they can all be used together to make concrete construction as sustainable as possible.