CarbonCure is a great technology, but it can easily lead to greenwashing

CarbonCure was recently named one of two winners of the $20 million NRG COSIA Carbon XPRIZE. And for good reason! It’s a cost-effective way to reduce the global warming potential (GWP) of any concrete mix by about 5%. But if you’re starting with a mix with above average GWP, then it’s a stretch to call the new mix “low-carbon,” even if it has CarbonCure.

This is why we need more mix-specific EPDs so designers can use actual GWP values as a design metric. CarbonCure is not a stamp declaring any mix that uses it “low-carbon,” but it’s often used as such in lieu of actual GWP data. There are CarbonCure mixes with GWP far below and far above that of NRMCA regional average concrete mixes. Only readily available mix-specific EPDs in a database like EC3 that can solve this problem. Other effective GWP reduction strategies for concrete include

  • Build less
  • Use Portland limestone cement (also known as GUL, or general use limestone) over regular Portland cement
  • Be mindful of cure times rather than arbitrarily specifying strength at 28 days
  • Move toward performance based requirements rather than specifying water/cement ratios or minimum cement content (perhaps even specify maximum cement content in lieu of EPDs)
  • Supplementary cementitious material (SCM) replacement, though keep in mind that it’s cement content that matters. % replacement is just one way to achieve cement reduction.
  • CarbonCure. A great next step would be for CarbonCure to encourage concrete suppliers using their product to produce mix-specific EPDs to show off their impact reductions and avoid greenwashing
  • Use carbon sequestering products like Blue Planet aggregate
  • Utilize precast for higher quality concrete (balanced against productivity pressures)
  • Geopolymer / alkali activated materials
  • Material substitution

(I’ll add to the list if anyone has other ideas in the comments!)

Buy Clean policies on local, state, and federal levels will help eliminate a frustrating catch-22 where concrete suppliers don’t want to spend money to produce EPDs because designers aren’t asking for them, but designers aren’t asking for them because concrete producers aren’t producing them. So take the first step and include EPDs in your specifications! Start the conversation. Bring up embodied carbon early and often, and make EPDs a part of that conversation.

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Congratulations to the CarbonCure team, but I agree 100%.

We also want to see more data on the emissions from capture, storage, transportation and injection of the CO2 into the mix. It is clear that CarbonCure currently use commercial suppliers of CO2 (Praxair) and cannot be considered to sequester CO2, rather the injected CO2 provides an increased nucleation site density of the mix, achieving higher strengths with less cement.

Low CO2 concrete strategies that I would add to the list are:

  • Optimizing the aggregate grading to reduce cement content,
  • Utilizing precast to enable better quality concrete (although this needs to be balanced against productivity pressures),
  • Using Blue Planet aggregate (I swear I am not an investor!),
  • Geopolymer / Alkali activated materials,
  • Material substitution,
  • Build less!

In the long run I don’t believe it is technically feasibly to produce zero emissions portland cement, at least without some sort of bacterially produced quicklime (@wsrubar?) - so design for disassembly and reuse of concrete elements is vital.

I feel that it is important to point out that the XPrize competition is administered by the Canada’s Oil Sands Innovation Alliance (COSIA) - and this organization wants to continue business as usual by finding ways to sequester the carbon their products and operations emit.

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@martintorres - Thank you! I completely agree with everything you said.

You’re right, CarbonCure is just one of many solutions that can be used today to reduce the carbon footprint of concrete. Today, on average, CarbonCure provides about a 5% reduction to GWP. In the final round of the Carbon XPRIZE competition, we demonstrated a new technology that beneficially repurposes CO2 in reclaimed water. Our early results indicate that the carbon savings may be significantly greater with this new innovation added to our portfolio (hopefully it will be available for commercial work in the not too distant future!). We continue to innovate as part of our quest to reduce 500 million tonnes of CO2 emissions annually by the year 2030.

A 5% reduction to GWP is a step in the right direction. Some of the concrete producers we work with are already the low-carbon leaders in their market and we help them reduce GWP even further. Some of our concrete producers are not the lowest GWP providers in their region. We are actively working with these providers to consider further optimization strategies and low carbon best practices. We absolutely encourage every concrete producer to publish EPDs in order to provide much-needed transparency to help designers/developers make informed decisions.

For engineers - specifying CarbonCure (as either a required, preferred or allowed product) is one strategy among many that an engineer may employ to reduce GWP. We encourage engineers to consider all of the best practices outlined here. I would also add to the list my number one recommendation:

Communicate your commitment to embodied carbon throughout the supply chain early and often.

I so often see GWP goals falling short due to communication complexity in the design-bid-build process. I would highly encourage anyone on a mission to reduce embodied carbon to pick up the phone and talk to your contractors and building material suppliers and have a conversation about why this matters to you and ask what they can do to help support the mission. You might be pleasantly surprised by the ideas that come to the table!

(By the way, when I found out we won the XPRIZE, I was hit by a sudden stroke of inspiration, and fuelled by both caffeine and adrenaline, I wrote a late-night blog that makes many of these same recommendations. We’ll be publishing it very soon - presumably after some much-needed editing - and I’ll be sure to post it to the CLF.)

Thank you Martin for the great insights you provide and the amazing work that you do. Keep it up!

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Repurposing CO2 in reclaimed water sounds interesting - is it still achieving reductions by reducing cement content or by actually sequestering carbon? I’m definitely interested to read more about that!

Glad to hear y’all are encouraging EPDs. What does this advocacy look like and how do you see building industry professionals supporting these efforts? When I talk to concrete suppliers about EPDs, I’m usually met with “nobody’s asking for them so why would we provide them?”, but designers might not be asking for them if they’re not being produced. I think we need a combination of approaches (designers asking for EPDs in specs, government procurement policies like Buy Clean, financial incentives, inclusion in green building rating systems), so I’m curious to learn more about the role CarbonCure is playing. For the producers that have higher GWP even with CarbonCure, I think CarbonCure may (unfortunately) be functioning as a sustainability checkbox for them as though it is sufficient, so they’re not interested in other measures.

Totally agree that engineers should allow CarbonCure. As we move towards performance-based GWP requirements, it’ll incentivize more producers to use technology like CarbonCure and support/reward continued innovation like you’ve mentioned.

Yes! Always have the embodied carbon conversation as early as you can and then keep that door open!

I look forward to reading that blog post. Thanks for sharing your thoughts :slight_smile:

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This is a really good discussion. Thanks for all the useful info. I’d agree that the 5% compared to what can be done with the mix selection isn’t huge but it’s a start and I’m interested to see where the technology goes.

As for Blue Planet Aggregates - I’d not seen this before and in theory sounds like a pretty great solution. Does anyone know of any further projects or case studies that have been done other than the SF airport or new articles on google? Or a timeline for their plant and expansion (surely with this kind of wonder product they’d be taking over the world soon enough…?)

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Yep, I’m similarly excited to see how all these different technologies develop! We need to support a market that does a better job of including carbon as a procurement metric (rather than just cost) so the best and most cost effective low-carbon solutions can rise to the top. EPDs are a great way to make that happen.

For BPA, I think right now it’s a matter of production capacity and cost. I haven’t seen or heard much about it outside the SF airport.

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Great discussion on reducing the GWP of concrete. What I constant seem to miss in these kind of conversations is the topic of ‘return concrete’. Its a known fact that 5-10% of the produced concrete is returned to the concrete plant. In the majority of cases (over 95%) this concrete is NOT reused but it is going to a reclaimer or is dumped. This is obvious an enormous waste of (raw) materials, transportation, production, time and CO2. The industry is in my opinion to much focused on new materials and looses sight of the most obvious and work on that. There are options and with ASTM guidelines make significant reuse/repurpose possible without adding extra energy and/or adding waste(water).

This is interesting. Where did you get the 5-10% figure from? I have often seen excess concrete being thrown into other areas on site rather than being sent back in the truck. I wonder if this waste should be accounted for in A5 module of life cycle as part of construction waste this does account for some but I don’t think it’s as much as 5-10%.

Hi Ross. The 5-10% is a number coming from the NRMCA. In many cases also 5% is communicated as an average. There are multiple reasons why the number was little blurry in the past and return concrete is to my opinion in many cases seen/handled as the ‘elephant in the room’. Having that said is exact why I think it should/could get more attention. The last few years we installed equipment in about 1000 concrete trucks. This equipment is able to measure slump but also temperature and volume. From that we also know that the 5-10% returning to the plant is accurate and rising. Rising as contractors tend to over order more and more. The 5% alone represents in the US a 16 million CY’s of concrete…for big part being dumped. This is something like 3 million tons of CO2.
With the ASTM guidelines and technology solutions we are able to reduce the amount that is ‘‘just’’ dumped significant. It needs to get attention and industry awareness, that reuse of return concrete as fresh concrete or as raw-material is a win-win. Carbon footprint reduction and a significant bottom line revenue.