MIT Concrete Sustainability Hub 2020: A Year In Review

MIT Concrete Sustainability Hub 2020: A Year in Review recaps a successful year of research briefs, topic summaries, and journal papers, along with webinars and presentations available on the CSHubMIT YouTube page. Looking forward, the CSHub will continue to conduct cutting-edge research and to disseminate valuable knowledge. Here are just a few of the many of the resources and reports produced by the MIT CSHub over the last year:


Thanks Martin - I think it is especially important to recognize that CSHubMIT is funded by the cement industry. The issue of carbon uptake in cement via carbonation requires a thorough rebuttal, but I’ll jot down some thoughts to get the conversation started.

When considering the lifetime carbon emissions of a pavement / building / structure, the carbonation of the concrete generally requires replacement, usually by more concrete, leading to further emissions. To assume that there is no replacement and thus only account for the uptake of carbon dioxide via carbonation is quite disingenuous.

In service the uptake of CO2 is typically ~3% of the production emissions, and although at end of life, crushing and exposing more surface area can greatly increase this number, assuming that 40% of your emissions will be absorbed in 100 years and thus can be discounted today is a massive problem when we know we need to reduce emissions to 0 as fast as possible. This also does not account for the time value of carbon / social cost of carbon, which is estimated to inflate by 3% p.a., due to compounding damages, thus the benefits of absorbing carbon at end of life are greatly diminished.

Concrete should be made to be durable and resist carbonation to get the most out of the ‘carbon investment’. What the concrete industry should be looking at in my opinion are the following options:

  • recognizing that zero emissions cements are technically challenging and some years away, focus on how concrete elements will function in a circular economy, not just downcycling / recycling at end of life, but reusing concrete elements.
  • rapidly shifting to electrification of kilns, perhaps via microwave calcination.
  • paving the way for alternative cementing technologies, including geopolymers / AAMs, and biocementation.

Finally, I really like Blue Planet aggregates, and this could be one avenue to make true net zero concrete (without offsetting), provided that the energy source is renewable.

I agree that carbonation does little to offset the carbon intensity required to produce new cement/concrete. Carbonation could be included in more complex GWP impact models over time, but should not be the center of the conversation. It’s more valuable to consider the full carbon story so we’re not “saving” carbon via carbonation that’s actually resulting in a lot of net emissions. I’m editing that story out of this summary because I agree that it’s misleading.

As for designing for reuse - this is a huge opportunity for precast elements, so we’ll see if that can become more standard practice. I agree with the other steps you’ve outlined as well, but I also think it’s important to acknowledge the big reductions we can implement sooner rather than later (being more conscious of cure time vs construction schedules, lower cement content, including GWP requirements in concrete specs). But to support continued reduction over time, we must implement policy mechanisms like Buy Clean. Performance-based requirements like this will provide market incentive that supports innovative technologies and changes that you’ve mentioned, and paves the way for design firms to follow suit in implementing GWP requirements.

Blue Planet is great!! I’d love to see that product get to a point where it can be scaled up.

Thanks for posting this, @martintorres, and thanks for your comments, @will.nash. You raise some important points, but I think you’re relying on an incorrect premise that carbonation automatically leads to accelerated deterioration of concrete structures. While it is true that carbonation can lead to durability issues in structures with reinforcing steel, proper design can easily avoid this and there is extensive evidence to support this. We are not saying that quantifying carbonation in concrete is a way to avoid talking about other kinds of emissions and proper design, which is why we always include those in our analyses. Indeed, we are skeptical of other published carbonation estimates that have used a top-down approach, which is why we have used a different approach that we think is more representative of actual carbonation. We simply think it is important to track both carbon that is emitted and sequestered in all building materials in the most accurate way possible, and that can certainly include approaches that deal with time value of carbon. We’d be glad to discuss this more with you so that we can clarify any misconceptions you may have. Please reach out if you’re interested.

I agree with this. It’s important to move towards telling a more complete carbon story of these materials as we improve LCA and carbon accounting methods/practices. Carbonation/sequestration is part of that, as is uncertainty which I know y’all have also studied. Carbon from concrete, wood, and whole buildings exists on a timeline so analysis should reflect that.