Carbon Recycling: It's Procuring Hardened Cement Stupid

citation:  Nick Beckelman, Scientific American, February 2023

A number of articles are emphasizing that "recycled carbon content" cement has the potential to reduce greenhouse gases even more than electric vehicles does.  

Solving Cement’s Massive Carbon Problem

New techniques and novel ingredients can greatly reduce the immense carbon emissions from cement and concrete production

BY MARK FISCHETTI, NICK BOCKELMAN & WIL V. SRUBAR

In this blog I explore how Recycling Policy Organizations like MassRecycle.org, NERC.org, ReMA.org, EarthwormRecycling.org, NRRArecycles.org have the experience to look at "recycled content" rules of procurement to become important to putting "hardened cement" (the value-added by captured carbon ash in the cement) into the quiver of EPR and procurement law.

How do we get our memberships to think about cement manufacturing as an important "recycled content" story, as we did with recycled content paper procurement in the 1990s?  I guess we need to write complicated blogs hoping to get the interests of academics who we can then get to make the "recycled content cement" case, invite them as conference speakers. Part of this "fishing for swordfish" strategy will involve incorporating keywords that keep the Tilapia and Perch of the press interested in our press releases.

If recycling advocates currently consider glass aggregate / daily cover in our recycling rates (never an obvious call to raw material originalists, but that referee's call has sailed), I was wondering about some forms of carbon sequestration, especially cement and concrete.  See article in Nature below.

https://www.nature.com/articles/s43246-024-00546-9

The process described captures carbon and re-infuses it in cement kilns.  Now I note 2 reasons not to claim this, but no reason not to make it part of our message even if it's outside our silo (similar to GMA1872 being outside the silo but in direct competition with recycling markets)..

1. Carbon at the point it's captured in the process is not "solid" waste - though it becomes solid, in the cement, after the process.

2. Cement manufacturing processes are outside our silo/focus at organizations like MassRecycle.

(I will later try to link all of the authors names so they find this eventually)

more

But dig more deeply, and the Science Magazine authors and researchers are themselves emphasizing that harder carbon value added cement carbon re-capture IS RECYCLING.

Green concrete recycling twice the coal ash is built to last

Date:

May 15, 2024 Scienc Daily

Source:

RMIT University

The argument for making this a big part of our Recycling Advocacy messaging:

1. Other recycling that's not municipal, such as automobile recycling or industrial waste recycling, has never been considered off-base

2. As a recycling education mission driven organization, it seems like malpractice not to point out that what's being called one of the most effective carbon sequestration at an industrial process far more carbon producing than MSW management is a form of recycling

3. This could also be labeled "source reduction" which is part of the Recycling Hierarchy.

4. Like mandatory recycled fiber content, or mandatory container deposits collected prior to consumption and sale, Procurement - a specialty of many recycling orgs in the 1990s and later - which I consider "EPR" - would be the best tool to promote this, and MR, NERC, NEWMOA, NRC etc. have more experience with procurement silo tweaking than anyone.

Here are the two key paragraphs explaining how the most carbon generating industry - cement produces more than TRANSPORTATION - can capture and re-sequester carbon by "hardening" the concrete/cement process - actually adding value.  I'd say it should at least be a section or talking point in any presentation of MassREcycle as a carbon-relevant organization. "Government needs to have recycled content carbon in its cement regulation, and here's how our organization can advocate for and advise you on those carbon waste diversion strategies".

From the article in Nature (full citation footnote below)

Hardened carbonation approaches involve concrete preparation and mixing, concrete casting, concrete exposure to CO₂ gas, and concrete hydration^23,24,25. The pressure, temperature, duration, and general environmental conditions at which CO₂ is placed in contact with hardened concrete distinguish the different types of hardened concrete carbonation approaches. Besides these differences, all hardened concrete carbonation approaches involve chemical reactions that engage the active cementitious constituents of hardened concrete with the conversion of CO₂ gas into solid CaCO₃ crystal forms. Nevertheless, as these approaches are driven by diffusion-controlled kinetics, they are limited by the minimal extent of CO₂ diffusion in hardened concrete, which enables carbonation reactions from the surface of hardened concrete to a depth of a few millimeters²⁶. Pressurized vessels, usually between 1 and 5 atm²⁷, can improve the carbonation degree and penetration depth^24,28,29. However, the resulting cost-effectiveness diminishes as the applied pressure increases³⁰, with CO₂ uptake rates that remain within 5–20%²⁴ at the expense of significant energy and infrastructure needs. Furthermore, the nature of these approaches limits their applicability to precast concrete, as they require CO₂-rich or high-pressure environments³¹.

Fresh concrete carbonation approaches involve concrete preparation and mixing with the simultaneous injection of CO₂ gas, concrete casting, and concrete hydration^20,32,33. With these approaches, chemical reactions engage fresh concrete with the conversion of CO₂ gas into solid CaCO₃ crystal forms. Therefore, two main advantages characterize fresh compared to hardened carbonation approaches: (1) the possibility to carbonate a greater volume of concrete via CO₂ injections during mixing; (2) the possibility to incorporate relatively easily CO₂ injection nozzles in industrial processes.

nature

communications materials

articles

4. article

• Article
• Open access
• Published: 26 June 2024

Storing CO₂ while strengthening concrete by carbonating its cement in suspension

• Xiaoxu Fu,
• Alexandre Guerini,
• Davide Zampini &
• Alessandro F. Rotta Loria 

Communications Materials volume 5, Article number: 109 (2024) Cite this article

Another paper on the same method, published in 2020, uses "Recycled" and might be easier to sell than the June 2024 article - if you need to emphasize the keywords to keep the Siloed Interests. 

Carbon Capture and Utilization by mineralization of cement pastes derived from recycled concrete

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