33 Comments

What about the company, Green Cement, that is using Pozzolanic Cement, https://greencement.com ? It is already in use in Texas at scale.

Pozzolanic cement was replaced 200 years ago because of the invention of Portland Cement which cured faster. This company has reengineered Pozzolanic cement to make it cure faster. The big advantage is that there is no heat required in the manufacturing process. According to this recent, detailed article in Forbes it sounds very promising and competitive, https://www.forbes.com/sites/erikkobayashisolomon/2023/11/13/eco-materials-sustainable-green-cement-is-transforming-construction/ . They are even it using to 3-D print houses in Austin, Texas.

Expand full comment

Natural pozzolans are going to be big business! Synthetic pozzolans like calcined clay will be used where the geology dictates... fly ash has been used before but will run out in due course.

Expand full comment

Ironically, green pozzolanic cement depends on burning coal in power plants and high furnaces, but it could be much cheaper to manufacture than the Portland cement (does not require heating for instance).

Basalte based cement seems to be much more expensive and energy-intensive to manufacture, so this will only be an option when we run out of coal and volcanic ash.

Expand full comment

Your helpful article points out that 40% of emissions come from the demand for heat in the conventional process of making cement from limestone, with temperatures of 1500 C. What are the comparable numbers for making cement from basalt?

Expand full comment

This will be key, the rock needs crushing and is quite hard, then there will be hydrometallurgy methods used, which may have high water demand and drying costs... and perhaps require chemicals... so its hard work, but I agree that CCS is lookin' darn expensive so this may still work out, especially if you can use green energy...

Expand full comment

I have recently discovered hempcrete, which could replace a lot of concrete:

https://www.hempbuildmag.com/home/hempcrete-approved-for-us-residential-building-code-update

Expand full comment

According to this article, https://www.ukhempcrete.com/faq/is-hempcrete-better-than-concrete/#:~:text=Hempcrete%20(in%20its%20usual%20“hemp,replace%20concrete%20for%20structural%20applications, hempcrete is a "non-structural" material. It is not a replacement for structural concrete. Most of its use to date is for non-load bearing walls, e.g. insulation, in the construction of houses. I would be cautious about suggesting it could replace a lot of concrete.

Expand full comment

an important conversation

there are some Kiwis (New Zealanders) on the job ... https://www.neocrete.com/

Expand full comment

Great article, as always! I believe https://sublime-systems.com/ are already meeting some building standards. Interesting episode on the Business for Good podcast: https://www.businessforgoodpodcast.com/cementing-a-better-future-leah-ellis-and-sublime-systems

Expand full comment

This article has benefited me a lot. Thank you very much for sharing. https://www.mill-sbm.com/

Expand full comment

One item if slight ambiguity is the 'concentration' of cement used in concrete, the way phrased makes it sound like concrete may be 78% cement... but those numbers actually refer to the concentration of clinker in the cement (used in the concrete).

OPC (ordinary portland cement) is 95% clinker but generally has gypsum added, but now we will add SCMs to 'extend' the cement... the resulting mix is then used in concrete roughly as normal as if it were OPC (10-25 wt.% dry basis vs sand and aggregate depending on the job). Check CEM I, II, III standards, and LC3-type cements for more detail.

Expand full comment

Very clear article. Thank you. Note that

"Concrete will slowly absorb CO2 from the atmosphere over time in a process known as carbonation. In the process of carbonation, CO2 reacts with calcium hydroxide (Ca(OH)2), a component of hydrated portland cement, to produce calcium carbonate and water: CO2 + Ca(OH)2 → CaCO3 + H2O. "

https://rip.trb.org/View/2255792#:~:text=Concrete%20will%20slowly%20absorb%20CO2,)2%20→%20CaCO3%20%2B%20H2O.

Expand full comment

nice article...

Expand full comment

One alternative is Biorock, or Seacrete.

https://en.wikipedia.org/wiki/Biorock

https://www.globalcoral.org/biorock-coral-reef-marine-habitat-restoration/#:~:text=When%20grown%20slowly%20(less%20than,stronger%20and%20harder%20with%20age.

Currently this is only being considered for marine structures like artificial reefs, but could it be "grown" in brick like moulds? Or could it be powdered like cement?

I was thinking we could also make massive marine structures using excess renewable electricity. For example causeways out into the Bristol channel to make place for a tidal barrier.

The use of Basalt is interesting. Basalt itself is a hard rock, so it's like taking basalt, turning it into powder form, and then recasting it as a basalt like rock.

Expand full comment

Thanks, Hannah, this is great! Could you share references or quantitative results on the studies that looked at strength versus cement concentration in concrete? I'd like to understand the claim that strength loss wasn't substantial in more detail.

Expand full comment

www.Betolar.com has a cement free green concrete solution. Betolar's Geoprime material innovation is a sustainable alternative to cement. It uses industrial side streams to replace cement in concrete elements. The resulting concrete elements have material properties that are equivalent to traditional concrete, but up to 75% lower CO2 emissions.

The solution has been developed so that it can be produced in existing concrete plants. The same equipment and process can be used, so manufacturers do not need to make large investments to start producing Green Concrete.

Expand full comment

And what about Sublime? https://sublime-systems.com They are using an electrochemical process to produce a drop-in replacement with the same engineering specs, and no emissions.

Expand full comment

A complete alternative to concrete for a multitude of applications is mass timber. Here in BC, Canada the building code has recently been changed to allow buildings up to 18 storeys using mass timber rather than steel and concrete. Here is an excerpt from the BC government website: Mass timber has an important role in increasing climate-friendly technology and buildings in the province. Mass timber buildings are made from wood and can store carbon for generations, keeping it out of the atmosphere. Mass timber buildings also replace more carbon-intensive materials, such as concrete and steel, and help to reduce construction waste.

Expand full comment

Hi Hannah, another important initiative to reducing emissions is using less concrete (and therefore less cement) in the design of structures. Will Arnold outlines the Institution of Structural Engineers’ approach in this blog: https://www.istructe.org/resources/blog/the-hierarchy-of-net-zero-design/

At the bottom of the hierarchy, when concrete must be used, cement alternatives should be specified. The IStructE has developed a helpful tracker for alternative concrete technology https://www.istructe.org/resources/guidance/concrete-technology-tracker/

Expand full comment

DOE/NETL have a procurement grant program that provides grants to state and local governments as well as public utilities/agencies to procure products that utilize anthropogenic oxides in their manufacture. Hopefully this can help catalyze cost reductions for the CCS pathway! https://www.netl.doe.gov/upgrants

Expand full comment