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Energy Solutions

Reinventing Concrete

A California company envisions a world in which the 8 billion tons of concrete used each year sequester billions of tons of carbon dioxide

Contractors placing concrete for the foundation of our home in Dummerston, Vermont. Someday soon, concrete may be able to sequester huge quantities of carbon.
Image Credit: Alex Wilson

I’ve been in the San Francisco Bay Area for the past week speaking at various conferences. (When I travel I try to combine activities to assuage my guilt at burning all the fuel and emitting all that carbon dioxide to get there. Between conferences, I’m now spending time with my daughter in Petaluma and Napa.)

I spent three days last week at BuildWell, a small conference organized by my friend and colleague Bruce King, P.E., that is focused on “innovative materials for a greener planet.” The roster of presenters included such well-known thought leaders as Ed Mazria of Architecture 2030, who is leading an effort to shift to zero-carbon buildings by 2030; John Warner, Ph.D., the father of Green Chemistry, which is transforming manufacturing by reducing toxicity; and Mathis Wackernagel, the founder of the Global Footprint Network.

A less-recognized presenter (and attendee throughout the three days) was Brent Constantz, Ph.D., the founder and CEO of Blue Planet and a professor at Stanford University. (Blue Planet has no website currently.) Little did I know how audacious Constantz’s plans are: to reinvent concrete, transforming it from one of the world’s largest emitters of carbon dioxide into one of the most important tools to sequester the carbon dioxide emitted from power plants.

Ordinary Portland cement

The Portland cement used today in concrete and a wide range of mortars, stuccos, and concrete masonry units (CMUs) consists largely of two forms of calcium silicate (calcium oxide plus silicon dioxide) with smaller concentrations of aluminum oxide, ferric oxide, and sulfate.

Portland cement derives its name from its similarity in appearance to Portland stone, found on the Isle of Portland in Dorset, England, and widely used in the early 19th century.

The primary raw material going into Portland cement manufacture is calcium oxide (CaO), which is produced by “calcining” limestone (CaCO3), under very high temperatures to form “clinker.” This calcining process drives off carbon dioxide (CO2). Because such huge quantities of cement are used globally (about 1.6 billion tons), Portland cement production is one of the largest sources of our carbon dioxide emissions.

Portland cement produces CO2 both from the calcining of limestone (a chemical process) and from the tremendous energy inputs used in that calcining process.

Note that Portland cement is only one constituent in concrete, accounting for about 12% of the mass of concrete. The rest of the mass consists of sand, water, and aggregate. Cement is the binder that glues the sand and aggregate together into a solid stone-like material.

Calcium carbonate cement

Constantz is focusing on a very different type of cement: a calcium carbonate cement. The calcium is derived either from seawater or — in more inland locations — from brine, and the carbonate comes from the carbon dioxide in power plant flue gases. He envisions a system in which the CO2 is extracted from flue gases to produce both a calcium carbonate cement and limestone aggregate.

Blue Planet, which has attracted some large investors, believes that concrete produced with their CarbonMix cement and limestone aggregate would be carbon-neutral or even carbon-negative, meaning that the more of it you use the more carbon is sequestered — or pulled out of the atmosphere and forever locked up.

Blue Planet is carrying out research at one of California’s largest power plants: a natural-gas-fired plant on the coast at Moss Landing (south of San Francisco). The Moss Landing power plant, now owned by Dynegy, produces four million tons of CO2 per year — CO2 that is contributing to global warming.

In producing concrete from CarbonMix cement, carbon emission reductions would be achieved in multiple ways: the production of Portland cement would be reduced; CO2 would be chemically tied up in the calcium carbonate cement; and the aggregate (a far larger constituent of concrete) would be limestone.

Using limestone as aggregate could be done immediately, with no changes in highway standards and concrete engineering standards. And Constantz claims that even the non-Portland cement could be used with very few changes — though the lower alkalinity in cement binder may mean that different re-bar is needed. (With standard concrete, the high alkalinity protects the steel re-bar from corrosion.)

Ancillary benefits of carbon-negative concrete

In addition to the huge benefit of sequestering carbon dioxide emitted from power plants, CarbonMix cement and aggregate production could provide a way to demineralize water. Such a facility would provide a wonderful complement to a desalination plant, for example.

In desalination, fresh water is extracted from seawater or brine in a process that concentrates the calcium and other minerals. Desalination is becoming more and more common, and getting rid of the highly concentrated brine can be a challenge. Texas, for example, has almost 50 desalination plants, nearly all of them using brine rather than seawater.

Reducing the mineral content of brine is also a key priority in fracking. The oil and gas industry would love to find someone wanting to use that brine, helping to purify it in the process.

A possible game changer

It remains to be seen whether Brent Constantz can realize his vision of transforming cement and concrete — among the most common materials used in construction today. If he can, it will be a game changer — something that attendees of BuildWell were quick to grasp.

If he succeeds, fortunes will be made in the process and the world will be far better for it. I look forward to watching the progress of Blue Planet over the coming months and years. BuildingGreen will be reporting on this technology as it evolves.

Alex is founder of BuildingGreen, Inc. and executive editor of Environmental Building News. In 2012 he founded the Resilient Design Institute. To keep up with Alex’s latest articles and musings, you can sign up for his Twitter feed.


  1. RZR | | #1

    Natural Building vs Concrete
    I think the home and commercial building industries should do its part in not using factory manufactured concrete, go back to natural methods like earth and soil. I know some rammed earth chemist use Portland cement as a ‘stabilizer’ but have switched to pozzolan a siliceous or siliceous and aluminous material which, in itself, possesses little or no cementitious value but which will, in finely divided form and in the presence of water, react chemically with calcium hydroxide at ordinary temperature to form compounds possessing cementitious properties (ASTM C618).[1] The broad definition of a pozzolan imparts no bearing on the origin of the material, only on its capability of reacting with calcium hydroxide and water. A quantification of this capability is comprised in the term pozzolanic activity.

  2. mfredericks | | #2

    This sounds similar to a local (to me) company started recently in Halifax, Nova Scotia. They're well on their way and are working with several concrete makers in the province and across North America.

  3. Alex Wilson | | #3

    I'm familiar with CarbonCure, and BuildingGreen actually recognized them as a top-10 Green Building Product a couple years ago, but that's very different. CarbonCure is infusing CO2 into concrete masonry units during manufacture. Blue Planet proposes a totally different type of cement as well as limestone aggregate, both of which pull CO2 out of power plant flue gases.

  4. user-939142 | | #4

    if you must
    If you have to use concrete for the foundation, or something similar, what is the best nationally available option??

  5. GBA Editor
    Martin Holladay | | #5

    Response to Bob Coleman
    It depends on what you mean by "best."

    In most cases, ordinary 3,000-psi concrete (what used to be called a "6-bag mix") is widely available, durable, and affordable.

  6. user-939142 | | #6

    by best
    I meant alternatives to concrete along green/sustainable lines.

    There really doesn't seem to be an option except to poor footers
    or to poor slabs for say a garage floor.

    Would be nice if they could find a way to reuse all the plastic waste like num 7 and other items that can't be reused; maybe make 4foot by 4foot foundation wall sections filled with rebar and UV stabilized exterior.

  7. nick57 | | #7

    Thank you for this article.
    Thank you for this article. The bright ray of hope it shines on the start of the day was just what I needed! It is interesting that cement (which was perfected by the Romans 2,000 years ago) and its concrete derivatives still lend themselves to modern building techniques and should remain a favorite of innovative architects and builders for generations to come. And yet the huge environmental cost of cement production and aggregate transport has always been its achilles heal. If this process can change that equation and make cement production part of the enviornmental solution-it will be one of the greatest modern discoveries in construction .

  8. RZR | | #8

    Here is another option for
    Here is another option for floors:

    Check out SIREWALL for walls...

  9. swettge | | #9

    All sounds very Familiar
    I am aware of Mr Constantz being involved in the development of this technology as far back as 2009 when he testified before a senate subcommittee on Energy and Water development as CEO of the company Calera. I believe Calera is still functioning judging by their current website which shows their pilot plant at Moss Landing........wonder why he is striking out on his own with Blue Planet?.......or is this just a name change?

  10. CalBungMelb | | #10

    Obtaining carbon dioxide from coal-fired power stations
    This is one of the technologies which is technically feasible but whether or not its useful in practice will depend on factors such as the economics and the Energy Return on Energy Invested (EROIE). Because the carbon dioxide in the exhaust stream from a coal-fired power station is a small fraction it takes kit and energy to separate it. This is the same problem faced by groups wanting to sequester carbon dioxide from fossil fuelled power stations. Despite having had a lot of research money over the last few years, sequestration hasn't seen any significant commercial takeup due to the expense and the reduction in energy sent out from the plant as energy is used to extract and process the carbon dioxide.

    Depending on how a commercial concrete manufacturing process - using CO2 from flue gas - stored and transported the gas the EROIE and expense might be better than the sequestration technologies currently identified. But they would have to be quite a bit better.

  11. servant74 | | #11

    Make concrete a 'little' greener
    It is possible to replace up to 30% of the Portland Cement (making it generates a lot of CO2 as part of the calcining process as the article notes) with the waste product called Fly Ash (typically from coal burning generators - sometimes called flue ash) and/or some Slag (from the making of iron/steel).

    Using these additives, can make a real difference in the carbon footprint of using concrete.

  12. newsie23 | | #12

    Atlas Block, a primary signee to CarbonCure, has been bought (at auction) by Brampton Brick. My original interest in Atlas Block was their lightweight block, using Poraver, as up to 30% of the aggregate. The Poraver product, is made from Blue Box, recycled, glass. The 8" block weights only 20 lb. I have also used Poraver to repair a Supaflu, poured in place, chimney liner, in a 'water access' location. Originally, I wanted the deteriorated brick, (not the liner) above the roof, to be carefully removed - 'use a nail file, if you need to' - of course, my contractor w/couldn't ! The Poraver, mortar mix, also has a high temperature, light weight, and 'slight' insulation value, and has worked well (2 winters).
    I hope the CarbonCure and Poraver knowledge, has not been lost.

  13. Concrete Producer | | #13

    Is this Your house?
    Alex, I am surprised to see you having a basement poured with Conventional forms! What was the reason you did not use Insulating Concrete Forms at least for the basement?
    In most areas of the country, you can get concrete with either fly ash or slag to replace 20% of Portland Cement. In the industry, we call these materials SCMs (Supplementary Cementitious Materials). Because of the chemical reactions and the increased density of these materials, the mixes are usually slightly higher in compressive strength, while increasing durabilty and finishability. If your project schedule allows you to wait longer for strength development, most producers offer mixes with higher amounts.of SCMs. You have to be careful with these in cool weather, because heating and protection can generate more CO2 than you save... With the closing of a lot of coal fired generating plants, fly ash is becoming very hard to get and expensive. It is not the waste product that some have been led to believe.

  14. ethan_TFGStudio | | #14

    Has Poraver knowledge been lost, as John suggests? Poraver seems like a way to create no-foam sub-slab insulation as well as potentially higher insulative qualities for cast in place concrete using it as part of a readymix concrete pour. The only project I can find using Poraver is the Endeavor Center:

    Chris Magwood writes

    In the future, we’d like to explore further uses for this material, including foundation walls and above-grade applications as well.
    Working with Poraver has been one of the highlights of a project that has included many innovations.

    Here is a video explaining Poraver in readymix:

  15. user-6551155 | | #15

    DO not overlook Compacted gravel or some such thing done way back in the day by Frank Loyd Wright and Steve Bazeks skipping the concrete floor under wood,
    There ARE many alternatives adobe , stone Etc helical piers.
    Perma Columns Concrete yes But so Minimal over all
    This would be a great article

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