A California company envisions a world in which the 8 billion tons of concrete used each year sequester billions of tons of carbon dioxide
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 binderGlue used in manufactured wood products, such as medium-density fiberboard (MDF), particleboard, and engineered lumber. Some binders are made with formaldehyde. See urea-formaldehyde binder and methyl diisocyanate (MDI) 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.
- Alex Wilson
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