Just how Green is this low carbon concrete?
Just how Green is this low carbon concrete?
ESGH Looks into a hot startup
I had a premium post (on an entirely different topic) about 80% to completion when I saw this Bloomberg story drop yesterday about XPrize winning startup CarbonBuilt.
CarbonBuilt’s technology tackles carbon on two fronts: replacing most of the cement in concrete with a proprietary mix of locally sourced, low-carbon material, and piping carbon into the curing chamber used to strengthen the blocks. Doing so permanently stores the carbon in solid form. According to CarbonBuilt, Blair Block’s converted production line will avoid at least 2,000 metric tons of CO2 emissions per year. In addition, the plant will remove more than 500 metric tons of CO2 from the atmosphere annually.
“One of the beauties of this thing is that the core production economics are better,” said Rahul Shendure, CarbonBuilt’s CEO and director. “We’re taking out one of the most expensive ingredients, which is cement, and we’re replacing it with a combination of low-value but easy-to-access industrial materials that deliver, in combination with CO2, the properties we need.”
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The startup is already in talks with dozens of other concrete producers about completing production line retrofits, according to Shendure. CarbonBuilt estimates that its technology can be rapidly integrated into all of the roughly 800 concrete plants in the US.
Besides Blair Block, CarbonBuilt also has another plant in Arizona that went online this year, as well as a few other feasibility studies underway. The company’s big focus for the second half of the year is signing additional contracts, with subsequent retrofits to come in 2024.
They’re in media hype mode, which usually is a sign in the startup world that another funding round is in the works. I had been following this project somewhat casually for some time, and since they want some coverage, why not indulge them?
Now, when discussing the concept of “Greenwashing,” there are levels and layers involved. Sometimes a greenwash involves outright fraudulent claims about a technology. Other times, there’s a different externality involved but not discussed (eg a low-carbon product that might generate more mining wastes and water runoff). More often than not, a “sustainable” product will entrench damaging societal behavior. The best example of this is Electric Vehicles. EVs are a valuable tool to shift consumption methods of fuel; this is undeniable. But to the extent that EVs are treated as a replacement for gas cars, especially in America, without dealing with the carbon impacts of disconnected, suburban sprawl and massive interstates… EVs are not much more than a panacea to make us feel better as we consume ourselves into destruction.
Low-carbon concrete hits all the notes for a great-sounding Green product. We need concrete to build infrastructure, from solar farms to substations and high-density housing. But let’s take a look at the facts we know and those we don’t and go from there.
Provided that CarbonBuilt isn’t outright lying (I don’t believe they are, to be clear), here’s what we know:
Lifecycle GHG emissions are 70-100% lower than traditional Portland Cement block making
Costs are the same as traditional casted concrete manufacturing
On a capex basis, retrofit involves a low-tech conversion of existing casted concrete facilities
The new facility they promote will “avoid at least 2,000 metric tons of CO2 emissions per year. In addition, the plant will remove more than 500 metric tons of CO2 from the atmosphere annually.”
When looking at flashy PR campaigns, the first thing I always ask is:
What are they NOT telling us?
In CarbonBuilt’s case, here are the questions I came away with:
What’s the output of this new facility? How many blocks will they make?
What is the basis for the 70-100% lifecycle emissions? There’s no white paper on their website.
What are they using as a replacement for Portland cement? They describe it as a “proprietary low-cost alternative made from widely-available low-carbon materials.” Is there a reason they’re not telling us where it comes from? (foreshadowing: the answer is yes)
How Many Green Blocks Merits a News Story?
In keeping with the theme of “Corporate Espionage,” I touched on last week, it is always so interesting to see companies give away information selectively that can be deduced from a simple mass balance and/or a conversion chart in an engineering textbook.
I wanted to know just how big the retrofit they discussed, the one that will “remove more than 5001 metric tons” of CO2 from the atmosphere, for a sense of scale. Luckily, the cement curing process is illustrated on their website:
Instead of using water evaporation + heat to facilitate the exothermic Ca(OH)2 crystallization process out of a lime solution by burning natural gas, this process involves piping high concentrations of CO2 at ambient temperatures into an “oven” to fix the calcium into CaCO3. We’ll get into the actual chemistry in a later section, but for this purpose, it doesn’t matter.
Using good old-fashioned Stoichiometry, we can get our answer. We know that one molecule of CaCO3 is formed by fixing one molecule of Carbon, and therefore one molecule of CO2.
Using the molecular mass of the two compounds:
CO2 - 44.01 g/mol
CaCO3 - 100.09 g/mol
And knowing that in commercial blockmaking, the cured hydrated lime (cement) concentration by mass is roughly 9.5%2, we can surmise the following:
The “standard” concrete block used in construction is about 28 pounds, so we can estimate this is a nice, round, one million blocks per year facility.
At a wholesale price of $1 per block (they cost $2 at Home Depot), this is a $1 million dollar revenue facility, and at gross margins of, say, 15%, we can say that gross profits would be $150k with net profits (based on industry leaders like Cemex) in the $40-60k range.
So… all of this is not to dump on CarbonBuilt’s PR; it’s a great story, but we’re a long way off from having to discuss some of the nuanced issues about their input supply chain.
Speaking of…
Is the by-product of a coal power plant actually “zero carbon?”
Now we get to the fun part. One potential red flag (🚩) from CarbonBuilt’s PR push is that they talk about a “proprietary low-cost alternative” to Portland Cement, describing it generally as carbon neutral but readily available compound without discussing further. This could be a trade secret, like Coke’s secret formula or the 11 Herbs and Spices in KFC, I suppose. Or it could be that they don’t want to have the uncomfortable (but necessary) conversation about the Green economy’s reliance on fossil fuels.
Portlandite, with the chemical formula Ca(OH)2, is a product of the lime (CaO) in Portland cement, being hydrated:
Once a sufficient amount of water is removed from the surface, concrete exposed to atmospheric pressure will react to form CaCO3 (or limestone), though this is a very slow process at atmospheric CO2 concentrations. This is an added effect of aging in traditional concrete and is not the primary means of strengthening or binding.
The last equation to understand is that of lime production, where mined Limestone is heated at high temperatures to create the soluble quicklime. It’s the reverse of reactions #1 and #2:
CO2 is released directly from the limestone, plus fossil fuel heat is used (also carbon intensive). This is how a Portland cement plant works. They heat the crap out of limestone to make a water-soluble cement that will crystalize into Portlandite.
What CarbonBuilt is doing is taking Calcium from other sources, once the Carbon has been removed somewhere upstream and turning it into Portlandite, then using that carbon-free cement as the binder in their blocks, putting them in a high CO2 concentration chamber to achieve a calcification and binding.
Still with me? Ok.
There are only a handful of sources of bulk carbon-free calcium floating around. For example, it’s created in some quantities by selectively de-watering chemicals like 100% ethanol, as lime added to impure alcohol-water mixtures will pull out the water, leaving only crystalized Portlandite.
But the primary source of Calcium is in slag. Not any slag, but the hard chunky residue from the processing of combusted coal residue. Coal fly ash contains numerous metals, as characterized in this EPA document:
Lignite and subbituminous coal contain on average 30% by mass CaO and 25% AlO3 (Aluminum Oxide). Processing the fly ash to remove alumina for recycling leaves a slag that is up to 50% Calcium by mass. The calcium is not readily soluble and, therefore must be heated up to leach out the mineral, which forms into Portlandite (CaOH2) during the process.
CarbonBuilt does not reveal the source for the Portlandite that they use as a cement, but some documents filed with the Department of Energy, authored by people associated with the company, spill the beans.
The above slide illustrates the process conceptually. The company uses coal combustion by-products of fly ash and slag (which is bottom residue + processed fly ash) in combination with heat from the power plant to leach out residual Calcium and convert it to Ca(OH)2. This chemical compound is used as the cement and, in the presence of excess CO2, calcifies into a binder for their concrete.
But using waste products from dirty fuels productively is green, right?
The answer: sort of. Maybe?
Looking at this from a big picture standpoint, one ton of coal will generate about 110 pounds of fly ash.
That fly ash will contain about 33 pounds of CaO equivalents. Assuming a 1:3:6 blend standard as a benchmark and a 60% recovery, that means 20 pounds or enough to make 10 concrete blocks like this one.
👀 10 Blocks from Burning One Ton of Coal
Now. Do we still want to call this a low-carbon building block?
I honestly don’t know the answer. A tremendous amount of energy and carbon emissions went into making this block appear. CarbonBuilt doesn't have to claim any of the carbon that goes into making the CaOH2. But that’s accounting as much as anything else, right?
Coal slag and ash used to get chucked into the dumpster. But these products have been upcycled into asphalt, aggragate and industrial supply chains for decades. If something generated creates economic benefit, even if it was once considered trash, do we not have to consider the end buyer when counting carbon?
Put it this way: if, say, Duke Energy puts a dollar value on slag and ash (and they do), does end demand for the byproduct, even if marginal, not impact their decision-making when keeping an old coal powerplant running for a few more years?
Or let’s say CarbonBuilt goes public. They take over the concrete market, everyone makes money, and they have a business to run. The ONLY supplier for the raw input to run their business is coal powerplants. It would be in their best interest, as a business, to keep coal burning for as long as possible. They’re bankrupt without it.
I certainly don’t want to discourage the repurposing of fossil fuel byproducts in a manner that can avoid or sequester carbon in the process, but let’s not kid ourselves: pretending like a green product is completely divorced from a “dirty” business that it 100% relies on as a feedstock is pretty disingenuous. Let’s instead talk about the issue with all the information available.
The 2000 tons of CO2 is likely just avoidance from
https://www.sciencedirect.com/science/article/abs/pii/S0022309319307343
I guess that's the classic problem where waste is often economical to use as an input -- until the producer/market realizes it has an economic value and gets sold as a commodity.
Nifty detail - CEO Shendure is the dad of the kid who tracks private jet emissions. https://www.cbc.ca/radio/whatonearth/private-jet-emissions-1.6758495
If they want fly ash they are going to have to compete like everyone else in the cement/concrete business.
Usable flyash that isn’t complete shit is more and more difficult to come by and they might have to start looking at some of the dirtier stuff.
Also, they show any compression data on their products vs normal blocks?