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.”
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.
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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.
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.
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