Epoxy Concrete Won’t Solve Cement Emissions Problem – CleanTechnica

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As I’ve been looking at solutions that people are proposing for eliminating cement’s high carbon dioxide emissions, a set of criteria are clearly emerging to assess whether they are going to be material. These include the source material availability, cost, and distribution. They include integration into worksites. They include the regulatory and building code changes.

Before starting to look at epoxy concrete, I was cautiously optimistic about one of those points, source material availability. Epoxy resins are made from petroleum. They are one of many durable petrochemical products that’s used globally. We extract 4.5 billion tons of crude oil globally today, and while we’re going to stop burning the stuff — the large majority use case — that means it’s a resource that is at least at the scale of cement, which is currently a 4.1 billion ton a year market.

I know that everything in the petroleum lifecycle, including extraction, processing, distribution, and refining can be electrified and made vastly lower emissions, and that burning it can’t. But using the stuff for epoxies which don’t get burned at least had scale of raw materials going for it.

But being a guy who realized long ago that he wasn’t particularly competent as a handy person, never mind a skilled tradesperson, I don’t use epoxy often. The last time I did was over ten years ago when I asked my Dad, who was a skilled tradesperson at multiple trades over his life, including furniture building, tinsmithing, radar technician, and appliance repair, how to repair a specific thing. He told me: epoxy. So I bought a little tube of it, did the repair and never thought about it again. I have no memory of how much it cost, how much of the tube I used, or when I discarded the remainder, that’s all lost to the mists of time and better things to think about.

Similarly, when a flood in the building wiped out the hardwood we’d installed and we decided to go with polished concrete floors, I gave no thought to the chemical composition of the concrete. Undoubtedly it was epoxy concrete. We just enjoyed the absurd durability, complete imperviousness to everything, the aesthetics, and went on with our lives.

So I had no idea why epoxy concrete was a complete non-starter to displace significant cement, and apparently neither did the three or four people who have suggested it’s the answer and that this problem is solved. Sometimes you just don’t know what you don’t know, even about things like epoxy that are used everywhere. There’s a really big problem with epoxy, but I’ll start with the basic ones.

Concrete made with Portland cement has a bunch of very nice characteristics for construction. Big construction jobs get it delivered by the truckload in those ubiquitous trucks with the heavy, rotating drum on the batch. They are filled at concrete batching facilities, where Portland cement is mixed with water, sand, aggregate, and maybe some other stuff depending on the requirements. They are driven through cities to the job sites. The concrete stays liquid for up to four hours, depending on factors like ambient temperature, cement composition, and the use of admixtures​. Pot life is the term that’s used for that, which sounds perhaps more interesting than it is.

The concrete can be poured from the truck and even pumped through long, supported hoses to the interior of buildings under construction to fill prebuilt forms awaiting it. The forms usually contain a wire mesh or steel rebar, and the concrete flows around the steel. The steel and mesh have to be fairly rust-free, but concrete is basically wet dirt, so a bit of dirt and dust isn’t an issue.

The concrete’s curing duration and quality is only moderately susceptible to ambient temperatures. It cures faster in hotter, drier conditions, and there’s a risk of the water in the concrete freezing at low temperatures. Both can cause problems, but they are in the range of manageable concerns for experienced construction teams. The water in concrete mostly binds with other minerals like the silicates, and that process releases a bit of heat, as much as 20° Celsius above ambient. That obviously has implications for summer time construction projects and worker health and safety, but heat rises and construction sites by definition aren’t fully enclosed and insulated. Concretes enhanced with fly ash and other substances typically produce a bit less heat than Portland cement.

Concrete doesn’t set quickly and can be smoothed and shaped after pouring for an extended period of time. Its strength develops slowly, with 28 days being a typical period when it’s considered fully cured, although it will continue to get stronger for a long time after that. Forms can be removed after a week or two. There are fast early curing cement mixtures that are often used in load-bearing structures to speed up overall construction, as waiting a month to be able to pour the next floor isn’t a great choice.

Concrete is alkali, some people develop allergies, and you don’t want to inhale concrete dust, but these are relatively easy matters to deal with for worker health and safety, basically long-sleeved shirts, alkali-resistant gloves, goggles, and basic masks.

How does epoxy concrete compare? Not well.

Epoxy concrete’s pot life is typically in the 35- to 45-minute range, so it can’t be made at a concrete batching site and trucked to job sites. It has to be mixed onsite. Both the ingredients and the evenness of mixing them require high precision, so much more skill has to be on each job site as it can’t be centralized in the concrete batching plant. More machinery too, and it has to be moved from location to location due to the short pot life. That also means a lot more inventory of raw materials on the site as opposed to at the batching plant.

It typically sets much faster than Portland cement concrete, so there’s much less opportunity to fix mistakes. If mistakes happen, the things that make it a superior product, like added strength, durability, and resistance to chemicals, also make the mistakes harder to clean up.

It’s less sensitive to rust on wire mesh and rebar, but it’s more sensitive to dirt. It’s much more sensitive to ambient temperature and moisture, requiring more careful climate control. Its fumes are much worse for human health, requiring much more significant respiratory protection. The combination of more climate control means more enclosure of the site, which means a lot more requirement for ventilation to get rid of the fumes.

What about the carbon emissions, the point of this exercise? While cement has a carbon debt of about a ton of carbon dioxide per ton of cement, epoxy has a current carbon debt of six to eight tons of carbon dioxide per ton of epoxy. While that’s going in the wrong direction, there is good news in that much less epoxy is required than cement for the same structure — perhaps a tenth.

So the carbon debt is actually 0.6 to 0.8 for the same amount of concrete. That’s a bit of a win, but not a slam dunk. As noted, a great deal of the emissions from petrochemicals are amenable to electrification along the supply chain. However, the energy requirements for unconventional oil extraction methods such as steam-assisted gravity drainage in the oil sands, shale oil, or cold heavy oil processing with sand are much higher than for conventional oil reserves where the pressure in the reserve does most of the work of bringing it to the surface. Firms using unconventional oil extraction processes get around this problem by burning enormous amounts of their products behind the meter. That means electrification would significantly increase the cost of extraction, making it uneconomical. That’s one of the reasons, by the way, why Alberta’s oil sands will be one of the first crudes off of the market. It’s just going to get more and more expensive.

This does mean that while we currently manufacture 4.1 billion tons of concrete, perhaps only 400 million tons of epoxy could replace it, less than 10% of current global crude oil mass annually. That does suggest again that it’s in the range of the scale of the problem.

However, I said that there was a real show-stopper, and it’s time for the reveal. Price.

Portland cement costs $60 to $150 per ton, depending on where in the world you are. Epoxies used for concrete cost from $1,600 to $3,700 per ton. Remember, only a tenth of the mass is required, so that’s $160 to $370 for the same concrete. Concrete and epoxy tend to show similar geographical cost variances, meaning cheaper in India and China than in North America or Europe. In general, this means that epoxy concretes are 2-3 times more expensive than cement for the same concrete. All of the rest of the constraints drive up labor and machinery costs, probably making them 3-4 times more expensive on average. Calcined clays, by comparison, are adding only 10% to 30% to the cost of cement and hence concrete.

There is a thread I still have to pull regarding plant-based epoxy concretes, but I’ll leave that for another day. In my experience, biologically-sourced replacements for petrochemicals are more expensive than the products that they replace, so I’m not terribly optimistic.

My assessment is that epoxy concrete will continue to be used almost entirely where it is used today. That’s in offshore environments where its high resistance to chemicals and strength is a necessity. It’s in mounting spots for heavy equipment, where cement’s strength is inadequate. It’s in factory-manufactured precast concrete products where high strength and chemical resistance is required. It’s on concrete floors in facilities with lots of chemicals moving about. But it’s not a decarbonization wedge for cement.