For all the talk and bluster nowadays surrounding low-carbon cement and technological advances in self-repairing concrete, we would be wise to remember that such gestures are not strictly about making up for lost time. (Roughly 200 years, by some counts, or about as long as Portland cement has been around). At its essence, the green concrete revolution is about returning to the building material’s roots.

A few weeks ago I posed the question in another article for GBA: What is the greatest thing since Ancient Roman concrete? The Romans’s recipe, which varied by region, was anything but simple. Last year, upon the release of a study on the unusual durability and longevity of ancient Roman concrete, its co-author Admir Masic, an MIT researcher, referred to attempts to reverse-engineer the stuff “a nightmare.”

While most of its secrets have yet to be unearthed, we do know a few things about those 2,000+ year-old relics. Many examples that stood the test of time incorporated gypsum and quicklime as binding agents, ceramic tile and lime clasts (mineral deposits that enabled self-healing) for aggregates, and natural pozzolans like volcanic ash and pozzolana, or pit sand, for cementitious admixtures. The Romans’s combining of seawater, volcanic ash, and quicklime to create seawalls was referred to by one engineer as “the most durable building material in human history.” And no one had to fire up a kiln to cook the stuff, either.

Solution in the mix

This is the point in the article when I would typically pivot and pose some hypothetical about what may come of the green “revolution.” Something like, Who has a modern-day answer to this ancient riddle? Alas, a suitable substitute has been in place and gaining market share for over a decade. Eco-Material Technologies, a Utah-based corporation, operates a manufacturing plant in the small town of Jewett, Texas, roughly equidistant between Dallas and Houston, that since 2011 has produced more than 1 million tons of a proprietary sustainable cement alternative known as PozzoSlag, a reengineered pozzolanic cement, in the form of upcycled coal combustion waste, that is manufactured at room temperature and is nearly zero carbon.

It’s not a geopolymer “in the purest sense,” according to Danny Gray, Eco Material’s executive vice president of strategy and business operations. “We make an activated pozzolan-based material.” The plant is currently expanding its capacity to produce over 165,000 tons each year, putting it on pace to become the largest producer of green cement in the country.

From big to biggest, and local

U.S. infrastructure is failing, and this is more than apparent in the country’s second-largest state. In response, Texas’s Department of Transportation (TxDOT) has been switching over to using PozzoSlag in some fairly significant projects. “It’s in the runways at [George Bush Intercontinental Airport], it’s in I-45 from Houston to Conroe, it’s in I-2 down in McAllen,” Gray says.

Eco Material’s product will also be used for continuous stretches of the planned I-35 expansion through central Austin and greater Travis County. Another Texas-based client is “the largest concrete pipe manufacturer in the U.S.,” he says. These clients “prefer this SCM [supplementary cementitious material] and they use it not because of the CO2 savings. We don’t market that in Texas. They’re using it because of the performance characteristics.”

PozzoSlag is priced at rates below that of Portland cement, Gray says, but “in terms of dollar per PSI delivered in the end product,” the overall durability of Eco Material’s product makes it a bargain. “We sell out 100% of our product every day, all within about 180 miles of our operating plant.”

Performance wise, the cementitious material is comparable to ground granulated blast furnace slag, in that it can replace between 50-60% of the cement in a typical concrete mix design, and achieve strength gains up to 20% or more compared to Portland cement, or performance grade 120-plus. (Eco Material produces another line that replaces 100% of the cement and has been used by “three or four small customers in Texas” to produce 3D printed homes in the Austin area, in partnership with the Texas company Hive 3D.)

Gray indicates that, pending a third-party verification, the Jewett plant’s manufacturing output comes to approximately 20 pounds of CO2e emitted per ton of PozzoSlag. EPA estimates approximately 1800 pounds is emitted per ton for Portland cement, depending on fuel types, raw ingredients, and plant efficiency. And because the waste products used to manufacture PozzoSlag is all locally sourced – resulting in near zero scope 3 emissions associated with mining and transporting of the raw material – the resulting emissions reductions come to 99%, “at least for the Texas-based operation.” And even when longer hauls come into play, Gray caps overall reductions at 90%. “That’s where we function, as an ultra-low carbon, locally made product.”

Coal plant to landfill

The global SCM market is expected to grow into a $34 billion industry by 2028. Comprising a sizable chunk of that is fly ash, the waste byproduct from coal combustion. Worldwide, coal power plants produce about 1.2 billion tons of fly ash each year. Practically and symbolically, this represents a huge opportunity, and one many SCM producers have capitalized on. All the same, Gray keenly points out that in the foreseeable future, those amounts will diminish greatly as coal-fired plants in the U.S. (and elsewhere around the globe) continue to shutter, becoming a scarce resource.

For its part, Eco Material Technologies is focused on “legacy sites” that presently contain an immeasurable amount of coal ash landfill. “We view those sites as our resources for harvesting throughout the United States,” Gray says. This view goes beyond sentiment, and beyond Texas. In addition to its Jewett plant, which is already one of the largest “green cement” manufacturing hubs in the U.S., Eco Material has a plant in Danville, Pennsylvania that harvests coal ash from a nearby landfill, another in Georgia, and three other plants under construction, each strategically located close to industrial landfills. “We’re using the natural pozzolans and byproducts from industrial operations that produce other minerals and turning all that into PozzoSlag.”

It’s not without a degree of irony that, for such a massive operation that’s been scaled up to build highways, airports, building foundations and more, the supply chains that make it all possible essentially amount to an artisanal product.

When in Rome

To be fair, not everything the Romans (and the Greeks, of course) constructed 2000 years ago was impeccable. Modern day forensic examinations of many ancient ruins have found that much of the concretes and mortars used for these civilizations’ commons consisted of a simple lime, a sturdy but compromised material that decomposed over time. But when it came to critical pieces of civil engineering, like aqueducts and cisterns, not to mention more ceremonial ouvrages d’art, let’s just say the standard for mix design was raised.

It was that very standard, in a manner of speaking, that paved the way for Eco Material Technologies. “Natural pozzolans and man-made pozzolans were the source materials we were focused on. We asked ourselves, ‘how can we treat it physically and chemically to activate it and get the same [results] as what the Greeks and Romans did?’ That was our underlying premise: how to activate pozzolans and have a replacement for [traditional] SCMs but with a dramatically lower carbon footprint.”

The diversion of industrial waste and the harvesting of toxic landfill materials for macro-scale projects are worthwhile pursuits. Couple them with the local element, be it in Texas, Pennsylvania, or elsewhere, and the pros of this massive operation just keep adding up.

_______________________________________________________________________