A thick, grey blanket covers the world’s cities, speeding global climate change. But it isn’t smog. It’s concrete.

Though cities from Houston to Shanghai rely on traditional Portland cement-based concrete, Jannie van Deventer has a better idea — just don’t ask him to tell you the exact details. He keeps the formula of his Zeobond E-crete secret, but the South African entrepreneur thinks his greener alternative can make a huge impact on a planet where concrete production is responsible for a surprisingly large share of global greenhouse gas emissions.

“We’ve constructed dozens of buildings in Australia and South Africa with Zeobond E-crete,” says van Deventer, “and they’ve all been successes.”

Van Deventer isn’t the only one looking to change the way we conceive concrete. As governments worldwide try to cut greenhouse gas emissions wherever they can, concrete production looms as an increasingly important target. It causes more than 5 percent of all manmade carbon dioxide emissions — more than aviation and almost as much as deforestation. But weaning the world off Portland cement is a major challenge because the industry is propped up by an extensive manufacturing and regulation infrastructure. Overcoming it could prove more difficult than toppling the gasoline-powered internal combustion engine, and would require public interest and support that has been lacking so far.

“Concrete is not a sexy topic,” says Ulrich Dewald, a researcher at the Karlsruhe Institute of Technology in Karlsruhe, Germany. People would rather talk about a shiny new electric car than changing the chemical composition of a cement block to reduce carbon dioxide emissions, he says.

Concrete is an ancient technology. The Romans used it to build roads, aqueducts and buildings — many of which are still intact thousands of years later. Made from a mixture of cement paste and rocks, it is strong enough to build the tallest skyscrapers, the longest bridges and the widest highways. It’s cheap and accessible too: you can pick up concrete mix at your local home center for only about twelve cents a pound.

Pound for pound, concrete production doesn’t generate as much carbon dioxide as some other building materials, like steel. But we use so much of it — a staggering three tons per person annually, second only to water — that it’s a major source of greenhouse gas emissions overall, says Sabbie Miller. Miller is a postdoctoral fellow in civil and environmental engineering at the University of California, Berkeley.

Cement, the binding material that makes concrete stick together, is made by heating a mixture of calcium carbonate (limestone), silicon, aluminum and iron to 2,700 degrees Fahrenheit. Both the fossil fuels burned to heat the mixture and the resulting chemical reaction release large amounts of carbon dioxide, a greenhouse gas that contributes to global warming.

So researchers across the globe, like Claire White, a professor of civil and environmental engineering at Princeton University, are working on ways to make concrete production cleaner, especially the manufacture of Portland cement.

The Portland cement mixed into conventional concrete is manufactured as clinker, concrete chunks roughly golf-ball sized or smaller. For every ton of clinker produced, approximately one ton of carbon dioxide is released into the atmosphere, so White is looking for alternatives to traditional clinker.

One way to reduce carbon emissions is to use cement made from leftover byproducts of steel production, such as coal-derived fly ash and blast furnace slag , says White. These cement-like materials are called “geopolymers,” a term coined in the 1980s by French materials scientist Joseph Davidovits , a pioneer of sustainable concrete and founder of the Geopolymer Institute

An American cement company called Lone Star Industries hired Davidovits in 1983 to invent a lower-pollution cement; the result was the geopolymer Pyrament. But Pyrament did not succeed “because the construction codes did not allow for the use of this new type of cement,” says Davidovits. To be permitted for use in the International Code Council’s building and construction regulations, a building material must be proven to have long-term durability. It needs to “last more than just five, ten or even twenty years,” he says.

But proving long-term durability takes years, of course, so builders overwhelmingly choose the traditional option, Portland cement. The only chance for innovation is if countries adopt performance-based standards that are based not on durability or material composition, but on a series of tests aimed at assessing strength. Australia has switched to such standards, which is why van Deventer’s Zeobond E-crete is finding a niche there. Now he and other entrepreneurs are pushing for similar reforms of construction regulations elsewhere.

“Industry standards are inhibiting innovations, and it is hard to compete against the billions invested in the Portland cement industry,” says van Deventer, who is a civil engineering professor at the University of Melbourne in Australia in addition to his entrepreneurial endeavors.

The sustainable cement business is very competitive, so van Deventer keeps the precise recipe for Zeobond E-crete secret, but he insists that “you don’t have to use Portland cement to have good, sturdy construction.” The cost, he says, can vary by a factor of three from country to country, based on the availability and price of source materials. If source materials cost less than Portland cement in a region, then Zeobond E-crete is cheaper there, but if the opposite is true, it is more expensive.

But the best news is that making Zeobond E-crete emits significantly less carbon dioxide than producing an equivalent amount of Portland cement. Because Zeobond E-crete uses only 10 percent Portland cement clinker, with the rest recycled byproducts of industrial production — the total reduction in carbon emissions is theoretically 90 percent.

Other entrepreneurs are trying to break into the market, too. The makers of Wagners’ Earth Friendly Concrete tout their product as “light years ahead of conventional concrete,” says Tom Glasby, the head of Wagners’ Earth Friendly Concrete division. It uses no Portland cement at all, only recycled industrial materials and a chemical activator, resulting in incredibly low carbon dioxide emissions, he explains. But these low emissions do come at a price: it costs 5 to 10 percent more than Portland cement. And Earth Friendly Concrete faces the same challenges as Pyrament and E-crete when it comes to global expansion, thanks to international building standards that require the use of Portland cement, says Glasby.

A major concern about geopolymer-based concrete alternatives is microcracking. As geopolymer-based concrete dries over time, microscopic cracks can form, allowing moisture to seep in and rust the steel beams underneath, weakening and eventually collapsing the structure. Though van Deventer claims this isn’t an issue with Zeobond E-crete, the same isn’t the case for many other similar products, according to Princeton’s White.

White’s team at Princeton has found that they can reduce microcracking by adding a small amount of zinc oxide nanoparticles (a billion of them would fit on the head of a pin), at very little additional cost — less than a one percent increase.

Ultimately, keeping costs down is essential to expand the market for concrete alternatives, and so is building an infrastructure to sell them, according to van Deventer. “Without an investment in sustainable infrastructure,” he says, “all the innovation in the world means nothing.”