It’s possible to make great concrete without the huge emissions from cement. Why isn’t this common?

Résumé détaillé

Cement produces huge volumes of emissions – comparable to Russia or India. Why isn’t this alternative being used?

Concrete is the most used human-made material on Earth. Billions of tonnes are produced every year.

Unfortunately, concrete is responsible for 5-8% of global carbon dioxide emissions. Concrete is typically made of sand, gravel and cement, the binding agent. The manufacturing of cement is the main reason why concrete is so high-emitting.

For two centuries, cement makers have relied on the Portland cement method. This requires heating limestone to about 1400°C in kilns. At these temperatures, limestone breaks down, releasing carbon dioxide. Kilns often run on coal or gas, which release even more CO₂ when burned.

Low-emissions concrete is entirely possible and it depends on substituting limestone cement with another binder. One of the best alternatives is geopolymer concrete, which often uses industrial byproducts. Emissions from geopolymers are up to 80% less than for Portland concrete. Australia has one of the largest geopolymer cement project in the world – Queensland’s Wellcamp Airport near Toowoomba, which used about 40,000 cubic metres of geopolymer cement.

But over a decade after the airport was built, geopolymer cement hasn’t taken off. Here’s why – and what we can do about it.

A polymer is a long molecule made up of repeating smaller chemical units. Geopolymers is the term for polymers made from minerals. They’re typically produced from mining byproducts such as clay or industrial byproducts such as fly ash and slag from blast furnaces. Alkaline chemicals such as sodium hydroxide are used as activators to convert these byproducts into a ceramic-like material able to bind together.

Australia produces about 10-15 million tonnes of fly ash a year – comparable to its annual cement consumption of about 11-12 million tonnes. Fly ash is challenging to dispose of and can become a major waste problem. Geopolymers offer a clever way to convert it into something valuable.

Australian companies such as Wagners (Queensland) and Zeobond (Victoria) started commercialising…

Geopolymer…

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