February 20, 2008

Cement manufacturers continue quest for “greener” technology

Construction Corner

Korky Koroluk

The World Business Council for Sustainable Development tells us that concrete is the most widely used material on Earth, apart from water. The council also tells us that we use almost three tonnes each year for every person on the planet.

Construction Corner

Korky Koroluk

That’s a lot of concrete and anywhere from seven to 15 per cent of it is made up of cement.

Since many of us have become concerned about global climate change, it has been frequently pointed out that the manufacture of a tonne of Portland cement releases almost a tonne of carbon dioxide into the atmosphere and that carbon dioxide is one of the greenhouse gases we are most worried about.

The industry has been working quietly to change that, so that most cement manufacturers now are using more efficient kilns and greater use is being made of such additives as fly ash and blast furnace slag.

Still, there are only so many improvements to be made in that direction.

The fact remains that the ingredients in cement need to be heated to about 1,400 C for the necessary calcination to occur. It is at that point that about 60 per cent of the carbon dioxide is formed.

Now, though, an Australian firm, Zeobond, is about to start production of what it calls E-Crete, which is a geopolymer — a type of inorganic polymer formed at room temperature. Its production (the details of which are so far a closely-held secret), involves treating such things as fly ash or slag with an “activator,” yielding a gel that can replace some or all of the Portland cement in the production of concrete. Since the process occurs at ambient temperatures, the amount of greenhouse gases released is only 10 to 20 per cent that associated with conventional concretes.

Apparently it is the “activator” that is the key to the process, since the starting materials for both geopolymers and normal cement can be similar.

The product is the brainchild of Jannie van Deventer, a chemical engineer and dean of engineering at the University of Melbourne. He has a lot of credibility within the scientific community.

But questions remain. Although geopolymers are known to be resistant to sulphate and chloride attack, we don’t know yet what all the structural properties of this new concrete might be.

How durable is it? Until there are answers, van Deventer acknowledges, their use will be limited to non-structural applications.

Geopolymer concrete should have some built-in advantages. Since the cement in them is made from waste materials like fly ash or slag, they could be cheap. They set quickly (too quickly sometimes, but that’s being worked on) and their curing time is much shorter than conventional concretes. They are also more resistant to acid, fire and microbial attack, which might make them useful in niche markets.

While there are several concrete products coming to market that emit less carbon dioxide, researchers are also working on turning emitted carbon dioxide into a virtue rather than a vice. Researchers in Australia and India are working on the idea of capturing carbon dioxide released from cement kilns (and the fuel that heats them), and using it to feed microscopic algae. That’s right: algae.

Scientists now know that biofuel can be produced from some types of algae using technology developed in the United States.

So what they are now trying to do is develop a closed-loop system in which the kiln produces carbon dioxide, which is captured and fed to algae, which is harvested and used to produce biodiesel, which fuels the kiln, which produces more carbon dioxide — and around and around it goes.

This is just a sampling of the kind of work that is going on in the background as the global construction industry grapples with the jigsaw puzzle of sustainability.

No single technology is going solve the puzzle, but these two might prove to be a couple of the pieces needed.

Korky Koroluk is an Ottawa-based freelance writer. Send comments to editor@journalofcommerce.com

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