Concrete is brilliant stuff. As the Romans could have told you, it provides a great way to get just the right shape without all that expensive and highly-skilled business of messing about with bricks or blocks. That’s why concrete is humanity’s most widely-used material, by tonnage.
The trouble is… that tonnage. Actually, that’s just one of concrete’s problems. Perhaps the biggest problem with concrete is that the manufacture of cement is responsible for at least 5% (some sources say 7%) of all mankind’s CO2 emissions… but low-carbon cement isn’t the subject of today’s post.
In between all that cement, you get aggregates. Historically, that meant sand, gravel and crushed stone… but when your species is making more than two billion tonnes of concrete per year, it’s all too easy to push the price of aggregates sky-high, along with the skyscrapers. That’s why it’s a good idea to introduce a recycled aggregate; making buildings out of old buildings has got to become the norm at some point during this century. It’s already happening, but inevitably the task of crushing up whatever waste you can acquire needs energy and has its own carbon consequences.
An alternative – in fact another part of the solution – is to manufacture artificial aggregates. That’s been going on for almost a century: Lightweight Expanded Clay Aggregate (or ‘LECA’) was developed in the USA around 1917. The manufacturing process involves pellets of clay that puff up when heated, like so much breakfast cereal. The resulting balls can then go into a concrete mix in place of natural stone: it’s ‘green’ because there’s less quarrying involved, and the product is more readily transported.
I might just pause to observe that when the Romans built the concrete dome on the Pantheon (still surviving 1,900 years on, and still the world’s largest unreinforced concrete dome) they used small clay pots and pieces of pumice in the mix, in order to reduce the weight in the higher layers of the dome.
So far so good… but a 21st century take on this promises still better performance. What if, instead of relying on clay, you could use a waste material? One of the exhibitors that impressed me most at Sustainability Live was Novagg Limited, would-be makers of just such a material. They propose to supply a new kind of aggregate, using almost entirely (98%) waste diverted from landfill – and not the ‘good’ high-value waste that everybody wants, but the real junk: industrial mineral wastes from the steel, aluminium, chemical and water industries, plus mixed glass.
The company adds a secret ingredient to make up the other 2%, and uses the same rotary kiln as the LECA manufacturing process. At a temperature some 400°C lower than with LECA (another clear advantage) the “novagg®” material puffs up into vitreous spheres that I’m told are lighter, but stronger than any competitor’s product.
“Where there’s muck there’s brass,” as we say in Yorkshire. (Or at least, we used to.) Someday, somebody is going to make a fortune from this invention, I think. Right now, though, Novagg Limited are making sample pellets by the bag-load, not commercially producing aggregates by the truck-load. If you happen to have ten million pounds kicking around, to fund the construction of a full-scale production facility for novagg® pellets, I believe the company would like to hear from you – and you might be doing the planet a favour, too.