That was the question asked of me by a colleague, followed by a clicking sound as his tongue was extracted from his cheek, where it had been firmly planted. He had just read the Guardian article “Concrete – the most destructive material on earth”. The piece was a literary assault on the ubiquitous construction material written with such venom (even by the standard of that newspaper, which often has a very myopic view of the world) that had it been written about an individual rather than a defenceless material, libel lawyers around the land would be rubbing their hands in anticipation of the fat fees they would earn.
I must be a Carbon Criminal in the eyes of the Guardian, having spent my whole career working in different parts of the Concrete Industry. Concrete is blamed for everything from supporting corrupt governments to causing global warming or supporting organised crime. I have been toying with the idea of a blog on concrete for sometime and this article has been the catalyst I needed. It looks like the Guardian is going to have a sustained attack on concrete as they are promoting Guardian concrete week which will investigate the “shocking impact” the material has on the modern world”
It’s true that cement is an energy intensive material to produce and often bandied about is the statistic that each tonne of CEM I (aka ordinary Portland cement) generates one tonne of carbon dioxide during its production (the figure is actually less than that). But let’s not forget cement is not concrete; the two words often get mixed up and used incorrectly. The Guardian article falls into this trap when it talks about digging a hole and filling it with cement, but they are not alone.
Dan Brown got it wrong so many times in the Da Vinci Code sequel Angels and Demons that it spoilt the book for me. It was not a “huge cement bulwark thick enough to ward off attacks even by tanks”; it was concrete. And Ian MacMillan, who wrote in Neither Nowt Nor Summat, that his “Uncle Charlie and his son Little Charlie made sure they drew their initials in the cement when they built their new garage in the back garden of 34 North Street in 1963”. Uncle Charlie and his son little Charlie either wrote their initials in the concrete floor or the mortar between the bricks in the wall. They almost certainly didn’t write it in the cement (a fine grey powder that’s used to make concrete and mortar) and if they did it would have been blown away with the first gust of wind. This is simply WRONG and is equivalent to Mary Berry eulogizing about a delicate carrot flour with a scrumptious flavour on The Great British Bake Off? Flour is a powder used to make cakes; cement is a powder used to produce concrete.
The fact is that not very much cement is used in concrete, the rest of the materials (aggregate, water, admixtures and supplementary cementitious materials like ground granulated blastfurnace slag and fly ash) are typically extremely low carbon materials, so that a tonne of concrete of the type often used in foundations can have an embodied carbon dioxide content well below 100kg per tonne rather than 1000kg.
As the article points out, concrete is the second most widely consumed material in the world (after water). It can be aesthetically beautiful, it can be ugly. The fact is that without concrete our health and education would be poorer. In fact without concrete, we wouldn’t have the transport infrastructure allowing those papers to be distributed or the journalists to get to work, or the office blocks they work in, or the buildings to house the printing presses, or the shops to sell the papers in, or the electricity to run their laptops or, or, or…. (the list is endless) but in short, there would be no Guardian newspaper.
Coal, oil and gas produce more CO2 than concrete (but are used in much lower volumes), concrete has much lower CO2 content on a weight by weight basis than steel, asphalt and plasterboard. Concrete is a low carbon material and it is a victim of its own success. It is widely used because it is durable and cheap.
The article is light on suggested alternatives to concrete. Cross laminated timber is one suggestion. Obviously not suited for most of the applications that concrete is put to, it can be used for the walls of buildings. I am a governor of a school in west London, that despite my best efforts, was built in CLT. It looks attractive but there’s one big problem. The noise! CLT, unlike concrete, does not absorb noise and it was impossible to use the classrooms when there was any chatter in the corridors as pupils moved between classrooms. By necessity, the school had to implement a silence in the corridors policy.
Concrete also has inherent fire resistance unlike timber. The CLT industry has argued that you do not need to worry about fire in CLT buldings, because when they start to burn, the timber chars, effectively producing an inflammable surface on the CLT. While this may be true for solid timber, CLT is built up in layers and recent work has shown that the layers can peel providing additional fuel for the fire. In the post-Grenfell era, do we really want to promote timber housing with question marks over its safety?
Don’t get me wrong, I think the cement industry could still make giant leaps at improving the sustainability of its product. CO2 sequestration is one area to be more seriously addressed but the concrete industry is already doing a lot of good work. The UK concrete industry diverts over five million tonnes of material from external waste streams and uses them in place of primary materials. In 2014 it used 107 times more waste than it sent to landfill.
Despite the Guardian’s outpouring on concrete, to quote one of their other bête noire’s, the late Lady Thatcher,
“There is no alternative”