If there’s a substance we take for granted, but would have unimaginable consequences for modern life if we were to lose it, it’s concrete. It gives us much of the built environment we daily take for granted.
Yet, as noted by a recent article in The Guardian, part of which is reproduced below, cement — the basic building block of concrete — comes at a high environmental cost. Cement-based building materials account for between 5% and 10% of all greenhouse gas emissions in the United Kingdom.
Each ton of cement produced requires an equivalent ton of carbon dioxide to be emitted into the atmosphere.
Good building design includes limiting the impacts a building makes on its immediate environment while ensuring that correct orientation, for example, lowers operating and maintenance costs.
Capital costs can be reduced through recycling, while insulation and intelligent choice of energy systems can significantly reduce operating costs. It should also make sense to vary sources of inputs such as not relying solely on Eskom, for instance, as your energy supplier.
But trying to build, especially in an urban environment, without cement is akin to trying to live in a public transport-challenged city like Johannesburg without a car.
A cool book on using concrete to make all kinds of things like counter tops, floors, basins, baths and the like, tells me that fly ash is a part answer.
This fine powder, a by-product of the coal-fired power-generation process, has cement-like properties. While it cannot be used in isolation from the real thing, it is a strengthening agent that can make up as much as 60% as a blend with cement. It is also much cheaper than cement.
On the face of it South Africa should be awash with fly ash, given that most of our power comes from coal. The product is not green because coal-fired power stations generate greenhouse gases, but re-using fly ash as a cement blend is an efficient usage of a waste by-product.
Ash Resources, a company in part co-owned by Eskom and Lafarge, one of the major cement manufacturers, is the main supplier of fly ash. A technical assistant from the company gave me the impression I could buy as much fly ash as I needed, but not in Johannesburg. I would have to transport it from the Lethabo power station on the Vaal River to Johannesburg and the minimum order is about two tons. The price was good, about a 30% saving if bought in 40kg bags.
My favourite building supplies store said it does not stock fly ash, but that they thought ordinary cement already contains fly ash. I checked a bag, which I had already bought, very closely: there was no mention of fly ash.
Fly ash is extensively used in construction. Blends containing up to 40% fly ash have been used to build the giant Katse dam, the principal dam of the Lesotho Highlands Water Scheme that meets Gauteng’s daily water needs.
Graeme Smith is the managing director of Ash Resources. He says Eskom makes a relatively small amount, 30%, of the fly ash it produces, available to the market. Most is used to solidify the waste water produced in electricity generation.
With the exception of a small export of specialised material, all locally produced fly ash is also locally consumed. It is much cheaper than cement, selling at R150 a ton compared with R700.
Smith says fly ash is a low-cost commodity that doesn’t travel well. Transport costs can exceed the cost of the commodity.
He says the cement industry in South Africa conforms to European Union standards. Fly ash is used both to reduce energy bills and for increased strength. In certain applications and techniques, such as in some Lesotho dams, as much as 60% fly ash is blended with cement. Typical building applications use between 16% and 25% fly ash in their mix. It carries a ”don’t try this at home” warning, it being ill-advised, for instance, to add fly ash to cement that has already been blended.
Smith says fly ash is often used where architects want a high-quality finish for concrete works, a prominent example being the Constitutional Court.
Each bag of cement includes a code that tells you its properties.
The symbol V tells you fly ash is present, the letters CEM II that the product is a blend. Smith suggested the fly ash blend would be about 5% to 8% cheaper than a pure cement product.
I asked the building supplies store if it could supply a CEM II V product.
Yes, but they’d have to order 560 bags, their minimum weekly order. The inference is that I’d have to buy 560 bags to get a fly ash blend.
I called a set of other nearby hardware merchants. Some offer CEM II, some not. Most offer no choice, perhaps because they are all ordering loads of 560 bags at a time.
The big cement companies all offer blends. But don’t expect the blend to be cheaper. They are marketed as a high-quality product even if it includes low-value input. From inquiries in my area, they sell at about an 8% premium.
Cemented (From The Guardian)
Beloved of master builders, detested by their labourers, cement supports the ground beneath your feet and keeps the roof from crashing in; yet few spare it much thought.
But maybe we should. Cement is one of the most environmentally hazardous materials in the world, adding more carbon dioxide to the atmosphere than the entire weight of the global airline industry.
Depending on how conservatively you do the sums, cement-based building materials, including concrete and asphalt, account for between 5% and 10% of all carbon dioxide emissions. Finding an alternative product to cement would, therefore, make excellent environmental sense.
But a world entirely without cement lies far out of reach, in an untamed place shorn of tarmac, airport runways, road bridges, skyscrapers, underground stations or modern reservoirs. Such is our dependence on the stuff.
But, while the environmental impact of cement production has been known for ages — Dickens described in Great Expectations ”the sluggish stifling smell” of the kilns — few call for it to be punitively taxed. Friends of the Earth, for example, could not produce a spokesperson to speak about cement’s effect on climate change. — Sean Dodson, Â