BENEFICIATION
deeper understanding of the material— the company sold the idea to Transnet. It was at this point that Attwell proposed to Murray & Roberts’ then-MD Anton Botha that they actually go for 100 % substitution.
“ Anton said he was happy for us to propose the idea to Transnet, but that I would have to be the one to sell it to them. So, we set up a meeting with the technical project manager, and he and I arrived there a bit earlier than Anton and the other guys. Before the others had even walked in the door, I had negotiated to 100 %, and based on the success we’ d had with the 70 % substitution, within two minutes, they had accepted. Although I think the fact that it would be the first site in South Africa to do 100 % cement replacement was probably also a factor. So we went ahead, and on 13 September 2013, we cast the first slab of 15m 3 of concrete— the first commercial application of 100 % cement replacement in South Africa.”
Three years later, in October 2016, the concrete was cored and tested. Not only had it maintained the 75MPa strength, but the durability had actually increased compared to the tests done a year prior.
The way forward
After the success of City Deep, the next big project for Attwell and his team was the Loeriesfontein and Khobab wind farms. While the cement substitution at the wind farms was also high— between 89 % and 95 % substitution with slag waste— the real improvement came in the decrease in the amount of commercial activator used. Whereas the City Deep project had seen the amount of activator used reduced to 4 %, at Loeriesfontein this was dropped even further to 0.4 %, or four litres of an activator per cubic metre of concrete. And this activator was a waste material from a different industry.
“ While the City Deep project was a massive accomplishment, the problem was that the activators we used there— the hydroxide and silicates— are very aggressive; they are not nice materials to work with. To counteract this, we decided to use a waste product from another industry as the activator. So we used 10kg, or four litres, of a neutral salt rather than one with a high alkalinity, which meant you could actually hold it in your hand without it doing any damage, making it much easier for people to work with.
Loeriesfontein Wind Farm
And then of course there is the fact that this is a waste product rather than a commercial product, which lowers your cost factor significantly as well.“ Through cement replacement, we were able to reduce the price at City Deep by about 30 %, and at Loeriesfontein by about 35 %. Now I am looking at ways of increasing the amount of waste used in concrete while decreasing cement— which is the most expensive part of concrete— with the aim of reducing the price by at least 50 %,” says Attwell.“ In future, the aim is to reduce the price by as much as 90 – 95 %.”
Through his new company, ARC Innovations, Attwell is working on ways to reduce the commercial content of concrete— including aggregate— to zero. He shows off a sample of his latest batch, saying,“ This sample here has no cement in it, and it is still using alkali, but the twist is it only contains 4 % commercial product. What we are doing is combining a liquid waste with solid waste, with approximately 100kg of commercial material per cubic metre of concrete to give you this product. So, we are not using any water at all, only liquid waste, and for a water-scarce country, this is very important.“ So here we are using just under 5 % of commercial product, and I believe the
Sources future is going to be using 100 % solid waste and 100 % liquid waste, combining it to make a concrete or an epoxy or a resin at costs that are ludicrously low, and with all the strength, durability, and other properties you need from the material. This sample here costs approximately R86 per cubic metre, compared to concrete of a similar strength that is probably in the region of R700 to R800 a cubic metre. In the future, the cost of your concrete is going to be primarily made up of your transportation and handling costs for the materials you use. So you will be reducing your costs by around 90 – 95 %, and reducing your greenhouse gases by 90 % at a minimum. And this is for the second most used material in the world after water, so the implications are staggering.“ This is what is on the cards for the future.” n
“ Last year alone, 4.2 billion tonnes of cement were produced.”
Statista. 2017.‘ Cement production globally and in the U. S. from 2010 to 2016( in million metric tons)’. https:// www. statista. com / statistics / 219343 / cement-production-worldwide.
At the Loeriesfontein Wind Farm, the amount of activator used was reduced to 0.4 %, or four litres of activator per cubic metre of concrete.
28 _ QUARRY SA | SEPTEMBER 2017