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