Replacing portland cement


Updated Fri, 05 Dec 2014 14:22:47 GMT

The construction industry has been caught with its trousers down with the rapid increase in construction coming out of the recession.

A new concrete developed by David Ball Group replaces Portland Cement (OPC) with ground granulated blast furnace slag (GGBS) achieving a 95% reduction in embodied CO2 emissions.The production of OPC generates 365kg/m3 of C02 and the industry as a whole accounts for about 5–8% of global emissions, making it the third-highest manmade producer of CO2 after transport and energy generation.</p> <p>In comparison, one cubic metre of Cemfree mix has an embodied CO2 of 17.3kg/m3. Cemfree also compares well to CEM III (a), which generates 196kg/m3 and CEM III (c), which produces 44 kg/m3.

The use of GGBS (a byproduct of ironmaking) and fly ash (a waste product of power stations) in concrete as an alternative to OPC is well known, but usually these additives are included as a partial replacement. About 85% of UK readymix concrete contains either GGBS or fly ash – some of the concrete used in The Shard was 70% GGBS.

The David Ball Group’s activator is the key to the Cemfree binder. GGBS has a glassy encapsulation and this has to be broken down for it to become hydraulically active. This is the part of the process that is under patent. Ball says Cemfree has benefits above normal cement – it has increased resistance to acid, it is stronger, has more durability, needs less steel reinforcement, and is sulphate and chloride resistant. ‘It very quickly surpasses the properties of OPC.‘We have been doing the large-scale field trials and worked with contractors, showing them how to use the product. We have laid large warehouse floors and have done the long-term tests that we have to do. The patents have been submitted. We are up there and ready to meet the challenge.’ When it comes to laying the product, current concrete professionals are expected to easily adapt to the slightly different technique.

John Provis, Professor at the Department of Materials Science and Engineering at The University of Sheffield, says the development of Cemfree concrete represents a significant step forward in the use of non-Portland cements in the UK. ‘The results that have been achieved in this project demonstrate that a concrete that does not contain Portland cement is able to meet the performance requirements associated with some demanding and important applications in the UK context.’

A barrier to the full roll out of Cemfree is materials supply. The Mineral Products Association says about 2.2 million tonnes of GGBS and 15 million cubic metres of GGBS concrete are produced annually in the UK. High demand earlier this year led UK building products manufacturer Hanson to reactivate two of its mothballed slag-grinding plants.

Ball says, ‘There are not enough bricks, not enough cement, not enough slag and not enough PFA or fly ash. The construction industry has been caught with its trousers down with the rapid increase in construction coming out of the recession.’