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67% carbon reduction is a UK first

67% carbon reduction in concrete is a UK first

Jackson Civil Engineering has achieved a 67% reduction in CO2 by using a new type of ‘cem-free’ concrete on a flood defence project in Woodbridge, Suffolk, for the Environment Agency.

This is the first time this concrete has been used in the UK commercially, and the potential for reducing carbon emissions on future construction projects is extensive.

Concrete is a significant contributor to the carbon footprint of the construction industry. The concrete ordinarily used on this type of flood defence project consists of 50% GGBS and 50% Portland cement, which has a typical CO2 value of 158 Kg per m3. In comparison, cem-free concrete is made up of 95% ground-granulated blast-furnace slag (GGBS) and a 5% alkali activator, and has a CO2 value of 52kg per m3.

Although not suitable for all applications, the cem-free concrete was successfully used as an infill in a 265m section of flood wall. This amounted to 51 cubic metres, about 35% of the total concrete used, which achieved a CO2 saving of 5 ½ tonnes. To put this in perspective, it would take five acres of forest one whole year to redress the balance of this carbon output, using the traditional material.

Pro’s and cons

As well as the potential for significant carbon savings, cem-free concrete has better long-term durability, produces less heat in the reaction, making it more suitable for large pours, and requires fewer expansion joints.

There are, however, some minor drawbacks, which make it unsuitable for some applications. For example, during the trials the material did not respond well to floating, which made it unsuitable for use in the floor slab, although with work on the mix design this should be overcome.

The curing time is also slower, which means that shuttering would have to be left for a day or two longer than usual. However, on the right project, with sufficient programming this issue could be overcome.

Jackson’s Project Manager Ashley Tate said: “Over the course of this project, we’ve learned a great deal about the suitability of cem-free concrete going forward. On the right project, and with the correct planning, this material has the potential to generate significant carbon savings for construction.”

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