The £100M Boston Barrier scheme has been highlighted as a prime example of low carbon innovation.

The flood defence scheme is pinpointed in the Low Carbon Concrete Routemap - published today - which is a collaboration between the Green Construction Board and the Institution of Civil Engineers (ICE), bringing together experts from across the industry including the Concrete Centre, Mott MacDonald and Cemex.

According to the routemap, minimising carbon emissions was a "significant driver" in the design of the Boston Barrier for both the Environment Agency and the BAM Nuttall Mott MacDonald joint venture working on the scheme.

The main flood gate used low-carbon concrete, which saved more than 1,300t of CO2e. The project also raised a control room above the flood level which avoided the need for deep piled foundations and saved a further 360t CO2e.

Meanwhile, the concrete mix for the barrier structure incorporated 70% ground granulated blast-furnace slag (GGBS), nearly the maximum permitted proportion. Limestone powder was adopted as the coarse aggregate in the mix, which is the preferred choice for water-retaining concrete as it minimises the coefficient of thermal expansion and therefore lowers the reinforcement requirements and potential for cracking.

There was also significant collaboration with the concrete supplier to reduce the actual cement content of the supplied mix while still ensuring it met minimum strength requirements.

The barrier gate has been fully operational since December 2020. Last year, three of the main challenges in the permanent works design of the scheme were revealed by engineers working on the project.

Other examples of best practice in the Low Carbon Concrete Routemap include Network Rail work to reduce the embodied carbon of precast concrete platform slabs by changing the types of concrete and reinforcement and Keltbray's Hiper Pile system which has been used on HS2.

Along with these case studies, the report proposes a standardised carbon rating system that would make it easier for clients and designers to choose low-carbon options.

It also sets out three decarbonisation routes to 2050 based on what action the industry takes and how fast carbon sequestration in concrete advances. Even under the most modest route, emissions are expected to fall from 10M.t CO2e in 2022 to 5M.t in 2035. Under the most optimistic scenario, the concrete industry could become a carbon sink – absorbing more greenhouse gases than it emits – in the 2040s.

The report predicts this will lead to major cost savings, ranging from £2.5bn to £10.5bn by 2050, depending on how quickly the industry decarbonises.

Concrete is a major source of carbon, accounting for 1.5% of all emissions in the UK and 8% globally. This is largely due to the production of cement, which involves heating limestone and clay to very high temperatures and a chemical reaction that produces greenhouse gases. Every year we use approximately 11.7M.t of cement in the UK, equivalent to the weight of more than 100 aircraft carriers.

As such, Low Carbon Concrete Group chair and report co-author Andrew Mullholland emphasised that the "next 10-15 years are critical in driving the carbon out of concrete".

He said: "There are steps we can all take immediately to minimise the quantity of concrete we use and the carbon intensity of production, and this change should be driven by clients. This will require motivation and substantial effort from across the industry.”

Construction Leadership Council co-chair Andy Mitchell added: “This report pulls together a wealth of practical advice and best practice from across the industry. But more importantly, it charts a route forward to net zero which must increasingly be the guiding principle of every construction project. I call on peers across the industry to read this report and take up its recommendations as soon as possible.”

A new UK Concrete Decarbonisation Taskforce, convened by the ICE, will oversee the delivery of the Low Carbon Concrete Routemap. This group will update the report each year and monitor progress across the industry.

Infrastructure Working Group chair Chris Newsome emphasised that "this is a routemap with a future and a group interested in taking this forward", while Environment Agency flood risk management director John Russon said that "the challenge is what we do next and what collectively we do with the routemap".

ICE director of engineering knowledge Mark Hansford added: “We have the solutions and a clear route forward. The UK Concrete Decarbonisation Taskforce has a vital role to play in unlocking funding and working across the industry and government so that we can drive a step change in the decarbonisation of concrete.”

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