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Driving down carbon

Reducing embodied carbon in transport infrastructure will help drive the sector’s contribution to achieving net-zero, says Kim Yates.

Embodied carbon in concrete, asphalt, steel and the other raw materials used to build roads, tunnels, rail lines, and airport terminals and runways adds considerably to the transport sector’s overall carbon footprint.

Initial plans for the Lower Thames Crossing (LTC), a planned tunnel between Essex and Kent in the UK, would have produced about 1.8Mt of CO2e in the construction process, with embodied carbon making up between 70% and 80%. Carbon emissions from building phase 1 of HS2, the high-speed rail line between Birmingham and London, including tunnels through the Chilterns, have been estimated at 6Mt.

There are ambitions to significantly reduce embodied carbon. National Highways is due to submit a revised Development Consent Order for LTC which will include bold measures to cut embodied carbon on the project. Meanwhile, the company developing HS2 has adopted a stretch target to reduce embodied carbon emissions in main works civil contracts by 50%.

Material difference

Material difference

Your journey to reducing carbon begins with assessing the need for new infrastructure in the first place.

Could alternative approaches achieve the same objective? Can travel demand management and measures to encourage behaviour change, for example, reduce demand or redistribute it in space, mode or time? If not, can maximising the use of existing assets – by optimising their operation and management – reduce the extent of the new construction?

Next is to consider how to reduce a project’s carbon footprint, using low-carbon materials, minimising resource consumption and streamlining the delivery process. Significant savings are possible.

Concrete is the major source of carbon. On the Northern Line extension (NLE) in London, our engineers helped to identify potential resource and carbon savings. This included reducing the thickness of the segments lining tunnel walls and replacing ordinary Portland cement with alternatives, such as ground-granulated blast furnace slag (GGBS) from steel manufacturing, to produce concrete with lower embodied carbon. Using concrete for secant piling with 95% GGBS reduced embodied carbon by 80% compared with conventional Portland cement.

The Northern Line is a good example of the potential for reducing embodied carbon on projects – and the UK infrastructure industry is moving in the right direction, and the government is leading the way through its recently published Construction Playbook. But it is not the norm.

Robust business case

Robust business case

Aside from helping to tackle climate change, there is a strong business case for action on embodied carbon.

Our Infrastructure Carbon Review for the UK government back in 2013 found that cutting carbon cut costs. It revealed that leading companies and their supply chains had cut capital or embodied carbon by 40% and reduced average capital costs by 25%.

Since then, we’ve worked closely with clients to optimise carbon reductions and secure financial gains through innovation, and by using digital design tools and our Moata Carbon Portal – the industry’s first platform to automatically calculate the carbon footprint of BIM-designed assets.

On the renewal of nine overbridges on the M4 motorway, we applied our carbon reduction hierarchy – build nothing, build less, build clever and build efficiently – to develop a strengthening solution that avoided costly and disruptive bridge replacement. It focused on building less and cleverer and was 40% less expensive and 90% quicker than completely replacing the bridges. It also halved embodied emissions.

National Highways chose Moata Carbon Portal over its own carbon assessment tool to assess emissions associated with construction of the A303 Sparkford to Ilchester improvement scheme in Somerset. By identifying and targeting carbon hotspots using the portal our design solutions cut carbon emissions by 46% on the 5.6km stretch of road. As part of a consortium, we’ve also been helping National Highways to develop its net-zero strategy published in June.

Our masterplans for both the expansion of London’s Heathrow Airport and modernisation of JFK Airport in New York emphasise low-carbon solutions. The design for Heathrow is focused on reducing construction and material quantities and only specifying products with low embodied carbon, while we assessed the operational, capital, construction and embodied carbon as part of the layout optioneering for JFK.

Sharing the risk

Sharing the risk

From transport authorities to major construction companies, there is a drive to reduce embodied carbon and work with supply chains to produce low- or zero-carbon materials.

New or modified materials mean doing things differently, challenging often long-standing and accepted norms, sometimes revisiting existing guidance and standards.

Trial mixes on site showed that the proposed concrete blend containing 95% GGBS would work on the NLE in London, leading to the restriction on the use of CEM III type cements being lifted on the project. It is evidence that engineers free of unnecessary specification restrictions can design solutions that minimise environmental impacts.

The commercial risks and rewards of developing low-carbon solutions need to be shared through the value chain – and needs agreeing early in the concept and design phase. This will improve whole life outcomes in the construction and operation of infrastructure and support industry innovation.

For embodied carbon, less is best. It’s a case of embedding a new way of thinking and working.

      Kim Yates is UK and Europe sustainability leader at Mott MacDonald

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