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Cutting carbon from infrastructure isn’t a burden – it makes good business sense Mark Enzer

With this winter’s unrelenting coastal surges and extreme rainfall leaving many areas in the country devastated, flooding has dominated headlines for weeks on end. The disaster has refocused national attention once again on climate change, culminating in the Met Office’s explicit assertion that all available evidence indicates that global warming will result in more intense rain events.

The distressing flooding scenes of recent months are a stark reminder of the urgent need to take action to limit the warming of the planet. In practice this means slashing carbon emissions, in line with the government’s legally binding commitment to achieve an 80% carbon emissions reduction by 2050, against the 1990 baseline.

The infrastructure industry has a sizeable part to play in this mission. Infrastructure accounts for 53% of the UK’s current total carbon emissions, and 16% of the UK’s total emissions are associated with constructing, operating and maintaining infrastructure assets – that is, the emissions directly controlled by the civil engineering industry as opposed to by end users.

Clearly, there is an environmental impetus for infrastructure organisations to reduce the carbon emissions resulting from infrastructure. But for this change in approach to be viable and sustainable it has to make business sense.

The UK’s most progressive infrastructure clients and their supply chains have tackled emissions on a programme level, driving down capital carbon by 39% and operational by 34% compared to ‘business as usual’, reducing average capital costs of assets by 22% in the process. If scaled up across the UK’s infrastructure sector, efficiency gained by pursuing low carbon solutions would yield a £1.5bn annual economic benefit.

Major clients are rapidly becoming carbon aware and demanding low carbon solutions. And the government itself is considering making carbon an assessment criterion for procurement of publicly funded infrastructure.

Carbon is a proxy for energy and resource use, and therefore for cost. Reduced carbon equates to efficiency. However, this is not the only economic driver: the increasing cost of carbon is a further incentive, with carbon credit prices poised to leap upward and continue rising annually.

Low carbon leaders have found that pursuing carbon efficiency goes hand-in-hand with innovation. Clients and even end users can enjoy the benefits of better performing infrastructure with less disruptive construction, minimised waste and resource consumption, better performance, improved capacity from existing assets, lower maintenance needs and enhanced durability.

Rather than taking the conventional cost-cutting approach of simply squeezing margins in the supply chain, pursuing carbon allows old problems to be seen through a new lens that highlights unexploited opportunities for improvement.

The Infrastructure Carbon Review (ICR), published in November by HM Treasury and the Department for Business, Innovation and Skills with the Green Construction Board, as a sister document to the 2010 Infrastructure Cost Review, sets out the business case for cutting carbon and strategies for doing so.

We researched and authored the review and are supporting technical report.

The following project studies show how the company is putting ICR theory into practice.

Pioneering technology: Thrandeston Bog embankment stabilisation

Dry soil mixing was an untested technique for the UK rail sector, but its use to stabilise the Thrandeston Bog embankment in Suffolk resulted in a 70% reduction in embodied carbon and 50% cost savings against the reference design.

The 5m high, 650m long railway embankment, consisting of 10m of peat and very soft clays over chalk, was suffering from continual settlement and was in danger of sudden failure. Client Network Rail proposed a solution consisting of 1200 tubular steel piles measuring 914mm diameter and with a combined length of 18km, forming continuous retaining structures either side of the embankment.

However, Mott MacDonald proposed that similar results could be achieved with dry soil mixing – an innovative ground improvement technique which uses an augur to whisk cement powder into the ground, creating columns of stiff material known as soilcrete. This technique would also use less material and could be implemented adjacent to the live railway and within 2.75m of the overhead lines.

The consultant carried out research and trials including numerical modelling, laboratory tests and field studies to demonstrate that the technique, never previously used on the UK railway, was viable.

Following successful trials, dry soil mixing was selected by Network Rail for the final project. The 11,500 soil mix columns used 5500t of cement powder, compared to the 7300t of steel that would have been used by the original 1200 piles. This represented an embodied CO2 saving of 12,200t, cost more than 50% less, and required fewer vehicle movements.

Building less: Covenham to Boston water transfer pipeline

The cost and carbon footprint of a water supply improvement project were dramatically reduced by a clever solution that made better use of existing assets. Client Anglian Water identified the need to provide new supply capacity to protect the growing town of Boston, Lincolnshire, against the minor risk of an extended outage at West Pinchbeck water treatment works. It planned to use 60km of new 600mm pipeline to connect the town to a reservoir and treatment works at Covenham, to the north. However, Anglian Water had also set itself challenging cost and carbon cutting targets to meet.

In a joint project team with contractor JN Bentley, Mott MacDonald undertook detailed network modelling and assessment of existing assets. This research revealed an opportunity to transfer 40% of the required water supply through existing assets, meaning the new pipeline’s diameter could be reduced from 600mm to 450mm, and the new pumping station downsized. By rerouting the new line, the need for an intermediate booster station was eliminated altogether.

Beyond the obvious cost and carbon advantages of building less, further benefits were realised through the selection of polyethylene pipe with wall thickness optimised for different water pressures along its length, and by having the pipe delivered in long 18m sections which reduced the number of deliveries by 30%.

Overall, the new design reduced embodied carbon by 57% (from 20,700t to 8830t) and cost by 25% (from £41.5M to £31.1M), against the original plan.

Smart design and specification: A2 highway lighting

Careful assessment of a highway lighting project to eliminate unnecessary illumination and optimise what remained resulted in a scheme that was lean in carbon and cost.

The Highways Agency called on highways design, construction and management joint venture Balfour Beatty Mott MacDonald (BBMM) to replace replaced life-expired street lighting on a 6km stretch of the A2 near Dover.

As the scheme had to contribute to the Agency’s target to reduce the carbon footprint of its projects by 25%, BBMM completed a detailed assessment of the system to unearth opportunities for efficiency and innovation.

A review of road safety data revealed that lighting on some sections of the road could be removed without increasing accident risk, reducing the number of columns needed from 185 to 117.

The new columns are made of 95% recycled aluminium, which has an embodied carbon footprint five times lower than that of virgin steel, and have a 50 year lifespan, compared to 30 years for steel alternatives. Columns are founded on driven steel piles that can be removed and reused or recycled in future.

The team selected energy efficient LED lamps for the new design. Compared to conventional lamps, these are brighter, last five times longer and improve drivers’ ability to detect colour and detail. The lamps are programmed to automatically dim in response to ambient light levels and traffic flow.

Compared to the previous lighting system, energy consumption is now 39% lower, delivering a CO2 reduction of 36t/annum – and the improved performance of the LED lamps means there are benefits to safety as well as carbon and cost.

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