Decarbonizing Infrastructure: Why Data, Collaboration and PAS 2080 Are Critical to Success
In the UK, construction activity accounts for around 50m tonnes of CO2 emissions, with cement and steel used for infrastructure being significant contributors. For the UK to meet its statutory climate targets, a whole lifecycle approach must be adopted to ensure the design, execution and operation of infrastructure delivers carbon savings. To make this possible, many actors within the supply chain are beginning to move toward PAS 2080 accreditation. COWI is one of the first engineering consultancies to be accredited.
Revised and relaunched earlier this year, PAS 2080 offers a global standard for managing infrastructure carbon that reduces cost and carbon across the whole value chain through more intelligent design, construction and use. The standard brings the value chain together around a carbon management plan that will help infrastructure projects deliver much more ambitious carbon-reduction targets than ever before.
Beginning at the design-development stage, a carbon assessment is created for each design option so that the client, and the project’s value chain, can better understand the impact of different design decisions and activities during project delivery.
Completing carbon calculations earlier creates an opportunity for the designer to collaborate with the client and contractor on construction materials, such as steel and cement—which account for approximately 15 percent of global carbon emissions, equipment and supplier choices before costs and schedules are agreed.
Carbon considerations then can be confidently factored into project recommendations and procurement specifications to ensure the execution delivers on their client’s carbon and sustainability goals. Once underway, robust processes and procedures, alongside frequent monitoring of carbon emissions and waste, are necessary to achieve the greatest emissions savings.
A Common Standard for Embodied Carbon
Supporting COWI in its compliance with PAS 2080 is its suite of inhouse tools and processes. One example is the Structural Carbon Rating Scheme for Bridges (SCORBS), which rates projects from A++ through to G. The Scheme captures data from more than 150 bridges to create an embodied carbon rating system with which the carbon performance of future design options and outputs can be benchmarked.
At present, SCORBS is calibrated so the average current practice delivers a bridge with a high D/low E rating. However, to achieve net zero by 2050, the average bridge rating must rise to a B rating by 2030—and extend to all infrastructure. As an initial step, COWI is actively working within the Net Zero Bridges Group to collaborate with other industry organisations to validate the rating systems. Within COWI, the next step is to extend the Scheme to masts and towers, tunnels, and offshore wind turbines.
Creating SCORBS has brought a new level of robustness to the carbon-reduction measures that are recommended, making it much easier to establish realistic baselines. The work is an important step forward in creating practical instruments that can support infrastructure decarbonization: to date, the limited volume of embodied carbon data in the public domain has hampered project lifecycle comparisons and accurate benchmarking.
While most organizations have committed to acting on the climate emergency, the issue of sharing commercially sensitive data remains. Initiatives such as the proposed Built Environment Carbon Database would create an open repository to share data from which a common industry benchmark could be created. It might also lead to better standardization of embodied carbon data, with the value chain required to collect and input information in a consistent and transparent way.
At the same time, projects with more formal carbon targets are becoming increasingly common, and PAS 2080 is likely to become a condition of tender in the next few years. Tools such as SCORBS that can readily be used to assess and benchmark the embedded carbon of different options will be highly valuable.
Reducing the Embodied Carbon of the Middlebeck Southern Link Road bridges
The detailed design of the River Devon Bridge and Flood Alleviation Bridge—part of the Middlebeck Southern Link Road in Newark, UK—offers an early example of how adhering to the PAS 2080 standard is helping COWI’s engineering design team in a partnership with SLR Consulting’s bridges design team to reduce the infrastructure project’s embodied carbon.
Designed by COWI and checked by SLR Consulting, the River Devon Bridge is a 100 meter-long, three-span, multi-girder composite deck bridge comprised of weathering steel with cast in-situ concrete slab. Reinforced concrete abutments, pier columns, and splayed wingwalls support and retain the deck superstructure and earth approach embankments. The foundations comprise reinforced-concrete bored piles and pile caps. The pier supports, which are aligned to the river, are at 35-degree skew to the bridge deck/road alignment.
The Flood Alleviation Bridge is a single square span fully integral bridge designed by SLR Consulting and checked by COWI. The deck superstructure comprises precast prestressed concrete U beams and an in-situ reinforced concrete slab. The substructure comprises integral frame abutments, taking the form of reinforced concrete cantilevers supported on bored pile foundations. Splayed reinforced concrete wingwalls also retain the earth approach embankments to the sides of the abutment.
Both bridges will carry a single-carriageway, urban all-purpose road providing alternative access for the south side of the town.
Revising the Bridge Design
The reference designs documented within the Approval in Principle (AIP) were assessed as having a baseline carbon intensity of about 2.6 tCO2e/m² (or an ‘E’ rating according to SCORBS). Through a series of design refinements and materials reductions, COWI expects to achieve a carbon intensity of less than 2 tCO2e/m² (or a C rating), with opportunities to reduce further considered in a systematic way following our carbon-management process.
To achieve this reduction in embodied carbon, COWI has made refinements and material reductions in many areas of the design, including to the steel within the main beams of the superstructure and the concrete volumes at the abutments. The team adopted lower-carbon mix designs as the preferred option in the concrete specification, using sustainably sourced cement replacements where possible. As a next step, the team plan to explore the development of a model low-carbon specification for the structural steelwork.
In terms of continual improvement within this design, the team is in discussion with the permanent formwork suppliers to calculate the embodied carbon of their systems and other specialist proprietary items. Lastly, the team also made alterations to the operation and maintenance schedule, including to bearing replacement, which has reduced both the capital carbon associated with the previous jacking arrangement plus the temporary works, including the potential traffic disruption associated with the previous arrangement.
The Path to Reduced Embodied Carbon
Minimizing carbon emissions associated with infrastructure is now a permanent challenge in the industry that can’t be postponed. By delivering design optimization at an early stage, and continuing to advocate for carbon reduction throughout procurement, engineers can have a significant influence on the embodied carbon outcome of many projects. Equally as important is open access to embodied carbon data. Decarbonization of infrastructure will heavily rely on the sector’s ability to collect, analyze and share data in a consistent and transparent way and is vitally important to innovation, best practice and ultimately a project’s sustainability.
PAS 2080 is an important step forward that’s helping engineering consultancies such as COWI and SLR Consulting to bring the construction industry around a common vision for embodied carbon, and its whole supply chain approach helps ensure that every opportunity to reduce carbon is identified and pursued.
About Cameron Archer-Jones
Cameron Archer-Jones is associate and carbon management lead, COWI in the UK; email: [email protected].
