Net Zero Airports | Reducing Pavement Thickness & Embodied Carbon on Airport Aprons

To contribute to global net zero goals, airport operators worldwide are increasingly focused on reducing their emissions and embodied carbon from airside infrastructure construction and maintenance activities.

United Kingdom | 21 December 2024
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This article sheds light on our future ready and innovative approach of using our industry-leading knowledge and experience of airfield design to reduce the thickness of the pavement under the nose gear of aircraft, therefore significantly reducing the embodied carbon and cost savings for our clients, whilst avoiding a compromise on structural integrity and design life.

Reducing Pavement Thickness and Embodied Carbon on Airport Aprons: A Sustainable Approach

Aircraft stands are typically constructed utilising Ordinary Portland Cement which has a high carbon footprint of approximately 0.17 tonnes of CO₂ emissions per tonne of concrete. To put this into context the CO₂ emissions are 17% of the total weight of the pavement itself. At WSP we are setting new standards by integrating carbon reduction as a core element of the design decision making process for airfield pavements. By prioritising carbon alongside cost and safety, we’ve been able to achieve both substantial carbon and cost savings, demonstrating that this approach is not only good for the planet but also economically advantageous.

Carbon emissions per tonne of concrete

0.17 tonnes

Reduction of carbon emissions per widebody aircraft stand

336 tonnes

Cost savings per widebody aircraft stand

£150,000

Our Approach

Apron pavements are typically designed using standards such as the American Federal Aviation Administration (FAA) guidance AC 150/5320-6G and the UK’s Design and Maintenance Guide 27 (DMG27), of which WSP is currently authoring the latest version. In general terms, the heavier the load on the pavement, the thicker the pavement needs to be.

Through our analysis it was found that both narrow body and wide body aircraft distribute on average 90% of their weight through their main landing wheel set (gear), with only 10% of their weight being transferred through the nose gear (at the front of the aircraft). Pavement design standards would lead the designer to provide the same thickness of pavement to all aircraft parking areas based on the heaviest gear. However, this uneven distribution of load means that the pavement under the nose gear experiences significantly less stress from the plane’s loading, therefore allowing the thickness of the head-of-stand pavement around the nose gear to be reduced.

Using software modelling, the WSP team have applied this assessment approach on multiple airport projects in the UK and overseas and found that for Code E widebody aircraft (B777, A350 etc.), the nose gear pavement thickness could be reduced by an average of 46%, and for Code C aircraft (B737, A320 etc.), by an average of 65%. This reduction translates to a potential reduction of 58 tonnes of CO₂ and a corresponding saving of £25,000 in concrete paving for each Code C stand, and a reduction of 336 tonnes of CO₂ and a saving of £150,000 in pavement costs for each Code E stand over traditional stand construction. The above amounts to an average carbon saving of around 26%, and cost saving of around 6%.

Challenges and Considerations

While the proposed methodology offers substantial benefits, it also presents some challenges which we work closely with our clients to evaluate and advise. These include:

Constructing stands with varying pavement strengths may limit future stand reconfiguration options, however this is only a risk associated with remote stands and not contact stands (whereby a passenger boarding bridge is usually employed).
Future aircraft designs with different weight distributions could affect the calculations, however it should be noted that the distribution of weight for aircraft has not changed significantly over the past few decades.
Ensuring proper sub-surface drainage and load transfer between different pavement thicknesses is also crucial to avoid long-term issues and therefore attention needs to be paid to the transition between the two thicknesses to mitigate this risk.

Continuous Innovation in Carbon Reduction

At WSP we push design boundaries and are already working with clients in the UK to investigate other initiatives to further reduce carbon in our airfield pavement designs:

Reduction of cement content

High-strength concrete can be made with cement contents below the current typical airfield specifications if the water-cement ratio is low and the fluidity and stiffness of the concrete (workability) controlled to ensure that the mix can be placed and compacted before setting.

Sub-base reduction/removal

Removing the need for additional granular sub-base layers can provide carbon savings with minimal impact on PQC thickness if the support platform can be improved and/or controlled.

Increasing design life

Typically, pavement thickness does not significantly increase once large volumes of traffic are designed. Therefore, an increase in the design life from 30 to 40 years is expected to reduce whole life emissions by 33% by providing a slightly thicker pavement designed for 40yrs vs a pavement designed for 30yrs. Essentially, by understanding operations it is possible to provide an asset with an increased design life to reduce future maintenance interventions.

Conclusion

As we navigate the future of the aviation industry, it is imperative that we recognise our collective responsibility in mitigating the environmental impact of our designs. By adopting innovative and sustainable practices, we can collectively drive significant change. This commitment goes beyond regulatory compliance or cost efficiency; it is about fostering a future where our contributions positively impact the planet.

Through collaboration with our clients, and a shared vision, we can pioneer solutions that uphold the highest standards of safety and performance while significantly reducing our carbon footprint.

Aviation

WSP has been delivering world-class aviation advisory, planning, design and project management services for the aviation industry.

Our Experts

Matthew Gyi

Technical Director, Aviation

Euan McMinigal

Associate, Airfield Civil Engineer

Kirsten Holden

Senior Pavement Engineer

Adam Twine

Associate Director, Airfield Civil Engineer