Reflecting on Lessons Learned in Airfield Pavement Design and Construction

Impacted by several factors such as overload, fatigue, weather, and mixed traffic, airfield pavements must be designed to withstand extreme events. And as air traffic continues to grow alongside the emergence of larger and heavier aircraft, the structural performance of these pavements is becoming paramount.

In this article, Tetra Tech’s aviation experts and engineers share key lessons from airfield pavement design and construction projects to improve performance, durability and lifecycle planning. From planning to post-construction stages, he sheds light on the diverse challenges, advancing methodologies, and the path forward to promote pavement longevity, durability, and sustainability.

Designing airfield pavements

Design risk

A key challenge for the design team is understanding the site characteristics at the start of a project. For pavement design, an essential component is understanding local ground conditions, so a geotechnical and geo-environmental assessment is required.

Ground conditions are a risk for any project, but a thorough site investigation should provide sufficient information to help prepare and mitigate any issues that arise. With site investigation costs generally being a small portion of the capital costs but carrying significant construction risk, ‘the more data, the better’ message should be reinforced to clients.

Local knowledge can also help deepen your understanding of ground conditions. Finding long-term employees who can provide historical information on the airport’s development will be an advantage. Interviewing the airport team can provide a useful backdrop to supplement a site investigation.

Reducing pavement failure

We’d like to think that stronger is better, but is that always the case? In composite and rigid pavement design, we utilise a lower-strength concrete layer. This is specified within a range of compressive strengths and designed to allow cracks to develop naturally and at certain distances to reduce the stress in the materials above.

The alternative, a significantly higher-strength concrete, may seem beneficial as it’s stronger and can withstand more loading, allowing it to last longer. However, this material will have different material properties, resulting in less self-induced cracking, with movements at these cracks larger than designed, which creates issues with the durability of the overlaying asphalt material.

It’s essential to provide material as specified and not to think ‘stronger is always better’.

Digital model

Pavement geometry for airfield rehabilitation projects uses digital models to provide horizontal and vertical information. However, the detailed information around tie-in areas, such as the runway to the taxiway, is often overlooked before construction. This may be due to the requirement for further, detailed topographical information in these areas to supplement initial survey data, which allows the tie-in design to move to the construction stage.

Once the tender design is finalised, going back to capture topographical information creates additional capital costs and risks for the project. To prevent this, we advise that a detailed analysis of tie-in areas is fully complete at the design stage. And, if it’s not undertaken, this should be recorded on the risk register so all parties are aware that additional detailed design is required, which should be undertaken early in the construction stage.

Constructing airfield pavements

During the construction stage, there are generally more opportunities for continuous improvement due to safety and operational requirements. Items to consider could include:

• Design stage surveys: Adopting the ‘more data, the better’ principle and including adequate survey information within the design. Remember, ground conditions and uncharted services can lead to costly project challenges. These can be reduced by detailed survey information and local knowledge.
• Mobilisation period: Is the contract mobilisation period sufficient? Working in the airside environment means safety is paramount. So, when construction starts, all the processes need to function effectively, while maintaining a safe environment and minimal disturbance to airport operations. Planning is essential, which necessitates time to programme and organise. Providing a longer mobilisation period than traditionally used may appear to be an additional cost, but this can be outweighed by getting it right the first time via safe and planned procedures.
• Closer working with operations: A successful project includes collaborating with airport stakeholders, especially the operations department. So why not include someone from operations as part of the construction team?
• Developing a Go/No-Go process: Optimum weather conditions are key, particularly when a project has limited possession times, such as runway rehabilitation undertaken at night. Cancelling construction due to weather can be costly, especially in terms of abortive material costs. A daily review of the Go/No-Go process by the project team can minimise this risk.
• Providing a ‘playbook’. Due to the nature of airside rehabilitation projects, there will be scenarios that occur during construction that have not been envisaged. With the constraints from limited possession times, there must be an agreed process to rectify these issues as they arise.
• A ‘what if’ manual can be helpful to identify and reduce risk and provide a sensible mobilisation period.
• It’s important that the entire project team understands the significance of the Airfield Ground Lighting (AGL) installation. AGL and civil engineering should be integrated as they’re not stand-alone projects.

Sustainable airfield pavements

The airfield pavement industry uses a mix of sustainable solutions to deliver durable and sustainable pavements. These include: 

• Designing to minimise thickness and use of materials
• Recycling and re-using materials during rehabilitation schemes
• Designing and constructing for durability to ensure longer life and reducing maintenance needs

The industry is continuing to develop innovative solutions such as low-carbon concrete incorporating graphene, sustainable additives like rubber and the production of low temperature asphalt. Polymer-modified binders (PMB) and asphalt reinforcement have been used on projects globally and provide savings in carbon emissions. Examples include Schipol and Dublin Airports, which reportedly delivered a CO₂ reduction during construction of 1030 and 230 tonnes, respectively.

Putting lessons learned into practice

Create and use lessons learned logs

• Review and document successes and failures for each project. Negative lessons learned are just as important, for example understanding what didn’t work
• Consider any previous lessons before starting a new project and incorporate them
• Get feedback on pavement performance over two, five and ten years and record it in your lessons learnt log

Share information with industry peers

• Share lessons learned in industry forums. A recent Airfield Pavement
• Engineering Forum organised by Heathrow Airport is a great start and should be developed
• Tap into trade bodies and industry institutions. For example, the British Cementitious Paving Association (Britpave) and the Institute of Asphalt Technology (IAT)
• Share your experiences via social media and industry events

By embracing lessons learned and integrating them into future projects, we can take a proactive approach to delivering the design and construction of durable and sustainable airfield pavements.

It’s critical to remember that documenting lessons learned is more than an exercise to develop a document at the end of a project—it should be integrated throughout the project’s lifecycle.