Future of Airports | GPS aids Brussels runway resurfacing

Belgium’s Brussels Airport handled more than 26M passengers in 2019 – a record breaking year. But despite these passenger numbers plunging by 74% in 2020 due to the Covid-19 pandemic and accompanying travel restrictions, operator Brussels Airport Company is focused on future proofing the airport’s infrastructure.

At the heart of this is a major refurbishment of one of the airport’s three runways. Previously upgraded in 1996, runway 07L/25R was resurfaced during a 41 day closure, with the project team working around the clock.

Replacing asphalt

Across the surface of the 3.3km long by 60m wide runway, the top layers of asphalt have been milled and replaced. 

Brussels Airport Company appointed main contractor Willemen Infra to deliver the project, with specialist subcontractor Top-Off brought in to undertake the milling. 

The project involved resurfacing the runway with asphalt across 222,000m². A total of 60,000t of asphalt was used for the project, which was milled at a rate of 10,000t a day. 

A smooth runway is crucial for safety during landings and take off, but is also important to reduce wear and tear on aircraft. Topcon’s 3D Millimetre GPS system was selected to help ensure that smooth and accurate milling would create the perfect foundation for the runway surface. 

Speed was of the essence for the project, with the airport operator keen to ensure the runway was fully operational again as quickly as possible. But as well as overhauling the runway itself, a series of other works was also completed at the same time including installation of a new drainage system and a new LED lighting system. Successful completion of the milling phase was key to ensuring that the other phases of the project could progress on schedule. 

If there was a delay with the milling, it would mean the other stakeholders would not be able to do their jobs

Milling was the first phase of work to begin on site. 

“We worked closely with Top-Off to see how we could offer the best solution for the site by equipping the milling machines with the right system,” says Topcon Positioning Belgium support specialist Arnaud De Cnijf.

He explains that the 3D Millimetre GPS system involves automating the elevation of a milling machine by equipping it with a hydraulic valve assembly, GPS receiver, sensors and a control box. A base station which connects to the GPS system on the milling machine via radio frequency was also set up at the centre of the site. 

“The base station gives us the exact position X and Y of the machine. Then around the job site and along the runway, the team set up control points where we have a laser [transmitter],” says De Cnijf. 

If the laser beam is interrupted – by a vehicle movement on site, for example – the 3D system can continue operating for a few seconds based on its last corrections. 

Lasers focus

Five lasers were set up, each capable of guiding several milling machines simultaneously. “This allows us to select different positions using the same laser signal and helps to increase productivity,” De Cnijf adds. 

“We could connect multiple milling machines to the 3D Millimetre GPS system, which was a real advantage for this project in terms of time. 

“If there was a delay with the milling, it would mean the other stakeholders would not be able to do their jobs. So, completing the work on time was very important.”

A combination of 3D milling and the traditional 2D method were used, allowing the team to utilise milling machines that were not equipped with the 3D Millimetre GPS technology alongside those which were. 

If you use the 3D system, it is a lot smoother and more consistent, so the top layers of asphalt will also be smoother

The traditional 2D approach requires the milling machine operator to control its elevation, whereas Topcon’s 3D system automates that process and adds greater accuracy. 

Top-Off CEO John Vastmans says: “We are milling the surface with two 3D machines leaving a pass of 3.8m wide in between. This pass will be milled with the 3.8m milling machine, without 3D guidance installed. 

“Due to the two passes, the 3.8m machine will follow the 3D milled design left and right with its [averaging] skis. This enables the 3.8m milling machine to actually mill in 3D without having a system physically installed.”

De Cnijf believes Top-Off made the right choice to combine the  two approaches and exploit the benefits of the 3D system when using the 2D method. 

Using the 2D method for the central pass was cheaper as this machine did not have to be equipped with the 3D GPS system, but use in combination with the 3D gave the precision needed.

Smoother and more consistent

He says: “With the 2D traditional milling principle, there is always some unevenness which means there will be some unevenness in the asphalt layer. If you use the 3D system, it is a lot smoother and more consistent, so the top layers of asphalt will also be smoother.” 

De Cnijf adds that the 3D system also benefits the operator. 

“It’s a lot easier for the operator because they just have to make sure that they’re going in the right direction. They don’t have to raise or lower the machine, they just control the direction,” he says.

With around 1,000 workers involved with the runway renovation and various types of heavy equipment and moving vehicles on site, De Cnijf says collaborating closely with the key stakeholders helped to ensure the work progressed smoothly. As such, the milling phase of the project was completed 12 hours ahead of schedule. 

Following surfacing with the new asphalt layers, along with the new drainage and LED system, the runway returned to normal operation just 41 days after the work started. The project has extended the runway’s life expectancy to 2035, ready for passenger numbers to begin returning to pre-pandemic levels in the years ahead.

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