'Cautious optimism' from Queensferry Crossing engineers after lab tests show cable cleaning has 'beneficial effect'

Laboratory tests have shown that cable cleaning on the Queensferry Crossing was found to have had a beneficial effect, but the bridge's operator says more work is needed to quantify the impact.

Engineers responsible for the Queensferry Crossing have expressed their cautious optimism at the results of recent tests of methods to mitigate against ice accreting on the bridge’s cables and towers following the £1.35 billion crossing's closure on a number of occasions since its opening in 2017 due to the effects of wintry conditions.

But more testing and monitoring on site will be carried out in the months to come.

The stay cables on the Queensferry Crossing's north tower were cleaned between September and November 2021. 

But the central and south towers were left uncleaned so that a comparison could be made over the winter period should any ice accretion occur.

Since then, the early stages of ice accretion have been detected twice, however on both occasions conditions had quickly improved and there was insufficient data to draw conclusions, as well as no risk to road users.

There were no further incidents of the conditions that previously required the bridge to be closed.

Cleaning of the cables was followed up in December by lab tests at the Jules Verne Climatic Wind Tunnel in Nantes, a specialised research facility which can replicate the specific combination of weather conditions that cause ice accretion to occur.

Cleaned, soiled, new and damaged sections of the high-density polyethylene pipes that encase the Queensferry Crossing’s cables were exposed to freezing temperatures, wind, sleet and snow inside a 6,000 square metre wind tunnel.

Tests had also been carried out on cable pipes coated with specialist icephobic coatings, omniphobic coatings, de-icing compounds and on a mock-up section of the Queensferry Crossing’s concrete towers.

Cleaning was found to be the best performing option for mitigating the build-up of ice on the cables and icephobic and omniphobic coatings were shown to reduce the build-up of ice on the concrete tower.

Chris Tracey, the South East Unit Bridges Manager for BEAR Scotland, explains: "We won’t know for sure until we experience another incident of ice accretion on the bridge itself, however these test results give cause for cautious optimism that cleaning may have a beneficial effect.

"Further tests are required to measure the extent of this effect under a wider range of conditions, and we will continue to monitor the cables closely on site.

"Tests of specialist coatings on the concrete tower also showed promising results, however further work is required to verify these results and to identify how these coatings might be used in practice.

"Ice accretion is not a problem unique to the Queensferry Crossing.

"Other major bridges around the world experience similar issues and we hope that the research and development carried out here will ultimately be of wider benefit."