November 28, 2022

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Why do Britain’s roads melt and rails harden in the heat? | infrastructure

Extreme temperatures have led to widespread problems and disruption to Britain’s railways, as trains operate at slow speeds and main lines are closed. Airport runways and some roads have also shown that they can be subject to heat.

Railways

Steel bars expand and tend to bend in temperatures – whatever the climate. according to railway network, railways around the world are designed to operate in the 45°C range, depending on local conditions. In the UK, steel bars are pre-stressed to the summer temperature of 27°C, while in countries with hotter climates, the bars are pre-stressed to higher temperatures.

Sleepers and ballast must keep rails in place in winter and summer in Britain. When the temperature reaches 40°C, the bars can reach 60°C, stretch and twist. A train traveling fast over the rails can speed up this process through the heat generated by friction, and can be at greater risk if flexing occurs – hence the Speed ​​restrictions are widespread.

Overhead wires on electrified roads also expand and hang in the heat, and contract in cold weather. Engineers have solutions, with tension relieved automatically by a pulley system. But eventually, the counterweights hit the ground and the wires sag — making them more susceptible to tangling in the pantomizer, the device on top of the train that draws power from the lines.

roads

Highways and strategic roads have been built with modified asphalt surfaces that – until now – must not begin to melt, be flex after 60°C, or an equivalent air temperature of 40°C, according to National Highways. However, the basic asphalt materials used in domestic roads – the vast majority – can begin to soften at temperatures up to 50 ° C. At this point, “The road can become soft and greasy, and hard for cars to brake,” says Professor Xiangming Zhou, Head of Civil and Environmental Engineering at Brunel University. This is why councils have put rock trucks, usually used in icy weather, on standby to cover the roads with sand and dust. He says paved and asphalt roads are cheaper and less abrasive to tires than some materials, but because they are black, they tend to heat up more quickly in the scorching sun.

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About 4% of roads in Britain are built of concrete, which is more popular abroad for motorways and motorways and can be more flexible, but it is not immune to the problems of extreme temperatures, as the closure of the A14 shows. The Double Road near Cambridge was built with asphalt over old concrete slabs that expanded and curved in the heat, creating enough bumps to close the road overnight for emergency repairs.

Rick Green, of the Asphalt Industry Alliance, says the route to handle all temperatures presents a “huge challenge for design engineers”. At very high temperatures, “the surface does not melt, but the bitumen in it can soften,” “which increases the risk of deformation.”


airport runways

Again, some of them can be tangible – but LutonAsphalt was the problem once temperatures rose in the mid-30s, Chu says. In the airport’s words, “high surface temperatures caused a small part to lift” — a buckle in the runway that engineers fixed within hours, but still caused major disruption to passengers. While local roads are often shaded by trees and houses, runways are completely exposed and exposed to more heat stress from planes landing and taking off. Repairs and maintenance are frequent.

Heathrow, which was hotter than Luton on Monday, also had a runway problem last week, when overnight repairs were not completed in time to land the planes. However, it has two listings and has not been forced to halt operations.

so what It’s the solution

Network Rail already spends hundreds of millions of pounds annually on climate change mitigation. However, most of it is to counteract erosion or damage through rainfall or storms. Future infrastructure can be measured for a warmer climate – but then it may be more likely to fail and crack in cold winter weather when the bars shrink. Some track materials, such as concrete girders, are more resilient in wider ranges of temperatures and conditions – and are significantly more expensive.

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The bars are already painted white in critical places to combat the heat. Countries with extreme weather are making seasonal adjustments on a larger scale to track, which is time-consuming and costly. Air conditioning was not a standard feature of the old trains still operating. Flexibility would become an economic and political option – and a few days of heat breaks each year might be seen as preferable to the bill for adjustments.

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