Blow-ups: Heat damage makes motorways dangerous to life

D a you have finally passed the 14-kilometer construction site and the round white sign with the sloping gray lines, accelerate - and then that:' Again, 80 km /h! 'No construction site, no narrowing of the lane. Just the regular staccato of the tires rumbling over the individual concrete slabs. What's that supposed to mean?

Rarely has a seemingly unfounded speed limit more justification: it might have saved a motorcyclist on the A93 in 2013. He drove on a hot runway at 160 km /h over a ski jump made of concrete parts suddenly breaking open - a 'blow-up'. The motorcyclist fell seriously and died.

There is a high risk of blow-up on hot days. Older concrete highways in particular are at risk. Also in 2019 there are corresponding speed limits with the record temperatures in June. The ADAC names the following:

• A9 Schkeuditzer Kreuz and Halle: From now on, 120 km /h applies here
• A9 towards Munich between Naumburg and Droy says and around Weißenfels is now 100 km /h
• A38 Merseburg-Süd and Merseburg-Nord (in both directions)
• A38 towards Leipzig between Lützen and the border with Saxony

In addition, according to the automobile club, the following motorway sections can be affected by blow-ups:

• A81 AK Weinsberg - Jagsttalbrücke Widdern (both directions)
• A81 Junction Boxberg - Osterburken (only driving north)
• A7 Ulm-Kreuz Feuchtwangen (both driving directions)
• A7 section south of AS Westhausen

Just a few years ago, a lot more motorway sections were affected by blow-ups, but most of them have now been renovated or made fit against heat damage through so-called relief cuts.

How does a 'blow-up' occur?

It's 2017 Josef Seebacher from the Southern Bavaria Motorway Directorate asked how the massive concrete slabs could burst. Blow-ups occur relatively often in southern Bavaria. In 2013 there was around 30 heat damage there alone. 'The problem with the old concrete roadways has been known for a long time,' said Seebacher.

There are dangerous blow-ups, especially on highways from the late 1970s and early 1980s. These highways consist of individual concrete slabs strung together. “In the summer, when the heat is up and in direct sunlight, the panels expand further than they can,” explains Seebacher. The joints calculated 30 years ago are not enough; the plates collide and push each otherup. 'You can imagine it like two paperbacks that are forcibly pressed together - at some point they push each other up,' says Josef Seebacher.

Compared to asphalt, concrete slabs have a particular problem: They are too hard, to deform. They break apart, stand up, and form the dreaded jump ramp. “However, that is the absolute extreme,” says Seebacher.

Where does the heat damage occur particularly frequently?

In principle, every roadway built with concrete slabs can break open, but does not have to. 'We have the problem with old routes that are not designed for today's traffic,' said Seebacher. The affected motorways were mostly planned and built before the unification of the FRG and the GDR.

Today, many expressways are used far beyond their actual capacity limits - with obvious consequences. The wear and tear is enormous, the risk of road damage high, not only heat, but also cold damage, especially on the A3, A92 and A93. 'These are our problem children', so Seebacher 2017.

All the more tragic that the motorcyclist died in 2013 on the A93, the 'best of the three high-risk motorways mentioned'. In 2017, the ADAC also warned of the A9 Nuremberg - Halle /Leipzig, the A10 Westlicher Berliner Ring, and the A94 Munich - Passau.

In view of such dangerous damage, the question arises whether the federal government and especially the Ministry of Transport have neglected the entire motorway infrastructure.

“We haven't done enough to maintain our highways.”

The answer is surprisingly clear: “Especially after After reunification, millions were shoveled into the east to build roads. That was more than necessary, ”said Seebacher, who assessed the situation in 2017. “But the cuts in the west mainly concerned the well-developed, intact infrastructure.”

Too short: Because the motorways have been left behind for so long, there is now an enormous repair backlog. 'We're trying to catch up,' says Seebacher. But there are various difficulties with this. Money is just one factor, says the road construction expert; but not necessarily the most important: 'For large construction projects there is only a limited number of companies that can handle this at all.' And ultimately, due to the traffic, it is not possible to repair all the highways at once. Society lacks acceptance for the urgently needed street care. “Citizens already have the feeling that they have to drive through a construction site every 500 meters.” Too often, therefore, people limit themselves to emergencies - such as the threat of heat damage.

What does the road maintenance department do against blow-ups ?

For the early detection of heat damage, a road maintenance depot monitors the motorway every day. Theis now also done by laser measurement. With this method, even the smallest cracks and bumps - usually the preliminary stage to major damage - are recorded. And what happens then? 'In Bavaria we act as soon as possible, often on the same day - at night,' says Josef Seebacher.

The affected sections of the route are milled off, and in some cases concrete is cut out of the slabs and covered with asphalt. “Then the panels will have enough space to expand again.” However, this is not a permanent solution, Josef Seebacher and his autobahn directorate also know that. Sawn panels lose their service life and become brittle and brittle at the cut edges. There is only one remedy for this: make new!

Asphalt is not a practicable solution everywhere

And even new highways will continue to be made of concrete. So with a blow-up guarantee? No. 'We use new construction methods, pay close attention to the quality of the concrete and use concrete slabs with greater thickness,' explains Seebacher.

One reason for continuing to use the currently hotly debated material: durability. “The concrete should last for 30 - 35 years. Normal asphalt motorways have to be renewed after 12-15 years at the latest, 'says Seebacher.

In this way we are lucky: At the moment 70 percent of our expressways are made of asphalt and only around 30 percent of concrete slabs. They will never completely disappear, just like the staccato when driving over them.