Could fireproof concrete have prevented Gotthard collapse?

The structure of the tunnel wouldn't have been damaged as severely if the concrete had been fireproof Keystone

Swiss engineers have developed a new type of concrete which they say can withstand the intense heat of tunnel fires.

The technology was used for the first time just four weeks ago in a small section of the Gotthard tunnel – where Wednesday’s crash and deadly fire occurred.

Parts of the roof need not have collapsed when temperatures reached 1,000 degrees Celsius, said mining engineer, Volker Wetzig, head of research and development at Hagerbach test gallery in canton St Gallen.

“The concrete certainly can’t prevent accidents,” said Wetzig. “But it could have saved the structure,” he claimed.

Normal concrete “spoils” at about 400 degrees Celsius. Tests have shown that the new concrete, which Wetzig and his colleagues have developed, can withstand temperatures of 1,350 degrees Celsius over a two-hour period. The high-heat resistance is due to the addition of polypropylene fibres.

Concrete is a composition of gravel, sand, cement and water. Under intense heat, water vapour inside the concrete begins to expand. When the water vapour can’t escape, the build-up of pressure is largely responsible for causing concrete structures to collapse.

“In addition, materials grow as you heat them up and that again causes stress on the concrete and damages the structure,” said Wetzig.

The solution lies in increasing the porosity of the concrete with polypropylene fibres. The fibres melt at temperatures of about 150 degrees Celsius offering a route for the water vapour to escape.

Some of the concrete in the Gotthard tunnel was replaced just a month ago with the new material. It was the first time it had been used out of the laboratory.

by Vincent Landon