Concrete is probably as close to a wonder material as we’re ever going to get. It’s extremely strong, cheap, versatile, and long-lasting. The Romans used it to build many of their oldest surviving structures, and it was so crucial that people spent hundreds of years trying to recreate the recipe after it was lost to history.
But concrete does have one big weakness: fire.
When concrete is heated to extremely high temperatures, it can actually explode. Those explosions can have pretty significant consequences when a fire breaks out near a concrete structure, but the actual process of how the blowups happen isn’t very well understood by scientists.
New research, however, attempts to change that by recreating these explosions in a lab.
In the study, Swiss and French scientists made their own high-performance concrete and heated it to several hundred degrees. Then, they filmed it with a standard camera and used neutron tomography, which resulted in a three-dimensional image of the exploding concrete.
Take a look at their camera footage:
The researchers already knew that these explosions were caused by evaporating water vapour trapped inside the concrete. The water expands as it heats up, and eventually, the pressure reaches a critical point where the structure shatters. But in this study, the scientists pinned down the exact mechanism.
Here’s what happens: When the concrete is heated, the cement inside becomes dehydrated, losing some of its water as vapour. That water vapour begins moving away from the source of the heat but becomes trapped inside the structure of the concrete.
Typical high-performance concrete is extremely non-porous, so eventually, the water vapour runs out of places to expand. When that happens, pressure starts increasing—and an explosion is only a matter of time.
Armed with that knowledge, the researchers were able to develop a collection of additives that could work to prevent these explosions from happening, making concrete safer when heated up.
That’s good news for firefighters who work near concrete. In the future, they won’t have to worry about entire structures exploding on them while putting out fires.
Originally published on Popular Mechanics