Talk about a fiery alliance -- that’s one. No wonder, then, that when a fire broke out in the Chunnel a few years ago cracks appeared in the concrete. Seems it was under pressure -- diplomatic and, yes, you guessed it, because of the gas laws. To make higher strength concrete, you increase the cement-to-water ratio in the setting mixture by adding silica and other fine particulates to the cement mixture. This is just the very technique that makes concrete waterproof -- but we’ll get to corrosion a little bit later.

Nevertheless, if it won’t allow water to penetrate, it won’t allow gas to penetrate, either. So when the concrete is subjected to very high temperatures (such as in a fire), the water inside the interstitial spaces of the concrete evaporates. But then it can’t escape, and the pressure builds up. Reminds me of microwaving eggs inside their shell.

Eggzactly! The concrete bursts from the generated pressure and the Chunnel becomes gravel. I don’t think that is the way it is cement to be.

Reference: Popular Science, April 1999, p. 46.