How do They Make Pre-Stressed Concrete?

They play hard rock music while it’s being poured. Sorry.

The strength of pre-stressed concrete doesn’t come from heat tempering, as in the case of windshield glass.

Pre-stressed concrete is concrete containing steel cables that have been subjected to tension, that is, that have been stressed by pulling on them lengthwise, before the concrete hardens. The cables then want to contract as if they were incredibly stiff rubber bands, but since they can’t, they keep the hardened concrete under constant compression.

In a sense, some of the stress energy from the original tension-pull has been locked into the structure in the form of compression, and that makes it stronger, because concrete is very strong under compression, but under tension it isn’t worth its weight in taffy.