Steel needs to be cared for. It needs to be sanded, inspected and painted. I worked on elevated roadways doing just that. I have never heard of tensioning concrete after it is dry enough to put in place.
“I have never heard of tensioning concrete after it is dry enough to put in place.”
post-tensioning concrete is a very standard technique:
https://www.google.com/search?q=post+tensioning+concrete