[systemjim]

I have wondered the same thing for years. The concrete used today seems to be SO deficient and has to be replaced every few years. Maybe that is the reason why? Planned obsolescence.

[Tom Tetroxide]

Scientists recently found out that Roman concrete is self-healing.
https://www.scientificamerican.com/article/ancient-roman-concrete-has-self-healing-capabilities/

If we can emulate this property our concrete will not break down and have to be replaced so often.