In the US, on large structural projects, things are generally well-specified, either by standard code, or long before the project goes to bid. The owner (usual

In the US, on large structural projects, things are generally well-specified, either by standard code, or long before the project goes to bid. The owner (usually another firm representing the government that's paying for it) and the contractor inspect and measure all the work done each day. There are undoubtedly going to be mistakes and corners cut, but that's what safety factors are for and it's hard for problems like that to be endemic without some serious corruption. On a related note to using the wrong concrete, things like this can be an opportunity to see master craftspeople in their element. We had a truck of concrete show up and the foreman rejected it with almost no hesitation. "Why the f*&($ won't you sign on off this!?" the driver yelled. "It's smells wrong", said the foreman. Nobody else noticed anything amiss, but he was the boss, so the truck went back to the plant and sure enough, they'd mixed it wrong.