It’s customary to prefix these comments with credentials, so I’ll just say that I’m a roadway engineer. Sampling at the batch plant or even at the truck is not going to give you the whole story. While the most common crime of contractors is to overwater the concrete slurry to make it flowable, other problems in workmanship can arise from failing to vibrate the concrete in its forms, leaving voids, or vibrating it too much, creating segregation of the aggregate. If the finisher overworks the concrete or tries to correct the shape when it’s green, the that can compromise strength. If the concrete is finished too early, you can get delamination. If time allows and your contractor is careful they might protect the freshly poured concrete and let it cure wet. That makes a huge difference in cracking. There is also a whole world of chemical additives that structural engineers don’t even think about in the design process.

I’m not trying to say that mix doesn’t matter, or that I’m not pleased to see that Facebook is doing something a little more noble than surveillance technology, but as with a lot of construction issues, it’s just not that simple.