There's like a thousand caveats to this though just as an aside. If someone realizes the concrete is tampered with, they're probably tossing the whole batch. It's better to be safe than sorry and they probably don't have time to wait for the lab report on what got added to the mix without their permission.

Not that I'm recommending that people do this, but if you wanted to fuck up concrete I'd think going for a compound that makes it cure faster would be the way to go. Too fast leads to more heat which leads to fractures in the concrete from the intense heat.