IIRC from my material science course, if you really want to fuck up a batch of concrete, you should use salt instead of sugar, cause it'll crack the concrete with every freeze and thaw cycle.

Put a couple packets of sugar in about two quarts of leftover bag concrete once just to see how it went. Initially it acted like it had plasticizer and got loose and wet again. A day or two later it was acting like it had just set and a month later I could still crumble the edges off with my thumb.

Problems with using this for sabotage. Any serious project will have an engineer checking every truck and it will not pass unless the person adding water at the plant was in on it and did some very good calculations. Then the saved samples would immediately give them away in the investigation. During and after the pour there are too many people watching. I would have to say putting brown sugar and salt in the footing trenches the night before it’s poured or spraying (big puddles will get drained) a solution on top of the plastic to look like rain or dew.

Why does this work, exactly?

How much wall does one tonne of concrete give you? Seems like you need tonnes of sugar to properly do this

Breaking in the container office building thing and turning the blueprints upside down has better chances of success.

You'd need at least 10lbs of sugar per ton of concrete, probably closer to 40. If it's a full truck it's probably around 800lbs of sugar to ruin the load.

Is this to stop the Suburban Rail Loop for some reason?

Useless "literally"

You can pour sugar in a car's gas tank, it will really fuck up the car. Go ahead, test it with your neighbors. They will be pissed af, but as long as you don't have a flock camera around, just walk up with a mask n shit and they ain't knowing whst you do if you don't do what is that you be, obviously.