First time I heard of the sugar trick was when the teamsters union was on strike against a local cement plant. They would randomly figure out a way to toss a bag in a ready mix truck driven by management between the plant and the delivery point.
At least they only did it to trucks doing street paving jobs and not any doing structural building pours.
Major paving contractor had to rip up a few sections of pavement on a major road project and re-pour as the concrete did not meet the lab tests due to the sugar.
