isn't that why we call 'em 'control jnts ' ?,,, so the crk'll be where WE want it ?,,, even in 100k sf flatwork laser-screed plac'd, no random cracking,,, yes, conc's subject to great tensile & flexural force,,, that's why we have dedicated labor just for sawing,,, yes, it'll always be the issue 'cause that 1 random crack ruins everything.
we've dump'd 2k cy a day & its not always that 'perfect mix' every time, even j-mix or 1" slump from our own plant,,, so 'tween the 3 of us, make it something like 100 yrs,,, still learning, too, but its not uncommon in our field,,, & every pour's different,,, only 6yrs down south, btw,,, the rest was in the ne & middle atlantic states.