More concrete on top alone will increase the slab strength if the bottom steel is in tension. If the top steel is in tension, they will need to add a layer of top steel in the topping. They can make the correction by scarifying the top surface. Add a bonding agent. Add a layer of top steel where needed. Place a topping concrete overlay.
“It may”. (increase strength)
You sound like you know more about the specifics than I do, me being only casually acquainted with a modest number of foundation pours, walkways, strictly residential stuff....although mostly in CA and EQ standards have REALLY cranked the req’ments in recent years. My brother just built an addition onto his house, single story but rather on a hill, with slidy clay soil, to boot. 600 sq foot addition, I think there were 16 qty 24” diam piers drilled 18’ below grade. There was a hell of a lot more 1” rebar (in quads) than I ever thought I would see in a residential build.
Personally, I belong to the school that says steel is very cheap and it is foolish to even come close to scrimping on it.
Nevertheless...I still say it would not be easy to add a 2.5” think “frosting” layer to an existing pour and have embedded steel well centered in the pour such that much add’l strength would develop. I think such a pour would have to be managed with a hell of a lot more skill than the current contractor exercised. And be subject to bad cracking over voids. I don’t know if it snows in MD thus implying freeze-thaw and salt but that is bad stuff when it comes to concrete and maybe that’s why the super fat slab was spec’ed in the first place. I agree that amazing things can be done with adhesives, but color me skeptical that the original as-spec’ed strength could be achieved with a frosting layer.
The issue with busways is that if cracks develop, you end up with heavy buses pounding and pounding on the divots in the surface.
Mentioning San Onofre nuke construction, back in my concrete (minor structures) construction days, reminds me of the time I was talking to a labor that worked on that project.
Seems when pouring one of the domes, after every section poured, it was x-rayed. Small bubbles were appearing, enough to at first recommend more extensive concrete vibration. Further pours and x-rays showed the same bubbles, enough to change the mix design besides the extensive concrete vibration. Further pours and more x-rays, bubbles still constantly appearing throughout the pours.
Finally due to stringent quality control for nuclear plant construction a section of a newly poured concrete showing these bubbles in x-rays was remove and sent to a lab for analysis. Result and recommendation that came back was to prevent concrete labors from spitting shells from sunflower seeds during the pours.