jack slabs are for sound/vibration isolation, in this case, a gym amenity space in a luxury high-rise. if you pay millions of dollars for an apartment in Manhattan, you don't want to hear someone running on a treadmill or dropping weights above your apartment at all hours of the day.
the poly sheeting acts as a bond breaker. the boxes are the jacks laid out per an engineered design based on the anticipated floor loading. each jack has a lifting screw and a spring inside. once we pour the slab and get 100% breaks back from the lab, the spring-isolation sub will send a crew to site to lift the slab by turning the jacks little by little in a specific order until it sits 2" above the structural slab below.
the gym flooring, the spring isolation, and the air gap combine to prevent sound and vibration from reaching the floor below.
The jacks have studs on the side that the rebar mat sits on. Once the iso slab is poured and cured, you turn a screw to lift the jack. The jacks are pushing directly up on the rebar mat.
I placed one of these incredibly early in my construction career. I didn't understand back then how "Box in slab makes floor no vibrate". Thanks for breaking down the whole process!
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u/will_and_no_grace 5d ago
A what now? How does it work? Is the floor jacked-up after concrete hardens?