concrete spec. for hot tub

huangyhg

concrete spec. for hot tub
i have been tasked with designing the reinforcing for a custom in ground hot tub, as well as the type of concrete to use.  i am considering a sand/gravel mix.  is a silica concrete necesary?  the hot tub is outdoors in the plains area of the u.s. (freeze/thaw), so air entrainment is typical.  shotcrete construction is not going to be used.  typical formed concrete walls with integral concrete seats.  i am planning on a slab foundation, water bars at all pour joints (vert. as well as hor.), and drain tile around the perimeter.  there are three floor heights, so there will be sand fill below the slabs as well as drain tile on the interior.  the slabs will be tied into the walls with reinforcing (and water bar).  does anyone have anything to add?  should i consider the use of fiberglass reinforcing for the slabs instead of welded wire mesh?  would the use of epoxy coated rebar be considered?
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you may want to insulate the tub base and sides if frost heave is an issue, or have founding of the sides below frost level.  floor can be cast on a void if soil heave is an issue.  i'd probably opt for epoxy coated wwm or rebar, just to minimize any rusting stains if rebar is too close, or if a minor crack occurs.
use absolute minimum slump to minimize shrinkage and cracking.
the footing slab will be frost protected.  the void below the elevated slabs (floors) is included.  convincing the contractor to use epoxy coated rebar will be challenging.
are you making the inside surface out of concrete or are you looking for a shell to hold the tub and a base to set it on...
i have to admit, i'm confused.
the hot tub will be constructed of concrete entirely.  it is designed with 3 elements.  the upper element flows into the middle element (this will have seating).  the middle element folws into the lower element.  the floors of all three elements are elevated above the foundation slab.  seats in the middle element will also be made of concrete and be poured integrally with the wall (i hope).  i hope that the concrete that is exposed to water is somehow protected (cover or coating).  any further information from someone who has experience with this type of project is appreciated.