PoolStructuralQ I was taught in engineering courses that conventional concrete should not be counted on to carry tensile stress. For steel reinforced concrete, the reinforcing bar is designed to carry all tensile loads. Although concrete obviously has some tensile strength, it is too low and prone to cracking failure to consider it in design. In fact, I believe you can assume it is cracked from the shrinkage during curing. Is gunite treated the same way? I have a pool that is developing a crack through an elevated wall/beam and down into the plaster to the bottom floor at the sun shelf. I witnessed the plumbers cutting some rebar in the beam to allow for PVC plumbing to water sheer (up at top of beam, just under the tile topping) and I worry this is the root cause along with settlement that put the top of the beam in tension. The rebar down low should be intact and I hope the crack width may stay minor down in the plaster. On top of the tiles beam where the maximum tensile stress would have been, the crack is fairly wide. The crack movement opened up a gap in the grout line between tiles of about 0.08 to 0.10 in. (2-2.5 mm). I think it was a real sin for them to have cut the rebar. If it is necessary to reinforce the tensile side to halt future movement, I would think cutting a slot or two in the gunite across the crack (say 12 in. [300 mm] each side. Up high just under the water sheer) and epoxy a rebar in the slots.
Shotcrete, both dry-mix (gunite) and wet-mix are a placement method for concrete. Wet-mix uses premixed concrete while dry-mix simply adds water to the concrete materials at the nozzle. Both dry-mix and wet-mix with proper materials, equipment, and placement with produce quality concrete sections. The embedded reinforcement in the pool shell is designed to carry tensile loads. This may be bending stresses from structural loadings (settlement or water/backfill), or volume changes from drying shrinkage and temperature changes. Cutting a reinforcing bar would certainly negate its ability to carry loads in the vicinity of the cut and reduce the load carrying capacity until the development length allows the reinforcing bar to start carrying it full load.
The layout of your cracked section isn’t clear from your description. An 8 to 10 mil (2 to 2.5 mm) crack is sizable in a water-containing structure. Fixing the existing crack with a reinforcing bar epoxied in place across the crack may be effective. However, that solution would only carry any additional load on the section (structural or volume change), as the existing loads have already created cracks. Thus, you should also address filling the crack as part of the solution. This may be with epoxy injection or swellable polyurethane grouts. You should consult with the pool design engineer for their recommendation on the best method for repair.
