If the job is for a friend or family, get REAL BUSY VERY QUICKLY. If it is for an old customer, read sentence #1. If for a new customer, RUN, DO NOT walk away........ FAR FAR away. this from an ex mason contractor who was in the biz for well over 30 years.
If that advice is not a possibility, there are things you must determine/consider before going any further.
1 Why did the concrete crack.
* if it is really 2 feet thick, it could have started cracking while it was in the original cure. The cracks could be from shrinkage
Any time there is a thick pour, the concrete should be mixed as dry as possible as there is a lot of water t evaporate.
You are a woodworker, so you know what happens to wood that dries too quickly. The process is the same, but quicker, with concrete.
From your description and the proximity to a pool, i doubt that is the problem.
2 It could be from frost heaving
* since it is around a pool, i do not suspect frost heaving. however, you are in Montreal. a bit colder than my experience in Connecticut.
If it is from frost heaving, the cause for the frost heaving must be considered.
Is there proper drainage. If the problem is frost, the drainage is poor. That will not improve by covering the cracks with masonry
It won't improve with overlayment of any kind. the only way to improve the problem is a major excavation. Tear up the entire slab.
Or as mentioned in the first paragraph >>> RUN
3 It could be from settlement.
* I got involved with a couple of pool companies for about six months. You would be surprised at how many corners they will cut to meet a contract price.
They do not like to spend the $$$ to properly fill and tamp around the pool when a deck is going to be installed.
Building codes do not specify footing depth and size specs for terraces un connected to a building structure.
The main reason i only worked for the pools companies for six months was because i rfused to do any terracing unless the decks were to be properly supported by footings with proper piers for support. I did not last for long.
I am suspicious that there was excessive shrinkage causing minor (possibly major) cracking.
Once the cracks appeared, water seeped to the soil base, froze and expanded. FROST in Montreal!!!
How is that possible
It is most likely that the base fill settled and eventually, the concrete followed. I would not rule out a combination of all factors noted.
no matter what the cause, i would not ouch the project without first determining the cause(s)
I suspect a major demolition should be in store and hiring a well qualified concrete mason to pour a new deck.
If that contractor tells you he is only going to replace the slab without adequate footings and piers for support, find a new contractor.
Pool work can be very tricky and can contribute to very unhappy relationships.
sorry i did not see this discussion earlier. I hope you have not proceeded without looking into the cause factors very carefully.
PS I am in sort of a rush to go see GS play his first LaCross game. I will review this again later and add if i think necessary.