We use a product here in OZ called Mr Crystal to repair leaks in concrete tanks and troughs
Basically you make a slurry and paint it over the crack and the product wicks in and forms crystals, stopping the leak and protecting the reo. If the tank is moving under load they tell you how to reinforce it with 2 rings of re-bar to stop the movement. One of our tanks has gone from leaking enough to bog a cow beside the tank to minor seeps, which I hope to beat eventually.
Now this is not a slab repair, but a BIL is a professional concreter, and they use a similar product to deal with surface cracks in slabs
For what it is worth