Engineered wood floors can be glued down or floated over a dry, clean, fully-cured concrete slab that is on or below grade. If moisture or humidity is very high at times of the year, perhaps a non-wood flooring option would be a better choice. There are installation methods used by some hardwood installers to install a 3/4″ solid wood floor over a concrete slab, which includes a vapor barrier and building up a wood subfloor on top of the concrete slab. This is not recommended by most hardwood manufacturers–and it also adds considerable cost to the project. Installing an engineered wood floor over a concrete slab would be preferable.