Joint sealants facilitate construction as many components are made of different materials that need a joint to allow for movement of the structure but must keep water, air, heat cold and vapor-tight seal.
Every concrete slab has moisture and will always have moisture. Concrete is a porous substrate that allows the movement of moisture dependent upon the temperature and humidity. The moisture in concrete is from both internal and external sources. Most of the excess water in the concrete mix, which is not needed in hydration, will bleed from the slab during consolidation and evaporate as the concrete cures. The remaining moisture will reach the equilibrium with the surrounding environment.