When the horizontal and vertical loads generated by an earthquake exceed the ultimate strength of the concrete slab, inelastic deformation occurs. The most common manifestation of this is a cracked slab. When the floor absorbs a tremendous amount of energy, it cracks. Furthermore, cracking of the floor causes an increase of the natural period of vibration in the building, thus shedding the amount of energy the building is called to absorb.
It is imperative, therefore, that the cracks be repaired by epoxy injection to prepare the building for future seismic activity. It is unfortunate that some people refer to these cracks as "cosmetic." If concrete has cracked, it means that it has absorbed energy. If these cracks are not properly repaired, the concrete can no longer absorb energy, and some other element will be called upon to absorb the energy generated by a future earthquake, with possible catastrophic results.
The Epoxy is injected into the crack from a port once the port is full the epoxy reaches the next port. This process is repeated until the entire crack is filled.