Concrete Lifting and levelling has been done for decades to repair sunken and uneven concrete instead of replacing it. Today, the use of polyurethane foam has become the new way to lift and level concrete. Sunken concrete can be repaired quickly and effectively using polyfoam and it is cheaper than replacing concrete. It also means that landfills will be unburdened by concrete that has been replaced by homeowners.
Prior to the use of polyfoam to lift and level sunken concrete people would use what was referred to as mudjacking or slabjacking. These traditional methods would use what was referred to as "mud" or slab slurry. So injecting cement slurry into the holes fills the gaps and voids beneath the slab stabilizing the soil underneath. The injection will also bulge the soil underneath the slab and lift it up and back to its original flat position if done right. This is where the name concrete levelling comes from as this process levels concrete slabs. When the drill holes and the crack lines are caulked after concrete levelling, slabs usually look as good as new.
The problem with these methods is that the void that resulted in the concrete becoming uneven and settling was potentially due to water erosion. Therefore, this slurry would erode again as well. That is the benefit of using the new method of polyurethane foam. Companies like Levelup Concrete Levelling, use polyurethane to lift and level concrete in Saskatoon and Northern Saskatchewan. They have been involved in using polyurethane foam for years including using it for spray foam insulation.