When a concrete sinks, it indicates a major problem. This can create an uneven surface that poses a safety hazard. A sinking concrete driveway can happen due to erosion caused by rainwater, removing the soil beneath the surface of the slab. It can also be caused by the characteristics of the soil to compress easily. This problem should be dealt with properly so that further sinking can be prevented.
Mudjacking: Mudjacking is very old, traditional way of raising the concrete driveway. It involves inserting wet materials under the concrete. Earlier mud was used as the wet material; hence it got the name mudjacking. Better alternatives such as cement and rock came to be used later, which gave better results. But this method has its own limitations as this not that durable and the problem may arise later due to groundwater.
Inserting grout micture: A core hole is made on the slab and a 12- inch deep hole is drilled through the core hole. A mixture of sand, silt, cement and water is made and this mixture is pumped into the core holes until the slab starts to rise up. The holes are then sealed using cement. This method is less expensive and more durable than mudjacking. But this cannot be termed as a long term solution as over time, small pores are created under the slab and there is chance of reiteration of the problem due to groundwater.
Polyurethane foam injection: It uses polymer foam to lift concrete slabs. It is a closed cell polymer and hence prevents water from being soaked up. This foam is injected into the ground under the slab through a hole. The foam has expanding properties. When it reaches the ground, reaction occurs and the foam expands. This makes the slab to rise up. It increases the density of the soil below it and takes about 15 seconds for the reaction to complete. Since, it does not retain any moisture, the water is drained out and there is no risk of erosion due to groundwater or running water. Since the injected polymer material cures itself very quickly, the slabs can bear the weight of any vehicles over it within a matter of minutes. The cost of this method is not very expensive and it is widely used nowadays. Its stability makes it a long term solution. It is more durable than mud or concrete mixture injections.
These are the main methods of repairing a sinking concrete driveway. There is always an option of replacing the concrete slabs with new ones. But that can be very expensive, so more affordable and efficient alternatives are chosen.