https://doityourselfrepair.net/what-are-chemical-grout-injections/

Concrete pavement can sink to certain areas on any property. This can create a tripping risk, and could cause problems for driveways and walkways. However, there is no need to replace your asphalt if this happens. Instead, you could fix the problem using chemicals to inject grout.

Concrete slabs are held by a solid base composed of dirt and gravel, which keep them level. If this base is disturbed because of water infiltration, burrowing animals, and other challenges, the concrete isn’t able to keep its level. It will instead fall into the uneven floor beneath it. The most obvious way to solve this is to use backfill to fill the gaps under the pavement.

In the past, it was a complicated project yet modern-day chemicals have provided a quick fix. It is a matter of create a concrete hole and inject the polyurethane foam under it. After the foam has been injected on top, it expands. The foam fully stabilises the dirt beneath the pavement and cures in minutes. You should be able to operate a car in just several days but you’ll also be in a position to walk even earlier.

Chemical grout injections can be an effective and fast method to fix the uneven surface.
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