Concrete Leveling 101
Concrete leveling refers to correcting uneven or sinking concrete slabs. This is done through a variety of methods that alter the foundation that is beneath the concrete surface. It is less expensive to level concrete than to remove and replace the slab. Concrete leveling can be used in residential, commercial, and municipal applications. Homes, warehouses, roads, shopping centers, airports, and more can all be helped with concrete leveling.
What Causes Concrete to Settle
There are several reasons that a concrete slab can settle. If the soil isn’t properly compacted during construction, it can compress or settle once the weight of the structure is placed on it. This could happen relatively soon or gradually over years. Another cause is soil that is either too wet or too dry. Oversaturated soil can swell and heave, putting tremendous pressure on the concrete. Soil that is too dry can shrink and crack, no longer providing strength and stability to the concrete above. If the area around the concrete doesn’t drain properly, the soil beneath the slab can erode, washing the support out from under the concrete.
Other causes that can damage concrete are tree roots that push against concrete slabs and seismic activity. Both of these can cause slabs to crack, move, or otherwise be damaged.
Methods of Concrete Leveling
Just as there are several causes of concrete settling, there are different ways to stabilize and lift the slab. Although the methods are different in cost, application, effectiveness, and time, the result is a level concrete slab. These methods all fall under the category of “slabjacking”. The premise is to lift the concrete by pumping a mixture through holes in the slab, lifting the concrete from below.
The initial injection fills the voids beneath the slab. Once the voids are filled, the remaining injection lifts the concrete. The holes are then patched and the project is done. All slabjacking methods take less time, cause less disruption, and cost less money than tearing up and replacing the concrete. Slabjacking is not an option if the concrete is too damaged. If there are too many cracks, you may be forced to tear up the old slab and replace it.
There are three types of slabjacking.
Stone Slurry Grout Leveling
This type of slurry is made from pulverized limestone, water, and Portland cement. This slurry is thick and pumped through holes that are around 1″ in diameter. The slurry is pumped below the slab, filling the voids below the concrete. Once the void is full, the slurry begins exerting pressure on the slab, lifting the concrete into place. An expert operator can precisely lift the concrete to the desired height without cracking the slab. When the concrete is level, the hoses are detached and the holes are filled.
The stone slurry grout has a compressive strength of 240 psi. If Portland cement is added, the compressive strength jumps to an amazing 6000 psi. Once the slurry dries, it forms a near-solid stone foundation. This method has the highest compressive strength of all the methods described here. Stone slurry grout takes more clean-up afterward and uses bigger holes than polyurethane foam. The slab that is being lifted usually has to be within 200 feet of the truck that is pumping the slurry.
Mudjacking uses a mixture of soil, sand, water, and cement that is injected through holes drilled in the slab. Other materials may be added to the slurry, including clay, limestone, fly ash, masonry cement, and pea gravel. The holes are typically larger than the ones used for stone slurry grout and polyjacking, coming in around 1 to 2″ in diameter. Like stone slurry grout leveling, the mudjacking slurry is injected through the holes beneath the slab. A portable pump is usually used, allowing better access to the slab than stone slurry grout leveling. When the void is filled, the remaining slurry builds under the concrete, lifting the slab. Once the concrete is level, the holes are filled and the project is complete.
The weight of the mudjacking and stone slurry grout can compromise soil that is already weak, causing more problems down the road. It also involves more clean-up than polyjacking and uses the biggest holes of the methods described here. This is also the slowest process of the three.
Expanding Structural Foam Leveling, or as we call it, polyjacking uses an expanding polyurethane foam in its injection process. The polymer is a combination of two different materials, that, when combined cause the mixture to expand. The holes needed for the injection are around 5/8″, the smallest of all the methods. The expanding foam first compresses any weak soil it encounters, consolidating the sub-soil and causing it to become denser. The foam then fills any voids beneath the concrete. Lastly, once the void is filled, the foam will lift the slab to the height needed for it to be level and stable.
The foam moves throughout the underside of the slab, expanding in all directions, filling the area below the concrete. The foam is also hydrophobic when cured, preventing heaving from occurring in freezing temperatures and avert erosion. The clean-up process is simpler than mudjacking or stone slurry grout leveling, uses smaller holes, and uses smaller equipment that can reach places trucks may not be able to access.
Contact the professionals at Polyjacking.com to learn more about the benefits and advantages of leveling your concrete with our method.