Concrete raising with polyurethane foam jacking

Concrete Raising with Foam Jacking

You’ve probably stumbled across uneven concrete slabs in your neighborhood. This is a common problem, especially if the concrete slabs are placed over soft ground. Fixing this issue isn’t as complex it may seem because replacement isn’t the only option. Concrete raising is a cheaper option as opposed to replacing concrete. One of the ways concrete is raised is by using polyurethane foam, a foam that expands instantly. This process is known as polyurethane foam jacking. Read on to learn more about how foam polyurethane can be used to aid in concrete raising.

Soil Load-Bearing Capacity

Another crucial aspect of concrete raising is soil load-bearing capacity. If the soils are weak or unconsolidated the weight-bearing ability of foam polyurethane isn’t effectively distributed into the ground. This is due to the fact that the soil, if not densified, will inevitably slip under the weight of the concrete. This, in turn, causes the concrete to become uneven once again. If soil densification is determined to be a necessary process, it’ll look something like this:

A lengthy inspection will be done to determine where the injections must be done in order to effectively densify the soil. A large 3-5ft square grid pattern will be laid out where the injections will be done at multiple depths.

The initial injections are completed at the top level in order to condense and strengthen the soil and use the concrete slab as a way of consolidating the top layers for the lower injections to work against.

The remaining injections are shot from the top-down, with each lower layer having the capability to densify against the denser top layers. This strengthens the overall weight-bearing ability and ensures that the slab will not slip back down by consolidating the lower soils over time.

Choosing The Right Type

There are two main types of foams that are used for concrete raising. The reactivity and density of the foam need to be determined before moving on with the concrete raising process. Here’s a guide to the two factors that come into play:

Reactivity

A foam that reacts slowly is typically used when a large void needs to be filled. The foam will spread evenly and thicker, allowing for more coverage. A foam that reacts quickly won’t spread evenly and won’t have the same amount of spread that is offered with a slow reaction. Having control allows the workers to ensure that the slab isn’t raised too much and lines up precisely with the other slab. This ensures the success of the concrete raising process.

Density

A foam that is much denser will be used if a larger weight needs to be born. If the slab doesn’t weigh as much and the void is large, a foam with a lower density will be used to fill in the void easier. Density is important to keep in mind as this determines the success of the operation and whether or not the polyurethane will be able to hold the weight of the concrete slab.

For Your Understanding

In short, though concrete raising is based around the environment, there is a basic process to it. Because polyurethane can be used to lift concrete in almost any area including foundation, sidewalks, driveways, steps, garages, pool decks, etc. it’s important to gauge the environment and reasons why the concrete slabs are uneven to begin with. This information will determine what kind of polyurethane will be used and what style of injection will be done. Slow reaction polyurethane is typically used for large voids to increase the spread and ensure an even rise. Density is also a factor that will be determined based on how much weight the polyurethane needs to bear. Polyurethane jacking is the most effective form of concrete raising and is far superior to replacing concrete altogether.

Analysis of Polymer Slab Jacking vs. Mud Jacking

We are often asked about the differences between mud jacking and the use of CST’s polymers for slab jacking. Below is a quick overview displaying what the key differences are between cure time, lift accuracy, footprint and lifecycle.

Production Savings:  Polymer Injection is 4 to 8 times faster than traditional methods and requires smaller crews.

Traffic Control Savings:  Total time required for closure is reduced 4 to 1 because of production savings.  Delay time before traffic may return to treated roadway after completion of injection is approximately 15 minutes.

Life Cycle Savings:  The Polymer Injection process has a minimum 4 to 1 advantage over conventional mud jacking’s life span of 1 to 2 years with a typical polymer 10 year warranty against shrinkage and deterioration.

CST Polymer Injection Traditional Mudjacking
PRESSURE OF INJECTION Low Pressure High Pressure
HOW IT LIFTS Chemical reaction creates expansion of polymer that lifts the slab. Fluid or Hydraulic pressure of grout lifts the slab.
CURE TIME Expands in less than one minute and reaches 90% strength within 15 minutes. Requires additional cure time of 4 hours or more to complete hydration.
ACCURACY OF LIFT Surgical precision lift to desired elevation is accomplished. An “over-lift” is necessary to compensate for water loss in the grout as it cures.
FOOTPRINT/PROPERTY IMPACT Small 5/8” holes, about the size of a penny, are drilled to inject polymer with no damage to existing concrete slab. Large 2 to 3 inch holes are drilled to inject high pressure grout. This can compromise the concrete causing breakout at the bottom of the slab.
LIFECYCLE OF REPAIR Permanent lift & stabilization is standard. Polymer material is guaranteed for 10 years. Longevity of lift/repairs is expected to last for approximately 1 year. University of Illinois Study 1985-1989.
COST IMPACT Savings over tear out and replace. One time cost. Ongoing cost due to need for rework/repair of same area.