Void Grouting

CJGrout Geotechnical Polyurethanes

void grouting

Void grouting refers to pumping grout into voids in and around structures or in soil. Unlike permeation grouting, which addresses the inherent voids between soil or fill material particles, void grouting generally refers to what we call bulk voids, or large cavities. Something’s usually referred to as a void because it’s not intentional, such as a large cavity below a floor due to a plumbing failure, or outside of a structure due to erosion.

Depending on the characteristics of the void and structure, different types of grout are most appropriate. Most void grouting work is done with geotechnical polyurethanes. Sometimes, for very large voids that have well-defined boundaries, CJFill cellular concrete is most appropriate.

When Grouting is Appropriate

If you can dump stone or flowable fill into a hole from the surface and have confidence that it’s full, grouting usually isn’t needed. When there’s an overhead floor, structure, or other obstruction, grouting is best. Grouting uses self-consolidating materials that are installed with pressure (occasionally just the head pressure of the liquid grout). This helps ensure complete fills where mechanical compaction isn’t possible.

CJGeo uses two different types of low density grout to perform void grouting: geotechnical polyurethanes, and low density controlled low density material (cellular concrete).

Geotechnical Polyurethane Void Grouting

Filling voids with structural polymers is the most common method.

What CJGrout Polyurethane Is Best For

  • Voids in and around occupied structures. Polyurethane grouting is by far the cleanest, least disruptive grouting process. Injection holes are only dime-size, and the grout cures within a few minutes. After curing any grout that escapes the void can be trimmed off and carried out by hand.
  • Voids over underlying compressible soils. Polyurethane grouts are strong, but very lightweight. Most weigh less than five pounds per cubic foot. This facilitates filling voids without adding more than nominal loads to underlying soils. The most common bulk void filling grout CJGeo uses is CJGrout 20SDB, which only weighs about two pounds per cubic foot, but provides 3,500 pounds per square foot of compressive strength.
  • Poorly-defined voids. A big downside of grouting voids with cement-based grouts is how long they take to set up (often hours). Polyurethanes are very highly mobile to ensure coverage into even the smallest of voids and cavities. They then set very quickly, which reduces the likelihood of them going where you don’t want them to. If you’re familiar with cementitious grouting, polyurethanes have the mobility of microfine for up to a few minutes, then over a few more minutes lose all mobility and reach 95% of ultimate compressive strength.

Cellular Concrete Void Grouting

Cellular concrete is a highly mobile, low density cementitious grout. Using the dry batch method, it’s pretty easy to make and place up to 200CY/hour of cellular concrete, which the American Concrete Institute calls low density controlled low strength material.

What CJFill Cellular Concrete is Best For

  • Filling massive voids. There are pretty strong economies of scale with cellular concrete. If voids are hundreds of cubic yards, cellular concrete can be an excellent choice.
  • Well-defined voids without the potential for leaks. Cellular concrete is one of the highest mobility cementitious grouts. If a void is well defined and contained, cellular concrete may be a good choice.
  • Less sensitive sites. Cementitious grouting can be pretty messy. While not great for occupied structures, it’s well-suited for infrastructure applications where a bit of mess isn’t a problem.

Speak With An Expert

Facing a void grouting challenge? Give us a shout or shoot us a text. Click the state marker for the location of the project for contact info for the appropriate rep.