Fixing Loose Joints
If you're responsible for a concrete pavement that supports highway trucks or forklifts, odds are good you'll face a problem with loose joints.
A loose joint lets the concrete slabs on either side move up and down independently of one another. Occuring outdoors on concrete highways and parking lots or indoors in warehouses and garages, loose joints cause problems when the traffic includes heavy trucks or hard-wheeled forklifts. They also cause trouble by:
- Increasing stress from traffic loading, leading to premature slab failure
- Spalling and chipping
- Damaging joint sealants
- Damaging vehicle tires.
A loose joint moves noticeably when a loaded vehicle drives over it. Other clues include knocking sounds and water or mud squirting up through the joint. Sometimes the joint is faulted, with one side sticking up above the other even when no load is applied.
What Makes Joints Loose?
Drying shrinkage, thermal contraction, slab curl, and sometimes subgrade problems can cause loose joints. One certain culprit: a lack of effective load transfer across the joint.
A good joint has the ability to transfer a vertical load. When you drive over it, the concrete may deflect but both sides move in unison. To achieve that, pavement designers specify load transfer devices often dowel bars or reinforcing steel, both of which have a good success record. Sometimes designers rely on keyways or aggregate interlock, though those methods are less dependable.
In contrast, a loose joint has little or no load transfer ability. Joints become loose when designers or contractors leave out the load transfer device, or when the specified device is inadequate.
Loose joints must be stabilized. The first step is to measure the deflection across the joints. Rarely do all joints in a pavement need repair. In a typical mix of loose and stable joints, you can leave the stable ones alone.
Once you have decided which joints need attention, you have five options:
- Total slab replacement
- Full-depth joint replacement
- Subslab grout injection
- Dowel bar retrofit
- Mechanical joint stabilizers.