The joints in our 4-year-old warehouse floor have spalled to different degrees--from minor edge chipping to more major ruts that are affecting forklift traffic. Can we just prepare the deteriorated areas, then fill the gap with a sealant or other material? Or do we need to reconstruct the slab edges and create a new joint?
Before repairing the joint, you should first determine if the deterioration is caused by a loss of subgrade support at the slab edges. If it is, simply repairing the spalled joint will probably provide only a temporary solution.Loss of subgrade support (often caused by slab curling) causes the slab edge to deflect when a forklift runs over the joint. The forklift wheels then impact the edge of the adjacent slab and spall the concrete (Figure 1).You often can detect slab deflections by simply standing on the joint while a forklift runs over it. To measure the exact deflection, consider using laser levels or dial gauges supported by Benkelman beams. Various rules of thumb can determine how much slab deflection is too much. References 1, 2 and 3 describe a few of these guidelines.Consider undersealing the joint to stabilize excessive slab deflections. Reference 4 contains excellent information on undersealing.Once you address the slab deflections, repair the joint spalls. Steve Metzger of Metzger/McGuire Co. (Reference 5) recommends repairing joint spalls less than 1 3/16 inches wide with an aggregate-filled semirigid epoxy joint filler (Figure 2). Use a semirigid epoxy with a minimum Shore hardness of A80 or D50 (ASTM D 2240). Add 2 1/2 parts silica sand to one part epoxy to give the sealant more deflection resistance. If the repair area is less than 1/2 inch wide, don't add aggregate to the epoxy.If spalled areas are wider than 1 1/4 inches, Metzger recommends creating a new joint by reconstructing the slab edges with a rigid epoxy mortar. After sawcutting and removing loose debris, insert a 1/8-inch-thick plastic strip into the joint. This will serve as a removable form. Mix a batch of neat epoxy and apply a prime coat to the bottom and sides of the repair area. Then add the recommended amount of sand to the liquid epoxy, mix thoroughly and apply the material to the repair area. Trowel the surface flush or leave it slightly high.After the mortar has cured, remove the form, clean the joint and install a neat semirigid epoxy joint filler. After the filler has cured, sand or grind the area flush to the surrounding floor.
Figure 1. Loss of subgrade support (often caused by slab curling) causes the slab edge to deflect when a forklift runs over the joint. The forklift wheels then impact the edge of the adjacent slab and spall the concrete.
Figure 2. Minor joint spalling can be repaired by routing and resealing the joint with an aggregate-filled semirigid epoxy. To repair more extensive spalling, reconstruct the joint edges with a rigid epoxy mortar and reseal the joint with a neat semirigid epoxy.
References1. Ron Bartelstein and Ed Weiner,
"Repairing Industrial Floors,"
Concrete Repair Digest, Spring 1990, pp. 7-12.2. Peter J. Nussbaum,
"Repairing Joints and Cracks in Industrial Floors,"
Concrete Repair Digest, April/May 1992, pp. 49-52.3. Bruce A. Suprenant,
"Repairing Curled Slabs,"
Concrete Repair Digest, December 1996/January 1997, pp. 296-301.4. John G. Meyers,
"Stabilizing Slab Deflection in Industrial Floors,"
Concrete Repair Digest, April/May 1992, pp. 57-60.5. Steve Metzger,
"A Closer Look at Industrial Floor Joints,"
Concrete Repair Digest, February/March 1996, pp. 9-14.