This document discusses partial depth repairs of a concrete surface.
How to Make Partial-Depth Concrete Repairs
Partial-depth concrete repairs can be used to repair spalls, scaling, and joints where "D" cracking and alkali reactivity have been a problem, as well as other concrete distresses. This type of patching can be very effective when properly placed and should last for as long as the remaining life of the pavement.
The type of material needed for such a project depends on the amount of time allowed for the repair, air temperature, size, and cost. Materials such as concrete, portland cement grout, or epoxy resin can be used as the patching materials. (When using an epoxy resin, follow the manufacturer's recommendations for placement.)
The concrete in this area should be removed using pneumatic tools until a sound surface is found (see Figures 3 and 4). When removing concrete, it is important to use equipment that is properly sized. The pneumatic hammer should not exceed 30 pounds, to keep from fracturing the concrete and ultimately causing a compression failure below the patch.
The patch should then be cleaned, using either air or water blasting to remove any loose or foreign materials. It is important that the surface be completely clean so that the patch will adhere to it.
The cement content depends on the desired concrete strength. If an early opening is needed, 3,000 psi at 24 hours should be specified. For high early strength, a rich cement content (eight bags per cubic yard) or a Type III cement is suggested. Either of these two methods will work to get the strengths needed for an early opening. If immediate use is not important, then a mix design that allows for a longer curing period should be sufficient.
The maximum aggregate size should be as large as possible to compensate for shrinkage. However, it should not exceed half the depth of the patch. For example, if the patch is 2 inches deep, the maximum aggregate size is 1 inch.
The concrete slump should be roughly 2 inches, which will reduce the amount of shrinkage. Place the concrete in horizontal layers, allowing the final layer to overflow the patch slightly. Then, strike off the surface and float. Wait until all the bleed water is off, then trowel the surface to the desired finish. Begin curing as soon as finishing is completed. When repairing a spalled joint, the joint reservoir should be maintained using roofing felt or some other material, as shown in Figure 5.