How To Deal With Surface Concrete Repairs
Surface failures are one of the most common ailments in concrete, whether caused by freeze-thaw action, aggregate popouts, or corroded reinforcing steel. Many surface failures on concrete slabs are purely cosmetic; the concrete remains functional but looks poor or has a chalky surface.
With any repair, the first step is to diagnose the cause of the failure. If a slab has cracked due to poorly compacted subbase, an overlay will simply crack again. However, if the sub-base is well compacted, then the repair should be durable.
Types of Repair:
Full-Depth Repair – Cutting out the damaged concrete and steel and then replacing reinforcing steel, then the concrete.
Partial Depth Repair — Cutting around the edges of the damaged area (not the reinforcing steel), removing damaged concrete, cleaning or replacing the reinforcing steel, then applying a repair mortar.
Overlays: Effective to cover up surface problems—so long as proper surface preparation is used.
Regarding Surface Preparation
Most repairs fail because of poor surface preparation. All failed concrete must be removed to leave clean and suitably roughened surfaces. In any overlay installation or surface repair, what makes a “suitable roughness” should be specified using ICRI’s Concrete Surface Profiles (CSP) a series of nine roughness levels ranging from acid etched to heavy scarification. The best way to determine what these CSP levels look like is to use a set of plastic chips from ICRI that simulate the surface profiles.
There exist a variety of ways to remove unsound concrete including high-pressure water jets, sand blasting, grinding, scarifying, and, of course, old-fashioned impact methods, such as with scabblers and jack hammers. Beware! The greatest danger with impact methods is a possible bruising of the concrete surface—even though the surface may look like solid strong concrete, impact methods create a zone of microcracking.