Q: My brother has a large driveway and parking area in front of his house in eastern Washington state. The concrete surface is spalling, possibly from overuse of deicers. The concrete is a minimum of 6 inches thick with rebar. The concrete is structurally sound but needs to be resurfaced. Any suggestions of possible repairs short of removing the old and pouring new?
A: Spalling is defined by ACI 302 as deep damage of 1 inch or more in depth. The surface you are describing is probably scaling and almost certainly due to freeze/thaw degradation. Well-cured, air-entrained concrete can handle deicing salts but not always during the first winter. The mechanism is physical, not chemical; the salt accentuates the freeze/thaw damage. Osmotic and hydraulic pressures develop during freezing, similar to the freezing of plain water in concrete, but more severe. But can the driveway be salvaged? If the concrete is structurally sound, then it can be repaired with an overlay as long as the reinforcing steel hasn't been contaminated by chlorides and continue to corrode.
The first thing you'll need is an exterior-use overlay, which allows for movement of moisture vapor through the concrete and has air entrainment to protect from freeze/thaw damage. Choose one that goes down thicker (at least 3/8 inch) because it will cover up the surface defects.
Prepare the surface by removing all unsound concrete. Power wash and degrease the surface. Repair any severe damage with a repair mortar. Cracks that don't seem likely to move can be filled and bridged over by the topping but may still reflect through. Contraction joints will need to be honored. Mark them carefully and cut the overlay to the full depth to match the original joint pattern.
Install the overlay by dampening the entire driveway to get a surface-saturated-dry condition. Apply a scrub coat as a bonding agent—usually just a neat cement and water slurry that is brushed into the surface. Before it dries, apply the overlay. Most overlays are polymer concretes that set up within 20 minutes, so work in sections so it can be finished in that time. Install the overlay in the morning when it's damper and cooler.
Always review and rely upon the material manufacturer's technical data sheets. If a product doesn't have good documentation, don't use it.