Q.: I had a new concrete driveway poured in September of 2000. In January of 2001, I noticed that the very thin top layer is chipping and flaking. There seems to be sand under this thin, flaking layer. I live in central New Jersey, where the climate is relatively moderate. No chemicals or rock salt have been used on this driveway, ever. The flaking actually is occurring where there is no activity, such as driving or walking. The problem is spreading over other parts of the driveway. Could you please advise me what could be causing this.
A.: Your driveway will probably continue to scale with continued freeze/thaw activity. The durability of the concrete is the issue, which could relate to the mix design, placement, or lack of adequate curing. Regarding the mix design, inadequate air entrainment is often the issue. But occasional porous aggregate that retains water is also a frequent cause of flaking. When concrete freezes, the water in the aggregate expands, breaks the aggregate, and breaks away the cement cover over the aggregate. You will see part of an aggregate in the bottom of the flaked area if this is the problem.
Your contractor placed concrete with a high slump, durability would be affected also. If the surface was over-finished, air entrainment could be lost in the surface area of the concrete. And if the slab wasn't cured properly (or at all), the surface will be weakened and could be susceptible to freeze/thaw damage. Often however, damage requires more than one of the above errors. Unfortunately for you, the reasons for your concrete failure can be known only by cutting out a sample of the concrete and requesting a petrographic examination which is expensive.