During the summer of 1999, a concrete contractor placed an exterior parking lot for a commercial building in the Midwest. The concrete was air entrained and received a broomed finish, followed by 3 days of moist curing with plastic-coated burlap. Because some of the concrete set at a different rate than the surrounding concrete, the appearance of the broomed finish wasn't uniform and "soft surface conditions" were reportedly exhibited. The parking lot owner questioned the quality of the concrete, and had cores sent to a test lab. The petrographic report stated that the coarse aggregates were generally sound but the entrained-air content in the top 1/4 inch of the two samples was inadequate to resist freeze/thaw damage. The petrographer further concluded that freeze/thaw damage was expected to be a problem for the concrete slab.
Based on results from the initial petrographic report, a decision might have been made to remove and replace the parking lot. But we conducted our own tests, which indicated that the parking lot could perform adequately for some time. The results from our investigation showed no problem with the near-surface air-void system but did show frost-susceptible coarse aggregate. However, scaling tests indicated good performance of the finished surface, despite the coarse-aggregate problem.
