Q.: We built a 2-acre parking lot for a local shopping center. It was salted regularly during the first winter and by spring there was widespread scaling. The owner had some tests made that showed that the air content was very low in the scaled areas. We are surprised because we ordered air-entrained concrete. We've made a practice of having the air content checked twice each year by an admixture manufacturer and we've never had this kind of trouble before. Does this mean we can't count on the tests the manufacturer runs for us? Is there something else we should be doing to avoid such trouble?

A.: You can't count on one air content test to guarantee the air content in all the mixes you buy over several months. You can't even be sure that the air measured for one truckload will represent the air content in the next delivery, though the chance would be better.

When you're constructing outdoor flatwork that will be exposed to severe weathering, and particularly if deicers will be used on it, it's worth testing the air content at least daily. Some would say that making sure the air content is adequate is even more important to the life of such flatwork than making sure the concrete meets strength requirements.

The cost of air test meters is not high compared with the value of the information they provide. It doesn't take long to learn to use them, though it is true you must be sure to use them properly. The test only takes about 5 minutes. We think every flatwork contractor in severe and moderate (not mild) climates should use them regularly. An article that provides further introduction to air meters is "Every Flatwork Contractor Should Own an Air Meter," published in the September 1986 issue, page 801.