Q.: Can concrete be guaranteed for outdoor service in a cold climate where freezing and thawing occur, and if so for how long?

A.: If you are thinking about concrete in general, the answer is No. Some concrete will last for years and years, if not centuries, and other concrete will be disrupted fairly soon. If you are thinking of air-entrained concrete, the answer is Maybe. It depends on whether the concrete was properly proportioned, batched, mixed, placed, finished, protected from the weather if necessary during curing, and properly cured. If you are thinking of air-entrained concrete placed by an experienced contractor who takes all the necessary precautions to use concrete adequate for the purpose and to perform all operations properly, the answer is Yes.

In general, the main consideration in producing concrete that will withstand numerous cycles of freezing and thawing is to use a mix with an adequate air content. ACI 301-72, "Specifications for Structural Concrete for Buildings," makes recommendations for the amount of entrained air depending on the maximum size of coarse aggregate. But it is not enough to rely entirely on air content if the water-cement ratio is high, if low-grade aggregates are used, or if good job practices are not followed.

As for how long concrete that is properly designed and built can be expected to last in a freezing and thawing environment, it is hard to say. The first concrete street built in this country has survived the freeze-thaw environment of Bellefontaine, Ohio since 1891. This street was not made of air-entrained concrete, but it had such a low water-cement ratio that it has survived anyway.

It was in full use until 1960 when obsolescence and economics dictated covering parts of it with a topping.