Aggregate and Sand Popouts

Popouts (pop outs) are surface defects that occur in concrete applications. It is important to recognize that popouts are not a defect in a concrete's paste, but rather in the aggregate (i.e. gravel, rock, etc.) itself. Moreover, these defects cannot be altogether avoided; they are a natural effect of the aggregates and sand used in concrete.

Most of the gravel and sand extracted in Minnesota was deposited during the last glaciation period about 10,000 to 15,000 years ago. Fortunately, about 98% of the gravels naturally found in Minnesota are hard enough and durable enough to withstand our climate's freezing and thawing processes. The remaining 2%, however, are not strong enough to survive our harsh circumstances intact, and consequently are prone to cracking

These particles include limestone, chert, shale, and others, which are already mixed in with the vast majority of otherwise durable gravel. The stress that aggregate is naturally subjected to in Minnesota includes the freezing of water within the rock's cavities. When that frozen water expands, the aggregate will often fracture the surrounding concrete. This is what's referred to as a popout.

The frequency of such blemishes can range from between one or two popouts per square foot, to more than a hundred per square foot. As a general rule, once any initial popouts have occurred, there will be no further deterioration.

It is also of note that some concretes will not contain popouts. This is largely due to the gravel pits from which those aggregates were extracted. In some cases, aggregate was originally deposited by standing or moving water, and some natural sorting may have taken place. Of course, a second, more determining factor will effect whether or not popouts occur: the exposure of that concrete to freezing and thawing.

Even by some of the most discriminating aggregate standards, including the American Society for Testing and Materials C33's specifications, popouts are a normal, expected characteristic of concrete manufactured with gravel and used in exterior flatwork in Minnesota.

If you have questions about cracking, popouts, or anything else concrete-related, Innovative Concrete can help. We invite you to call us at 952-292-2937.

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