Question: Are you aware of a concrete pavement “serviceability index” that deals specifically with the acceptable levels of popouts, particularly in residential or commercial flatwork. ASTM D 5340 “Airport Pavement Condition Index Surveys” refers to in excess of three popouts per square yard but states that “no degrees of severity are defined for popouts.” Similarly SHRP-P-338 tells how to measure the number of popouts per unit area but states that severity levels are “not applicable.” I'm interested in any technical references to acceptable levels of this type of distress.

Answer: Dave Robson, chair of the Alberta Ready Mixed Concrete Association's Technical Committee, responded that popouts due to unsound aggregate are an issue in most areas. The problem aggregates vary widely from place to place. Coal, ironstone (ochre), and shale are some of the more common. The number of popouts considered excessive also varies, depending on the local aggregates. Some locations are infamous for popouts, and it is difficult to state how much is too much. Other agencies specify limits on unsound material content of 0.8% to 1.0% by mass of dry aggregate. The ARMCA has attempted to come up with a general limit for most areas, and numbers of one popout per square meter or even one popout per driveway panel (about 6 m2) were discussed. We did reach a consensus with the following concept: If you can count the popouts quickly, there is no issue in areas where popouts are common. However, if the count is many, and a whole bunch more, then it is likely an issue.

Gregory Johnson notes that the important thing is that popouts are an aesthetic issue, not a serviceability issue, and that a pamphlet developed by the Minnesota Aggregate & Ready Mix Association is available at

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Aggregate Research Industries' Web site ( includes topic-specific forums where forum members can pose questions and respond, creating an interactive discussion group. All questions and answers in this Problem Clinic are based on ARI concrete construction forum postings.