Q.: Why do we occasionally run into concrete pavement buckling on hot summer days? So far as we know there is no trouble in our area with expansion from reactive aggregates.

A.: Theoretically this shouldn't happen because, after normal drying shrinkage, concrete seldom becomes larger than its size when cast. Buckling does happen in practice, however, and the usual cause is that foreign material has been worked into the joints so that they no longer function properly. The foreign material could be pebbles that have penetrated the joint sealant or dirt and debris that have intruded after joint sealant has been torn out. The more wide open the joints when they become filled with foreign material, the greater the stress when they try to close in hot weather. Ultimately this causes some joints to buckle or "blow up" in the hottest weather. The problem seems to be worse on pavements that have longer distances between joints. Prevention is a matter of keeping joints well sealed and clean.