Major highway concrete pavements in Iowa have exhibited premature deterioration. The Iowa Department of Transportation (DOT) has responsibility for determining the cause of the deterioration and implementing measures for avoiding similar future problems. The cause(s) of the deterioration has been the subject of much controversy. Various investigators have used different methods to characterize the processes and have arrived at different interpretations. The deterioration has been attributed to effects of ettringite formation (including delayed ettringite formation), alkali-silica expansive reactions, and to frost attack, or some combination of them. Evidence for all three processes have been reported. While one or more of these processes is likely to be the cause of the deterioration, the possibility that there may be other deleterious processes should be considered.