A recent popout problem in a Minnesota parking ramp shows how valuable petrographic analysis can be. The ramp is a multi-level, precast concrete, double-tee bar structure that was constructed during a fall and winter. Shortly after the snow melted, popouts were observed throughout the ramp. Six 4-inch-diameter concrete cores were sent to the laboratory for petrographic examination. To everyone's surprise, three other problems were discovered in addition to the shale in the cores. First, the entrained air content of all six cores was very low, averaging 1.6 percent. Second, the cores showed the classic overfinishing profile- in two cores the aggregate had subsided up to 1 inch from the top surface. Last, two cores showed dark gray bands of cement paste completely lacking sand-sized aggregate.