THE SUBJECT OF VARIABILITY OF CONCRETE making materials was first covered in ASTM STP 169C. It was derived from the work of the joint ASTM C01/C09 Task Group on Variability of Concrete-Making Materials. The Task Group provided the impetus for development of guidelines on determining uniformity of concrete-making materials, which eventually became ASTM Standard Practice for Determining Uniformity of Ingredients of Concrete from a Single Source (C 1451).