A series of laboratory tests and a full scale test pavement are carried out to examine the effects of classified fly ash (CFA) on improving quality and work-ability of roller compacted concrete (RCC) pavements. From those experiments, it became clear that CFA can improve the compactibility, reduce the unit water content and increase optimum sand percentage. Furthermore, CFA can contribute to increase RCC slab thickness up to 35cm executed in one layer without loss of flexural strength in lower part of com-pacted slabs. These are desirable results to apply RCC for heavy duty pavements in airports and seaports.