The soil compaction method is widely used in the design of roller compacted concrete (RCC) pavements. The tools used in the compaction of laboratory specimens do not fully reflect the field compaction performance. Therefore, the mixture designed according to the soil compaction method in the laboratory may not be the ideal mixture for field application. In this study, interlayer cold joint formation and its treatment method, strength, and permeability of high volume fly ash RCC mixtures produced in the laboratory and field were compared. For this purpose, in addition to the control mixture, 60% (by weight of cement) of either cement or aggregate was replaced with fly ash (FA). In the laboratory, the specimens with and without 1 cm interlayer mortar were prepared in two layers and compacted by a vibrating hammer. As the preliminary field study, platforms 100 cm long, 80 cm wide, and around 40 cm (compacted) depth were produced from each mixture. The platforms were cast in open-air conditions and were compacted in two layers by using a 70x50 cm steel pressure plate with the same laboratory vibratory hammer. As a result of laboratory and preliminary field study the mixture where aggregate was partially replaced with fly ash was selected for the construction of a single layer (about 0.20 m compacted thickness), 7 m width, and 100 m length RCC road. The placement of the RCC in two layers, even without any delay in placement and compaction of the top layer, caused interlayer cold joint and subsequent reduction in the strength. Furthermore, Laboratory specimens with and without interlayer bedding mortar showed higher strength than the similar field (core) specimens. The fact seems to be arisen from the differences in the compaction, curing, and the nature of the cold joint between the laboratory and field specimens, as well as from the damaged caused during core drilling.