Effect of delayed placement of layers on permeability and durability of roller-compacted concrete containing fly ash

Interlayer cold joint formation in roller compacted concrete (RCC) structures is inevitable because of typically applied in layers. In this study, the effect of interlayer cold joint formation on the water absorption and freeze–thaw resistance of RCC with fly ash was investigated. After the first layer of specimens is placed and compacted, the second layer was cast with a delay of 0, 60, 120 and 180 min in order to investigate the cold joint effects. In addition, RCC specimens were produced by applying the mortar between the layers to prevent interlayer cold joint formation. Water absorption and freeze–thaw experiments were performed on RCCs. According to the test results, cold joint formation arising from prolongation of delay increased the water absorption of RCCs and reduced freeze–thaw resistance. However, the application of mortar is an effective method to overcome the interlayer cold joint. Besides, partial substitution of aggregate with fly ash in mixtures improved the workability, impermeability, strength and freeze–thaw resistance of RCC. However, although partial replacement of the cement with fly ash improved the workability and freeze–thaw resistance of some of RCC mixtures, it increased the water absorption and decreased the compressive strength.