Study On Specific Characteristics And Qualification Requirements Of Lift Joints In Roller Compacted Concrete

Roller-compacted concrete (RCC) is probably the most important development in concrete dam technology in the past quarter century. Since the emergence of Roller Compacted Concrete, it has been widely used in water conservancy works, and the application expanding to larger and higher dam field is also in the ascendant in China and other countries. Generally speaking, the dam construction technology for Roller Compacted Concrete is successful. Horizontal joints are inevitable in mass RCC because of its layered or lift method of construction, the leakage of RCC lift joints is very common experience if treated improperly. Therefore, the quality of bonding and the leakage between lift joints of RCC have become a key technical problem in civil engineering communities. Studying the characteristic of bonding between lift joints of RCC and establishing qualification requirements have important realistic significance and construction project value on RCC dams.In this paper, the setting mechanism of RCC is analyzed theoretically, and the several test methods of setting time of RCC are compared. Under simulated conditions, the effect of set-retarding compound in high range water reducing agent on setting of RCC mixture is evaluated. When fresh RCC lose thixotropy, the initial setting is beginning. RCC is a concrete that is characterized by lean cementitious material and dry consistent, a criterion for initial setting time was set up when the resistance penetrated into RCC mixture reaches 4MPa～7MPa. This method greatly lowers the discreteness and randomness of the initial setting time of RCC determined by penetration resistance, which have laid a foundation for determining maximum allowed exposure time and selecting proper treatment measures of lift joints.The results from joint shear tests of RCC under indoor simulated and on-site conditions show that both the joint shear parameters are lower than that of parent RCC (no joints). The longer exposure time of lifts is, the greater the extent of reduction of the shear parameters is. The frication coefficient f' generally hadless reduction than the shear cohesion c'. The shear parameters of lifts within maximum allowed exposure time have been slightly reduced as compared with parent RCC. When the exposure time is beyond the maximum allowed exposure time, a bedding mixture will be necessary to achieve the required shear or tensile strength. Compared with untreated lift surfaces before using bedding mortar, the shear cohesion on treated lift surfaces increased about 30%. Using bedding mortar after treated joint, the shear parameters can approach that of parent RCC.The ultimate shear strength and the shear cohesion c' of field in-situ shear strength test are greatly lower than that of indoor in-situ shear strength test, and the average ratio is 0.78. But the frication coefficient f' has no large difference.Based on the research results of indoor and outdoor characteristic of lift joints strength, influence factors on quality of bonding between lift surfaces were synthetically analyzed. Combining the project experience, the identical criterion of hot(warm,cold) lift joints is characterized and qualification requirements of joints are put forward. The improvement measures for good bond of lift joints and mechanism under various adverse conditions is discussed in details.