Study Of The Effects Of Vibration Conditions On The Inter-layer Bonding Properties Of RCC

The risk of the weak interlayer links when constructing roller compacted concrete (RCC) dams is higher than when constructing common concrete dams in that they are paved in layers. Experiments show that, as the interlayer intermittent time(short for IIT), which refers to the period from the time when we add water to the RCC mixture to the time when we finish paving the upper RCC layer, increases, the shear strength of the RCC decreases. Therefore, it is urgent to study the inter-layer bonding quality of RCC. In order to simulate the vibrated status of RCC when paving RCC layers on-site, we vibrate the RCC specimens without weight blocks every hour after these specimens are made in form, where the vibrating time periods are 4s,8s, 12s respectively, as in contrast to RCC specimens which are not processed in any approach after they are formed.First, the initial setting time of RCC is studied from the perspective of micro-mechanisms of cementitious materials by changing temperatures of liquid, mixing portions of water reducer and vibrating conditions, where the results of RCC setting time experiments are analyzed. This result shows that effects of material temperatures when stirring the mixtures on RCC are relatively small; effects of mixing portions of water reducers containing retarding component on it are significant. Vibration conditions, where we vibrate the RCC specimens without weight blocks every hour after these specimens are made in form, have significant effects on RCC setting times. Further, the longer the RCC specimens are vibrated, the greater the elongating effects are, though limited.We define the direct allowed paving time (short for DAPT) as the IIT when the shear strength equals 85 percent of that of RCC body(RCC specimens whose upper layers are immediately paved after the lower layers are paved.). The results show relatively great difference between DAPTs of RCC whose specimens are vibrated and of those whose specimens are not; plus, the results show little difference between DAPTs of RCC whose specimens are vibrated under different time period(4 seconds, 8 seconds and 12 seconds, respectively).Furthermore, DAPT increases as the normal stress rises.The water absorbing dynamic test result shows that both vibration conditions and long IIT can contribute to the increase of RCC absorbing ratios in weight and the average diameters of pores in RCC specimens. Results of Scanning electron microscopy test verify the validity of results of water absorbing dynamic test.