Study On The Rheological Behavior Under Shear Of SCC Used In CRTSⅢ Slab Ballastless Track

The filling layer with self-compacting concrete(SCC) is an important component of the CRTS III slab ballastless track, whose performance has a significant impact on the ride comfort and durability of track structure. SCC is highly sensitive to raw materials and construction process as a kind of special concrete material with super fluidity. In order to improve the stability and robustness of SCC and ensure the construction quality of the filling layer with SCC in the CRTS III slab ballastless track, the effects of raw materials, mixture proportion and the mixing procedure on the rheolohical behavior under shear were researched by means of rheometer(RHM-3000 ICAR). The mechanism of shear thickening of SCC were revealed by means of order-disorder transition theory, transient hydro-dynamic clusters theory and grain inertia theory. The main research results are as follows:(1) The correlation and sensitivity of H-B model and modified Bingham model to characterize the shear thickening behavior of SCC were compared and analyzed. And the results show that both H–B model and the modified Bingham model can be used to describe the shear thickening behavior of SCC, and they have a distinct linear correlation. The c/μ of the modified Bingham model is more sensitive to shear thickening behavior than the n of the H–B model, and the c/μ is more suitable for evaluating the shear thickening response of SCC.(2) The effects of the composition of cementitious materials, the maximum size of coarse aggregate and the type of viscosity modified materials(VMA) on the rheological behavior of SCC under shear were studied. Adding fly ash and slag meanwhile could intensify the degree of shear thickening. The yield stress of SCC was decreased with adding fly ash and slag meanwhile, and opposite was ture for plastic viscosity. The particle inertia of coarse aggregate was increased with the increasing maximum particle size of coarse aggregate, which decreased the degree of shear thickening. But the yield stress of the mixture was also increased with the increasing maximum particle size of coarse aggregate. The thickening effect from large to small in order was welan gum>xanthan gum> cellulose ether> modified starch. The shear thickening of SCC was relatively serious when the VMA was xanthan gum. The thickening effect of modified starch was not obvious in experiments, which meant it was not suitable for the VMA of SCC.(3) The effects of the key parameters of mix proportion including water-binder ratio, slump flow, air content, volume fraction of coarse aggregate on rheological behavior under shear of SCC were researched. The increase of water-binder ratio resulted in the increase of yield stress and the decrease of plastic viscosity. The probability of forming particle clusters was greatly reduced with the water-binder ratio increasing, which weakened the degree of shear thickening. The yield stress and plastic viscosity were reduced significantly when increasing superplasticizer content for improving slump flow. The degree of shear thickening was increased with increasing superplasticizer content because the superplasticizer could disperse the cement particles in static state and desorption phenomenon occurred in shear effect. There were phenomena of particle aggregation and the molecule of superplasticizer intertwined in the system under the action of shear stress. The increase of air content increased the deformation ability of the mixture. Therefore the degree of shear thickening was decreased with the increase of air content. With the increase of the volume fraction of coarse aggregate, the yield stress was increased, the plastic viscosity was decreased, and the degree of shear thickening was decreased.(4) The effects of mixing sequence, mixing time and mixing speed on the rheological behavior under shear of SCC were studied. During the mixing process, the degree of shear thickening could be reduced if mixing aggregate and water firstly. But the direct contact of aggregate and water could lead to free water adsorbed by the aggregate system and the yield stress of the mixture was increased. In order to ensure the fresh SCC with sufficient flowability and low shear thickening behavior, the mix time should be controlled in the range of 4~5 minutes and the mix speed should be controlled in the range of 50~75 Hz.