| CRTSIII slab ballastless track structure is a new track structure with intellectual property rights in China.It was widely employed in the construction of 300 km high-speed railway in China.The essential structural layer of the CRTSIII slab track structure is the self-compacting concrete filling layer（hence referred to as SCC）.Through the door reinforcement and bonding interface,it forms a composite slab structure with its upper precast steam-cured concrete track slab.SCC filling layer is a thin-layer structure with a 14 m2 slab area and a 9cm thickness.It undertakes the functions of leveling,support,force transfer and bonding,and is related to the smoothness,safety and durability of the whole track structure.Because the development history of the CRTSIII slab track structure is still relatively new,there are few research findings on the self-compacting concrete filling layer of the CRTSIII slab track,as well as its bonding interface performance and microstructure characteristics between the CRTSIII slab track and the track slab.In light of this,this dissertation systematically studies the performance and microstructure characteristics of CRTSIII slab track filling layer and its bonding interface using a combination of on-site full-scale test and indoor simulation test,as well as the research methods of theoretical analysis,numerical simulation calculation,and test analysis,in order to provide scientific support for mastering its service performance.The meaningful results obtained in this dissertation are as follows:（1）The suitable filling mode of self-compacting concrete（SCC）mixture in the filling layer and its influence on the filling quality of the filling layer are clarified.Master the SCC filling layer performance and microstructure characteristics distribution law and key influencing factors;It is clear that the strength,dynamic elastic modulus and coarse aggregate distribution of SCC filling layer gradually decrease from the position of the central filling hole to the four outlets.When the filling layer filling quality is excellent,the following is the suitable range of SCC mixture workability and filling process parameters（filling time）:SF is about 620～670 mm,T500 should be within 3～6 s,and the filling time should be at least 6 minutes.（2）It is revealed that the bonding interface zone of the filling layer presents gradient structure and variation law in the vertical direction,that is,from the bottom of the steam-cured concrete track slab to the SCC matrix,the bonding interface zone exhibits gradual characteristics of porous bubble layer,paste layer,mortar layer to SCC matrix.Microhardness value was used to determine the micro mechanical properties of the bonding interface.The width range of the bonding interface zone of the filling layer is around 15μm when the workability of SCC mixture and filling process parameters are in the above optimal range.The bonding interface zone has a dense structure,and the gradient change is not obvious.（3）The evolution law of SCC filling layer interfacial bonding performance with the main SCC constituent materials（fly ash,granulated blast furnace slag,and viscosity modifying materials）,rheological parameters,and age was mastered;A mathematical relationship model is established between the bonding performance of the bonding interface and the rheological parameters of the SCC mixture.（4）Acoustic emission（AE）technology is used to monitor and characterize the growth law of splitting tensile strength and bonding failure characteristics of filling layer bonding interface samples at different ages.With the increase of load,the cumulative acoustic emission impact number and energy of specimens at different ages gradually increase,and the cumulative AE hits and energy increase with the increase of specimen age.At the same time,the initial point of rapid increase of AE hits is advanced with the increase of age.（5）The microstructure evolution law and mechanism of the bonding interface are investigated.The gradient structure characteristics of the bonding interface zone weaken with the increase of age.With the increase of age（especially after the age exceeds 7 days）,the content of hydration reaction products in the interface area gradually increases,the number of unhydrated cement particles significantly decreases,and it can be seen that the particle size is smaller,the interface and matrix are more dense,and the microhardness value increases.The hydration rate of the interface zone is higher than that of the matrix,and the generated C-S-H is mostly LD C-S-H with a low elastic modulus,and the average elastic modulus is about 22 GPa. |
