Research And Application On CA Mortar In Ballastless Slab Track Of High Speed Railway

High speed railway is an important pillar in the transportation development of China. Ballastless track has manifold advantages of excellent structural integrity and stability, lower maintenance requirements, bearing the potential for railway to high speed. Slab track is an advanced structure form, consisting of concrete roadbed, elastic cushion, track slab, etc. The elastic cushion, cement asphalt mortar (more often known as CA mortar) is sandwiched between two slabs and serves the purpose of supporting slab track and cushion the impact of wheel rail. CA mortar is composed of cement, asphalt emulsion, fine aggregate and a variety of admixtures and is a high performance composite material. It has the combined merits of high strength and good elasticity, and is crucial to the durability, safety and economy of slab track. With the implementation of the construction and design of China's high speed railway network, ballastless track has become the key technology deserving keen attention and rapid development.The paper undertook a systematic study on the physical and mechanical properties, durability and weatherability, in-situ construction technology and the design and preparation of CA mortar, and clarified the relationship between composition, structure and performance, providing essential basis for the development and application of CA mortar.The paper was organized into five section and main results were briefly given as follows:The first section revealed the mutual interaction between cement hydration and asphalt emulsion breaking and proposed a hypothesized evolution in the hardening of CA mortar, which was divided into four stages: suspension and dispersion, cement hydration and asphalt emulsion breaking, formation of a continuous asphalt network and development of hardened matrix. An ideal model of CA mortar was established in which asphalt was the continuous phase, cement and other inorganic components acted as the dispersed phase and underpinned the theoretical foundation for the design and preparation of CA mortar.Based on the previous section, the second section proposed a model to calculate the thickness of asphalt film (FT) coating the inorganic phases, constructed a correlation between FT and performance, and presented a method to control and modify the optimum asphalt content in proportioning CA mortar. Results of this section could guide the preparation of high performance CA mortar.CA mortar is characterized by its variety and mutual interaction in material composition, thus the third section staged a comprehensive investigation on the compatibility of asphalt emulsion, cement, sand and admixtures, and further clarified their effect on the workability and mechanical properties of CA mortar. This section, also established the selection standard for raw materials, identified the key parameters and the mix proportioning method of high performance CA mortar.The fourth section discussed systematically the viscoelastic properties of CA mortar, clarified the effect of composition and mix proportioning on its viscoelasticity and established the formula to characterize the stress-strain curves. Based on the time temperature superposition principle, this section constructed a master curve using Arrhenius Equation and sigmoidal function, which could predicate the performance of CA mortar under extremely high or low conditions. The fatigue property and equations of CA mortar at moderate (18℃) and low (-20℃) temperatures were explored and established.The final section studied the volume stability, freezing-and-thawing and chemical resistance and the weatherability of CA mortar, proposed the volume stabilizing and freezing-and-thawing improvement method. The aging property residue asphalt and CA mortar was correlated, providing a important reference for the preparation of CA mortar of high durability and weatherability.Based on the previous research, in-situ experiment was conducted, including the proportioning, pouring of CA mortar in an experimental slab track which possessed the same dimensions as was used in the railway. Results indicated that CA mortar met the requirement of high speed railway construction.