| Cement asphalt (CA) mortar is one of the key engineering materials with a certain strength and elasticity, which is composed of cement, sand, asphalt emulsion and many other variety of additives and mainly used to support the rail slab and buffer the high-frequency vibration loads in high-speed railway ballastless slab track structure. Its performance directly affects the durability, traveling comfortness and security of the entire track structure.At present, the durability of engineering materials and structure was generally emphasised on at abroad and domestic. Recent researches have mainly focused on the freeze-thaw resistance in water-saturation state and the fatigue resistance at low-frequency vibration of the CA mortar. This paper mainly focused on the freeze-thaw resistance of the type â…¡ CA mortar in water-saturation and humidity-insulation state and the fatigue resistance of type â… and type â…¡ CA mortar, at high-frequency vibration by using a self-designed setup under load, high-frequency vibration and temperature environment. The results showed that:(1) The water saturation of the type â…¡ CA mortar under humidity-insulation curing for28days was about86.1%. The CA mortar might be damaged during freeze-thaw process while the specimens were surface-immersed in the water, the surface-scaling amount of which keeps arising with increasing of the freeze-thaw cycles. However, the mortar still showed excellent frost resistance with much lower surface-scaling amount than the requirement after188freeze-thaw cycles and will never be damaged for the specimens being freeze-thawed under humidity-insulation condition.(2) After CAM was dried, the speed of water re-adsorption was very slow and the water saturation was only50.5%even the dried CAM was immersed in water for19days due to hydrophobic behavior of the asphalt in the CAM. In actual projects, hardened CAM was often dried to be lower water-saturation, thus it is impossible to be damaged due to freeze-thaw of the water in the CAM.(3) The elastic modulus of both the type I and the type II CA mortar was obviously improved after fatigue experiments under load, temperature cycling and high-frequency vibration, thus the elastic buffer properties will gradually lose with fatigue in actual projects.(4) The elastic modulus growth rate showed an increasing then decreasing tendency after the fatigue experiments and it reached the highest growth rate at50Hz. The main reason might be related to the inherent frequency of the type I CA mortar, which needs further study.(5) The fatigue resistance of the CA mortar under load, high frequency vibration and temperature can be clearly improved by incorporating polymer emulsion in CA mortar. After the fatigue experiments, the elastic modulus growth rate was significantly decreased for the mortar with polymer emulsion addition. The introduction of polymer emulsion can also diminish the exhalation of the asphalt during the fatigue experiments.(6) The SEM observation showed that the pore deformed and the asphalt migrates easily to fill the pore structure under load, temperature cycling and high-frequency vibration. The MIP analysis revealed that the harmful large pores were clearly decreased but the micropores increased. The densification of the pore structure of the CA mortar might be the main reason of the elastic modulus growth after fatigue experiments. |
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