| Cement and emulsified asphalt mortar (CA mortar) is the key material of China Railway Track System (CRTS) I slab ballastless track, which provides functions of supporting, adjusting, reducing and isolating vibration, blocking crack. Its quality has significant effects on durability of the track system and safety of the train course. Diseases of cracking and crushing were found during lifetime of CA mortar filling layer. Nowadays, systematic research on the damage and deterioration mechanism of CA mortar is lacking in China and abroad. Aiming at the damage problem of CRTS I type CA mortar, this paper carried out theoretical and experimental research on the deterioration mechanism of mechanical properties of CA mortar filling layer. Considering the viscoelastic properties of CA mortar, this paper established the viscoelastic calculation model of slab track, calculated the strain rates of CA mortar filling layer, and carried out mechanical properties tests of CA mortar under different conditions. Using the viscoelastic calculation model of slab track, the effects of CA mortar deterioration on the mechanical properties of track and the fatigue life of CA mortar were analyzed. And this paper explored the damage deterioration law of CA mortar under vertical compressive stress wave preliminary based on stress wave theory. The main research contents and results obtained are as follows:1. Research of viscoelastic calculation model of slab ballastless track and strain rate of cement and emulsified mortarThe creep phenomenon of viscoelastic materials is obvious. Based on the uniaxial creep testing of field sampling CA mortar specimens, the viscoelastic properties of CA mortar was researched, and the creep process of CA mortar was simulated by finite element software. Considering the viscoelastic properties of CA mortar, the viscoelastic calculation model of slab track was established based on the elastic foundation beam-body theory, and then the strain rates of CA mortar filling layer were researched. The research results show that both the existing burgers model and four-unit-five parameters model can simulate compression creep properties of CA mortar well. The error of calculated results and experiment data is within 2%, which demonstrate that the viscoelastic properties of CA mortar can be simulated and analyzed by finite element software. The comparision of field observations with the relevant simulation verified the reliability and validity of the viscoelastic calculated model of slab track. The strain rates of CA mortar filling layer ranging from 1 × 10-5/s to 1 × 10-1/s under moving load. The loading rates should be 0.03mm/min to 300mm/min according to the current test of CA mortar specimen size. However, in China, temporary technology criterion of cement and emulsified asphalt mortar in CRTS I type slab track of passenger dedicated railway stipulates the loading rate of 1mm/min, which can’t reflect the service properties of CA mortar fully.2. Damage law research of CA mortar under different strain rates, loading history and environment conditionCombining with the actual service condition of CA mortar filling layer, the damage deterioration law of CA mortar under different strain rates, loading histories and environment conditions were studied systematically based on the simulated strain rates of CA mortar filling layer. Research results show that the mechanical properties of CA mortar have obvious strain rate sensitivity. With the increase of strain rate, the compressive strength, elastic modulus and peak strain of CA mortar grew exponentially. The power-exponent form, y=a+bxc can better fit the relation between the compressive strength, elastic modulus and peak strain of CA mortar and strain rates. Because of hysteresis effect of stress and strain in CA mortar, the lower the strain rate, the more serious damage of CA mortar under the same strain. The damage stress threshold and damage strain threshold of CA mortar will increase with the increase of strain rate.The compressive strength of CA mortar has a tendency to reduce with the increase of initial static load. Under cyclic loading, the compressive strength and elastic modulus of CA mortar still have a power-exponent relation.. The compressive strength of CA mortar decrease with the increase of amplitude and frequency of cyclic loading, but the elastic modulus of CA mortar has a tendency of increase. The compressive strength of CA mortar under repeated loading and unloading is lower than that under monotonic loading, which shows that the repeated loading and unloading has caused unrecoverable damage to the CA mortar. The curve equation of CA mortar under repeated loading and unloading was established according to the experiment result, which could reflect the mechanical properties of CA mortar under repeated load.CA mortar has serious soaking softening phenomenon. Comparing with the same age specimens, the compressive strength and elastic modulus of CA mortar decreased about 50% after long water immersion. Drying and wetting cycle is similar to water immersion, also will lead to softening, which indicates that water damage is one of the main factors of CA mortar deterioration.3. Establishment of mathematical model of stress-strain relationship of CA mortar, and verified with the measured stress-strain curveOn the base of systematic mechanical property test of CA mortar and refering to the concrete research method of mathematical model of stress-strain, The mathematical model of stress-strain relationship of CA mortar, which can take the strain rates into consideration, was established. Then fit the mathematical model with the measured stress-strain curve under different working conditions. Research results show that the mathematical model of stress-strain relationship can be good at representing the stress strain curve of CA mortar under different strain rates, loading histories and environment conditions.4. Study on the effect of CA mortar deterioration and debonding on the mechanical properties of slab track, and put forward the measures to improve the water resistance of CA mortarUsing the viscoelastic calculation model of slab track, the effects of CA mortar deterioration, debonding and both deterioration and debonding existed on the mechanical properties and fatigue life of CA mortar were researched. The effect of charge type of emulsified asphalt and different sands on the water resistance of CA mortar was studied, considering the water damage is one of the main factors on CA mortar deterioration. Research results show that the displacement and stress of track will increase if the CA mortar deterioration and debonding both exist, the vertical compressive stress of CA mortar will increase 8 times and the fatigue life of CA mortar will not be able to meet the requirements of the 60 years service life. Use the quartz rock as the fine aggregate, and select the cationic emulsified asphalt can improve the water resistance of CA mortar.5. Exploration of deterioration law of CA mortar under vertical compressive stress waveOn the base of the theory of stress wave, the damage deterioration law of CA mortar under vertical compressive stress wave was researched, and then the effect of different stress amplitude of stress wave, compressive strength of CA mortar filling layer and pressure rabbi on the damage of CA mortar was considered,. Studies show that the damage of CA mortar under the vertical compressive stress wave was found from corner. The damage area of CA mortar increases with the increase of stress amplitude, the decrease of CA mortar’s compressive strength and the increase of the pressure rabbi. |
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