| Nowadays,the total mileage of high speed railway exceeds 20000 kilometers in China,and CRTS Ⅱ slab ballastless track accounts for 30%of all track types.CA mortar is sandwiched between two slabs and serves the purpose of supporting slab track,buffering high-speed train load and reducing the vibration effect.Its performance directly affects the traveling comfort and security of the entire track structure.CA mortar is composed of cement,fine aggregate,asphalt emulsion and a variety of additives and is a high performance organic-inorganic composite material which has the combined merits of strength of cement and good elasticity of asphalt.In order to improve the performance of cement asphalt mortar,internal addition method is used to mix nano-SiO2 into CA mortar,studying the effect of nano-SiO2 on the properties of cement asphalt mortar.Research work and results in this paper are as follows:(1)Fluidity test,slump flow test and penetration test were carried out on CA mortar.The results show that nano-SiO2 would reduce the workability of CA mortar and as the dosage increase the more significant the phenomenon.(2)Uniaxial compression test was carried out on CA mortar speciments of different ages.The results show that early stress-strain curve of ordinary and nano CA mortar decline slowly after the peak stress,which are typical brittle materials with a little toughness.With the increase of age,the decline rate gradually increasing after the peak stress,which are more brittle and less toughness.Adding nano-SiO2 can improve the early strength and elasticity modulus,and have little effect on the later strength and elastic modulus.The nonlinear fitting natural logarithm function of strength and elastic of ordinary and nano CA mortar related to age was obtained according to the experimental results.(3)Uniaxial compression test was carried on CA mortar speciments of different loading rates.The peak stress and elasticity modulus of ordinary and nano CA mortar increases with the increasing loading rates,exponential function can be used to fitting its trend.The mechanical properties of nano CA mortar loading rates sensitivity is significantly lower than ordinary CA mortar.CA mortar’s peak stress sensitivity to loading rates significantly is higher than the elasticity modulus.The sensitivity of the mechanical properties to loading rates of CA mortar with 3%nano-SiO2 is the lowest.(4)Uniaxial compression test was carried on CA mortar speciments of different temperatures.The results show the peak stress and elasticity modulus of ordinary and nano CA mortar decreases with the increasing temperature,linear function can be used to fitting its trend.CA mortar’s peak stress sensitivity to temperature significantly is higher than the elasticity modulus.The mechanical properties of nano CA mortar temperature sensitivity is significantly lower than ordinary CA mortar,and decreases with the addition of nano-SiO2 increases.The sensitivity of the mechanical properties to temperature of CA mortar with 1%nano-SiO2 is the lowest.(5)Fatigue resistance test and fatigue tensile tests were carried on CA mortar speciments of different temperatures.The results show that S-lgNf curve of the fatigue resistance and fatigue tensile of ordinary and nano CA mortar shows a good linear correlation.At the same temperature and stress level,the fatigue life of nano CA mortar is higher than ordinary CA mortar and the fatigue life of CA mortar with 1%nano-SiO2 is the highest.The fatigue life of nano and ordinanry CA mortar decreases respectively at the temperature of-20℃,15℃ and 40℃.In summary,adding nano-SiO2 would reduce the workability of CA mortar,which can be compensated by adding superplasticizer.With addition of proper quantities of nano-SiO2,can improve the early strength and fatigue properties of CA mortar,and reduce the sensitivity of the mechanical properties to temperature and loading rates.By adding 1%nano-SiO2,the performance of the CA mortar can be best improved. |
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