Study On Performance Of Cement Macadam Subgrade Ofhigh Speed Railway In Cold Region

In recent years, with the construction of high-speed railway in China, cement graded crushed stone as a high-speed railway subgrade materials, will be more widely used, research on cement macadam performance become an urgent problem to be solved. In this paper, considering the performance requirement of cement gravel, gradation design, cement macadam basic physical and mechanical properties, permeability and frost resistance were studied through the experiment cement macadam basic physical and mechanical properties, permeability and frost resistance, provide a basis for further study and application of cement gravel. The main conclusions of the study are as follows:1. By using the theory of gradual filling, based on the vibration compaction density and void ratio, after four stages of filling, designed to meet the requirement of aggregate gradation, and set up two groups of contrast gradation according to standard size limit. To determine the optimal time of vibration cement graded crushed stone interior molding 120 s.2. Cement gravel unconfined compressive strength increases with the increase of cement content, but decreases with the increase of the replacement rate of fly ash;The compressive strength of gradation design is significantly higher than the two group comparison of gradation;Cement content is more than 5%, three grade can reach the requirements of compressive strength, but taking into account the economic and environmental requirements, recommend the use of 5% content of cement or with a small amount of fly ash instead of cement.3. With the increase of cement content, the coefficient of permeability of Cement Macadam decreases, the permeability coefficient of gradation design is between 0.01~0.1, and the void ratio is greater than 13%, belonging to the drainage effect is better;Increase the rate of permeability coefficient of cement graded crushed stone was not replaced by fly ash; two times polynomial relations between permeability coefficient and porosity of cement gravel.4. In freezing thawing environment, cement graded crushed stone weight loss rate decreased with the increase of cement content, with the fly ash replacement rate increases, the best anti freezing effect grading design.After 9 cycles of frost heave, cement graded crushed stone weight loss rate is high of more than 60% quick freezing; gradation design in a freezing cycle strength decreased by 19.88%~41.49%.Cement macadam capillary water absorption rate increases with the increasing of freezing cycles. In the same frost cycles, the capillary water absorption rate decreased with the increase of the amount of cement, increases with the increase of the replacement rate of fly ash.5. Under the condition of low temperature, with the increase of cement content, Cement Macadam frost heave rate gradually decreases; the frost resistance of fly ash replacing part of cement can improve the cement gravel. Temperature reducing frost can increase cement graded crushed stone rate, but the temperature is lower than-12 ℃, the maximum heave rate remained unchanged. Low temperature environment, cement graded crushed stone in the immersion environment of frost heaving ratio, gradation design of maximal swelling rate was 0.24%.6. Graded crushed stone mixed with P.O42.5 cement while the permeability is lower than that of the graded crushed stone mixed with P.O32.5 cement,but its compressive strength is increased by 7.5%,and better frost resistance,low expansion rate decreased by 12.86%.