Study On The Practical Mechanical Properties Of Cement Stabilized Cold Recycled Subbase In The Section Of Yuzhong Section Of S217 Line

China's highway construction has been developing rapidly in recent years,but each grade of highway has a designed service life.With the passage of time,the highway under early construction has entered the maintenance and repair stage.For Gansu province,if the asphalt highway waste materials that need to be maintained are discarded,it will cause a lot of pollution and land occupation.Therefore,it is of great significance to deal with waste asphalt pavement milling material reasonably.A great deal of research and achievements have been made on highway recycling in foreign countries,while the research on highway recycling in China is relatively late.Based on the reconstruction project of Jingtai to Dingxi Highway Yuzhong section of S217,this paper adopts cement stable cold regeneration technology to lay the pavement bottom base,and conducts relevant research on the mechanical properties of the mixture.The specific research contents are as follows:Through a large number of studies on the mix design of cold recycled mixture at home and abroad,a series of tests are carried out on the asphalt pavement milling material of S217 line.According to the screening test results,the particle size of the milled material was relatively large.In order to make the mixture meet the requirements of the grading range of the base layer,5mm crushed stone and natural gravel were used to mix with the old asphalt pavement milling material.According to the obtained gradation curve,5mm crushed stone is the best choice.The gradation curve blended by 5mm crushed stone and old asphalt milling material shows that within the gradation curve range,three gradations close to the upper limit,design median and lower limit are selected as the mix ratio of the cold recycled mixture.Determine the optimal moisture content of the cold recycled mixture through experiments,and perform the 7d unconfined compressive strength of the prepared specimens according to the specifications to determine the optimal cement content.In order to further study the mechanical properties of the three cold recycled mixtures,the three-graded mixtures were subjected to 7d,28 d and 90 d bending strength,splitting strength and unconfined compressive strength mechanical index tests,through the analysis of the data It is concluded that the bending strength,compressive strength and splitting strength will increase with the increase of cement dosage.The strength of the same cement dosage will increase with age.The strength increases from 7d to 28 d faster,28 d By 90 d,the intensity increased slowly.Beishan in Yuzhong county belongs to the seasonal frozen area.Due to the frequent change of temperature difference and the effect of groundwater and rainwater,once cracked,water will enter into the pavement structure,resulting in the frost heaving damage of the pavement structure.With the decrease of bearing capacity,the pavement structure will sinkand churn mud in the spring thawing season.For this reason,the indoor test is designed,and the test piece after 90 days of curing is used for experimental research to explore the change of mechanical properties of the mixture.CT scanning technology was used to observe the microstructure of the samples after freeze-thaw cycle,and to study the internal damage of the samples caused by freeze-thaw cycle,so as to elaborate the effect of freeze-thaw cycle on the mechanical properties of cold recycled mixture subbase.By comparing the mechanical properties and economic benefits of the three mixtures,S30 mixture was finally selected as the cold recycled subbase mixture for the paving test section,and the compactness,flatness and thickness of the pavement on site and the ash dosage of the mixture The water content and water content were tested,and the deflection test was conducted after the 7d curing of the subbase pavement,and the results met the design requirements.