Subgrade Performance And Application Of PAM And Cement Composite Modified Windblown Sand In Qinghai

With the continuous advancement of the "Western Development" strategy,the road construction mileage in the aeolian sand accumulation area is increasing,and the construction quality is continuously improved.In order to alleviate urban traffic congestion and improve the transportation capacity between Qinghai Province and other provinces,a large number of desert highways have been built in Qinghai Province.Qinghai aeolian sand has a wide area,and it has the following features:less powdery clay content,finer particles,lower surface activity,almost no cohesion,low shear strength,good water permeability,low water content,poor water retention,and underdeveloped capillary,which causes it to be easily loosened and displaced by external force.In order to use local aeolian sand as road construction materials in Qinghai,which can utilize waste and reduce the cost of road construction,the first step is to solve three major problems:overall strength,durability and water stability of the roadbed filler.Therefore,this paper takes aeolian sand of Qinghai as the research project and uses it as the filling material of the road base layer.Based on improving the road performance of aeolian sand,it is systematically explored the strength,dry-wet cycle capacity,freezing-thawing cycle capacity,anti-scour ability and its micro-action mechanism under the combined action of cement,MK and PAM in this research.The main research contents are as follows:（1）The amount of cement and PAM is the variable（fixed cement content is 2%,4%,6%,PAM dosage is 0,0.01%,0.05%,0.1%,0.3%,0.5%and 0.8%of the total of 21 groups）,the unconfined compressive strength of different ages（7D,14D,28D）under standard curing conditions was determined,and the strengths of cement with different dosages,different ages and different PAM conditions were discussed.alternative relation.The test results show that the more cement is added,the higher the strength.The average strength of 4%cement is 2.29 times of the strength of 2%cement,and the strength of 6%cement is 4.83 times of the strength of 2%cement.Under the same conditions of cement content,the optimal blending amount of PAM is 0.1%-0.3%,the highest strength growth rate is 127%,and the strength of C6P0.3 group is 1.42MPa,which fully meets the aeolian sand.Engineering strength requirements for the subbase;（2）Exploring the strength variation law and its influencing factors of the aerated agent dosage on the aeolian sand dry-wet cycle,freeze-thaw cycle and rainwater scouring,combined with the unconfined compressive strength,comprehensively determine the PAM by multiple evaluation indicators.Optimal dosage.The experimental results show that through the unconfined compressive strength,dry and wet,freeze-thaw cycles and anti-scouring tests,it is found that the optimum amount of PAM is present,which makes the modified aeolian sand more resistant to water stability and durability.The optimum dosage is 0.1%⁰.3%.The dry-wet cycle test found that the addition of PAM reduced the water absorption rate of aeolian sand and increased the dehydration rate;the strength of C2P0 group not incorporated into PAM was only 0.1 MPa after 10 times of dry and wet cycles,and the strength increased by 0.23 MPa after adding PAM;After the number of dry and wet cycles is more than 6 times,the strength drops sharply.After 10 dry and wet cycles,the average intensity is about 67%of the initial value.The strength of the group without PAM in the freeze-thaw cycle decreased rapidly.After 10 cycles,the intensity decreased to about 15%of the initial value.After 10 times of freeze-thaw cycles,the strength of the PAM-incorporated group decreased to the initial value of 48%,that is,the incorporation of PAM can effectively resist the freeze-thaw cycle,and the damage ability of the freeze-thaw cycle is greater than the damage capacity of the dry-wet cycle;the anti-scouring experiment clarifies the relationship between the amount of curing agent and the amount of sand washed,and is washed by rainwater.In the granules,with the increase of cement content,the proportion of 1-2mm particles decreases,and the particles of 0.075-1mm increase;the flow rate and strength also have a certain relationship.The larger the water flow,the lower the strength,because the water flow rate is higher.Large,under the same scouring time,the large particles gradually take away the small particles,causing the overall structure of the aeolian sand to be destroyed,and the strength is rapidly reduced;（3）Using the combination of scanning electron microscopy and energy spectrum analysis（EDS-SEM）to explore the microscopic mechanism of PAM and cement modified aeolian sand:PAM and cement composite modified aeolian sand is the essence of PAM It can react with divalent cations such as Ca²⁺in cement hydration products to form a cation bridge,and together with cement hydration products,form a dense spatial skeleton network structure,increase the cohesive force between particles,and improve strength;PAM and cement When compounding aeolian sand,the optimal amount of PAM exists.This is because when the PAM content is too high,on the one hand,the hydration reaction of the cement is suppressed.On the other hand,the product after the hydration of the cement is wrapped under the film formed by the PAM,and the reaction of the cement and the aeolian sand is hindered,and a dense space cannot be formed.a reticular structure,resulting in reduced cohesion and reduced strength;（4）Through the particle flow software PFC^2D,the parameters of the modified aeolian sand and the dynamic path of the aeolian sand roadbed during the scouring process are cognized,and the relationship between the macroscopic parameters of the modified aeolian sand and the mesoscopic parameters is clarified.