Study On Arch Expansion And Damage Mechanism Of Cement Stabilized Macadam Base Under The Action Of Temperature And Salt

The arch expansion is a special disease form of cement stabilized macadam base asphalt pavement in Gobi saline soil area.The effect of temperature and salt is the direct cause of expansion and damage of cement stabilized macadam base.Under the action of temperature and salt,physical erosion and chemical erosion occur in the cement stabilized macadam base materials,which change the composition and pore structure of the cementitious material,and affect the compaction characteristics,mechanical properties,deformation characteristics and stress state of the cement stabilized macadam.This paper intends to use the combination of field investigation,indoor test,theoretical analysis and numerical simulation to study the arch expansion and damage mechanism of cement stabilized macadam base under the action of temperature and salt systematically from the perspective of macro,meso and micro.The specific research contents and conclusions are as follows:1)The typical arch expansion disease sections in the investigation area are investigated,and the disease characteristics from the shape,development characteristics and development time of pavement arch expansion are analyzed;Combined with the test results of strength,microstructure,erosion products and salt content of base material,the causes of arch expansion are analyzed.The results show that high sulfate content is the direct cause of chemical and physical erosion of cement stabilized macadam,and the effect of temperature intensifies the erosion process;The base salt content mainly comes from fine aggregate and mixing water;Erosion causes expansion deformation and strength attenuation of base materials.2)Considering the factors such as sodium sulfate content,molding temperature,cement content and enclosing materials time,the compaction test of cement stabilized macadam is carried out.Combined with SEM(Scanning Electron Microscope)and EDS(Energy Dispersive Spectroscopy)test,the compaction characteristics of cement stabilized macadam under the action of temperature and salt are analyzed from the macro and micro point of view.The results show that the content of sodium sulfate,temperature and enclosing materials time affect the formation of ettringite and mirabilite,and the content of cement affects the content of ettringite;Thus,the pore structure of cementitious material is changed,resulting in the change of optimal moisture content and maximum dry density;The range and variance analysis show that the molding temperature and sodium sulfate content have significant effects on the maximum dry density and the proportion of total pore area of cement stabilized macadam cementitious materials after compaction.3)Considering the factors such as sodium sulfate content,molding temperature,cement content,the unconfined compressive strength,splitting strength and flexural tensile strength tests are carried out,and the damage characteristics of cement stabilized macadam are collected to analyze the strength characteristics of cement stabilized macadam under the action of temperature and salt.The results show that the content of sodium sulfate,temperature,cement content affect the type and content of erosion products.The cementation,filling and extrusion of erosion products change the damage characteristics of specimens and lead to the change of strength.Based on the strength change law,the strength prediction model of cement stabilized macadam under the action of temperature and salt is established by using the least square method and normalization method.4)Considering the factors such as sodium sulfate content,age temperature and cement content,the deformation tests of design age and high-temperature operation period are carried out.Combined with SEM and EDS test,the deformation characteristics of cement stabilized macadam under the action of temperature and salt are analyzed from the macro and micro point of view.The results show that in the design age stage,the sodium sulfate content and age temperature affect the formation of ettringite and mirabilite,and the cement content affect the ettringite content.These erosion products are filled in the pore structure of the cement stabilized macadam,resulting in deformation;In the high-temperature operation stage,the sodium sulfate content,age temperature and cement content affect the composition and content of erosion products.Under the action of high temperature during the operation period,the distance and bond length between molecules of erosion products change,resulting in expansion and deformation of the cement stabilized macadam.5)The uniaxial compression tests of cement stabilized macadam were carried out under different sodium sulfate content,molding temperature and cement content,and the effects of various factors on the mechanical properties of uniaxial compression were analyzed.The results show that the sodium sulfate content,molding temperature and cement content have effects on the peak stress,peak strain and elastic modulus of the cement stabilized macadam.Combined with the variation law of stress-strain curve,the stress-strain curve constitutive model of Guo Zhen-hai is modified,and the uniaxial compressive stress-strain full curve constitutive model of the cement stabilized macadam under the change of sodium sulfate content was deduced considering factors such as temperature and cement content.6)Based on the existing test data,combined with the theory of continuous damage mechanics and Ottosen failure criterion,the Ottosen damage failure criterion and constitutive model of the cement stabilized macadam influenced by sodium sulfate content,temperature and cement content are established.The constitutive model is verified by Ottosen module built in COMSOL;Based on this,Ottosen constitutive model is applied to analyze the effects of sodium sulfate content,construction molding temperature,cement content and expansion tank spacing on base arch expansion and damage.