Research On Expansion Of Cement Stabilized Filler By Sulfate Attack

The expansion of cement stabilized filler by sulfate attack is a special type of soil expansion,which is caused by the chemical reaction of cement and sulfate.At present,the problem of subgrade heave caused by sulfate attack expansion has been found in many countries at home and abroad.In view of the insufficiency of expansion mechanism and deformation of cement stabilized filler by sulfate attack,the thesis considered the background of the actual engineering application and construction demand in inland sulfate area,through the means of field long-term monitoring,sampling test,microscopic analysis and mineral composition analysis,combined with theoretical analysis and systematic experiment,the paper carried out a systematic study on the expansion mechanism,deformation law,heave characteristics and engineering characteristics of sulfate attack cement stabilized filler.1.On the basis of the crystal chemical theory of the increase of solid phase volume generated by sulfate attack reaction,through scanning electron microscopy microscopy and multiple mineral analysis methods,combinded with the solid-liquid two-phase layer structure of cement stabilized filler,the microscopic expansion mechanism of expansive crystal formation on soil particles was proposed.During the formation of ettringite and thaumasite,the volume of solid phase increases due to the absorption of water and salt.Clusters of pore formed on the surface of solid particles make the soil particles repel each other and cause the expansion of cement stabilized filler by sulfate attack2.From the aspect of soil structure,reaction conditions and mineral components,the influence of various factors of sulfate attack expansion was studied by laboratory test.High PH alkaline environment and the relative humidity of water environment is sulfate attack expansion necessary environmental conditions,sulfate content in the soil and grain size and mineral composition is the key factor affecting the expansion deformation.3.Based on sulfate migration accumulation theory under the typical climate condition,the longitudinal distribution of subgrade deformation by sulfate attack was studied by sampling test,the characteristics of sulfate migration under temperature and humidity gradient were analyzed by migration simulation test.Combinded sulfate attack reactive ion precipitation,chemical reaction,crystal precipitation,ion migration process,sulfate erosion expansion multiple process,expansion physical model is established,the key index of the deformation rate in the process of sulfate expansion is clarified.4.Through the long-term deformation monitoring data and the analysis of sample test of sulfate attack subgrade heave worksite,the characteristics of long-term continuous expansion and seasonal deformation law are analyzed.The differences and similarities of sulfate attack expansion characteristics with frost heave,swelling soil mudstone expansion and sulfate expansion were studied.5.The limit value standard of sulfate content in cement stabilized filler was proposed.It is necessary to strictly control the sulfate content in cement modified filler and prevent salt migration to prevent sulfate attack expansion and deformation in sulfate environment.The research results of thesis have important significance and engineering application value for clarifying the mechanism of sulfate attack,analyzing the law of sulfate attack expansion,improving the relevant standards of cement stabilized filler,guiding the design of cement improved filler and subgrade engineering construction under sulfate environment.