Study On The Resistance Of Limestone Powder-Fly Ash Mortar To Magnesium Sulfate Under The Combined Action Of Electric Field-Low Temperature-Magnesium Sulfate

By the end of 2019,a total of 40 cities in mainland China had opened urban rail transit operations,with 6,730.27 kilometers of lines in operation,the data from the China Urban Rail Transit Association,according to data released by the China Association for Energy Conservation’s Urban Rail Transit Energy Conservation Professional Committee.It is inevitable to generate stray current in the running of railway train,When the stray current exists in the environment of sulphate,it will cause the influence on cement-based materials that cannot be ignored.Fly ash and limestone powder are increasingly used in the modern concrete industry to produce high-performance concrete.Therefore,the resistance to sulfate erosion of limestone powder and fly ash admixture cement-based materials in a variety of different sulfate erosion environments such as low temperature,electric field and electric-low temperature coupling is worth studying.This paper will base on single mixing with lime stone powder,fly ash or double mixing admixtures mortar as the research object,at normal temperature,low temperature,electric field and electric-low temperature coupling specimens of magnesium sulfate long-term immersion environment such as apparent change evaluation,compressive strength test,and the change of quality and microscopic test,such as scanning electron microscopy（SEM）,energy dispersive X-ray spectrometry（EDS）and X-ray diffractometry（XRD）,as well as comparative analysis of different erosion environment admixture mortar sulfate erosion resistance evolution law,the results showed that:.Normal temperature-under long-term immersion in magnesium sulfate erosion environment,in the early stage of erosion,the addition of limestone powder can improve the resistance of the mortar specimen to sulfate erosion and slow down the formation of erosion products;in the later period of erosion,the addition of limestone powder will exacerbate the erosion of the specimen Degree;double-doped limestone powder,fly ash and single-doped fly ash can improve the resistance of mortar specimens to sulfate corrosion.In the low-temperature-magnesium sulfate long-term immersion erosion environment,the addition of high content（more than 10%）of limestone powder will greatly reduce the resistance of the cement mortar to magnesium sulfate corrosion;double-doped limestone powder,fly ash,and single-doped coal powder.The effect of ash on magnesium sulphate resistance of cement mortar is not obvious;before 120days of erosion,the test specimen of cement mortar mixed with gradeⅠfly ash is relative to the cement mortar mixed with gradeⅡfly ash The test piece has better resistance to low temperature-sulfate erosion;from 120d to the end of erosion,different grades of fly ash have little effect on the low temperature-magnesium sulfate erosion resistance of the admixture test piece.Under the electric field-magnesium sulfate long-term immersion and erosion environment,the presence of the electric field will greatly reduce the number of MSH generated after the cement slurry is eroded by magnesium sulfate;the addition of single-mixed fly ash and double-mixed limestone powder and fly ash to a certain extent It is good for cement mortar to resist sulfate attack.In the environment of long-term immersion and erosion by electric field-low temperature-magnesium sulfate,double-doped limestone powder and fly ash have no obvious effect on the resistance of the specimen to electric field-low temperature-magnesium sulfate corrosion,but considering the economic and environmental protection of double-doped limestone powder and powder Coal ash still has certain application value.Under the different magnesium sulfate long-term immersion erosion mechanism,the resistance of each group of admixture mortar specimens to sulphate corrosion is most affected by the electric field-low temperature coupled erosion environment,because the environment includes two environments where the specimen is subjected to low temperature and electric field Characteristics during erosion:The test piece is more prone to TSA（Thaumasite form of sulfate attack）;the rate of SO₄^2-entering the test piece in the erosion solution is accelerated,which shortens the time required for the test piece to occur in the TSA.This article has 71 figures,15 tables,and 104 literarures.