Study On The Rapid Strengthening Repair Of Deteriorated Concrete In High-speed Ballastless Track

With the successful construction and operation of the Beijing-Shanghai high-speed railway,China high-speed railway construction has entered a period of rapid development,and new trains and new ballastless track structure systems have been developed.China has a vast territory and complex climatic and geographical conditions.During the operation of ballastless track of high-speed railway,some of the ballastless track structure of the railway line section has deteriorated concrete under the combined effect of train load and natural environmental factors.In view of the deterioration of ballastless track structure concrete,the existing repair methods mostly use polymer cement mortar or resin polymer,and mainly focus on the repair of concrete cracks.The rapid strengthening repair of surface concrete still needs further research.Based on the deterioration status of ballastless track concrete for high-speed railways,this paper proposes to use Magnesia-phosphate cement(MPC)-based new repair materials for rapid strengthening and repairing of ballastless track deterioration concrete.Among them,it focuses on the theoretical and experimental research on the physical and mechanical properties of magnesium phosphate cement-based materials and the static bending and fatigue bending of MPC mortar to repair reinforced concrete beams.The main research contents and results of this article are as follows:(1)The magnesium phosphate cement-based material suitable for rapid strengthening and repairing of high-speed railway concrete is prepared,which has excellent physical and mechanical properties.The compressive strength of 2h can reach 28.1MPa,which is about 9.4%higher than the C30 concrete used in this article,and the bending resistance of 28 d Various performance indicators,such as strength and positive tensile bond strength,meet the requirements in the current high-speed railway maintenance regulations.(2)The bending test of 7 magnesium phosphate cement mortars for repairing reinforced concrete beams was designed and completed.The main parameter variables were the thickness and setting time of the repaired magnesium phosphate cement mortar.The failure characteristics and laws of MPC mortar-concrete composite beams are obtained,that is,the specimens under the ultimate load are subjected to bending failures characterized by increasing deflection in the middle of the span,continuous increase of cracks,and yielding of the tensile steel bars.During the continuous loading process after bending failure,cracks appeared in the mid-span superimposed surface of the specimen;and according to the influencing factors of bond shear strength,the calculation formula of MPC mortar-concrete bond strength was given.(3)The fatigue bending test of three magnesium phosphate cement mortars for repairing reinforced concrete beams was designed and completed.The fatigue load levels S were taken as 0.7,0.8 and 0.9,respectively.The test results show that the compressive strain of magnesium phosphate cement mortar in the compression zone,the tensile strain of the tensile steel bar,the mid-span deflection and the width of the crack all show three stages of rapid growth,stable development,and rapid development;fatigue loading accelerates the MPC mortar-concrete stack The failure of the joint surface is detrimental to the stress of the structure after repair;and the fatigue life is predicted to be more than 2 million times when the fatigue load level is 0.55 through the fatigue equations of Tepfers and Shi Xiaoping.(4)The ABAQUS finite element software was used to model and analyze the whole process of the test component.The concrete used a plastic damage model.The simulation results showed that the damage of the concrete was consistent with the test result,and the ultimate bearing capacity of the component was similar.On this basis,a more in-depth study of the factors affecting the thickness of post-cast magnesium phosphate cement mortar.The results show that the thickness of post-cast magnesium phosphate cement mortar has a certain improvement on the ductility of the overall member after repair,the ultimate bearing capacity has been reduced to a certain extent,and the most unfavorable working conditions have dropped by 21.5%.