Study On Shrinkage Characteristics And Cracking Prevention Of Railway Integral Track Bed Concrete

In the vast area of Northwest China,due to the complex climate characteristics and harsh environmental conditions,cracks appeared in the whole ballastless track bed in the early stage of construction and operation of high-speed railway,and serious diseases occurred in some areas,which will inevitably affect the safety performance and service life of the whole ballastless track bed.Based on the scientific research project of "the influence of dry shrinkage of concrete on ballastless track cracks in Northwest windy arid area and the research of crack control technology",the cracking problem of the whole ballast bed in northwest area due to dry shrinkage is explored in this paper.Based on the investigation of cracks in monolithic ballast bed,experimental studies were carried out on the key factors affecting the relative humidity and shrinkage deformation of concrete,such as gale and drying.The aim is to explore the relationship between relative humidity and drying shrinkage in concrete under strong wind and dry environment,and on this basis,the measures to control cracks are studied.The main research work is as follows:1.By collecting and sorting out the relevant literature and investigating the actual cracking situation of the whole ballast bed in Northwest China,the shrinkage mechanism of concrete and the cracking law of the whole ballast bed are analyzed and summarized,and the research ideas of controlling the dry shrinkage cracking of concrete are put forward.2.Dry shrinkage specimens of concrete under different wind speed grades and curing conditions are designed and fabricated.Temperature and humidity sensors are embedded inside the specimens.The relative humidity of concretes are measured while the dry shrinkage deformation of the specimens from 0 to 30 days are tested.In addition,the effects of wind speed and curing con ditions on the dry shrinkage deformation and internal relative humidity distribution of concrete specimens were studied.3.According to the test results,the relationship between relative humidity and dry shrinkage deformation of concrete specimens is fit ted by least square method.According to this relationship,the method of measuring relative humidity in concrete structure can be used to predict and control the dry shrinkage deformation of concrete structure in practical engineering.4.The relative humidity of concrete specimens at different depths under different wind speeds and curing conditions was studied.In the test,the relative humidity of concrete at the distances of 30 mm,45mm and 60 mm from the drying sur face was measured and analyzed.The moisture field of concrete is simulated and analyzed by ANSYS finite element software,and the test results are verified and analyzed.5.According to the results of experiment and numerical analysis,the causes and preventive measures of cracking in integral ballast bed are elaborated from two aspects of design and construction,and the effect of the preventive measures adopted in practical projects is tracked and verified,which proves the effectiveness of the measures.6.On the basis of the research and summary of the existing crack repair measures and techniques,this paper puts forward the method of combining pressure grouting with surface sealing to repair the cracks in the integral ballast bed,and the corresponding repairing technology is improved.