Research On Detection And Evaluation Of Interface Defects Of The Filling Layer In The CRTS Ⅲ Slab Ballastless Track Structure

The CRTS Ⅲ slab ballastless track structure is a new track structure of the high-speed railway with completely independent intellectual property rights in China.Its under track part is composed of the steam-cured concrete precast plate,the self-compacting concrete(SCC)filling layer,the geotextile isolation layer and the base plate.The lower part of the steam-cured concrete precast plate is provided with door type rebars,which is connected with the SCC filling layer to form a composite slab structure.Due to the complexity of the construction technology and the difference of the aggregate and the slurry in the SCC mixture system,there are often bubble defects in the interface between the SCC filling layer and the steam-cured concrete precast plate after construction,which affects the interface adhesion between the SCC filling layer and the steam-cured concrete precast plate,and even endanger the safety and durability of the entire track structure in service.At present,scientific and efficient detection and evaluation methods have not been formed for the defects of the hidden interface between the SCC filling layer and the steam-cured concrete precast plate.In view of the above,combined with the important requirements and technical status of the SCC filling layer interface defect detection and evaluation of a large number of the CRTS Ⅲ slab ballastless track structure in China,through theoretical analysis and a large number of field tests,this dissertation innovatively develops the nondestructive detection method of the SCC filling layer interface defects based on the principle of the impact stress wave,and constructs the evaluation method of the SCC filling layer interface quality based on the interface defect rate and the bonding performance.The corresponding nondestructive testing and evaluation system is developed to realize the rapid and reliable detection and evaluation of the SCC filling layer interface defects.The main achievements are as follows:(1)The main types and characteristics of the interface defects in the SCC filling layer were clarified.Based on the characteristics of the interface defects,the apparent state of the SCC filling layer interface was divided into five types: well-bonded,a local small bubble group,a local bubble loose thin layer,edge crack and continuous honeycomb vesicle layer.In the case of interface defects,the statistical analysis showed that the proportion of a local small bubble group defects was about 70%,the proportion of a local bubble loose thin layer defects was about 20%,the proportion of edge crack was about 5%,and the proportion of continuous honeycomb vesicle layer was about 5%.It provided an important basis for the detection of interface defects via impact stress wave.(2)The propagation law of the impact stress wave in the CRTS Ⅲ slab ballastless track structure was revealed,and the mapping relationship between the impact-echo spectrum and various defects in the SCC filling interface was established.Therefore,the SCC filling interface defect detection technology based on the impact-echo method was proposed.The influences of factors such as the distance between the measuring points,the wet and dry state of the surface to be measured,and the age of the SCC via the impact-echo detection results were obtained,and the corresponding effective detection conditions were established.(3)The identification function of the SCC filling layer interface defect was constructed with the characteristic peak amplitude of the impact-echo spectrum as the basic parameter,and the value distribution range of the interface defect identification function corresponding to different types of interface defects was obtained.The reliability and practicability of the interface defect identification function were verified through on-site uncovering tests,and the accuracy rate of the interface defect identification function could reach 90%.(4)The correlation between the interface defect of the SCC filling layer and the interface splitting tensile strength was analyzed.By constructing a model of joint support vector machine and particle swarm optimization(SVM-PSO),a prediction method of the interface splitting tensile strength based on the interface defect rate was proposed.The relative error rate between the predicted value and the experimental value was less than 5%.(5)A detection and evaluation method of the interface quality based on the interface defect rate and the interface bonding performance was proposed,and three quality levels were divided.A special filling layer interface quality detection and evaluation system of the CRTS Ⅲ slab ballastless track structure was developed.An intelligent platform construction method based on the combination of the intelligent detection and the intelligent evaluation was proposed.