Effect Of Temperature Load On CA Mortar Filling Layer Of CRTS ? Slab Track

CRTS ? slab track is a popular track type used in the high-speed railway in China, which can provide necessary riding safety, quality and comfort for high speed trains. The so-called SLAB is composed of several layers, which, under the combined effect of train load, temperature and other environmental factors, may lead to various failures in the track structure system. Among them, CA mortar filling layer may suffer most, and is prone to a series of defects, such as debonding, gap, cracking, spalling. The CA mortar is the critical functional material packed between track slab and base slab, providing the functions in terms of support, adjustment, damping, vibration isolation and crack prevention. Therefore, the performance of CA mortar directly matters the durability of the entire CRTS ? slab track and the riding safety of trains. However, no systematic study has ever been reported on the effect of temperature load on CA mortar filling layer of CRTS ? slab track. This paper is intended to fill this gap. The paper includes the field study on the defects of CA mortar filling layer, summarizes previous achievements in relation to the damage of CA mortar filling layer, and then studies the rules of temperature load in effecting CA mortar filling layer by analyzing:(i) the effect of solar temperature on CRTS ? track slab; (?) deformation characteristics of C A mortar of different degradation forms under the effect of variable temperatures; (?) mechanical properties of CA mortar under the effect of variable temperatures, water-temperature coupling and acid rain; and (?phase composition and microstructure of CA mortar. The main efforts and achievements are follows:1. The boundary conditions for analyzing the effect of solar temperature on ballastless track was constructedThe paper summaries the basic features of solar temperature distribution and temperature stress for the ballastless track and provides basic assumptions and basic differential equation and definite conditions of thermal conduction for the study of temperature effect of the ballastless track. Then, the paper, by relying on applicable theories of solar physics, general astronomy and heat transfer theory, describes the mechanism of heat transfer between the ballastless track and the ambient, and then establishes the boundary conditions for analyzing the effect of solar temperature on ballastless track.2. A 3D solid thermal-structure coupling model for analyzing the effect of solar temperature on ballastless track was constructed and the temperature field of CRTS I slab track was analyzedA 3D solid thermal-structure coupling model for analyzing the effect of solar temperature on ballastless track was set up based on FEM and in consideration of the features of CRTS ?slab track, and was thereby validated. The distribution characteristics of the temperature field of CRTS ? slab track was analyzed by calculation and the relevant influential factors were studied. The results show that:(?) The variation in track temperature lags behind the variation in air temperature, this fact changes non-linearly with the depth, and the greater the depth, the severer the lag; the track temperature changes non-linearly in lateral direction, and the severest variation occurs at the peripheral of the track. (?) The intensity of solar radiation, wind speed, daily temperature difference, thermodynamic parameters of material and structural dimension are all influential factors of the distribution of temperature field. Among which, the intensity of solar radiation has the most notable effect, the track temperature rises linearly with increasing the intensity of solar radiation; the greatest amplitude of temperature rise occurs at slab surface, however, the amplitude of temperature rise decreases and the temperature difference between layers is enlarged with depth.3. The distribution characteristics of solar temperature field and temperature load for CA mortar filling layer was analyzedThe distribution characteristics of temperature field and temperature load for CA mortar filling layer was analyzed by calculation with the above 3D solid thermal-structure coupling model. The results show that:(?) the temperature of CA mortar filling layer changes non-linearly in lateral direction, forming a high lateral temperature gradient within 0.2m of the slab side; (?) the slab corner suffers from the greatest interlayer stress, which explains the initiation of debonding and gap at slab corner and sides; as the elastic modulus of CA mortar increases, the interlayer stress increases significantly and linearly; (?) the temperature of CA mortar filing layer may change between -40? and 60? during the service life; and (?) When the track slab and CA mortar layer debond, the upwarp may be worsened, besides, the combined effect of train load and temperature load further aggregates the fatigue rupture of CA mortar filling layer.4. The creepage and deformation characteristics under cyclic loading/unloading for CA mortar of different degradation forms under the effect variable temperatures were analyzedThe creepage and deformation characteristics under cyclic loading/unloading for CA mortar of different degradation forms under the effect variable temperatures were analyzed by single-axis dead load test. The results show that:(?) the CA mortar is obviously viscous-elastic, then the creep compliance curve of the mortar at different temperatures can be well fit with Burgers model; (?) as the test temperature rises, the instantaneous elastic deformation increases, the viscous flow deformation of the CA mortar under loading increases, and the slope of creep curve becomes elevated; the creep accumulated deformation of CA mortar is dependent on the ageing, wastage of asphalt and water softening effect, and increases with temperature rise; however, the creep stiffness module of CA mortar test piece decreases with temperature rise; (?) the compressive strength of CA mortar linearly decreases with increasing the strain increment of cyclic loading and unloading; under the effect different test temperatures and strain increments, both the common point strain and residual plastic strain increase linearly with increasing the strain at unloading initiation point; and (?) the creepage characteristics and deformation characteristics under repeated loading/unloading of CA mortar are the main cause of the extrusion of CA mortar layer, debonding from track slab, as well as gaps.5. The effect of variable temperatures, water-temperature coupling and acid rain on mechanical properties of CA mortar was analyzedThe effect of variable temperatures, water-temperature coupling and acid rain on mechanical properties of CA mortar was analyzed with single-axis dead load test. The results show that:(?) the CA mortar suffers from flexible failure under single-axis compression, the test piece has cracks on the surface but remain integral; (?) all test pieces have similar stress-strain curves; the ageing of asphalt, erosion by acid rain, softening effect of water as well as train load have great impact on the stress-strain curve of CA mortar; (?) the elastic modulus and compressive strength of test pieces decrease slightly with temperature rise, and the relationship between the two parameters and temperature presents an approximate Doseresp function; the compressive strength and elastic modulus of test pieces are basically in linear relation under different test temperatures; (?) the damage stress threshold of CA mortar drops with increasing the test temperature; (?) water-temperature coupling effect significantly degrades the mechanical properties of CA mortar, and (?) the long-term effect of acid rain leads to serious chemical corrosion and biological damage to CA mortar.6. The microstructure and phase composition of CA mortar of different degradation forms was analyzed by means of XRD, TG-DTA, FTIR, SEM and EDSThe effect of environmental corrosion and loads on the microstructure and phase composition of CA mortar was analyzed by means of XRD, TG-DTA, FTIR, SEM and EDS. The results show that:(?in practical operation, the degradation of CA mortar is dependent on ettringite erosion, acid erosion and ageing of asphalt; (?) under the effect of acid rain and water erosion, the components of low molecular weight in the asphalt of CA mortar is washed away, the components in asphalt changes, where component B (asphaltene-related) was changed into component A (aromatics-and colloid-related)(?) for the CA mortar in practical operation environment, its inner structure is loose under long-term effect of train load, a lot of elongated needle-shaped crystals occur, the asphalt membrane on the surface of hydration product gradually disappears, and the pore structure was totally destroyed; and (?) train load and water erosion are the root cause of the wastage of asphalt and the destroy of grid structure of CA mortar filling layer.