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CA mortar, as a filling layer, has been widely used in slab ballastless track. Since the creep deformation directly determines the track regularity and the train ride comfort, we investigated the effect of various stress levels on CA mortar creep. Results showed that the creep strain of CA mortar increased by 10 times when the stress level increased from 10% σ p to 40% σ p . Furthermore, it was first discovered that creep of CA mortar was attributed to the organic–inorganic interface slip and the propagation of microcracks. This work proposed a new CA mortar creep model based on the micro-meso structure characteristics, and its accuracy of prediction was much higher than previous models, R2 > 0.93. [ABSTRACT FROM AUTHOR]

Cement and emulsified asphalt (CA) mortar is a critical viscoelastic component of ballastless track systems, exhibiting pronounced temperature sensitivity. However, accurately predicting the mechanical responses of CA mortar due to temperature fluctuations remains a challenge. This work proposes a novel variable-order fractional Maxwell (VOFM) model to investigate the viscoelastic properties of CA mortar under temperature variations. The VOFM model is numerically solved using a time-varying coefficient ladder (TVL) model. The VOFM model is validated by comparing with both numerical integration methods and experimental data. The basic properties of the VOFM model, the viscoelastic responses of CA mortar under varying temperatures and alternating stress are systematically investigated. The results show that the mechanical properties of VOFM model agree with the FM model when time-dependent parameters of the VOFM model correspond to that of the FM model. Moreover, high temperatures have a promoting effect on the deformation of CA mortar under both alternating and constant stress conditions. The peak amplitude of CA mortar strain under practical varying temperature and stress loading correlates with the trend of temperature changes. • A VOFM model predicts CA mortar's viscoelasticity under temperature variations. • The VOFM model is numerically solved by a time-varying coefficient ladder model. • The VOFM model is validated with numerical methods and experimental data. • High temperatures have a promoting effect on the deformation of CA mortar. • The strain of CA mortar shows a positive correlation with temperature fluctuations. [ABSTRACT FROM AUTHOR]

The fatigue life of the cement asphalt (CA) mortar in the slab track of the China Railway Track System (CRTS) II is crucial to the smooth and safe operation of high-speed railways. To investigate the fatigue life of the CA mortar under the combined thermal action and vehicle loads, this paper develops a new coupled thermal-mechanical finite element (FE) model for the concrete slab track at the mesoscale. First, the meteorology and heat transfer principle are adopted to simulate the temperature distribution of the concrete slab track. The heterogeneous characteristics of the concrete of the precast slab are modelled by the three-phase composite material at the mesoscale using the new developed random aggregate algorithm. Then, the energy-based exponential cohesive zone model is adopted to simulate the interface between the CA mortar and the precast concrete slab. The proposed mesoscale numerical model can provide reliable predictions for the temperature distribution and the deformation of the precast concrete slab under thermal action, which are confirmed by the relevant field measurements. Finally, the fatigue life of the CA mortar is estimated by the nonlinear damage cumulative method associated with the stress time history under the combined thermal action and vehicle load. From the obtained results for the numerical example, the thermal action can decrease severely the fatigue life of the CA mortar, and the fatigue life varies significantly at different positions, with the most vulnerable zone located near but not directly below the rails. • Proposing the coupled thermal-mechanical FE numerical modelling for railway concrete slab tracks. • Developing new random aggregate algorithm for modelling heterogeneous concrete at the mesoscale. • Predicting reliably CA mortar fatigue life using nonlinear damage cumulative method under combined action. [ABSTRACT FROM AUTHOR]

In acid rain regions of Southwest China, cement-emulsified asphalt mortar (CA mortar), a key structure component in China Railway Track System (CRTS), is reported with more serious damaged signs than other locations. To investigate the effects of acid rain on its durability, the CA mortar specimens were immersed in acid solutions with pH values of 3.0, 4.0, and 5.0 for 21 months. Scanning electron microscope (SEM), energy dispersive spectrometer (EDS), differential thermal analyzer (DTA) and biological microscope were applied to evaluate the deterioration mechanism. Cracking, desquamation, pulverization, and decreased compressive strength were observed in them. The results of SEM and EDS show that a large number of crystals, rich in Ca, S and O, deposited on surfaces of the specimen soaking in the solutions, which is related to gypsum as shown in DTA pattern. Also, DTA patterns show that the decomposition peak of calcium silicate hydrate (C–S–H) gel in CA mortar specimens decreased gradually from the internal to the external surface. The analysis of acid solution based on the biological microscope indicates that large amounts of filamentous fungi and yeast existed in the solution during the long-term soaking, which corresponds to the investigation of the seriously damaged CA mortar in the field. In conclusion, deterioration mechanisms of CA mortar by acid rain includes CaSO 4 ·2H 2 O crystalline expansion damage, decomposition and dissolution of C–S–H gel and biological corrosion when the alkaline environment was damaged. [ABSTRACT FROM AUTHOR]

Dynamic compression test of cement asphalt (CA) mortar specimens, due to water immersion history of 0d, 7d, 14d and 30d, are carried out using a universal electronic test machine, with the strain rates ranging from 1×10-5 s-1 to 1×10-2 s-1. The stress-strain full curves, the compressive strength and the elastic modulus of CA mortar at different strain rates and water immersion durations are analyzed and the effects of strain rates and water immersion duration on these behaviors are studied. Experimental results demonstrate that the compressive strength and elastic modulus increase with the strain rate. In the same strain rate, the compressive strength decreases with the increase of water immersion duration, but the elastic modulus decrease first and then increase with the increase of water immersion duration. The largest reduction of average compressive strength of CA mortar is 46.5 %, and the largest reduction in the average elastic modulus of CA mortar is 47.5 %. A vertical coupling vibration model for a vehicle-railway track-subgrade system was established on the base of wheel-rail coupling dynamics theory and experimental results. The effects of elastic modulus deterioration of CA mortar on the dynamic responses of the vehicle and railway track system were studied. The results show that the reduction of CA mortar has little influence on the dynamic properties of the track and the running stability. [ABSTRACT FROM AUTHOR]

In this paper, water seepage of cement asphalt emulsified mortar (CA mortar) was studied in a small-scale track model, including the seepage rate, the chemical composition of the seeping water and its effects upon CA mortar. It is shown that the seepage time is negatively correlated to the environment temperature. A higher temperature would lead to a shorter seepage time, while the cumulative amount of seepage is similar. Seepage may be induced by the volume expansion of CA mortar in the early age, which is evidenced by a positive correlation between the seepage rate of the small-scale mortar sample and the expansion rate measured on a cylindrical sample. The solid components in the seeping water is low, initially less than 12% and ultimately at 3–4%, thus has negligible effect on the mix proportion. In addition, a “size effect” is noted, in which the water seepage is more significant in the field, compared with the small-scale model. [ABSTRACT FROM AUTHOR]

Cement and emulsified asphalt mortar (CA mortar) consists of cement, emulsified asphalt, sand, water, and other additives, which can be used as a vibration attenuator and isolation casting layer in modern high-speed railway. However, the dynamic mechanical properties of CA mortar have not been well documented until now. In this paper, a series of experiments were carried out to characterize the dynamic properties of CA mortar. It can be found from the test results that the compressive strength, the compressive strain, and the elastic modulus are much more sensitive than traditional Portland cement mortar and concrete in a specified range of strain rate. Meanwhile, experimental results from an impacting acceleration test presents that CA mortar had excellent vibration attenuation and isolation functions. [ABSTRACT FROM AUTHOR]

• Interface damage properties were experimentally investigated by a combination of AE and DIC techniques. • The microscale damage characteristics were studied by the AE technique. • The macroscopic deformation processes were studied by the DIC technique. • A bilinear CZM model for the interface was proposed and its parameters were calibrated by the experimental data. Since the interface is often regarded as the weakest part of the ballastless track structure, there is a great need to investigate the interlayer bonding performance to ensure the safety of train operations for high-speed railways. In this study, the damage characteristics of the interface between China Railway Track System II (CRTS II) slab track and cement emulsified asphalt (CA) mortar (T-CA interface) under shear loading were thoroughly investigated. The interfacial deformation and damage development process during the direct shear experiments were recorded by a combination of acoustic emission (AE) and digital image correlation (DIC) techniques. Consequently, a bilinear cohesive zone model (CZM) of the T-CA interface was proposed. The results show that the AE activities are rare in the initial stage of loading, while they increase sharply when the shear loading approaches the interface bonding strength. The AE parameters can well characterize the entire process of interfacial failure. Through the DIC technique, the macroscopic deformation process was well captured and the shear stress versus relative displacement curves were derived. Subsequently, the relationship between the shear stress and relative displacement of the interface was well fitted by a bilinear CZM, of which parameters are calibrated through the experimental data. The effectiveness of the proposed bilinear CZM is validated by using a three-dimensional finite element model. This work provides a better understanding for the damage mechanism of the bond performance between CRTS II track slab and CA mortar. [ABSTRACT FROM AUTHOR]

Cement-asphalt mortar (CA mortar) is an inorganic-organic composite, which combines both advantages of the mechanical property of cement and flexibility of asphalt. Therefore, it has been widely applied in high-speed railway and used as a kind of semi-flexible pavement material. Cement hydration process can affect the rheological property of fresh cement-asphalt paste as well as the mechanical and durability properties of the hardened cement-asphalt paste. Whereas, the interaction of emulsifier and cement particles will significantly affect the hydration process. Hence, the influence of emulsifier on cement hydration was investigated though measuring of setting time, hydration heat, ions concentration and electrical resistivity. It is indicated that the cement hydration process was retarded with the addition of emulsifier according to the results of the setting time and the hydration heat, and meanwhile, the hydration process was delayed gradually with the increasing dosage of emulsifier. The mechanism of the retardation effect can be attributed to the occupation of emulsifier at the active sites of cement particles, therefore, the delaying of cement hydration was further confirmed by the results of the lower ions concentration of the paste mixed with emulsifier. More specifically, for the cement mixed with emulsifier, a protective layer formed around the cement particles and this protective layer hindered the releasing of ions. As is well known, electrical resistivity is an indicator parameter which can indicate the cement hydration process and the formation of micro-structure effectively, thus, the variation law of the electrical resistivity can also reflect well the retardation effect of emulsifier on cement hydration. [ABSTRACT FROM AUTHOR]

Abstract: This contribution first presents a fatigue model to elaborate fatigue behavior of materials subjected to thermal mechanical effect. To calibrate the presented model, a valid experiment is then conducted on cement asphalt mortar. The model can be further extended to other materials and valid experimental data from literature is utilized for verification. Results suggested the model is sufficient to describe thermo-mechanical fatigue behavior of cement-based materials, under the condition that no phase or morphological change occurred in the fatigue temperature range. Finally, the developed model is applied to predict fatigue life of one current track. [Copyright &y& Elsevier]

Abstract: In order to find a new test method to investigate the relationship between the compositions and fluidity of the cement and emulsified asphalt mortar (CA mortar), the conductivity and the fluidity properties of the fresh CA mortar with different mixtures were studied by analysis of the relationships among the liquid fraction, the “J” type funnel flowing time and the conductivity. Results showed that (1) the electrical conductivity was linear relationship to the liquid volume fraction of the slurry, but markedly influenced by thickening agent, (2) there exist apparent relationship between the flowing time of fresh CA mortar through “J” type funnel and liquid volume fraction, also and electrical conductivity, (3) the difference of the density showed good linear relationship with the difference of the electrical conductivity caused by the segregation. [Copyright &y& Elsevier]

Abstract: A laser diffraction particle size analyzer was employed to measure the particle size variations of two asphalt emulsions under stress conditions to evaluate their storage stability, freeze–thaw stability, and mechanical stability. Results showed that when the dosage of non-ionic emulsifier was increased from 0.4% to 0.8%, the particle size and its increasing magnitude were both reduced, indicating a more stable emulsion. This new method can provide the desired information for fast and continuous evaluation on the dynamical changes of emulsion stability under stress conditions, compared to the traditional storage stability tests. [Copyright &y& Elsevier]

• The newly developed two-phase model class selection algorithm for void detection is firstly proposed. • The time-domain Bayesian model updating is successfully conducted for the CA void detection of the ballastless slab track by determining the most probable values (MPVs) of mortar stiffness scaling factors. • Not only the void location but also the severity of CA mortar are detected for ballastless slab track. This paper reports the feasibility study on the use of measured vibration of a railway slab track system in detecting void on the cement-emulsified asphalt (CA) mortar layer utilizing the Bayesian approach. By following the specification of the China Railway Track System (CRTS)-I ballastless slab track structure, two scaled models (with and without void in the CA mortar layer) were built and tested in the laboratory to demonstrate and verify the proposed CA void detection methodology. A three-dimensional finite element model was built using ABAQUS to calculate the time-domain data of the ballastless track system for Bayesian model class selection and model updating. A new two-phase model class selection algorithm was developed for identifying the CA void region. The proposed methodology identified the distribution of CA mortar stiffness using impact hammer test data from the scaled CRTS-I ballastless slab panel under laboratory conditions. The model updating results are consistent with the simulated CA mortar stiffness distribution. In addition, the posterior uncertainties of the identified CA mortar stiffness under different sensor configurations were quantitatively investigated. The results from the experimental case studies show that the proposed Bayesian methodology is feasible to detect CA void even with only a single accelerometer with the associated posterior uncertainties being kept at an acceptable level. [ABSTRACT FROM AUTHOR]

• The secondary development of fatigue damage constitutive for CA mortar was conducted. • A damage-finite element full-couple calculation method of CA mortar was established. • Stress redistribution of CA mortar for ballastless track was caused by severe damage. • 0.5 was a critical stress level to determine whether the redistribution should be taken into account. Ballastless track withstand tens of millions or even hundreds of millions of times of train loads, its functional parts are prone to fatigue failure. In this paper, the high-cycle fatigue damage constitutive relationship of CA mortar was developed as a material subroutine, to embed into the refined FE model of CRTS-I ballastless track, establishing a damage -finite element full-couple method to analyze the influence of key factors such as void, initial deterioration and wheel load on the accumulation of fatigue damage of CA mortar. Main conclusions are as follows: void plays a more important role in the accumulation of fatigue damage of the CA mortar than initial deterioration and wheel load change. When the void length is 2.0 m, the damage value of the structure under 15 million times of wheel loads has exceeded 0.36, which is 5 orders of magnitude higher than that under the non-void condition. Laterally, the load stress below the loading point on the rail is significantly larger than at other positions, and the load stress distribution gradually gets uniformed. Along the longitudinal direction of the CA mortar, the stress at core bearing elements gradually decreases with the increase of damage, while the decreased stress is compensated by the increased stress in a certain distance from the void end along the longitudinal direction. With an initial deterioration of 50%, when the wheel load is 150 kN, the position below the rail reaches the maximum damage first, followed by the void edge, and then the damage spreads further into the middle part of the CA mortar along the lateral direction until the whole elements from the top surface at the void edge is damaged. In our study that spanned 15 million times of fatigue loading cycle, the stress level 0.5 was a critical value to determine whether the load stress redistribution caused by damage should be taken into account when using the damage - finite element full coupled method. [ABSTRACT FROM AUTHOR]

• Study the relationship between mechanical properties and composition of CA mortar. • A mechanical model of CA mortar from four different levels was proposed based on experimental results and theoris. • The asphalt has a limited contribution to the static compressive strength f and elastic modulus E CA of the CA mortar. As an organic–inorganic composite material, the mechanical properties of cement asphalt mortar (CA mortar) are closely related to its composition. In order to studying the relationship between mechanical properties and composition of CA mortar, a mechanical model of CA mortar from four different levels (i.e.,cement hydration products, cement gel skeleton, cement-asphalt composite system and CA mortar) was proposed based on the microscopic experimental results, the gel-space ratio theory and the Hashin composite ball model. The mathematical relationships among the elastic modulus of CA mortar, compressive strength f and composition parameters were derived. The results shown: The volume fraction of cement hydrates is an important parameter affecting the CA mortar elastic modulus E CA and the compressive strength f. When the asphalt is regarded as a pore or a low modulus phase, the static elastic modulus of the CA mortar E CA and the volume fraction of cement hydrates V CH , the compressive strength f and gel-space ratio x all have a power function relationship, and R 2 > 0.7. The cement hydrates in the CA mortar are still a continuous phase and constitutes the composite gel skeleton, asphalt interspersing among them, and the contribution of asphalt to the CA mortar strength and elastic modulus is relatively limited. [ABSTRACT FROM AUTHOR]

• The influence of cyclical temperature treatment on the interface between CA mortar and concrete was studied. • The mechanism of interface damage was analyzed by SEM, MIP, TG and DTA. • The softened asphalt moved into capillary pores at high temperature. Cement and emulsified asphalt mortar (CA mortar) has been widely used as a filling layer between concrete bed plates and track slabs for high-speed railways. This study analyses the cracking mechanism of the interface between CA mortar and the concrete under CT treatment (cyclical temperature from −40 °C to 60 °C) and CTI treatment (cyclical temperature from −40 °C to 60 °C then immersed in water) by means of scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), thermos-gravimetric analysis (TG) and differential thermal analysis (DTA). Results showed that cracks were observed on the interface after 16 CT cycles, while 25 cycles were required to observed cracks for sample under CTI treatment. The samples subjected to the CT treatment had a larger length difference between the CA mortar and concrete at high temperature. The volume proportion of 2–10 μm-level pore in CA mortar was declined after CT or CTI treatment, which was caused by removal of asphalt component in CA mortar from the matrix to the capillary porosity as confirmed by SEM results. CT treatment made it clear that the substance of low melting point in the asphalt either volatilized or turned into the substance of high melting point from TG and DTA analysis. [ABSTRACT FROM AUTHOR]