Cement Emulsified Asphalt Mortar Research Articles

Microstructure in Adhesion Development Process and Strength Formation Mechanism in Early Stage of Cold Recycled Mixture with Emulsified Asphalt

With the large-scale maintenance and renovation of asphalt pavement, a considerable amount of reclaimed asphalt pavement (RAP) will be generated. Stacking these wastes occupies a large amount of land and seriously damages the ecological environment. Hence, efficient regeneration of RAP through recycling technology has gained more and more attention. In this paper, some topics were reviewed to further promote the cold recycling (CR) technology and better follow-up the research progress. First, it discussed the raw materials and the differences and similarities between cement-emulsified asphalt mortar (CEAM) and cold-recycled mixtures with emulsified asphalt (CRME). Second, it reviewed the adhesion development of emulsified asphalt mastic, the application of X-ray technology in microscopic study of CRME and the characteristic of strength development of CRME. The adhesion development of CRME begins with the process of demulsification and hydration caused by the migration and dissipation of water inside the emulsified asphalt mastic. In addition, many factors would influence this process simultaneously. However, the microbehavior mechanism of internal water transport in emulsified asphalt mortar has not yet been thoroughly revealed, and it lacked scientific measurement research on the promoting effect of complex conditions on the development of adhesive properties of mixtures. Therefore, in this paper, they were suggested for future research.

Laboratory investigation on the fracture toughness (Mode I) and durability properties of eco-friendly cement emulsified asphalt mortar (CRTS II) exposed to acid attack

Cement Emulsified Asphalt Mortar (CEAM) has gained prominence as a vital material for its energy and noise damping properties between the concrete roadbed and track slab in a high-speed railway system. Therefore, it is evident that CEAM properties need to be better understood and optimized. Since cracking caused by traffic loading and atmospheric conditions is one of the primary causes of failure in CEAM, addressing this issue is of great importance. Furthermore, there is a growing need for more environmentally friendly and durable CEAM due to the environmental impact of cement production in the form of greenhouse effect. The objective of this study is to assess the impact of partially replacing cement content in CEAM Type II (CRTS II) specimens with pozzolanic materials such as silica fume, metakaolin, and granite sludge to investigate how these pozzolans affect the fracture toughness (Mode I) performance under both normal (water curing) and sulfuric acid exposure conditions with the main focus on evaluating the pozzolans ability to resist acid attack from a fracture toughness perspective as the research novelty. For this purpose, specimens containing pozzolans at 5 %, 10 %, and 15 % substitution level (by weight of cement) were subjected to Semi-Circular Bending (SCB) test both under normal and exposure to 5 % sulfuric acid solution conditions. Moreover, water absorption test was conducted on specimens in normal condition as a durability index. The test results of this study revealed that substitution of these pozzolanic materials enhanced the fracture toughness in normal condition. Specifically, at a 10 % substitution as the optimal level, silica fume and metakaolin resulted in 18 % and 15 % increase in fracture toughness performance compared to the control specimen in normal condition. However, granite sludge exhibited almost the same performance as the control specimen at 5% substitution as its optimal level. In acid exposure condition, the detrimental effect of acid on the fracture toughness performance of specimens was reduced by 61 %, 55 % and 13 % for samples containing silica fume, metakaolin and granite sludge at 15% substitution level, respectively. Furthermore, water absorption test results showed that inclusion of silica fume and metakaolin at a substitution level of 15 % results in 56 % and 47 % reduction in water absorption compared to the control specimen, respectively, while for granite sludge, it was almost the same as control specimen. These results were also confirmed by SEM studies. Since the use of these pozzolans as cement substitution not only improves the fracture toughness in normal condition but also provides protection against acid-induced degradation, this study contributes to the development of a more durable and environmentally friendly CEAM.

Exploring the influence of cement and cement hydration products on strength and interfacial adhesion in emulsified cold recycled mixture: A molecular dynamics and experimental investigation

This study employed experimental methods and molecular dynamics simulations to investigate how cement and its hydration products affect the mechanical strength and interfacial properties of emulsified cold recycled mixtures (ECRM). The effects of cement hydration product characteristics, such as content, number of nucleation sites, calcium-silicon (Ca/Si) ratio, degree of hydration, and types of hydration products, on the adhesion and water resistance of the cement-emulsified asphalt mortar (CEAM)-aggregate interface, were studied. The findings revealed that increasing the cement content by up to 2% improved the ECRM's mechanical strength. However, the mechanical strength decreased beyond a cement content of 2%. Molecular dynamics simulation demonstrated that augmented cement hydration product content fostered greater adhesion at the interface between CEAM and the aggregate. The presence of an adequate number of nucleation sites was crucial for cement hydration products' effectiveness in strengthening the interface adhesion. Moreover, hydration products with higher degrees of hydration or Ca/Si ratios exhibited a more pronounced impact on enhancing interface adhesion. Furthermore, cement hydration products enhanced the interfacial water resistance of the CEAM-aggregate interface. Nonetheless, the extent of this improvement depended on the interfacial water content. When the interfacial water content was high, the water resistance decreased, and the influence of cement hydration products became negligible. These results highlight the important role of cement and its hydration products in determining the mechanical properties and interfacial characteristics of ECRM and provide insights for optimizing the design and application of such materials in engineering practice.

Study on the interface damage of CRTS II track slab under high- and low-temperature cycles based on acoustic emission

China Railway Track System (CRTS) II slab tracks have been widely used in high-speed railway construction. Interface debonding between the track slab and cement-emulsified asphalt (CA) mortar is one of the typical diseases of the CRTS II slab tracks. Properly evaluating the interfacial strength of the track slab and CA mortar under high- and low-temperature cycles is crucial for optimizing the repair in engineering practices. In this study, the track slab and CA mortar (TSCAM) composite specimens were prepared for high-low temperature cycle (HLTC) tests. Then, the shear and tensile tests were carried out to study the interlayer bonding properties of TSCAM under different HLTCs. In addition, the acoustic emission (AE) technique was employed to monitor the signals generated in the specimen during the tests. Furthermore, the AE parameters were analyzed, including ringing counts, energy, b-value and amplitude-frequency. The results show that the number of HLTCs significantly contributed to the deterioration of the interface bond strength between the track slab and the CA mortar. The interface normal bond strength showed a higher decrease than the tangential bond strength with the increase of HLTCs. In addition, the relationships of the shear and tensile bond strength of the TSCAM composite specimen with HLTC were deduced. The tangential and normal bond strength degradation properties of the composite were well fitted by the function of quadratic polynomial and power exponents, respectively. The AE activities of the composite specimens in the shear and tensile tests were gradually reduced with increased HLTC. The AE signals were the strongest when the specimen failed along the interface. Furthermore, the intensity of AE events during the shear test was higher than that during the tensile test under the same HLTC. The overall b-values of the shear and tensile specimens without HLTC were the largest and did not change significantly with the increase of HLTC. The amplitude range of the peak frequency gradually decreased as the HLTC increased. The amplitude and peak frequency of the tensile test was smaller than that of the shear test under the same HLTC. This indicates that the AE technique can monitor the interface damage evolution pattern of the TSCAM composite specimen throughout the tests.

Mixed mode (I&III) fracture behavior of cement emulsified asphalt mortar under freeze and thaw cycles

The present study was designed to evaluate the impact of freeze and thaw cycles on pure tensile (I), pure shear (III), and mixed tensile–shear (I/III) fracture of Cement Emulsified Asphalt Mortar (CEAM) with diverse mix designs. For this purpose, a large number of Edge Notched Disk Bend (ENDB) specimens were fabricated with 16 different random mixture designs with various amounts of cement content (C) and different proportions asphalt-to-cement (A/C) and water-to-cement (W/C) proportions. The specimens of each mix design were divided into five groups: one control group (no freeze and thaw) and four test groups where the specimens underwent 1, 3, 5 and, 10 cycles of freezing and thawing. All of the specimens were then fractured in pure opening mode (I), pure tearing mode (III), and mixed opening–tearing modes (I/III). The results evinced that applying the cycles of freezing and thawing diminished the mortar’s fracture energy in each of the three modes. This drop was more intense after the initial cycles and became less so with an addition in cycles. The freeze and thaw-induced change in the fracture properties was measured in terms of the ratio of the fracture energy of the conditioned specimen in the specified mode to that of the control specimen, denoted by FERi. The FERi of mortars with different mix designs was estimated by developing multiple regression models to explain the relationship between this index’s experimental values and mix design variables (A/C, W/C, C) at the 0.05 significance level. Among the independent variables, A/C had the greatest effect on mode-I fracture energy changes, and C had the greatest effect on mode III and mixed-mode I/III fracture energy changes due to the freeze and thaw damage. Considering the predicted FERi values, freeze and thaw cycles appear to have more damaging effects on the mixed mode I/III fracture properties of CEAM.

CA mortar void identification for slab track utilizing time-domain Markov chain Monte Carlo-based Bayesian approach

This paper investigates the feasibility and practicability study on the use of Markov chain Monte Carlo (MCMC)-based Bayesian approach for identifying the cement-emulsified asphalt (CA) void of the slab track system utilizing the measured vibration data. A newly developed model class identification algorithm was extended and integrated with the MCMC-based Bayesian approach for the first time to identify the CA mortar void that may partly extend to a neighborhood region. Not only the most probable values of the scaling factors to the mortar stiffness can be calculated, but also the damage probability of model parameters using the posterior probability density function (PDF) can be estimated, and the void can be clearly identified by the MCMC-based Bayesian approach. The proposed methodology was experimentally verified and positive outcomes were obtained. The detection results illustrate that the proposed method not only can successfully assess the void location of the CA mortar but also provide the information of the damage severity, and the posterior PDFs of model parameters can be also calculated by using kernel density estimation to quantitatively describe the uncertainty of the model.

Evolution Law of Micro-Pore Structure of Cement-Emulsified Asphalt Mortar Based on NMR

Cement emulsified asphalt mortar (CA) is widely used as the cushion of two types of ballastless track (CRTS I and CRTS II) in high-speed railways. Nowadays, the lack of durability of CA mortar has severely affected the quality of high-speed railways, failing to meet the requirements of sustainability. Since CA mortar is a kind of porous material, its performance can be significantly affected by its microstructures, which means that revealing the evolution law of its microstructures can provide the basis for improving its durability. Therefore, CA mortar species with different asphalt-cement ratio under different curing ages were prepared based on the requirements of CRTS II in this research and the pore structures were determined based on SEM and NMR methods. Then, a fractal model of CA mortar pore volume was proposed based on the concept of box fractal dimension, and the fractal dimension of pore volume was calculated. The relationship between fractal dimensions and mechanical property was analyzed based on Pearson correlation coefficient and regression analysis. The results suggested that the overall microstructure of CA mortar shows a loose porous space structure with cement hydration products being the continuous phase and asphalt being the dispersed phase. With the increase in A/C ratio, the hydration products produced by cement hydration decrease, and the total porosity and average porosity of CA mortar gradually increase due to the increase of asphalt hindering the hydration process of the cement. With the increase in curing age, the pore structure of CA mortar becomes more compact. However, the evolution law of CA mortar pore structure with age is not consistent under different A/C ratios due to the influence of asphalt. The pore structure of CA mortar was proved to have obvious fractal characteristics based on the concept of box fractal dimension and the experimental data of NMR. In addition, the correlation analysis proves that the fractal dimension of pore structure has an obvious positive correlation with the compressive and flexural strength, which suggests that the fractal dimension of pore volume can be a bridge for connecting the macro-property and micro-structures of CA mortar.

Experimental and statistical exploring for mixed-mode (I&II) fracture behavior of cement emulsified asphalt mortar under freeze–thaw cycles and aging condition

This study has been investigated the effect of freeze–thaw cycles and aging condition on the pure mode I, pure mode II and mixed-mode I/II fracture resistance of Cement Emulsified Asphalt Mortar (CEAM). The experiments were conducted on SCB specimens designed with 16 randomized mix designs with different cement contents (C), asphalt-to-cement ratios (A/C), and water-to-cement ratios (W/C) using the d-optimal response surface methodology. The specimens were divided into three groups: control specimens (n = 144), aged specimens (n = 144), and specimens subjected to 1, 3, 5, and 10 freeze–thaw cycles (n = 576). The experiments were performed in three modes of loading: pure tensile (I), pure shear (II), and mixed-mode tensile-shear (I/II). To assess the impact of freeze–thaw and aging damage on fracture properties, the Fracture Energy Ratio (FER) was defined as the ratio of fracture energy of the damaged/conditioned specimen to that of the corresponding control specimen. Then, a number of statistical models were developed for the relationship between FER and mix design variables (A/C, W/C, and C). The results showed that the application of freeze–thaw cycles reduced the fracture energy of CEAM in all three modes. The independent variable with the greatest impact on fracture energy changes was A/C for the pure tensile mode, and C for the pure shear mode and the mixed-mode tensile-shear. The initial freeze–thaw cycles were found to have a greater impact on fracture energy than later cycles. Also, freeze–thaw cycles are more detrimental in reducing mode II fracture energy than mode I and mixed-mode I/II fracture energies and therefore have a more damaging impact on the pure shear fracture properties of CEAM. Aging also reduced the fracture energy of CEAM in all three modes; an effect that was most greatly influenced by the amount of asphalt in the mortar composition. Aging had a greater impact on mode I fracture energy than mode II and mixed-mode I/II fracture energies.

Mixed mode-I/II fatigue performance of Cement Emulsified Asphalt Mortar: Experimental and statistical analysis at intermediate temperature

This study has investigated fatigue life of Cement Emulsified Asphalt Mortar (CEAM) under mixed-mode I/II loadings at the intermediate temperature. For this investigation, SCB specimens of 16 randomized mixture designs with different cement contents (C), asphalt-to-cement ratios (A/C), and water-to-cement ratios (W/C) were prepared and subjected to the cyclic mixed tensile-shear loading with Me = 0, 0.5, 1.0 at three frequencies of 2, 4 and 8 Hz. The results were analyzed using the d-optimal response surface method and revealed that for all three loading modes, the fatigue life increased with increasing C and A/C. The CEAM also showed a longer fatigue life in the pure shear mode than in the pure tensile mode. The difference between the fatigue life of mode I and II was found to be increasing with the increase in cement content and loading frequency. Increasing the loading frequency increased the fatigue life of the mortar in all three modes.

Experimental study on interfacial damage characteristics of CRTS II slab track and CA mortar with AE and DIC techniques

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.

Aging effect on the mixed-mode (I/III) fracture toughness of cement emulsified asphalt composite: Experimental and statistical investigation

Aging can affect the fracture behavior of bitumen-containing composites due to an increase in the total stiffness of the material. In this study, the effect of aging on the behavior of Cement Emulsified Asphalt Mortar (CEAM) under the mixed-mode I/III fractures was investigated at an intermediate temperature, and its fracture behavior was modeled with the aid of Response Surface Methodology (RSM). To collect the experiential data, several mix designs with different cement contents (C: [460, 500] kg/m3), bitumen-to-cement ratios (A/C: [0.3, 0.5]), and water-to-cement ratios (W/C: [0.4, 0.6]) were generated by Central Composite Circumscribed (CCC) method. Then, a series of fracture tests were performed on aged and unaged Edge Notched Disc Bend (ENDB) specimens. The results showed that for both aged and unaged (control) specimens, the highest fracture toughness is obtained under pure tensile mode and by increasing the contribution of mode III the corresponding value of fracture toughness decreases. The developed statistical models revealed that for unaged specimens, the increase in the A/C ratio has a significant effect on the stress intensity factors of mode I, mode III and mixed-mode I/III. However, for aged specimens, the effect of A/C is significantly observed in its interaction with W/C. The effect of aging on the fracture toughness of mortar was also measured with an index called the ratio of Aged to Unaged Fracture Toughness (FTRiAged/Unaged). The results showed that aging decreases the critical stress intensity factor of the mortar in the mode mixities, with the highest decrease of 15% under pure mode I.

A feasibility study on void detection of cement-emulsified asphalt mortar for slab track system utilizing measured vibration data

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.

A Review on Cement Asphalt Emulsion Mortar Composites, Structural Development, and Performance

The use of cement emulsified asphalt mortar (CA mortar) in the track structure of high-speed speed railways has been gaining considerations by many researchers due to its coupled merits of the strength of cement as well as the flexibility of asphalt material. The asphalt to cement ratio (A/C) and the compatibility among constituent materials are crucial to the properties of CA mortar. To improve the performance properties and application of CA mortar, it is imperative to have a broad understanding of the composition mechanisms and compatibility between constituent materials. This paper summarizes interesting research outcomes related to the composition and properties of CA mortar. The consumption of water by cement promotes the breakdown of emulsified asphalt, likewise, the adsorption of asphalt droplets on the surface of cement grains retards the hydration process of cement. An appropriate A/C is required for the cement hydration rate to match the speed of demulsification of asphalt emulsion. Depending on the type and properties for which the CA mortar is designed to possess, the A/C ranges from 0.2 to 0.6 for type 1 (CAM I), and 0.6 to 1.2 for type 2 (CAM II). This paper also discusses measures taken to improve performance properties, compatibility, the interaction between constituent materials of CA mortar, and the use of additives as a partial replacement of cement in CA mortar production. The current review also suggests areas of interest for future research studies. This paper is useful to those who aim to understand or study the composition mechanisms and performance properties of CA mortar.

Mechanical Performance of a Ballastless Track System for the Railway Bridges of High-Speed Lines: Experimental and Numerical Study under Thermal Loading.

The mechanical performance of China Railway Track System type II (CRTS II) ballastless track suitable for High-Speed Railway (HSR) bridges is investigated in this project by testing a one-quarter-scaled three-span specimen under thermal loading. Stress analysis was performed both experimentally and numerically, via finite-element modeling in the latter case. The results showed that strains in the track slab, in the cement-emulsified asphalt (CA) mortar and in the track bed, increased nonlinearly with the temperature increase. In the longitudinal direction, the zero-displacement section between the track slab and the track bed was close to the 1/8L section of the beam, while the zero-displacement section between the track slab and the box girder bridge was close to the 3/8L section. The maximum values of the relative vertical displacement between the track bed and the bridge structure occurred in the section at three-quarters of the span. Numerical analysis showed that the lower the temperature, the larger the tensile stresses occurring in the different layers of the track structure, whereas the higher the temperature, the higher the relative displacement between the track system and the box girder bridge. Consequently, quantifying the stresses in the various components of the track structure resulting from sudden temperature drops and evaluating the relative displacements between the rails and the track bed resulting from high-temperature are helpful in the design of ballastless track structures for high-speed railway lines.

Factors influencing the performance of cement emulsified asphalt mortar – A review

Cement emulsified asphalt mortar (CEAM) is an essential component in the ballastless slab track system. It is a semi-rigid composite material consisting mainly of hardened cement paste and demulsification asphalt, possessing the advantages of both ordinary Portland cement and asphalt. Its primary functions include: supporting structures, adjusting the slab track's geometry during construction, and dissipating/reducing orbital vibration. In this review, the preparation technology of CEAM was introduced at first. Subsequently, the hardening mechanism between asphalt emulsion and cement in CEAM was summarized. Meanwhile, the influence of asphalt emulsion type and dosage, sand to cement ratio (S/C), water to cement ratio (W/C), common auxiliary additives, and temperature on the properties of CEAM were compared and analyzed. This current review concludes that the most significant influence on CEAM performance is the mass ratio of asphalt to cement. With the increase of asphalt content, hardened cement asphalt paste (CA paste) would show two different overall mechanical properties. Besides, the effects of the S/C ratio and W/C ratio on high strength CEAM are not the same as that of low strength CEAM. Future research is recommended: to develop sustainable CEAM without prejudice to the performance; and to further analyze the interaction mechanism between emulsified asphalt and cement materials from the microscopic perspective.

Partially Replacing the Emulsified Asphalt in Cement Emulsified Asphalt Mortars with Epoxy Emulsion: Mechanical Properties and Durability Study

Cement emulsified asphalt (CEA) mortars achieve insufficient bond strength with substrate cement concrete slab. To ameliorate problems emerging from this, the emulsified asphalt (EA) in CEA mortars was partly replaced by epoxy emulsion (EE) at contents of 0%, 10%, 20%, and 30%, yielding CEA mortars with enhanced properties. The bond strength, mechanical strength, toughness, and durability (including drying shrinkage and erosion resistance) of modified CEA mortars were assessed. The results showed that partial replacement of EA with EE improved the bond strength, mechanical strength, drying shrinkage, and erosion resistance of CEA mortars. A good correlation was found between the proportions of the EE replacement and the bond strength of CEA mortars. Partial replacement of EA with a small amount of EE exerted no significant effect on the toughness of CEA mortar. The stronger network structure of CEA mortars containing EE improved the compactness, thus improving the performance of CEA mortars. Based on these findings, EE is suggested as partial replacement of EA for enhancing the properties of CEA mortars.

Mixed mode (I/II) fracture energy of cement emulsified asphalt mortar under intermediate temperature

Being a combination of sand, cement, water, and asphalt emulsion, Cement Emulsified Asphalt Mortar (CEAM) has better toughness and flexibility properties than cement mortar. Given the multiphase nature of CEAM, it is susceptible to micro-cracking during the setting process and also due to other factors such as traffic loads, undesirable atmospheric conditions. Given the typical direction of loading and cracking in these mortars, they are likely to experience mixed-mode fractures. Therefore, this study investigated the fracture properties of CEAM at service temperature in mixed mode I&II fractures. For this investigation, the mixed-mode fracture energy was determined through experiments on Semi-Circular Bending (SCB) specimens with the volume fractions of mortar treated as independent variables and the material behavior assumed to be viscoelastic at ambient temperature. Considering the need to investigate the effect of mix design ratios and their interactions, to reduce the number of experiments, and to limit these ratios to the ranges that produce acceptable rheological and mechanical properties, the D-Optimal mixture design method at 5% significance level was used to optimize the design of experiments and related analyses. Next, a regression model was developed for the relationship between fracture energy in each mode (I, II, I&II) and the mortar constituents. Also, the optimum mix design range to reach maximum fracture energy in all three modes was determined by graphical optimization. Analysis of the results with ternary contour plots showed the dependence of fracture energy and the optimum mix design range in the studied modes on the mix ratios of the CEAM constituents. The Cement and asphalt were identified as the independent variables with greatest effects on fracture energy variations and the optimum mix design. The results also revealed that as the asphalt emulsion-to-cement ratio increased, the maximum carried force decreased and the deformation corresponding to this force increased.

Low temperature fracture resistance of cement emulsified asphalt mortar under mixed mode I/III loading

Having asphalt in Cement Emulsified Asphalt Mortar (CEAM), this composition has higher toughness and ductility but also higher thermal sensitivity than conventional cement mortar. This study was aimed at investigating the fracture behavior of CEAM under out-of-plane shear and tensile loadings (Mode I, I/III, III) at low temperature. This investigation was performed by testing Edge Notched Disc Bending (ENDB) specimens with different asphalt-to-cement and water-to-cement ratios at three temperatures. Scanning Electron Microscopy technique (SEM was also employed to evaluate the effect of asphalt-to-cement and water-to-cement ratios on the structure of CEAMs. The findings revealed that for CEAM, the fracture toughness attains its highest value at pure tensile mode I, decreases as the share of out-of-plane shear in the mixed-mode I/III loading increases, and reaches its lowest value in the pure out-of-plane shear mode III. Furthermore, a multiple regression model was extracted for the relationship between each critical stress intensity factor (KC) and asphalt-to-cement ratio (A/C), water-to-cement (W/C), and temperature (T). The analyses showed -at the 95% confidence level- that A/C have a significant impact on KC in all examined modes and also the fracture toughness of CEAM decreases with increasing A/C. Changes in W/C also had a significant impact on the pure shear mode and mixed tensile-shear mode (I/III) stress intensity factors. Temperature changes in the studied range only affected the pure tensile mode stress intensity factor.

Experimental Studies and Microstructure Analysis for Rapid-Hardening Cement Emulsified Asphalt Mortar

A cement emulsified asphalt mortar (CEAM) made with calcium sulfoaluminate cement was prepared and tested indoors, which has a relatively slight environmental impact compared with ordinary Portland cement. The effects of asphalt to cement (A/C) and water to cement (W/C) ratios on the performance of CEAM were systematically evaluated, such as the fresh properties, mechanical properties, volume deformation, temperature dependence, permeability, and frost resistance. Meanwhile, the microstructure images and void characteristics were also obtained by computed tomography technology and scanning electron microscope. The results indicated that with the increase of A/C ratio, the flow time, setting time, and air content of fresh CEAM increase, while the slump flow decreases. The fast-hardening CEAM has higher early strength, which decreases with the W/C and A/C ratios increasing. In addition, the A/C ratio also has a significant influence on the long-term performance of CEAM. High emulsified asphalt content will reduce shrinkage, temperature dependence, and impermeability, but will increase its frost resistance. In addition, different emulsified asphalt and cement contents have a significant effect on microstructure and pore characteristics of CEAM, which directly determines its macroscopic properties. This paper contributes to the structure formation of calcium sulfoaluminate CEAM and provides a reference scheme for the construction of track slabs in winter.

Quantitative evaluation of cement emulsified asphalt mortar and aggregate adhesion performance with dynamic mechanical analysis

Low adhesion between emulsified asphalt mortar and aggregate can enormously result in poor properties of emulsified asphalt mixture. The adhesion performance can also be directly influenced by the viscosity of cement emulsified asphalt mortar (CEAM). In this work, Brookfield viscometer was used to test the viscosity of CEAM with different cement content, temperature and mixing time. Then, influence degree of each factor on viscosity was determined by gray correlation analysis (GCA) and significance test. Furthermore, dynamic mechanical analysis (DMA) was used to quantitatively evaluate the adhesion between CEAM and aggregate. Besides these, scanning electron microscope (SEM), energy dispersive X-ray (EDX), alkali content test, Fourier transform infrared spectroscopy (FT-IR) were adopted to analyze the interaction between cement and emulsified asphalt. The results show that the viscosity of CEAM increases with the increase of the cement content, mixing time and temperature. The cement content has the highest effect on the viscosity of CEAM, followed by mixing time; and temperature has a lowest effect. When the cement content is less than 50%, hydration products in the mixture can improve the fatigue life of CEAM. While it is higher than 50%, the adhesion is weakened and the fatigue life is shortened. Cement hydration and asphalt emulsion demulsification can mutually promote, which generates a network structure and improves the adhesion performance of CEAM to aggregate.