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Because of the combined benefits of cement's strength and asphalt's flexibility, researchers are increasing their interest in the use of cement emulsified asphalt mortar (CA mortar) in the track structure of high-speed trains.
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For the qualities of CA mortar, the compatibility of the constituent materials, as well as the asphalt-to-cement ratio (A/C), are crucial.
To improve the performance and application of CA mortar, a thorough study of the composition mechanisms and constituent material compatibility is required.
This paper presents surprising findings from research on the composition and properties of CA mortar.
Cement hydration is hampered by asphalt droplets adhering to its surface, whereas emulsified asphalt degradation is expedited by cement's consumption of water.
A sufficient A/C is necessary for the cement hydration rate to meet the rate of asphalt emulsion demulsification.
The A/C for type 1 (CAM I) and type 2 CA mortars ranges from 0.2 to 0.6 and 0.6 to 1.2, respectively, depending on the kind and features of the mortar (CAM II).
This research also looks at the use of additives as a partial replacement for cement in the creation of CA mortar, as well as methods for improving performance attributes, compatibility, and the interaction of the constituent materials of CA mortar.
The current assessment also recommends potential research study subjects for the future.
Anyone interested in the compositional mechanics and functional aspects of CA mortar will find this paper relevant.
High-speed rail development has raised the need for a high-quality railway system that includes rails, communication, a signal system, and other components.
One of the most significant innovations for high-speed railroads is the non-ballasted slab track.
It is used all over the world because it has advantages over traditional ballasted tracks such as lower structural height, less frequent maintenance requirements, longevity, high lateral track resistance, allowing for future speed increases, and no ballast churning.
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The China Railway Track System (CRTS), which is divided into CRTS I, CRTS II, and CRTS III, is the most common form of ballastless track system used on the Chinese mainland in recent decades.
Rails, fasteners, a prefabricated concrete slab, an in-situ concrete trackbed, and an interim cushion layer comprise the structural design of the CRTS I and II track systems.
A top-down and bottom-up building method is recommended for CRTS I and II; this strategy reduces installation time while simultaneously controlling the level and alignment of the high-speed railway operation.
This method involves creating a little void between the track slab and trackbed, which is subsequently filled with grouting material after hardening to act as a cushion layer.
Cement-emulsified asphalt mortar was utilized to cushion the CRTS I and II structures.
CA mortar (often abbreviated to CAM) is one of the primary building materials used in high-speed railroads for slab ballastless tracks; it is an intermediate layer thrown between the track slab and the trackbed of CRTS I and CRTS II.
Cement and asphalt mortar is an organic-inorganic composite material made up of cement, sand, water, asphalt emulsion, and other chemical additives.
This composite material has specific features that distinguish it from concrete and asphalt alone because it combines the strength of cement with the flexibility of asphalt.
As a structural component of the non-ballasted slab track, CA mortar provides numerous system benefits such as supporting the track and train, adjusting track precision, facilitating load transfer, absorbing shock, improving the track system's dampening ability, and improving the comfort of high-speed rails.
Its properties are primarily influenced by the asphalt to cement ratio (A/C ratio), which is the mass or volume ratio of asphalt material to cement content; it is also commonly referred to as the asphalt emulsion to cement ratio (AE/C).
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CA mortar is created by combining varying proportions of its components.
To ensure mixing stability and equal dispersion of the CA mortar particles, sand and water are added to the slurry.
The slab ballastless high-speed train track system makes use of two kinds of CA mortar: type I (CAM I) and type II (CAM II), which are utilized to build CRTS I and CRTS II, respectively.
In contrast to CAM II, which has a high cement content with less asphalt content and an A/C ratio of 0.2 to 0.6, CAM I has a high asphalt content, less cement, and a higher A/C ratio of 0.6 to 1.2.
However, the characteristics and mechanisms of these two CAMs differ.
The inject depth of CAM I is 50 to 70 mm, the 28-day compressive strength is 1.
8 MPa, and the elastic modulus is 100 to 300 MPa; the inject depth of CAM II is 20 to 40 mm, the 28-day compressive strength is 15 MPa, and the elastic modulus is 7000 to 10,000 MPa.
Previous research has shown that CA mortar exhibits viscoelastic properties, implying that pressure, temperature, and strain rate all affect how it performs and behaves.
The structural possibilities of CAM are determined by its viscoelastic characteristics.
Furthermore, because asphalt qualities are more temperature-dependent than cement properties, the dynamic mechanical reactivity of CA mortar at different service temperatures may vary.
Each of the CAMs, I and II, has advantages and disadvantages.
Before determining which data to employ for a certain track installation, engineers weigh the available data.
When the railway structure demands more strength than damping performance, more asphalt (higher A/C) is required in CAM I, but more cement (lower A/C) is required in CAM II.
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CA mortar's properties are altered by interactions between its elements, such as how cement affects how emulsified asphalt breaks down and how emulsified asphalt affects how cement hydrates.
The cement hydration process is started by water from the demulsification of emulsified asphalt.
As a result, the differences between the asphalt emulsion's water-repelling properties during demulsification and the water need of the cement hydration process are addressed.
As a result, CA mortar enhances not only the benefits of cement and emulsified asphalt materials but also their drawbacks.
The amount of asphalt emulsion and cement used has a significant impact on the properties of CA mortar, such as damping and strength.
During the design process, engineers analyze the damping performance and strength qualities of CA mortar using a number of criteria such as the kind of railway track structure, load, environmental conditions, and so on.
Recent studies have prioritized CA mortar's mechanical qualities, as well as the impact of train loads and environmental variables (such as temperature and moisture) on its long-term performance.
Researchers from all around the world are working hard to replace cement in the manufacturing of CA mortar with industrial byproducts, naturally occurring minerals, and other supplementary cementitious materials (SCM).
This method has helped to save the environment while also cutting the cost of creating CA mortar.
CA mortar, according to a recent study, has the potential to be used in ballasted railroads.
A ballasted track, on the other hand, combines CA mortar and ballast to produce a novel composite material known as CA mortar-stabilized ballast.
The innovative material is expected to provide the benefits of a ballastless track while also acting as a fouled ballast rehabilitation alternative, reinforcing the ballast layer by increasing its longevity and reducing construction time.
In a similar study, Le et al.
proposed a method for analyzing if anchoring the ballast using CA mortar is a viable alternative as a major means to prevent losing track quality due to particle abasement and ballast settlement.
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They believe that letting the CA mortar mixture circulate through the ballast system will result in strong inter-particle bonding by covering the ballast particles with new CA mortar.
The bonded material will be viscoelastic due to the asphalt membrane and stiff due to the cement hydrates.
Although the qualities of asphalt are sensitive to climatic conditions such as moisture and temperature, using this technique will help to solve this problem.
Despite the attention this method has gotten from academics worldwide, it is not without limitations.
Despite past research on the performance characteristics and structure of CA mortar, a thorough analysis of the composition method and the compatibility of the constituent materials is rarely documented.
These variables have a huge impact on how CA mortar acts.
As a result, this research provides a thorough examination of constituent material compatibility, the microstructure of cement asphalt binder (CAB), structural development, and the effect of A/C on the properties of CA mortar.
The study addresses important findings from studies on the characteristics of composite CA mortars and their constituents.
The current study, based on earlier research, describes the interaction of asphalt emulsion and cement, as well as their influence on the performance characteristics of CA mortar.
The microstructure of cement emulsified asphalt binder (CAEB), the A/C ratio, and the usage of admixtures to partially substitute cement in the production of CA mortar are all described and given in simple words.
Finally, potential study directions are proposed based on the findings of prior studies.
Depending on the type of CA mortar and the location where it will be used or applied, an appropriate mix proportion of the constituent materials is utilized to manufacture it.
Combination proportions are often determined in compliance with the regulations issued by various regulatory authorities around the world.
These proportions include ratios such as A/C, S/C, W/C, and others, as well as the percentage of each constituent material by mass or volume.
The components are then blended in accordance with the mix proportions using the required procedure and equipment.
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As a result, CA mortar must have good qualities in order to adapt to such a technique and improve the stability and comfort level of the ballastless slab track structure.
CA mortar is grouted in the region between the bottom concrete track bed and the top track slab using gravity.
Two mixing strategies are typically utilized in the laboratory fabrication of CA mortar: dry and wet mixing techniques.
The primary distinction between the two techniques is that in the dry-mixing strategy, the liquid components (asphalt emulsion, water, and auxiliary chemicals) and the dry components (cement and sand) are mixed separately before being combined.
In contrast, in the wet-mixing process, the emulsified asphalt and other auxiliary agents are injected after the cement and sand have been individually mixed with water and superplasticizer.
The appropriate mixing time and speed (critical mixing speed) are determined by the applicable standards.
According to several publications, the amount of time, rate, and order in which the raw materials are added all have an impact on the quality of CA mortar.
The mixing process used to make CA mortar should be designed to meet two important goals: particle dispersion on both a macro- and micro-scale and air bubble entrainment.
To generate a product with sufficient mechanical qualities, the air content of CA mortar should be between 8% and 12%, and it has been discovered that fluidity, mixing time, and speed all have a direct effect on the air content of CAM.
The amount of air present was varied by varying the mixing speed and defoaming agents, which influenced air bubble entrainment and retention.
The two phenomena of air entrainment and air retention, which are related to the mixing process and the properties of fresh or liquid CA mortar, are the causes of air content in CA mortar (i.e., density, viscosity, and surface tension).
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To manage the air content in CA mortar preparation, defoamers or defoaming agents, as well as the proper mixing speed and time, are utilized.
Defoamers reduce air bubble surface tension, making them less stable and prone to rupture.
Deforming chemicals also generate an elastic layer on the paste's surface, preventing air bubbles from forming.
Defoamers try to minimize air-entraining ability when the mixing speed is high; however, when mixing speed is low, defoamers may have little influence on air-entraining ability.
As a result, maintaining the critical mixing speed is vital.
Anything less than or greater than critical speed has a direct impact on the volume of air in a CA mortar.
The slab ballastless track's structure is largely comprised of cement-emulsified asphalt mortar.
In the ballastless slab track system, a layer of CA mortar is cast between the top track slab and the lower track bed.
It supports the track and improves the weight transmission, shock absorption, and vibration dissipation capacities of the track system.
The A/C ratio has a significant impact on the characteristics of fresh and hardened CA mortar.
Asphalt emulsion affects both cement hydration and asphalt emulsion decomposition.
As a result, a sufficient A/C ratio must be employed to manufacture CA mortar with the required strength, damping ability, durability, and other mechanical attributes.
An appropriate A/C is also necessary for the components of the CA mortar to be compatible.
The amount of air in the mortar has a significant impact on its quality.
To impact air entrainment and retention, defoamers, mixing speed, and mixing duration is employed to adjust the air content of the CA mortar.
Another area of investigation has been the use of additives such as SCMs, pozzolans, industrial byproducts, and other naturally occurring minerals as a partial replacement for cement in the production of CA mortar.
The use of these chemicals in CA mortar manufacture fosters a greener approach to building construction and sustainable development, in addition to cost-effectiveness and environmental protection.
As a result, CA mortar will be widely used as a building material in a number of civil engineering sectors.
Future research should look into the effects of partial cement replacement with additional cementitious materials on improving CA mortar characteristics under a variety of environmental and climatic circumstances.
This study is expected to be valuable to anyone looking for a comprehensive understanding of CA mortar composites and performance characteristics for research purposes.
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