Description:FIELD OF INVENTION :

The invention relates to Cement Asphalt Mortar (CAM) in general and more specifically preparing CAM for use in the “track structure” of high-speed railways, which couples the merits of the strength of cement as well as the flexibility of asphalt material.

OBJECT OF THE INVENTION :

The object of the invention is to form a mortar concrete comprising acrylic emulsion in the CAM composition.

PRIOR ART :

There are many known prior art and some as known to inventor are detailed below.

Mixing Method of CAM

There are generally two mixing methods commonly used for the laboratory preparation of CA mortar. These methods are known as dry and wet mixing methods. The major difference between the two methods are that liquid components (bitumen emulsion, water, and liquid additives) and dry components (cement and sand) are mixed independently in the dry-mixing method, and after which they are blended. On the other hand, for the wet-mixing method, firstly, cement and sand are mixed with water and superplasticizer separately, and then the emulsified bitumen and other liquid additives are added. The mixing time and mixing speed (critical mixing speed) are selected appropriately. Mixing time, mixing speed, and the sequence of adding raw materials affect the properties of CA mortar. Mixing process aim to achieve two major functions:

i. Dispersion of particles on the macroscale and microscale
ii. Entrainment of air bubbles.

To produce CA mortar with desirable mechanical properties, the air content should be within the range of 8% to 12%. Mixing speed, mixing time, and fluidity has direct effects on the air content of CAM. The mixing speed and defoaming agents influence air content by affecting air bubble entrainment and retention. The air content in CA mortar is a result of air entrainment and air retention. This is related to the mixing process and the properties of fresh or liquid CA mortar. Defoamers or defoaming agents are used in CA mortar preparation to control the air content together with the appropriate mixing speed and mixing time. Defoamers lower the surface tension of the air bubbles, making the air bubbles less stable and can be easily burst or rupture. Additionally, deforming agents form an elastic film on the paste surface and consequently prevent the formation of air bubbles. When the mixing speed is high, the defoamers try to depress the air-entraining ability and when the mixing speed is low, the defoamers may have a slight influence on air-entraining ability. Therefore, a critical mixing speed should be maintained. Anything below or above critical speed will have a direct influence on the air content of CA mortar.

Structural Development of CA Mortar

When cement and bitumen emulsion form a mixture, cement hydration and the demulsification of emulsified bitumen begin to take place. The bitumen droplets usually form bitumen film after demulsification and cement grains are hydrated. The structural development of CA mortar is associated with the change of state of the mixture of cement and bitumen emulsion from flow paste to a solid or hardened mortar.

Interaction between Cement and Bitumen Emulsion

The interaction among the components of CA mortar influences its behaviour and properties. Cement and emulsified bitumen are the two major components in CA mortar, comprising about 21% and 25% of the whole volume of CA mortar, respectively. When bitumen emulsion and cement are mixed, they interact with each other in such a way that the consumption of water due to the hydration of cement accelerates the breakdown of emulsified bitumen. Likewise, adsorption of bitumen droplets on the surface of cement grains slows down the cement hydration process. Emulsified bitumen affects both the rate of cement hydration and the degree of hydration. The degree to which bitumen emulsion affects the hydration process relies on the type or class of emulsified bitumen used. Nevertheless, the incorporation of anionic emulsified bitumen into cement causes a remarkable delaying effect than cationic emulsified bitumen. This could be due to the different manner of their adsorption to the surface of cement grains

Formation of Bitumen Net Structure

Once in contact with water, Portland cement begins to hydrate, set, and then hardens due to the number of chemical reactions among different chemical substances and water. As soon as cement and emulsified bitumen are mixed, cement consumes water from emulsion, and this consequently decreases the distance between bitumen droplets. As a result, bitumen droplets make contact and coalesce and finally form a continuous bituminous film

Structure and Strength Development of Hardening Mortar

The strength development mechanism in CA mortar relies highly on the Bitumen to Cement (A/C) ratio. For CAM with a high A/C ratio, the bitumen phase usually dominates the structure of the hardened CA mortar and therefore weakens the framework of the hydration product of cement. Meanwhile the bitumen network is also weak and the whole structure of CAM experiences weak strength, especially at an early age. For CAM where bitumen to cement ratio is low, the framework formed by hardened cement paste dominates the structure of the hardened CA mortar and therefore determines its strength. The higher the cement content, the faster the strength of CA mortar at an early age; this indicates that the A/C ratio significantly affects the early strength gain by CA mortar.

Damping Performance of CA Mortar

The damping performance of a material refers to the dissipation ability of vibration energy in that material. The damping property of a system is also the capability of that system to transform vibrational energy into other forms of energy. Strength and damping ability are among the basic functions for which CA mortar is designed to serve in the structure of a non-ballasted track system. The basic concept of damping is the loss of energy by converting the induced vibrational energy to other forms of energy so that a system can return to its initial state promptly. The damping performance and strength of CA mortar are affected mainly by the A/C ratio. The interaction between cement and bitumen emulsion ensures that after the process of cement hydration, cement hydrates provide strength to the CA mortar while bitumen emulsion provides toughness to the CA mortar after demulsification. Thus, the composition of cement and bitumen emulsion produces a material (CA mortar) with adequate damping ability.

Effect of Asphalt to Cement Ratio (A/C) on the Mechanical Properties of CA Mortar

The A/C ratio is one of the most important parameters that determine the properties of the CA mortar. A higher A/C (usually above 0.6) signifies that the amount of bitumen in the CA mortar is more than the amount of cement, and therefore the properties of CA mortar made with a higher A/C are dictated by bitumen. Likewise, a lower A/C (below 0.6) means that the content of cement exceeded the content of bitumen in CA mortar, thus, the behaviours of CA mortar made with a lower A/C are controlled by cement. Cement and bitumen are entirely different materials in CA mortar, and although there are other constituent materials in CA mortar, the A/C is the major factor that controls the strength and modulus of elasticity in CA mortar compared to the Water to Cement ratio (W/C) and the ratio of Sand to Cement (S/C). Both bitumen emulsion and cement contribute to the mechanical properties of CA mortar. When introduced or incorporated into cement mortar, bitumen emulsion generally has a negative influence on its strength and modulus of elasticity but improves its deforming ability. Due to the fact that ballastless tracks in highspeed railways are not only subjected to repeated train– track dynamic interaction loads, but also suffer from complex environmental loads, the fundamental understanding of mechanical performance of ballastless tracks under sophisticated service conditions is an increasingly demanding and challenging issue in high-speed railway networks. It is known that the temperature difference between upper and lower surfaces of ballastless tracks could be formed under the action of solar radiation and heat convection due to their poor heat conduction performance. A higher surface temperature of the track slab will result in an arching deformation of the track slab, whereas a lower surface temperature of the track slab lead to an unwarping deformation of slab edges. When the bonding strength of ballastless track interlayers is less than the stress caused by the temperature-induced deformation, cracks would be initiated at the track interface and expand along the interface under train dynamic loads and finally form the track slab void, which will significantly affect the service life of ballastless tracks.

SUMMARY OF INVENTION :

The cement-Asphalt mortar (CAM) layer plays a vital role in the slab-track system of high-speed rail, acting as a filler layer between the track slab and the roadbed. CAM has two crucial roles in high-speed rail construction, and they are geometric adjustment and coordination of the track slabs during construction and load transfer from the track slab to the roadbed during service. Cement and Asphalt mortar is an organic–inorganic composite material primarily composed of bitumen emulsion, cement, sand, water, and other chemical admixtures. This composite material couples the strength of cement as well as the flexibility of bitumen material. CA mortar offers tremendous advantages to the system which include providing support to the track and train, adjusting the track precision, facilitating load transfer, shock absorption, improving the damping ability of the track system and improving the riding comfort of high-speed rails. The cement asphalt mortar contains cement, anionic bitumen emulsion, calcium sulfo aluminate and foaming agent. In place of Anionic Bitumen Emulsion, Cationic or Non-Ionic Bitumen Emulsion could also be used. This cement asphalt mortar could be used as filler layer between track slab and roadbed. CA mortar is produced by mixing its components using different mix proportions; its properties are mainly controlled by the proportion of bitumen to cement (A/C ratio), which is the ratio of the content of bitumen to the content of cement by mass or by volume; sometimes expressed as the ratio of bitumen emulsion to cement (BE/C). The addition of sand and a suitable amount of water ensures mixing stability and homogeneous distribution of CA mortar particles.

For construction of slab track, mortar is injected into a flat plastic pouch placed in the annular space between roadbed and concrete slab matching the desired thickness and alignment. The mortar shall have sufficient workability with specific physical characteristics on curing.

CAM Preparation flow chart as illustrated in fig. 1.

Part No. Description
1 Low Speed
2 • Bitumen emulsion
• Acrylic Emulsion
• Antifoaming Agent
• Water
3 3mins
4 High Speed
5 • Admixture
• Cement
• Fine aggregate
• Al Powder
6 7mins
7 Low Speed (7 Mins)
8 Air Entraining Agent

CAM Specification :-

No. Item Unit Specification
1 Temperature of mortar ? 5 - 40
2 Fluidity s 18 - 26
3 Working time min =30
4 Air content % 8 - 12
5 Apparent density kg/m3 > 1300
6 Compressive strength 1d MPa > 0.10
7d > 0.70
28d > 1.80
7 Elastic modulus(28d) MPa 100 - 300
8 Materials separation % < 1.0
9 Expansion rate % 1.0 - 3.0
10 Pan-Pulp ratio % 0

DESCRIPTION OF THE INVENTION :

The viscoelastic properties of CAM are the determining factors of its structural functionalities. Moreover, with the properties of bitumen being more influenced by temperature as compared to cement, the dynamic mechanical response of CA mortar under varied service temperatures may differ. Addition of Acrylic emulsion is new invention. An acrylic emulsion is a mixture of water and acrylic polymer. This invention explores the utilization of acrylic polymer emulsion as a mitigation measure to drawbacks suffered in prior art. Addition of acrylic emulsion polymers improve flexibility, reduce cracking, improve water resistance, improve UV resistance and increase hardness of mortars. As a styrene acrylic resin that is stable in both anionic and cationic bitumen emulsions, it is also cement-stable. This acrylic polymer imparts many desirable attributes to cement mortar and does not suffer delayed hydration, excessive air entrapment and moisture induced loss of strength.

Blending Ratio :-

Bitumen emulsion (Anionic) Acrylic emulsion Anti-Foaming agent Water Admixture High early strength cement (53G OPC) Fine Aggregate Al Powder AE agent Total Percentage (%)
25.64 4 0.01 1.13 2.36 22.95 44 0.003 0.58 100

Performance Comparison with and without Acrylic Emulsion in CAM

The conventional asphalt mixture tests were adopted to characterize the performance differences between CAM with and without Acrylic Emulsion along with standard methods of characterization.

Fatigue Cracking

Fatigue cracking can be greatly influenced by environmental and other effects while traffic loading remains the direct cause. The concept of a fatigue life centers around the universal idea that most materials undergo a gradual deterioration under repeated loads that are much smaller than the ultimate strength of the material. A plastic strip can be broken by repeatedly bending it. The flexural fatigue test is used to characterize the fatigue life of asphalt at intermediate pavement operating temperatures. This characterization is useful because it provides estimates of layer fatigue life under repeated traffic loading. In a well-designed layer, strains are low enough so that fatigue is not a problem.

The basic flexural fatigue test subjects CAM beam to repeated flexural bending in a controlled atmosphere.
Flexural Fatigue @20 oC No of Cycles @300 µm
Curing, No of Days 7 Days 14 Days 28 Days
Without Acrylic Emulsion 285490 54720 39740
With Acrylic Emulsion 539850 216890 77350

Rutting

Rutting refers to permanent deformation of the asphalt surface that accumulates in the wheel paths. It is primarily the result of repeated traffic loading cycles. Rutting may be accompanied by fatigue cracking and other distresses, making it a serious concern and potential indicator of failure. The stability of the asphalt mix is an important element in its ability to resist rutting and thus a key factor to evaluate. At the same time, however, the performance of a particular mix depends on environmental conditions including traffic, temperature, and humidity. Since these factors are often seasonal and mixtures can be exposed to a variety of environments across different projects, this makes it a challenge to reliably predict the rut resistance of a given mix.

The Hamburg Wheel Tracking Device (HWTD) tests rut resistance by tracking a loaded steel wheel back and forth across a cylindrical sample of CAM. By repeating this for thousands of cycles, it simulates the effect of traffic loading on the pavement over time. The device measures the rut depth in the sample continuously during the test.

HWTD testing is commonly performed on a sample while it is submerged in water. This allows it to be used to evaluate resistance to moisture damage as well. After the sample is consolidated by the initial load cycles, the rate at which rutting develops will be determined by the stability of the mix at first. Then, once the load cycles reach a certain point (which varies depending on the moisture susceptibility of the mix), rut development will accelerate as damage from stripping kicks in.

Moisture damage is the result of moisture interaction with the bitumen binder-aggregate adhesion within a mixture. This interaction can cause a reduction of adhesion between the bitumen binder and aggregate, called stripping, which can lead to various forms of distress including rutting and fatigue cracking. Moisture susceptibility tests attempt to quantify a mixture’s ability to resist moisture damage, no matter what the source. They are typically capable of providing gross results or comparative results and are not able to predict the degree of moisture damage.

Rutting Behaviour @55 oC Mm
Curing, No of Days 7 Days 14 Days 28 Days
No of Cycles 200 7000 10000
Without Acrylic Emulsion 21 mm 23 mm 24 mm
With Acrylic Emulsion 12 mm 10 mm 10 mm

Elastic Modulus

An elastic modulus (also known as modulus of elasticity) is the unit of measurement of an object's or substance's resistance to being deformed elastically (i.e., non-permanently) when a stress is applied to it. The elastic modulus of an object is defined as the slope of its stress–strain curve in the elastic deformation region: A stiffer material will have a higher elastic modulus

Elastic Modulus @ 25 oC MPa
Curing, No of Days 28 Days
Without Acrylic Emulsion 242
With Acrylic Emulsion 195

Compressive Strength

Compressive strength refers to the ability of a certain material or structural element to withstand loads that reduce the size of that material, or structural element, when applied. A force is applied to the top and bottom of a test sample, until the sample fractures or is deformed.
Compressive Strength @ 25 oC MPa
Curing, No of Days 1 Day 7 Days 28 Days
Without Acrylic Emulsion 0.5 0.879 2.1
With Acrylic Emulsion 0.13 1.1 1.98

ITS

Indirect tensile strength test is an indicator of strength and adherence against fatigue, temperature cracking and rutting. The split tensile test is an indirect way of evaluating the tensile test of concrete. In this test, a standard cylindrical specimen is laid horizontally, and the force is applied on the cylinder radially on the surface which causes the formation of a vertical crack in the specimen along its diameter.

ITS – Dry @25 oC kPa
Curing, No of Days 7 Days 14 Days 28 Days
Without Acrylic Emulsion 217 344 479
With Acrylic Emulsion 411 464 529

ITS – Wet @25 oC kPa
Curing, No of Days 7 Days 14 Days 28 Days
Without Acrylic Emulsion 179 276 379
With Acrylic Emulsion 342 390 455

Summary

No. Item Unit Specification Result – With Acrylic Emulsion Result – Without Acrylic Emulsion
1 Temperature of mortar ? 5 – 40 24.8 25
2 Flow Time (by J10 Funnel) s 16 – 28 21.8 18.5
3 Expansion Ratio % 1 – 3 1.58 1.8
4 Air content % 8 – 12 10.67 10.2
5 Bleeding Ratio % 0 0 0
6 Elastic modulus(28d) MPa 100 – 300 195 242
7 Materials separation % < 1.0 0.58 0.55
8 Compressive strength 1d MPa > 0.10 0.13 0.5
7d > 0.70 1.1 0.879
28d > 1.80 1.98 2.1
9 Rutting @10000 no of cycles 28d mm
10
24
10 Fatigue Cracking, no of cycles@300 µm Strain 7d no 539850 285490
14d 216890 54720
28d 77350 39740
12 ITS – Dry 7d kPa 411 217
14d 464 344
28d 529 479
12 ITS - Wet 7d kPa 342 179
14d 390 276
28d 455 379

Addition of Acrylic Emulsion into the Cement Asphalt Mortar has imparted multiple functional benefits to the Cement Asphalt Mortar.

1. The specification parameters of CAM are met satisfactorily including compressive strength
2. Most materials undergo a gradual deterioration under repeated loads that are much smaller than the ultimate strength of the material. With the addition of acrylic emulsion, the fatigue life of Cement Asphalt Mortar is found to be improved by >150%
3. The rutting resistance of Cement Asphalt Mortar at 50 oC is improved by 140%
4. Indirect Tensile Strength values are improved by 10%

In one aspect, the invention claim a method of producing Cement Asphalt Mortar (CAM) wherein air content is in range 8-12% comprising of mixing Asphalt emulsion, Polymer emulsion alongwith antifoaming agent and water at low speed in the range of 40 – 60 rpm wherein the antifoaming agent lowers the surface tension of the air bubbles, thereby lessening the stability of air bubbles and bursting them eventually and the duration is 3 minutes for preparing the Ad-mixture paste having an elastic film of Antifoaming agent thereby formation of air bubbles is wholly prevented. Thereafter mixing the Ad-mixture so prepared with cement, fine aggregates such as sand alongwith aluminium powder at a high speed in the range of 100 – 120 rpm and for a duration of 7 minutes, which help dispersion of particles on the macroscale and microscale alongwith entrainment of air bubbles. Then continuing to mix in furtherance with an addition of Air Entraining agent at a low speed in the range of 40 – 60 rpm for a duration of 7 minutes to induce effect of brining entrained air i.e., closed-cell microbubbles into concrete and thereby improving the resistance to frost damage. The said method is characterised in the use of polymer emulsion in the method and the range of 1-6% of the composition.

In another aspect the polymer emulsion is specifically acrylic emulsion.

Accordingly, the industrial advantage of the present invention is great. The disclosure herein above made in description and/or illustrations are capable of other embodiments or of being practiced or carried out in various ways and hence the embodiments is only for purpose of description and should not be regarded as limiting.
, Claims:WE CLAIM :

1. A method of producing Cement Asphalt Mortar (CAM) wherein air content is in range 8-12% comprising of :-
a. mixing Asphalt emulsion, Polymer emulsion alongwith antifoaming agent and water at low speed in the range of 40 – 60 rpm wherein the antifoaming agent lowers the surface tension of the air bubbles, thereby lessening the stability of air bubbles and bursting them eventually and the duration is 3 minutes for preparing the Ad-mixture paste having an elastic film of Antifoaming agent thereby formation of air bubbles is wholly prevented,
b. thereafter mixing the Ad-mixture of step (a) with cement, fine aggregates such as sand alongwith aluminium powder at a high speed in the range of 100 – 120 rpm and for a duration of 7 minutes, which help dispersion of particles on the macroscale and microscale alongwith entrainment of air bubbles, and
c. continuing to mix in furtherance to step (b) with an addition of Air Entraining agent at a low speed in the range of 40 – 60 rpm for a duration of 7 minutes to induce effect of brining entrained air i.e., closed-cell microbubbles into concrete and thereby improving the resistance to frost damage, the said method is characterised in the use of polymer emulsion in the method and the range of 1-6% of the composition.
2. The method of producing Cement Asphalt Mortar (CAM) as claimed in claim 1, wherein the polymer emulsion is specifically acrylic emulsion.