TECHNICAL FIELD

The present invention belongs to the technical field of railway engineering. In particular, the present invention relates to a method for preparing a track bed.

BACKGROUND

Ballasted tracks using ballasts as track beds (also referred to as ballast beds) have a wide range of applications in the world's railway tracks. Such ballast beds are basically composed of ballasts, which have a rich source and low cost, and will be used on railway tracks for a long time. In recent years, with the rapid increase in people's travel and freight transport, higher requirements also have been placed on the ballast beds that have been used in railways and highways. Ballast beds bear the huge loads transferred from high speed trains and heavy haul trains via rails and sleepers. Under the action of huge loads, the ballast stones that constitute a ballast bed are more prone to collide, displace and crush over time, leading to deformation, subsidence and functional degradation of the ballast bed such that the ballast bed must be frequently maintained and repaired, which is time- consuming and laborious with high cost.

Currently, various methods for reinforcing ballast beds with polymeric materials have been used.

CN 1399035 A discloses that a mixture of high molecular polymers such as styrene- butadiene latex, butylamine rubber, aniline rubber and liquid rubber is poured onto the ballasts of a bedrock bed so that these liquid high molecular polymers with a certain viscosity flow down along the gaps of the ballasts, fill the gaps of the ballasts and become coagulated quickly, wherein the coagulation time can range from more than 10 seconds to 5 minutes. The optimum coagulation time is such that coagulation begains when these liquid high molecular polymers arrive the lowermost layer of the ballasts along the gaps of the ballasts. However, this method is limited by its spray construction method and the characteristic of materials cured to form a rubber body. An integrated bed has a long curing time and the construction quality of the cured bed is not easy to guarantee. The cured integrated bed has a short service life and often needs to be repeatedly constructed.

US 2007172590A and CN 101370983A disclose a process for preparing a ballast bed, wherein the ballast bed consists of ballast stones and polyurethane foams, and the polyurethane foams are prepared by the reaction of isocyanates with isocyanate -reactive compounds.

DE 2305536A discloses a method for reinforcing a ballast bed by pouring a polyurethane foaming material into the voids in track sleepers, foaming and curing.

Since polyurethane materials are foaming materials, when an excess amount of polyurethane liquid is injected into ballast stones, the ballast bed will be lifted up during polyurethane foaming, thus destroying the smoothness of the bed and posing a hazard to train operation. Before foaming, ballasts need to be heated and dehumidified at a high temperature and then cooled by high-pressure air. That is because the polyurethane system is very sensitive to humidity and temperature, wherein water vapor can react with an isocyanate in the polyurethane system to form carbon dioxide; and temperature greatly increases the reaction rate of polyurethanes such that the reaction is too fast and foaming is out of control. When the polyurethane system is foamed, the injection amount of a foaming area needs to be accurately metered; and a foamed bed is pressed by a locomotive or loading to prevent the bed from bulging.

CN 102561114B discloses a method in which a polyurethane foaming material is prepared first and railway gravel is first prepared into a cured molding polyurethane bed plate, which is placed on a railway track bed to form a bed with part of gravel, and then the polyurethane foaming material is poured to cure the railway ballast bed.

CN 102251442B discloses a method for preparing a polyurethane cured ballast bed by pouring a polyurethane foaming material on site into the voids in track sleepers, foaming and curing to form a polyurethane cured ballast bed which is then externally sprayed with a polyurethane elastomer protective layer.

However, the method for preparing a polyurethane cured bed by pouring polyurethane on site still has the following technical bottlenecks to be overcome:

• Polyurethane micro-foaming elastic system as a 2K (two-component) system: the polyurethane micro-foaming elastic system as a 2K (two-component) system requires accurate metering and pouring equipment, and the foaming performance is reduced or even ballasts cannot be bonded in case of metering deviation.

• The polyurethane system is sensitive to water vapor, and an isocyanate component in polyurethane will foam when contacting water, which greatly reduces the bonding performance of foams to ballasts and shortens the service life of the entire cured bed. The entire polyurethane system needs to be isolated from water vapor during storage and construction, and has high requirements on outdoor pouring equipment for polyurethane cured beds.

• The polyurethane system is sensitive to water vapor, and an isocyanate component will foam when contacting water; water vapor needs to be removed from ballasts; and railway ballasts must be pre-dried with complex drying equipment and cooled, and the drying equipment is expensive.

• The polyurethane system is sensitive to temperature, which reacts slowly and has poor bonding to ballasts at a low temperature while reacting rapidly and having a large foam expansion force at a high temperature. The bed can be greatly raised and the smoothness of the bed is destroyed such that the bed cannot be opened to traffic. Ballasts need to be heated and cooled.

In addition, polyurethane cured beds are greatly affected by weather and environment, and have application limitations in the following circumstances: 1) under heavy rain and storm; 2) for water-soaked beds; and 3) for beds on which trains in existing lines are running.

Accordingly, there is a need to develop a method for curing a railway ballast bed more effectively than using polyurethane foams.

SUMMARY OF THE INVENTION

A main object of the present invention is to provide a method for preparing a track bed, which can overcome the construction disadvantage of an existing polyurethane cured bed system that the bed needs to be dried and dehumidified.

A main object of the present invention is to provide a method for preparing a track bed, which can overcome the following construction disadvantage of an existing polyurethane cured bed system: a foamed bed needs to be pressed by heavy loads to prevent the bed from expansion and bulging that affect the smoothness of the bed.

A main object of the present invention is to provide a method for preparing a track bed, which can overcome the following construction disadvantage of an existing polyurethane cured bed system: it is necessary to use dozens of locomotives and two (or multiple) tractors which have low construction efficiency, high cost and complex organization.

The above objects can be achieved by the following technical solutions.

According to one aspect, the present invention provides a method for preparing a track bed, which comprises the steps of:

i) stacking ballasts to form a ballast substrate and tamping the ballast substrate; and ii) applying a mixed system of an aqueous polychloroprene dispersion and a coagulate agent onto the ballast substrate and curing the mixed system together with the ballasts.

According to another aspect, the present invention provides a track bed prepared by the above method.

According to still another aspect, the present invention provides a track comprising the above track bed.

According to yet another aspect, the present invention provides use of a mixed system of an aqueous polychloroprene dispersion and a coagulate agent in the preparation of a track bed.

The method for preparing a track bed according to the present invention can realize rapid preparation of the track bed without heating or special cleaning of the ballasts. In the case that there is dirt on the surfaces of the ballasts, construction can be performed immediately after the ballasts are flushed with high-pressure water. Accordingly, the method for preparing a track bed according to the present invention is suitable for both a newly built clean ballast line and an existing railway line with some dirt.

The method for preparing a track bed according to the present invention is not affected by the water content of the ballasts and the environmental moisture, in which both continuous and intermittent construction can be achieved. Construction can be carried out during the train running interval so that the construction efficiency is high, and the track bed can be opened to traffic immediately after construction, without affecting the normal operation of trains.

Furthermore, the track bed prepared by the method of the present invention has a long service life.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described and explained below in more detail with reference to the drawings, in which:

Fig. 1 shows a schematic structural view of an example of a track comprising a track bed prepared according to the method of the present invention, wherein 10 represents a railway roadbed, a concrete pavement or a bridge, 20 represents a track bed, 30 represents a drainage layer, 40 represents a ballast mat layer, 50 represents a track bed, 60 represents sleepers, and 70 represents rails; and

Fig. 2 shows photographs obtained after ballasts are cured using a mixed system of an aqueous polychloroprene dispersion and carbon dioxide.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is now described for the purpose of illustration rather than limitation.

According to one aspect, the present invention provides a method for preparing a track bed, which comprises the steps of:

i) stacking ballasts to form a ballast substrate and tamping the ballast substrate; and ii) applying a mixed system of an aqueous polychloroprene dispersion and a coagulate agent coagulate agent onto the ballast substrate and curing the mixed system together with the ballasts.

The ballast used in the invention is not particularly limited and can be any ballast commonly used in the preparation field of track beds.

In the case that there is dirt on the surfaces of the ballasts, the ballasts can be subjected to high-pressure cleaning with water or an aqueous calcium chloride solution having a calcium chloride concentration of 2-5 wt.%. The use of the aqueous calcium chloride solution having a calcium chloride concentration of 2-5 wt.% can accelerate the coagulation of the aqueous polychloroprene dispersion and allow its rapid bonding to the ballasts.

Accordingly, in some preferred embodiments, the method for preparing a track bed according to the present invention further comprises: subjecting the ballasts to high- pressure cleaning with water or an aqueous calcium chloride solution having a concentration of 2-5 wt.%, prior to stacking ballasts to form the ballast substrate and tamping the ballast substrate. The high-pressure cleaning can be carried out using, for example, a high-pressure water gun.

The mixed system of an aqueous polychloroprene dispersion and a coagulate agent used in the present invention can be obtained by mixing an aqueous polychloroprene dispersion with a flocculant.

The aqueous polychloroprene dispersion is a dispersion of polychloroprene in water.

The polychloroprene in the aqueous polychloroprene dispersion used in the present invention may be a chloroprene homopolymer or a copolymer of chloroprene and a copolymerizable ethylenically unsaturated monomer.

The copolymerizable ethylenically unsaturated monomer is one or more preferably selected from the group consisting of compounds having 3-12 carbon atoms and 1 or 2 copolymerizable C = C double bonds. Examples of the most preferred copolymerizable ethylenically unsaturated monomer are 2,3-dichloroprene, 1 -chloroprene, 2-chloroprene, acrylonitrile, acrylic acid, maleic acid, fumaric acid and ethylene glycol dimethacrylate.

When the copolymer of chloroprene and a copolymerizable ethylenically unsaturated monomer is used, the amount of the copolymerizable ethylenically unsaturated monomer is not more than 20 parts by weight based on 100 parts by weight of the chloroprene.

The polychloroprene may have a number average molecular weight of from 20,000 to 1,000,000, preferably from 100,000 to 800,000.

The aqueous polychloroprene dispersion used in the present invention may also be selected from those commonly used as adhesives in the art.

The solid content of the polychloroprene in the aqueous polychloroprene dispersion is not less than 20 wt.%, preferably 20-70 wt.% and more preferably 25-60 wt.%.

The aqueous polychloroprene dispersion is preferably an anionically stabilized aqueous polychloroprene dispersion.

Preferably, the alkali ion concentration (e.g. Na ⁺ and/or K ⁺ ) is 500-10,000 ppm in the aqueous polychloroprene dispersion.

The coagulate agent used in the present invention is preferably one or more selected from the group consisting of: a pH adjuster, carbon dioxide, a cationic emulsion, a nonionic emulsion, an acid coagulate agent or a salt flocculant.

As examples of the pH adjustment agent glycine, boric acid and the like may be mentioned.

As examples of the cationic emulsion, an aqueous cationic polyurethane dispersion, an aqueous cationic epoxy dispersion and an aqueous cationic acrylic dispersion may be mentioned.

As examples of the acid flocculant, acid solutions such as hydrochloric acid and citric acid may be mentioned.

As examples of the salt flocculant, salt solutions such as calcium chloride, sodium chloride, potassium chloride, aluminum sulfate, zinc sulfate and sodium sulfate may be mentioned. Preferably, the coagulate agent is carbon dioxide.

In the mixed system of an aqueous polychloroprene dispersion and a flocculant, the amount of the coagulate agent is 0.01-10 wt.%, most preferably 0.1-0.5 wt.% by mass of the aqueous polychloroprene dispersion.

When the mixed system of an aqueous polychloroprene dispersion and a coagulate agent has a pH of s _¾ 8, the coagulate agent is carbon dioxide, and the amount of carbonic acid in the mixed system is 0.01-10 wt.%, thus the mixed system of an aqueous polychloroprene dispersion and a coagulate agent is in a metastable state.

In some embodiments, relative to per kilogram of the mixed system of an aqueous polychloroprene dispersion and a flocculant, 0.3-300 L of carbon dioxide is added to the aqueous polychloroprene dispersion, and preferably added to an anionically stabilized aqueous polychloroprene dispersion at 1-100 °C. and 0.5-10 bar.

The carbon dioxide source used may be, for example, compressed gas containers such as bottles, cylinders or cartridges. For example, carbon dioxide is obtained by an in- situ chemical reaction of an alkali metal carbonate with a suitable acid, or obtained from a liquid saturated with carbon dioxide (e.g. water, mineral water and soft drinks) or by sublimation of dry ice or from a reversible carbon dioxide absorber.

The supply of carbon dioxide can be carried out, for example, by introduction, penetration, passing or covering in a mixing tube by means of a static or dynamic mixer, or in the form of a carrier gas or a propellant gas.

A method without mechanical contact such as passing or covering is preferred, in which the mixed system to be activated is not in contact with metering equipment, thus preventing the metering equipment from being contaminated or blocked by possible coagulates.

It is also preferred to use carbon dioxide directly as a carrier gas or a gas propellant, for example, in the form of a spray can containing an aqueous polychloroprene dispersion and carbon dioxide in a separate phase, or by mixing an aqueous polychloroprene dispersion with carbon dioxide in a defined flow area, e.g. using a static mixer or a simple hose segment of a suitable length prior to use. Preferably, carbon dioxide is metered from a compressed gas bottle, cylinder or cartridge using a simple movable valve system similar to bicycle and automobile tire valves, wherein the valve system can be reversibly assembled on, for example, an aqueous polychloroprene dispersion packaging material. After the introduction of the desired amount of carbon dioxide, the original lid can be closed again if necessary, and the canister can be shaken, oscillated, stirred and stored until the aqueous polychloroprene dispersion is saturated with the carbon dioxide added. For a soft container, the activation process can be easily monitored by a decrease in the visual apparent volume of the container.

For example, carbon dioxide can be supplied by covering an aqueous polychloroprene dispersion in an elastic container. For example, a container having a volume of 20 L can be filled with (X<18) L of an aqueous polychloroprene dispersion (optionally excluding air) and then filled with (20-X) L of carbon dioxide. The container is then oscillated or stirred or stored until a gas phase of the carbon dioxide is absorbed in the aqueous polychloroprene dispersion to reach the desired decrease in volume, thus the aqueous polychloroprene dispersion is activated and optionally excess carbon dioxide is released.

The inventors of the invention have surprisingly found that when an aqueous polychloroprene dispersion is used in combination with carbon dioxide, the entire system not only can form a gum- like film, but also can be further cured to form a rubber elastomer in a short period of time. After being applied to ballasts, the mixed system can be cured together with the ballasts as a whole, and the curing speed of the system is not affected by the cleanliness or water content of the ballasts. Such cured bed has a stable ballast substrate and a long service life.

Railway ballasts are cured using a mixed system of an aqueous polychloroprene dispersion and carbon dioxide, regardless of the dampness or water content of the ballasts.

The mixed system of an aqueous polychloroprene dispersion and a coagulate agent further comprises at most 30 wt.% of other dispersions or emulsions relative to the total weight of the mixed system of an aqueous polychloroprene dispersion and a coagulate agent to save cost. As other dispersions or emulsions that may be used, examples which may be mentioned may be one or more selected from the group consisting of: aqueous nano-silica dispersions, polyacrylate dispersions, aqueous polyurethane dispersions, polyurethane-polyacrylate dispersions, acrylonitrile-butadiene dispersions, ethylene-vinyl acetate copolymer emulsions, petroleum resin polymer emulsions, rosin polymer emulsions, polybutadiene dispersions, styrene-acrylate copolymer emulsions, styrene- butadiene copolymer emulsions, terpene-phenolic aldehyde polymer emulsions, polyvinylidene chloride dispersions, natural latex and the like.

The mixed system of an aqueous polychloroprene dispersion and a coagulate agent most preferably comprises at most 25 wt.% of other dispersions or emulsions relative to the total weight of the mixed system of an aqueous polychloroprene dispersion and a flocculant.

The mixed system of an aqueous polychloroprene dispersion and a coagulate agent optionally comprises additional binder auxiliaries and/or additives.

For example, a thickener can be added, which is preferably selected from an acrylic alkali swellable thickener and a polyurethane associative thickener.

For example, a light stabilizer, an ultraviolet light absorber and an antioxidant can be added.

For example, a filler such as quartz powder, quartz sand, barite, calcium carbonate, chalk, dolomite or talc can be added. For example, a wetting agent, e.g. a polyphosphate such as sodium hexametaphosphate, naphthalenesulfonic acid, ammonium polyacrylate or sodium polyacrylate can be added.

Relative to the mixed system of an aqueous polychloroprene dispersion and a flocculant, the amount of the light stabilizer, the ultraviolet light absorber and the antioxidant may be 0.01-5 wt%, preferably 0.05-35 wt%; the amount of the filler is 10-60 wt%, preferably 20-50 wt%; and the amount of the wetting agent is 0.2-0.6 wt%, wherein all the amounts are based on non-volatile components.

Preferably, the mixed system of an aqueous polychloroprene dispersion and a coagulate agent has a pH stability of < 24 h, as determined according to DIN 53381, Method B.

Most preferably, the mixed system of an aqueous polychloroprene dispersion and a coagulate agent has a pH stability of < 3 h, as determined according to DIN 53381, Method

B.

In the present invention, curing the ballasts with an aqueous polychloroprene dispersion can completely eliminate the railwaytrack bed or dike subsidence and ballast collision, displacement and crushing of a track under the vibration of trains, tide or other huge loads and sleepers, which fundamentally solves the problems of railwaytrack bed or dike subsidence and ballast collision, displacement and crushing, thus improving the safety and maintenance-free performance of a railway roadbed, and reducing the maintenance cost, workload and working strength of the railway roadbed.

Curing a bed with a mixed system of an aqueous polychloroprene dispersion and carbon dioxide does not cause the expansion and foaming of the polyurethane cured foam, in which neither pressure maintaining nor post-curing is required after the construction of the cured bed. The mixed system of an aqueous polychloroprene dispersion and carbon dioxide enables trains to pass immediately after construction, thus greatly improving the production efficiency and quality.

According to another aspect of the invention, there is provided a track bed prepared by the above method.

According to still another aspect, the present invention provides a track comprising the above track bed.

Fig. 1 shows a schematic structural view of an example of a track comprising a track bed prepared according to the method of the present invention, wherein 10 represents a railway roadbed, a concrete pavement or a bridge, 20 represents an uncured track bed, 30 represents a drainage layer, 40 represents a ballast mat layer, 50 represents a cured track bed, 60 represents sleepers, and 70 represents rails; and

As shown in Fig. 1, on a railway roadbed, concrete pavement or bridge 10, ballasts of different particle diameters are gradually laid and tamped to a certain thickness (e.g. 35-60 cm). Moreover, according to the loading needs of the track, the ballasts are gradually tamped and dynamically stabilized to reach the desired bed density and stiffness. A drainage layer 30 and/or a ballast mat layer 40 is optionally disposed between the railwaytrack bed 10 and the ballasts.

According to actual needs, the drainage layer 30 may be either one drainage mat, or one or more transverse or longitudinal drainage channels and/or drainage ditches to further reduce the hydrolysis probability of a polymer in a wet environment, thus improving the service life of the track.

According to actual needs, the ballast mat layer 40 may be either one ballast mat, or one or more composite ballast mats. The ballast mat may be either a ballast mat based on a molding polyurethane material or a rubber material, or a ballast mat based on a polyurethane-bonded rubber material or other materials. The ballast mat layer 40 can be used to further improve the vibration damping and noise reduction performance of the track, thus improving the service life of the ballasts and a cured track bed 50.

According to the actual needs of the operation design of the track bed, part of the ballasts which reach the desired bed density and stiffness are cured using a mixed system of an aqueous polychloroprene dispersion and a coagulate agent to form a cured track bed 50. The cured track bed 50 has non-limiting shapes, and can be adjusted to the desired shape according to actual needs.

Sleepers 60 and rails 70 can be laid on the cured track bed 50 provided according to the present invention.

According to yet another aspect, the present invention provides use of a mixed system of an aqueous polychloroprene dispersion and a coagulate agent in the preparation of a track bed.

The terms “ comprising” and “ including” described in present application cover the circumstances which further comprise or include other elements not specifically mentioned and the circumstances consisting of the elements mentioned.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art of the present invention. When the definition of a term in the present description conflicts with the meaning as commonly understood by those skilled in the art of the invention, the definition described herein shall apply.

Unless otherwise specified, all numerical values expressing amount of ingredients, reaction conditions and the like which are used in the description and claims are to be understood as being modified by the term “ about” . Accordingly, unless indicated to the contrary, the numerical values and parameters described herein are approximate values which are capable of being changed according to the desired performance obtained as required. Examples

The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the examples and drawings so as to fully understand the objects, features and effects of the present invention. It will be readily understood by those skilled in the art that the examples herein are for illustrative purposes only and the scope of the invention is not limited thereto.

Description of some raw materials and test methods:

Raw materials:

Table 1: Aqueous polychloroprene dispersions used

Table 2: Aqueous anionic amorphous nano-silica dispersion used

Table 3: Polyurethane foaming systems used

Table 4: Additives used

Table 5: Coagulate agent used

Test methods:

Determination of pH:

A single-rod measuring electrode (e.g. a Sentron pH meter, including a measuring electrode and a reference electrode) is immersed in the dispersion or solution to be tested. The potential difference between the measuring electrode and the reference electrode is read on a measuring device as the pH. The manufacturer's operating instructions are to be followed for handling of the single -rod measuring electrode. Optionally, the pH can also be determined using other pH measuring equipment or initiator test paper or indicator solution.

Fatigue resistance test on track bed:

Super-grade ballasts for railway gravel are placed into a metal mold with an inner diameter of 60 cm*60 cm*36 cm in a layered manner, and then stabilized and compacted by vibration. Three block samples are made for each formulation and averaged during the test. About 160 mm thick ballasts are placed for the first time and then stabilized and compacted on a vibrating table, 100 mm thick ballasts are placed for the second time and then stabilized and compacted on the vibrating table, and ballasts are placed into the mold for the third time until their thickness reaches the actual track bed thickness of 350 mm to simulate the real thickness of a railway ballast bed. The density of the simulated bed in the mold is calculated according to the volume of the mold and the mass of the ballasts. When the supergrade ballasts have a density of 2.75 kg/m ³ , the bed density is stabilized to about 1.75 kg/m ³ in a vibration state, and then step 1) or step 2) is carried out.

1) Comparison experiment of polyurethane system: a polyurethane foaming system is mixed in the proportion shown in Table 6 and then poured into the above mold, and the mold is locked by a mold fastener, so that the molded foam has a density of 400 kg/m ³ or 600 kg/m ³ . The bed stiffness is determined to be similar to that of the bed without polyurethane foam poured. The performance is tested after standing at room temperature for one week.

2) A mixed system of an aqueous polychloroprene dispersion and a coagulate agent is mixed in the proportion shown in Table 6 and then poured into the above mold. The performance is tested after curing and then standing at room temperature for one week.

The specimens before filling and a fatigue resistance test are tested for their static stiffness, and the load is increased to at most 12.5 kN to test the vertical displacement.

The specimens after filling are subjected to the fatigue resistance test. Alternate loads are applied to the specimens from a minimum load of 5 kN to a maximum load of 25 kN, wherein the loading cycle is 2xl0 ⁶ and the loading frequency is (4+1) Hz. In the first 1000 cycles, ® the dynamic stiffness and dynamic stress of the specimens are determined for at least one loading cycle, © the static stiffness and stress of the specimens are determined, and © the residual deformation of the specimens is determined. The above tests ®, © and © are repeated every 500,000 times.

The above experiment is to simulate the deformation of the bed by compression when a train with a certain load passes on the track bed, and to simulate the situation of vehicles of different axle loads passing on the track bed according to the different pressure per unit areas applied, thus deducing through the number of tests that after how many trains have passed, the track bed may be deformed. The number of trains passing on a given track bed per year is specific, thus deducing the service life of the track bed obtained by curing the aqueous polychloroprene dispersion- coagulate agent system.

Comparative Example 1

Ballasts of different particle diameters (having a density of 2.75 kg/m ³ ) were gradually laid and tamped to 35 cm in a mold. The ballasts were gradually tamped and dynamically stabilized to reach a bed density of 1.75 kg/m ³ .

A polyurethane foaming system Bayflex 51BD14/DABCO 33LV/Desmodur 18IF19 was poured into a stacked structure of the ballasts in an amount of 100/0.5/45 by weight percentage as shown in Table 6 using a conventional high-pressure pouring machine, so that the molded foam had a density of 400 kg/m ³ and 600 kg/m ³ respectively; and 2-3 tons of metal weights were pressed on the bed to prevent the bed from rising due to foam expansion. The polyurethane system was foamed and cured for 60 minutes to form a polyurethane-filled ballast layer to obtain a track bed.

After reaction and demolding, the product was tested for its hardness and tensile strength and subjected to a fatigue resistance test. The results are shown in Table 6. Comparative Example 2

Ballasts of different particle diameters (having a density of 2.75 kg/m ³ ) were gradually laid and tamped to 35 cm in a mold. The ballasts were gradually tamped and dynamically stabilized to reach a bed density of 1.75 kg/m ³ .

An aqueous polychloroprene dispersion Dispercoll®C 84 was poured into a stacked structure of the ballasts in the amount shown in Table 6 using a conventional high-pressure pouring machine. The dispersion was cured for several days to form a ballast layer filled with the aqueous polychloroprene dispersion to obtain a track bed.

After reaction and demolding, the product was tested for its hardness and tensile strength and subjected to a fatigue resistance test. The results are shown in Table 6.

Examples 1-7

Ballasts of different particle diameters (having a density of 2.75 kg/m ³ ) were gradually laid and tamped to 35 cm in a mold. The ballasts were gradually tamped and dynamically stabilized to reach a bed density of 1.75 kg/m ³ .

A mixed system of an aqueous polychloroprene dispersion and a coagulate agent was poured into a stacked structure of the ballasts in the amount shown in Table 6 using a conventional high-pressure pouring machine, and then cured for 60-300 minutes to form a ballast layer filled with the mixed system of an aqueous polychloroprene dispersion and a flocculant, thus obtaining the track bed 50 as shown in Fig. 1.

After reaction and demolding, the product was tested for its hardness and tensile strength and subjected to a fatigue resistance test. The results are shown in Table 6.

Table 6: Raw materials used in Comparative Examples 1-2 and Examples 1-7 and the obtained product performance

The comparison between the performance obtained in Comparative Example 2 and Examples 1-7 in Table 6 can show that, when no carbon dioxide is added to an aqueous polychloroprene dispersion, the system has a pH of 10.4 and a long storage time, indicating that the liquid storage stability is good. When an aqueous polychloroprene dispersion is added with carbon dioxide and oscillated in a closed space, the system is unstable and cured quickly. The storage time is less than one day. When carbon dioxide is introduced to Dispercoll®C 84 and Dispercoll®C 2325, wherein the carbon dioxide is in amount of 0.35% by weight of the dispersion, the storage time is less than 2 h, which is particularly suitable for curing ballasts.

The comparison between the performance obtained in Comparative Example 1 and Examples 1-7 in Table 6 can show that, the tensile strength of the bed formed from the mixed system of an aqueous polychloroprene dispersion and carbon dioxide in the Examples 1-7 are better than the tensile strength of the bed formed from the polyurethane foam system in the Comparative Example 1 under similar hardness conditions, indicating that the bed in the Examples 1-7 has much better mechanical properties.

It can be seen from Examples 1-7 that an aqueous polychloroprene dispersion which is commonly used as an adhesive will flocculate after contacting an appropriate amount of a coagulate agent, , and then a cured film is formed on the surface of an adherend. When carbon dioxide is used as a coagulate agent for an aqueous chloroprene dispersion, not only a cured film is formed on the surface, but also the inside of liquid is gradually cured, so that the entire aqueous polychloroprene dispersion becomes an integral rubber body. Moreover, such cured rubber is not only a gum-like film, but also an elastomer having a thickness of more than 5 cm. This performance of changing from an aqueous polychloroprene dispersion into an integral rubber body can be used to cure ballasts. Fig. 2 shows photographs in which ballasts are cured using a mixed system of an aqueous polychloroprene dispersion and carbon dioxide. It can be clearly seen from the photographs that the mixed system of an aqueous polychloroprene dispersion and carbon dioxide is cured as an integral elastomer.

In the fatigue resistance test results in Table 6,“+++” represents excellent bed performance while “+” represents that the bed performance satisfies the basic requirements.“+++” represents that the service life is theoretically estimated to be 45-60 years (based on that 113 trains with 16 carriages and an axle load of 17 tons are passing per day).

The fatigue resistance test results can show that the fatigue resistance test results of both the bed formed from the mixed system of an aqueous polychloroprene dispersion and carbon dioxide in the Examples 1-7 and the bed formed from the polyurethane foam system in the Comparative Examples 1-2 satisfy the fatigue performance requirements of the track bed.

The exemplary embodiments or examples of the invention have been described above, but are not intended to limit the invention. For those skilled in the art, various modifications and changes can be made to the invention. Any modification, equivalent replacement and improvement, etc. made within the spirit and principle of the invention shall be included within the scope of the claims of the invention.