polyurethane ballast bed by using the same

Field

[0001] The present invention relates to a polyurethane composition for repairing polyurethane ballast beds, and the process of repairing ballast bed by using the same.

Background

10002 ] A railway track bed usually refers to a bal last layer laid beneath sleepers and above a roadbed, which serves as a basis for a track frame and is mainly used to support sleepers and to distribute a massive railway vehicle load transferred from the steel rail and sleepers evenly to a surface of the track bed, thereby reducing deformation of the roadbed and ensuring traffic safety. A railway track bed having ballast layer is also referred to as a ballast bed. In addition, ballast beds also offer buffering and v i b r a t i o n - re d u c i n g effect, and have good versatility and low construction cost, thus they have been widely used in the industry.

[0003] When high speed and heavy loaded train passes, the heavy load will be transformed to substantial impact to the ballast beds through rails and sleepers.

To prevent collision, disposition, crush and desertification of the ballasts, the track bed is often reinforced by polyurethane foam. When polyurethane is injected to a ballast bed, it rapidly penetrates to the voids among ballasts, and forms a composite structure comprising ballasts as matrix and polyurethane foams filling the voids after curing. The ballast bed having this composite structure is particularly suitable to bear high speed and heavy loaded trains, because it has high loads and high impact energy absorbing characteristics, high durability and high resilience under dynamic loads.

[0004] However, polyurethane ballast beds may suffer settlement after used for a period of time under dynamic loads, immersed in water or with natural subground settlement. In order to ensure polyurethane ballast bed functions well to spread the load and improve the track vertical and horizontal resistance and elasticity, the settled ballast bed must be repaired.

[0005] Existing repairing method mainly uses a stamping machine to I i ft the track up. However, the stamping machine cannot be applied to polyurethane ballast bed wh ich has been stabi l ized by polyurethane foam.

[0006] Therefore, a repairing method is needed for repai ring settled polyurethane ballast beds. Summary

[0007] In one aspect, the present invention provides a polyurethane composition for repairing polyurethane ballast bed, comprising:

(a) one or more polyisocyanate;

(b) a polyether polyol mixture comprising:

(bl) a first polyether polyol selected from amine initiated polyether polyols having a functionality of 2-6 and a hydroxy! number of 10- 1 200 mg KOH/g;

(b2) a second polyether polyol selected from polyol initiated polyether polyols having a functionality of 2-3 and a hydroxy I number of 1 2- 1 20 mg KOH/g;

(b3) a third polyether polyol selected from polyol initiated polyether polyols having a functionality of 3-8 and a hydroxy 1 number of 1 50- 1 200 mg KOH/g;

Wherein the first polyether polyol has an amount of 10-60 wt. %, the second polyether polyol has an amount of 1 -70 wt. %; the third polyether polyol has an amount of 1 0-70 wt. %, based on 100 % by weight of the polyether polyol mixture.

[0008] In one embodiment of the present invention, the first polyether polyol has a functionality of 4-6 and a hydroxyl number of 300- 1 000 mg KOH/g; preferably, the first polyether polyol has a functional ity of 4 and a hydroxyl number of 400-800 mg KOH/g; more preferably, the first polyether polyol has an amount of 30-60 wt.%, based on 1 00 % by weight of the polyether polyol mixture.

[0009] In another embodiment of the present invention, the second polyether polyol has a functionality of 2-3 and a hydroxyl number of 25-60 mg KOH/g; preferably, the second polyether polyol. is 10-30 wt.%, based on 1 00 % by weight of the polyether polyol mixture.

[0010] In stil l another embodiment of the present invention, the third polyether polyol has a f unctionality of 3-6 and a hydroxyl number of 1 50-900 mgKOH/g; preferably the third polyether polyol has a functionality of 3-5 and a hydroxyl number of 250-700 mgKOH/g; more preferably, the third polyether polyol has an amount of 30-50 wt.%, based on the 100 % by weight of the polyether polyol mixture. 1001 11 In yet another embodiment of the present invention, the polyisocyanate is one or more selected from the group consisting of the diphenyimethane diisocyanate, toluene diisocynate or the combination thereof.

[0012] In another aspect, the present invention provides a process for repairing settled polyurethane ballast beds, wherein the sleepers for supporting the track are disposed on the ballast bed, and the process comprising the step of injecting the polyurethane composition mentioned above to the void between the sleepers and the surface of the polyurethane ballast bed such that the polyurethane composition is cured to fil l the void.

[0013] In one embodiment of the present invention, the void between the sleepers and the surface of the polyurethane ballast bed is formed by lifting the track to a preset position; preferably the void between the sleepers and the surface of the polyurethane ballast bed has a height of about 10-100 mm.

[0014] In one embodiment of the present invention, the process further comprises the step of applying reinforcement material; preferably the reinforcement material is the one or more selected from the group consisting of alkali-free glass fabric, non-woven fabric, textile, glass fiber, carbon fiber, a ram id. fiber, stones, bricks, concrete blocks, metal blocks, rubber particles, plastic particles, yellow sand, glass bead and the combination thereof.

[0015] In still another aspect, the present invention provides a railway system, comprising sleepers and polyurethane ballast bed, wherein a polyurethane foam prepared from the polyurethane composition mentioned above is disposed between the sleepers and the polyurethane ballast bed to support the sleepers.

[0016] In one embodiment of the present invention, the polyurethane foam has a thickness of 10- 100 mm.

[0017] In another embodiment of the present invention, the polyurethane foam has a tensile strength of 2-40 Mpa, and a hardness of 30-90 Shore A and 40-80 shore D.

[0018] In still another embodiment of the present invention, the polyurethane foam has a density of 1 .5 g/cm ³ and an elongation at break of 2-55 %. Detailed Description

Polyurethane composition

[0019] In one aspect, the present invention provides a polyurethane composition for repairing polyurethane ballast bed, comprising:

(a) one or more polyisocyanate; (b) a polycthcr polyol mixture comprising:

(b l ) a first poly ether polyol selected from amine initiated polycthcr polyols having a functionality of 2-6 and a hydroxy! number of 10- 1 200 mg

KOH/g;

(b2) a second polycthcr polyol selected from the polyol initiated polycthcr polyols having a functionality of 2-3 and a hydroxyl number of 12- 1 20 mg

KOH/g;

(b3) a third polyether polyol selected from polyol initiated polycthcr polyols having a functionality of 3-8 and a hydroxyl number of 1 50- 1 200 mg KOH/g;

Wherein the first polycthcr polyol has an amount of 10-60 wt. %, the second polycthcr polyol has an amount of 1 -70 wt. %; the third polycthcr polyol has an amount of 1 0-70 wt. %, based on 1 00 % by weight of the polycthcr polyol mixture.

[0020] The polyurethane composition of the present invention doesn't comprise additional small molecule catalysts. Therefore the polyurethane composition doesn't cause pollution after being applied to the ballast bed. Moreover, the prepared polyurethane foam has similar or even better hardness and mechanical strength compared to sleepers, therefore can support the sleepers and fix the settled polyurethane ballast bed.

[0021] The polyurethane composition of the present invention may be one component composition or multi-component composition, preferably two-component composition. The two-component polyurethane composition may comprise component A which mainly comprises polyisocyanates, and component B which comprises polycthcr polyol mixture.

[0022] Component A comprises one or more polyisocyanates. The polyisocyanates may be described by the formula, R(NCO)n, wherein n = 2-4, and R represents an aliphatic hydrocarbon radical containing 2-18 carbon atoms, an aromatic hydrocarbon radical containing 6- 1 5 carbon atoms, or an araliphatic hydrocarbon radical containing 8-15 carbon atoms.

100231 Suitable examples of the polyisocyanates i ncl ude but not l im ited to ethylene diisocyanatc, 1 ,4-tctramcthylcne diisocyanatc, 1 .6-hexamcthylcne diisocyanatc (HDI), 1 ,2-dodccanc di isocyanatc, cyclobutanc- 1.3-diisocyanatc, cyclohcxane 1 ,3- and 1 ,4-diisocyanates, l -isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane, 2,4- and 2,6-hcxahydrotol ucne diisocyanatcs, hcxahydro- 1 ,3- and 1 ,4-phcnylcnc diisocyanatc, perhydro-2,4- and 4,4'-diphenylmethane diisocyanatc, 1 ,3-and 1 ,4-phcnylcnc diisocyanate. 1,4-durol diisocyanate, 4,4'-stilbene diisocyanate, 3,3 '-dimethyl-4,4'-biphenyiene diisocyanate, toluene 2,4- and 2,6-diisocyanates (TDI) and any mixtures of these two isomeric compounds, diphenyimethane-2,4'-, 2,2'- and 4,4'-diisocyanates (MDI), and n ap ht h y I ene- 1.5 -d i i socyanate (NDI), their isomers and the combination thereof. The poiyisocyanate is preferably selected from methylene diphenyl diisocyanate, toluene diisocyanate or the combination thereof, more preferably methylene diphenyl diisocyanate.

[0024] The polyisocyanates also include the modifications of the above mentioned isocyanates containing carbodiimide, uretoneimine, allophanate or isocyanurate structures, preferably methylene diphenyl diisocyanate modified by methylene diphenyl diisocyanate or carbodiimide, their isomers and the combination thereof.

[0025] The polyisocyanates can also be prepolymers produced by the common process known in the prior art. The prepolymcr preferably has a NCO content of 8-50 wt.%, more preferably 10-33 wt.%.

[0026] Component B comprises polyether poiyol mixture (b) which comprises amine initiated polyether poiyol (the first polyether poiyol), and long chain polyether poiyol (the second polyether poiyol) and short chain polyether poiyol (the third polyether poiyol) prepared from polyols as starter.

[0027] The first polyether poiyol is prepared from amine as a starter and epoxy compounds.

[0028] As used herein, the term "epoxy compound" refers to the compound having the following formula ( I):

[0029] Wherein Ri and R? are independently selected from the group consisting of H, Ci-C(, straight chain or branch chain alkyl, and phenyl and substituted phenyl.

[0030] It is well known to a person skilled in the art for the preparation process of the "epoxy compound", for example prepared by the oxidation of alkene.

[0031] Examples of epoxy compound suitable for use in the present invention include, but not limited to, ethylene oxide, 1 .2-propylene epoxide. 1 ,2-butylenc oxide, 2,3-butylene oxide, phenylethylene oxide or the combination thereof.

[0032] As used herein, the term "epoxy compound" further comprises oxacycioalkane, such as, but not limited to, tetrahydrofuran and oxetane.

100331 As used herein, the "amine" refers to the compounds comprising primary amine group, secondary amine group, tertiary amine groups or the combination thereof. The examples of amine suitable for use in the present invention include, but not limited to tricthanol amine, ethylene diamine, toluene diamine, diethylcne triamine, triethyiene tetramine and the derivates thereof, preferably ethylene diamine or toluene diamine. 100341 The first polyether polyol su i table for use in the present i nvention may be selected from the group consisting of: the polyether polyols prepared from the ring-opening polymerization of ethylene diamine as starter and propylene oxide, the polyether polyols prepared from the ring-opening copolymerization of ethylene diamine as starter and propylene oxide and ethylene oxide, the polyether polyols prepared from the ring-opening polymerization of toluene diamine as starter and propylene oxide, the polyether polyols prepared from the ring-opening polymerization of toluene diamine as starter and propylene oxide and terminated with ethylene oxide, the polyether polyols prepared from the ring-opening polymerization of toluene diamine as starter and ethylene oxide and terminated with propylene oxide. 100351 In one embodiment of the present invention, the first polyether polyol has a functionality of 2-6, and a hydroxy! number of 300-1000 mgKOH/g, preferably a functional ity of 4 and a hydroxy I number of 400-800 mgKOH/go

[0036] The method of determining hydroxy! number is well known to a person skilled in the art, for example the method disclosed in Houbcn Weyl, Methodcn der Organ ischen ( ^' hemic, vol. XIV 2 Makromoiekulare StotTc, p. ! 7, Georg Thicme

Verlag; Stuttgart 1963, the disclosure of which is incorporated by reference in its entirety herein.

[0037] The first polyether polyol may have an amount of 10-90 wt.%, preferably 30-60 wt.%, based on 100% by weight of the polyether polyol mixture.

[0038] Examples of the first polyether polyol suitable for use in the present invention include, but not l imited to, GR 403 (ethylene diamine as starter, hydroxy! number 760 mgKOH/g), GR 405 (ethylene diamine as starter, hydroxy! number 400 mgKOH/g), GNT-400 (the mixture of toluene diamine and tricthanolamine as starter, hydroxyl number 400 mgKOH/g) commercial available from SIN OPEC Shanghai Gaoqiao Company, and Dcsmophcn 4050 E (ethylene diamine as starter, hydroxy! number 620 mgKOH/g) and Dcsmophcn 405 1 B (ethylene diamine as starter, hydroxy! number 470 mgKOH/g) commercial available from Bayer material Science.

[0039] The second polyether polyol is prepared from polyhydric alcohols as starter and epoxy compounds. As used herein, the "polyhydric alcohol" refers to the compounds having at least two hydroxy! s and a hydroxy! number of 1 0- 1 20 mgKOH/g, the hydroxyl incl ude primary, secondary and tertiary hydroxy I and the combination thereof. Example of the polyols suitable for use in the present invention include, but not l imit to ethyleneglycol, dicthyleneglycol, triethylencglycol, tctracthyleneglycol, 1 ,2-propanediol, 3 ,3 -propanediol, 1 .4-butanediol, 3-mcthyl- l ,5-pcntancdiol , 1 ,5-pcntanediol, 1 ,6-hexanediol, 1,

1 0-dccanediol, glycerine, 1 ,2,4-butanetriol, 1 ,2,5-pentanetriol, 1 ,3,5- pentanetriol, 1 ,2,6-hexanetriol, 1 ,2,5-hexanetriol, 1 ,3,6-hexanetriol, trimethyiolbutane, trimcthylolpropane or di(trimethylolpropanc), trimethylolcthanc, pentacrythritol or dipentaerythritol. The epoxy compound is defined as above.

[0040] In one embodiment of the present invention, the second polyether polyol has a functional ity of 2-3, and a hydroxyl number of 10- 1 20 mgKOH/g; preferably a functional ity of 2-3, and a hydroxyl number of 20-80 mgKOH/g; more preferably a functional ity of 2-3, and a hydroxyl number of 25-60 mgKOH/g. The second polyether polyol has an amount of 1 -70 wt.%, preferably 1 0-30 wt.%, based on 100% by weight of the polyether polyol mixture.

100411 Examples of the second polyether polyol suitable for use in the present invention include, but not l imited to: Arcol 102 1 (propylene glycol initiated, hydroxyl number 56 mgKOH/g), Arcol 1 01 1 ( propylene glycol initiated, hydroxyl number 1 1 2 mgKOH/g), Arcol 1 026 ( propylene glycol initiated, hydroxyl number 28 mgKOH/g), Arcol 1032 ( propylene glycol initiated, hydroxyl number 35 mgKOH/g), Arcol 3553 and Arcol 1053 (glycerol initiated, hydroxyl number 35 mgKOH/g) and Arcol 1 362( glycerol initiated, hydroxyl number 28 mgKOH/g), Arcol 5603 and Arcol 5613 (glycerol initiated, hydroxyl number 54 mgKOH/g), all commercial available from Bayer Material Science, and GE 2 1 ()( propylene glycol initiated, hydroxyl number] 1 2 mgKOH/g). GE 220 ( propylene glycol initiated, hydroxyl number 1 12 mgKOH/g). GE 330 (glycerol initiated, hydroxyl number 35 mgKOH/g), al l commercial available from SINOPEC Shanghai Gaoqiao Company ₀ 100421 The third polyether polyol is prepared from polyhydric alcohol as starter and epoxy compound. As used herein, the "polyhydric alcohol" and the "epoxy compound" is defined as above.

100431 In one embodiment of the present invention, the th ird polyether polyol has a functional ity of 3-8, a hydroxy! number of 150-1000 mgKOH/g, preferably a functional ity of 3-6, and a hydroxyl number of 1 50-900 mgKOH/g, more preferably 3-5, and a hydroxyl number of 250-700 mgKOH/g. The third polyether polyol has an amount of 1 0-90 wt.%, preferably 10-70 wt.%, more preferably 30-50 wt.%, based on 100% by weight of the polyether polyol mixture.

[0044] Examples of the third polyether polyol suitable for use in the present invention include, but not limited to: GE 303 (glycerol initiated, hydroxy! number 480 mgKOH/g), GR 635s (sorbitol and glycerol initiated, hydroxy 1 number 500 mgKOH/g), GSU -4501. (sucrose and glycerol initiated, hydroxyl number 435 mgKOH/g), GMN -450 (glycerol initiated, hydroxyl number 450 mgKOH/g), all commercial available from SINOPEC Shanghai Gaoqiao Company, and Desmophen 3601 (sucrose and glycerol initiated, hydroxyl number 260 mgKOH/g), Desmophen 21AP27(sucrose and glycol initiated, hydroxyl number 440 mgKOH/g).

[0045] Besides above mentioned polyether polyol mixture, component B may further comprise one or more high molecular weight polyols, for example, polyester polyol, polycarbonate polyol and polymer polyol, which are added to the composition according to the actual needs. These high molecular weight polyols may have an amount of I -30 wt.%, based on 100% by weight of the polyurethane composition.

[0046] S u itabl e polyester pol yols may be produced from the reacti on of organ i c dicarboxylic acids or dicarboxylic acid anhydrides with polyhydric alcohols. Suitable dicarboxyl ic acids are preferably aliphatic carboxylic acids containing 2 to 1 2 carbon atoms, for example, succinic acid, ma Ionic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, d ec a n e - d i c a r b o x y I i c acid, maleic acid, fu marie acid, phthalic acid, isophthal ic acid, terephthalic acid, and the mixture thereof. Suitable anhydrides are, for example, phthalic anhydride, terachlorophthalic anhydride, and maleic anhydride. Representative polyhydric alcohols include ethanediol, diethylene glycol, 1 ,2- and 1 ,3-propanediols, dipropylene glycol, 1 , 3 - me t h y I p ro p a n ed i o 1 , 1 ,4-butanediol , 1 .5-pentanediol, 1 ,6-hexanediol, neopentyl glycol, 1 , 1 0-decanediol, glycerol, t r i me thylol-p ro pane, or mixtures of at least two of these diols. Polyester polyols of lactones, for example, ε-caprolactone, can also be used.

[0047] The polycarbonate polyol is preferably polycarbonate diols wh ic h may be prepared by the reaction of diols and dialkyl or diaryl-carbonatcs. The diols are preferably, but not l imited to, 1 ,2-propanediol, 1 .3-propanediol, 1 .4-butanediol,

1 .5-pentanediol , 1 ,6-hexanediol, diethylene glycol, trioxymethylene glycol and their mixtures. The dialkyl or diaryl-carbonatcs are preferably, but not l imited to, diphenyl carbonate.

100481 The polymer polyols are the stable dispersions formed by dispersing sol id enhanced particles in polyols l iquid. Any polymer polyol (or dispersion) known in the art can al l be incl uded in the polyol component of the present invention, including but not limited to SAN polymer polyol, PH D polymer polyol, PI PA polymer polyol. SAN polymer polyols are obtained by in-situ polymerization of the mixture of acrylonitri le and styrene in basic polyols, PI ID polymer polyol are obtained by in-situ polymerization of the isocyanate mixture and diamine in basic polyols, and PI PA polymer polyols are obtained by in-situ polymerization of the isocyanate mixture and diol and/or diol-amine in basic polyol.

[0049] The cha i n ex tenders typ i ca l l y are sel ected from act i v e hydrogen atoms comprising compounds with molecular weights lower than 800, preferably from 18 to 400. The active hydrogen atoms comprising compounds are preferably, but are not limit to alkanediols, dialkylene glycols, and polyalkylene polyols and their mixtures. The examples arc ethanediol, 1 ,4-butanediol, 1 ,6-hexanediol, 1 ,7-heptanediol , 1 ,8-octanediol, 1 ,9-nonanediol, I J O-decanediol, diethylene glycol, dipropylene glycol, polyoxyal kylenc glycols or the mixture thereof. Other suitable substances are branched chain and unsaturated alkanediols such as 1 ,2-propanediol,

2-methyl- l ,3-propanediol , 2.2-di methyl- 1 ,3-propanediol,

2-butyl-2-ethyl- l ,3-propanediol, 2-butene- l ,4-diol and 2-butyne- l ,4-diol, alkanolamines and N -a I ky I d i a I kano I am i nes such as ethanol amine, 2-aminopropanol and 3-amino-2,2-dimethylpropanol . N-methyl and N-ethyl-diethanolamines, as w el l (cyclo) aliphatic and aromatic amines, e.g. 1 .2 ethylenediamine,

1 ,3-propylenediamine, 1 ,4-butylenediamine,

1 ,6-hexamethylenediamine,isophoronediamine, 1 ,4-cyclohexamethylenediamine, Ν,Ν'-diethyl-phenylenediamine, and 2,4 and 2,6 diaminotolune. The chain extender dosage is 0-20 wt.%, based on 100% by weight of the B component.

[0050] Optional ly, the polyurethane composition may further comprise blowing agent.

The blowing agents may be any conventional physical foaming agent and chemical foaming agent, including but not limited to water, halohydrocarbons, and hydrocarbons. Examples of ha I oh yd rocarbo ns are monoch lorod i fu loromethanc, dicholoromonofluoroamnethe, dichlorofluoromethane, and trichlorofhiromethane or the mixture thereof. Examples of hydrocarbons include but not limit to butane. pentane, cyclopentane, hexane, cyclohexane, heptane and the mixture thereof. The blowing agent is most preferably w ater. The amount of the blowing agent depends on the desired density of ballast layer filled by the polyurethane, preferably 0.3-4.5 wt.%, more preferably 0.5-3.6 wt.%, most preferably 0.6-3.2 wt.%, based on 100% by weight of al l the polyols in the polyurethane reaction system (both including the polyols used as reaction component, and those used as chain extender and other components).

[0051] The B component can optionally comprise catalyst, surfactant and flame retardant and the like.

[0052] The catalyst is p re fe rab l y, but not I i m i t to, am i n es a nd organic meta l compounds and their mixtures. The amine catalyst is preferably, but not limit to, tricthylamine, tributylamine, tricthylene diamine, N-cthylmorphol ine, Ν,Ν,Ν',Ν'-tetramethyl-ethyienediamine, pentamethyl diethyl ene-triaminc, N.N-mcthylanil inc, N.N-dimethylani l inc and mixtures thereof. The organic metal catalyst is preferably, but not limit to, stannous diacetate, stannous dioctoate, stannous diethyihexoate, and dibutyitin diacetate, dibutyltin dilaurate, ditutyltin maieate, and dioctyltin diacetate and mixtures thereof. The catalyst dosage is 0.001 - l Owt.%, based on 100% by weight of the B component.

[0053] Suitable surfactants may be selected from the compounds for improving homogenization of raw materials of adjusting foam's cellular structure, preferably from but not limited to polyo.xyalkylene derivatives of siloxane, in an amount of 0.01 to 5% by weight, based on 100% by weight of B component.

[0054] The flame retardant can be an organic flame retardant or an inorganic flame retardant. The organic flame retardant is preferably but not limited to tri(2-chioroethyl)phosphate (TCEP), tri(2-chioropropyl)phosphate (TCPP), trichloropropyl phosphate (TDCPP), di methyl mcthylphosphonate ( DM M P), triphenyl phosphate, melamine phosphate (MMP) the mixtures thereof; the inorganic flame retardant is preferably but not l imited to hydrated aluminium hydroxide, hydrated magnesium hydroxide, monoammonium phosphate, diammonium phosphate, ammonium chloride, boric acid, hydrated zinc borate (FB) or the mixture thereof.

[0055] In the polyurethane reacti on system, the mole ratio of NCO groups to OH groups is preferably 70-130: 100, more preferably 90-115: 100, wherein the OH groups comprise al l the OH groups from polyols, cross-linker, filler, blowing agent. The process for repairing polyurethane ballast bed

[0056] The process provided in the present invention comprising the step of injecting the polyurethane composition in situ to the void between the sleepers and the surface of the polyurethane ballast bed such that the void is filled with a high density polyurethane rigid foam obtained from the polyurethane composition. Because of the high density, the polyurethane rigid foam has similar or even better mechanical property and stiffness compared to sleepers, thus fixing the settled polyurethane ballast bed. Moreover, the polyurethane rigid foam and the polyurethane material in the ballast bed belong to the same kind of polymer, therefore they have better compatibility and cohesiveness.

[0057] The process of the present invention can be applied to settled polyurethane ballast bed caused by various reasons, such as geological hazard, rain washing, and heavy load of train. The settlement could be caused by the damage of the polyurethane ballast bed or ground settlement and the like.

[0058] As used herein, the void between the sl eepers and the surface of the polyurethane ballast bed refers to the space between the sleeper's underside surface and the polyurethane ballast bed's surface. In the present invention, the height of the void refers to the distance from the bottom to the top of the void. The void may have different height and shape due to different cause of the settlement.

[0059] In the present invention, the height is preferably 1 0- 1 00 mm. When the height is lower than 10 mm, it is not convenient to inject the polyurethane reaction system to the void, and when the height is more than 100mm, more polyurethane composition are needed to fil l the void thus improving the maintenance cost.

[0060] In the present invention, the void may have irregular shape, wherein the length of the void refers to the distance of the two ends along the sleeper. The process of the present invention may be appl ied to any void of any length, for example 20-260 cm.

[0061] In one preferable embodiment of the present invention, the void between the sleepers and the surface of the polyurethane bal last bed is formed by l ifting the track to a preset position. The void may have different height and shape according to different cause of the settlement.

[0062] The preset position can be any desirable position to a person skilled in the art, the sleeper may be lifted to the preset position by any device known to a person skilled in the art, for example, track lifting device.

[0063] In one embodiment of the present invention, the preset position is the standard height position of track, that is to say the height when the track surface is in the datum height.

[0064] Figure 1 is a schematic illustration of a process for repairing the polyurethane ballast bed in accordance with an embodiment of the present invention. As shown in figure 1 , the process of repairing polyurethane ballast bed of the present invention comprises l ifting track 110 together with sleeper 120 to the standard height position of track by track lifting device 150, that is to say the track surface is in the datum height. At this moment, a void 140 is formed between the sleepers 120 and the surface of the polyurethane bal last bed 130, then the void 140 is injected with polyurethane composition, which foams and cures in situ to form a polyurethane foam to fill the void 140, thus repairing the settled polyurethane bal last bed.

100651 In figure 1 , the void 140 has a cuboid shape, which is only an example of the present invention and should not be deemed as limitation to the present invention. The void may have different shape due to the settlement of the polyurethane bal last bed.

[0066] In one embodiment of the present invention, the void 140 can be appl ied with a reinforcement material and then injected with the polyurethane composition, or be injected with the polyurethane composition and then applied with enforcement material before the polyurethane composition cures. When comprising reinforcement material, the obtained polyurethane foam has better strength thus is favored for supporting sleepers. In another embodiment of the present invention, the component B can be firstly mixed with reinforcement material such as sand, glass fiber, and then injected into the void by extrusion machine.

[0067] The examples of epoxy compound su itabl e for use in the present i nvention include, but not l imited to alkali- free glass fabric, non-woven fabric, textile, glass fiber, carbon fiber, aramid fiber, stones, bricks, concrete blocks, metal blocks, rubber particles, plastic particles, yellow sand, glass bead and the combination thereof. Railway system

10068) The present invention further relates to a railway system, comprising sleepers and polyurethane ballast bed, wherein a polyurethane foam prepared from the polyurethane composition mentioned above is disposed between the sleepers and the polyurethane ballast bed to support the sleepers.

[0069] The polyurethane foam is prepared by injecting the polyurethane composition to the void 140 and cure to fil l it, wherein the reinforcement material mentioned above may be comprised.

[0070] Because the polyurethane foam fil ls the void, the polyurethane foam has the same thickness of 10- 100 mm as the void. 100711 In addition, the polyurcthanc foam has a tensile strength of 2-40 Mpa, a density of 0.4- 1 .5 g/cm ³ , a hardness of 30-90 Shore A and 40-80 shore D, and an elongation at break of 2-55 %.

Examples

[0072] The following examples are included to demonstrate preferred embodiments of the invention. It should be appreciated by those skilled in the art that the techniques disclosed in the following examples represent techniques discovered by the inventor to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a similar result without departing from the spirit and scope of the invention.

100731 The materials and devices mentioned in this invention are l isted as fol lows:

Desmophen 4050 E, the first poly ether poiyoi, EDA as initiator, OH number 620, functionality 4.0, supplied by Bayer materialscicncc Ltd;

Desmophen 405 1 B, the first polyether poiyoi, EDA as initiator, OH number 470, functional ity 4.0, supplied by Bayer materialscicncc Ltd;

GR 403, the first polyether poiyoi, EDA as initiator, OH number 770, functionality 4.0, supplied by Shanghai Gaoqiao PU company;

GR 405, the first polyether poiyoi, EDA as initiator, OH number 450, functionality

4.0, supplied by Shanghai Gaoqiao PU company;

Arcol 1026, second polyether poiyoi, PG as initiator, OH number 28, functional ity 2.0 suppl ied by Bayer matcrialscience Ltd;

Arcol 1021 , second polyether poiyoi, PG as initiator, OH number 56, functionality

2.0 suppl ied by Bayer materialscicncc Ltd;

Arcol 3553, second polyether poiyoi, glycerin as initiator, OH number 35, functionality 3.0 supplied by Bayer materialscicncc Ltd;

Arcol 1 362, second polyether poiyoi, glycerin as initiator, OH number 28, functional ity 3.0 suppl ied by Bayer materialscicncc Ltd;

GE 220, second polyether poiyoi, PG as initiator, OH number 56, functionality 2.0 supplied by Shanghai Gaoqiao PU company;

GR 635, third polyether poiyoi, sorbitol glycerin mixture as initiator, 01 1 number 500, functionality 4.5, supplied by Shanghai Gaoqiao PU company; Arcol 3601 , third polycthcr polyol, sorbitol/glycerin mixture as initiator, OH number 360, functionality 4.2, supplied by Bayer materialscience Ltd;

Arcol 3607, third poly ether polyol, sorbitol 'glycerin mixture as initiator, OH number 450, functional ity 4.7, supplied by Bayer materialscience Ltd;

Desmophen 21AP27, third polycthcr polyol. sorbitol/EG mixture as initiator, OH number 440, functionality 2.8, supplied by Bayer materialscience Ltd;

GE 303, third polycthcr polyol, glycerin as initiator, 01 1 number 480, functionality

3.0 supplied by Shanghai Gaoqiao PU company;

Stepanpoly PS- 1922, PTA polyester polyol, 01 1 number 1 90, functional ity 2.0. supplied by Stcpan;

Tego Stab B 8715, stabilizer, supplied by Evonik;

DEC, dicthylcne glycol, chain extender, common chemical product;

DPG, dipropylcnc glycol, chain extender, common chemical product;

DBTDL, Dibutyltindilaurate, catalyst, supplied by Air Products

KAC DEG solution, catalyst, common chemical product;

Dcsmodur 44 V20L, PMDI, NCO 31 .5%, suppl ied by Bayer materialscience Ltd; Dcsmodur 44 P90, MDI prcpolymcr, NC028.1%, s u p p l i ed by B aye r materialscience Ltd;

Dcsmodur 1 5 1 1 L, PMDI, NCO 31.5%, suppl ied by Bayer materialscience Ltd; H-X P3 type spray machine, with mix head : suppl ied by GRACO company;

YQ-245 hydraulic rail lifter, YUFENG hydraul ic machinery company LTD;

CG -600- 1 - 1 , Caulking gun, suppl ied by Naishangjiong company.

Example 1

[0074] The rails, together with the fasteners and sleepers were lifted up by YQ-245 hydraulic lifting device to the standard height position of the track, thus a void with a height of about 25 mm was formed between sleeper and polyurethanc bal last bed. The void was first filled with small gravel ballast. Polycthcr polyols were mixed according to table 1 at room temperature. The mixed polyols and isocyanate were injected to the void within 60s by GC-600-1- 1 caulking gun. After 30 minutes the polyurethanc composition cured to form a polyurethanc foam fi l ling the void between the sleepers and the polyiirethane ballast bed.

Table I : the polyurethanc composition and the Physical and mechanical properties thereof

[0075] The polyurethane foam of the present example is prepared by the way of onsite casting and in situ reaction, thus has a wide application for the cases wherein the sleepers has an irregular bottom surface or the polyurethane ballast bed has an irregular surface.

Example 2-3

[0076] The rails, together with the fasteners and sleepers were lifted up by YQ-245 hydraulic lifting device to the standard height position of the track, thus a void with a height of about 25 mm was formed between sleepers and the polyurethane ballast bed. The polyurethane compositions according to table 2 were injected to the void within 30s by conventional H-XP3 high pressure foam machine. After 30 minutes the polyurethane composition cured to form a polyurethane foam mat filling the void between the sleepers and the polyurethane ballast bed.

Table 2: the polyurethane composition and the physical and mechanical properties thereof

[0077] The polyurethane composition in example 3 comprising glass fiber has better physical properties, for instance tensile strength and elongation.

Example 4

[0078] The rails, together with the fasteners and sleepers were l i fted up by YQ-245 hydraulic li fting device to the standard height position of the track, thus a void with a height of about 50 mm was formed between sleeper and polyurethane ballast bed. The void was first filled with continuous Z-type pads which were prepared by folding glass fiber cloth and kraft paper. The component B was first mixed according to table 3 under room temperature, and then injected to the void with isocyanates at a ratio of 1 : 1 within 30s by conventional H-XP3 high pressure foam machine. After 30 minutes the polyurethane composition is cured to form a polyurethane foam mat filling the void between the sleepers and the polyurethane ballast bed. Tablc 3 : the polyurethane composition and the physical and mechanical properties thereof

[0079] The polyurethane foam mat of the present example is prepared by the way of onsite casting and in situ reaction, thus has a wide application for the cases wherein the sleepers has an irregular bottom surface or the polyurethane ballast bed has an irregular surface. Moreover, the polyurethane composition has a fast curing speed which is basically unaffected by environment temperature, thus well suited for fast repairing and repairing work at cold or high elevation area.