BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a slab track repairing material, a cured product thereof, a method for repairing slab tracks using the repairing material, a slab track, and a resin composition. 2. Description of the Related Art [0002] Slab tracks are conventional tracks that are used widely. A structure made of concrete or the like, such as an elevated structure, an underground structure or a bridge, is used as a roadbed (hereinafter, such a structure will be also written as the "roadbed structure") . A track slab made of, for example, concrete is fixed on the roadbed structure via a filling layer that is formed of a cement asphalt mortar (hereinafter, also written as the X,CA mortar") obtained by mixing cement, an asphalt emulsion and a fine aggregate- Track rails are then fastened to the track slab. [0003] 2 Such a slab track 10 is specifically illustrated in Fig. 1. As illustrated, a track slab 24 is disposed on the top surface of a roadbed structure 20 via a filling layer 22, and a pair of track rails 30, 30 are installed on the top surface of the track slab 24. The track slab 24 has notches 26, 26 at its both ends. The notches 26 of the track slab 24 are aligned with projections 28 disposed on the roadbed structure 20 at prescribed intervals. [0004] For example, the filling layer 22 is formed by keeping the track slab 24 uplifted at a prescribed position above the roadbed structure 20, filling the gap between the track slab 24 and the roadbed structure 20 with a CA mortar as a filler that is applied, for example, through a hole (not shown) perforated in the track slab 24, and curing the filler. Alternatively, the filling layer 22 is sometimes formed by keeping the track slab 24 uplifted at a prescribed position above the roadbed structure 20, inserting a bag made of a nonwoven fabric or the like which contains a CA mortar into the gap between the track slab 24 and the roadbed structure 20, and solidifying the mortar so as to fill the gap. [0005] The filling layer 22 made of a CA mortar is degraded little by little due to reasons such as the expansion and contraction of the track rails 30 by temperature change,, the force applied by trains running on the track rails 30*- and the formation of pores in the filling layer 22 (the filling layer 22 being rendered porous) as a result of the dissolution of alkali components by water and the like that have penetrated into the filling layer 22 . In particular, repeated freezing and melting of water that has penetrated into the filling layer 22 accelerates the degradation of the filling layer 22 and is of significant influence in cold climate areas. Once the filling layer 22 is degraded, defects such as cracks, separations and collapses occur at portions of the degraded filling layer 22 that are exposed to the outside. Early repairing is desired if any degradations are found. [0006] Non-Patent Literature 1 presents a slab track repairing method in which a filling layer is repaired by removing a degraded portion of the filling layer, arranging a formwork so as to enclose the cleared area, filling the formwork with a repairing material, which is then cured, and thereafter removing the formwork (hereinafter, the method will be also written as the "frame repairing method") - From points of view such as workability, curability and durability, the repairing material that is used in the method is a resin-based repairing material such as a vinyl ester (-based) resin or a polyurethane(-based) resin. [0007] A material for repairing slab track filling layers is known also from Patent Literature 1. This repairing material is obtained by mixing a radically curable polyester acrylate as the base with high-molecular weight elastic chips and an inorganic aggregate, and adding a curing agent to the mixture. CITATION LIST PATENT" LITERATURE [0008] Patent Literature 1: JP-A-H11-256504 Non-Patent Literature [0009] Non-Patent Literature 1: "Surabu kidou kakubu hoshuu no tebiki (Guidance on repairing of slab track parts)". Railway Technical. Research Institute, May 1, 1998,. Second edition, pp. 21-35 SUMMARY OF THE INVENTION [0010] Unfortunately, cured products of the repairing materials used in the above literature cannot support a track slab sufficiently when a train runs on the repaired sections because of the fact that the Young' s modulus of the cured products is low as compared to CA mortars. (For example, the Youngfs modulus of cured products of conventional vinyl ester(-based) resins or polyurethane{-based) resins is about 15 to 70 N/mm2 in contrast to approximately 2,000 N/mm2 Young*'s modulus of CA mortars.) In the repairing of slab tracks, the width of degradation in a filling layer (the length, from an end of the filling layer, of an unhealthy portion to be removed during the repairing) is generally small and thus the repaired sections have little mechanical influence on the track slab. This is the reason why repairing has been possible with a conventional repairing material with a low Young' s modulus . However, recent studies have shown that in very cold regions such as Hokkaido, Japan, the degradation of a filling layer by freeze damage is so severe that the width of degradation is as long as 100 mm or more, or sometimes 200 mm or more. It has been then found that in such cases a conventional repairing material applied to the filling layer cannot support the track slab sufficiently and can give rise to a dynamic displacement or the like that causes troubles such as uncomfortable ride during the running of a train. Thus, there has been a demand for the development of a repairing material which can give cured products having as high a Youngfs modulus as that of CA mortars. [0011] The present invention has been made in light of the problems discussed above. It is therefore an object of the invention to provide a slab track repairing material which can give cured products having a high Young' s modulus and can be suitably used as a slab track repairing material, and a method for repairing slab tracks using the material. [0012] The present inventors carried out extensive studies to solve the problems discussed above. As a result, the present inventors have developed a specific repairing material which can solve the problems, thereby completing the present invention. Some example aspects of the present invention are as follows. [0013] [1] A slab track repairing material comprising a polyfunctional polyol (A) having a functionality of more than 2, a difunctional polyol (B) and an isocyanate compound (C). [0014] [2] The repairing material described in [1] , wherein the polyfunctional polyol (A) is a tetra or higher functional polyol. [3] The repairing material described in [1] or [2], wherein the content of the polyfunctional polyol (A) is not less than 150 parts by mass per 100 parts by mass of the difunctional polyol (B). [0015] [4] The repairing material described in any of [1] to [3], further comprising an inorganic pigment (D). [5] The repairing material described in [4] , wherein the content of the inorganic pigment (D) is not more than 450 parts by mass per 100 parts by mass of the difunctional polyol (B) . [0016] [6] The repairing material described in any of [1] to [5] , which satisfies the following requirement: Requirement: The Young's modulus of a cured product of the repairing material is 700 to 2,700 N/mm2. [0017] [7] The repairing material described in any of [1] to [6], wherein the polyfunctional polyol (A) is a castor oil polyol having a functionality of more than 2. [8] The repairing material described in any of [1] to [7], wherein the difunctional polyol (B) is a difunctional castor oil polyol. [0018] [9] The repairing material described in any of [4] to [8], wherein the inorganic pigment (D) comprises at least one selected from silica and calcium carbonate. [0019] [10] The repairing material described in any of [1] to [9], wherein the isocyanate compound (C) comprises at least one selected from an aromatic polyisocyanate and an araliphatic polyisocyanate. [0020] [11] A cured product of the repairing material described in any of [1] to [10] . [12] A slab track repairing method comprising a step of applying the repairing material described in any of [1] to [10] to fill a defective site of a filling layer disposed between a track slab and a roadbed structure, and curing the repairing material to form a cured product. [0021] [13] A slab track comprising a roadbed structure, a track slab, a filling layer disposed between the roadbed structure and the track slab, and a track rail installed on the track slab, at least part of the filling layer being a cured product of the repairing material described in any of [1] to [10]. [0022] [14] A resin composition comprising a polyfunctional polyol (A) having a functionality of more than 2, a difunctional polyol (B) and an isocyanate compound (C). [0023] According to the present invention, cured products with a high Young's modulus can be formed. Such a cured product, when used as a filling layer disposed between a track slab and a roadbed structure, can support sufficiently the track slab and thus can inhibit problems such as a dynamic displacement generated during the running of a train, allowing the slab track to offer a comfortable ride. The repairing material of the invention with its sufficient fluidity even in the absence of plasticizers can be suitably used as a slab track repairing material, in particular, as a material to be poured between a track slab and a roadbed structure, and thus can facilitate repairing of slab tracks while eliminating or reducing the bleed out of plasticizers into the environment. Further, the inventive repairing material can be cured while ensuring a close contact with an existing CA mortar filling layer, and consequently the cured product can fill the gap between the track slab and the roadbed structure without leaving any clearance. In the presence of clearance or voids in the filling layer, water that has penetrated into the filling layer collects there to increase the risk of freeze damage. It is therefore desired that a repaired filling layer have few voids. A slab track filling layer that has been repaired with the inventive repairing material contains a reduced amount of voids and is therefore less prone to freeze damage and is highly durable. BRIEF DESCRIPTION OF THE DRAWING [0024] Fig. 1 is a partially sectional, perspective view of an example structure of a slab track. DESCRIPTION OF THE PREFERRED EMBODIMENTS 5 [0025] {{Slab track repairing materials and resin compositions)) A slab track repairing material of the present invention includes a polyfunctional polyol (A) having a functionality of more than 2, a difunctional polyol (B) and an isocyanate 10 compound (C). A resin composition of the present invention includes a polyfunctional polyol (A) having a functionality of more than 2, a difunctional polyol (B) and an isocyanate compound (C). Hereinafter, the repairing material and the resin composition are sometimes collectively written as the 15 "present material". The present material, by virtue of its containing the above compounds, attains the advantageous effects described above. In particular, the present material exhibits sufficient fluidity and at the same time can form cured products 20 having a high Young's modulus. Thus, the present material can be suitably used as a material for repairing a slab track, in particular, as a material to be poured between a track slab and a roadbed structure, while eliminating or reducing the bleed out of plasticizers into the environment. [0026] The conventional slab track repairing materials have been incapable of forming cured products with a high Young'' s modulus while exhibiting high fluidity at the saJne time. For example, one possible approach to obtaining cured products with a high Young'' s modulus is to increase the amount of pigment components such as an inorganic pigment (D) described later. Unfortunately, such a material exhibits poor fluidity and is difficult to pour between a track slab and a roadbed structure, possibly leaving a clearance or voids ifi the repaired filling layer due to its poor fluidity. It is therefore not desired to use such a material as a slab track repairing material. In contrast, the present material £an form cured products with a high Young's modulus while exhibiting sufficient fluidity by virtue of its containing, as polyol components, a polyfunctional polyol (A) which has a functionality of more than 2 and a difunctional polyol (B) which does not bleed out unlike conventional plasticizers. [0027] Although the present material may be a one-part composition, a two-part form is preferable for reasons such as excellent storage stability. In this case, the polyols (A) and (B) are usually present in the main agent, and the isocyanate compound (C) is usually present in the curing agent, and the 12 present material may be prepared by mixing the main agent and the curing agent with each other. [0028] (Polyfunctional polyols (A) having functionality of more than 5 2> The polyfunctional polyol (A) having a functionality of more than 2 (hereinafter,, also written as the "component (A)") is not particularly limited. For reasons such as that cured products with a higher Young's modulus can be obtained, a 10 polyfunctional polyol having a functionality of 2.7 or above is preferable, and a polyfunctional polyol having a functionality of 3 or above is more preferable. In particular, for reasons such as that cured products having a similar Young' s modulus as CA mortars can be obtained easily, a polyfunctional 15 polyol having a functionality of 4 or above is still more preferable, and a polyfunctional polyol having a functionality of 5 or above is particularly preferable. In the present specification, the functionality means the average number of hydroxyl groups per molecule. For example, 20 a polyfunctional polyol having a functionality of more than 2 indicates a polyol having more than two hydroxyl groups in the molecule. The components (A) may be used singly, or two or more may be used. 13 [0029] Specific examples of the components (A) include castor oil polyols, polyether polyols and polyester polyols. Here, the castor oil polyols include castor oil polyether polyols 5 having a polyether structure, castor oil polyester polyols having a polyester structure, and castor oil polyester polyether polyols having a polyether structure and a polyester structure„ For reasons such as that the present material attains 10 excellent low-temperature curability, high curing rate and low environmental loads and can give cured products having a higher Young's modulus, the component (A) is preferably a castor oil polyol or polyether polyol, and more preferably a castor oil polyester polyol or a castor oil polyester polyether polyol. 15 Note that, in this specification, castor oil polyol(s) mean(s) castor oil-based polyol (s). In the similar: way, polyether polyol(s) mean(s) polyether-based polyol(s), polyester polyol(s) mean(s) polyester-based polyol (s) , castor oil polyether polyol(s) mean(s) castor oil-based polyether 20 polyol(s), castor oil polyester polyol (s) mean(s) castor oil-based polyester polyol(s) and castor oil polyester polyether polyol(s) mean(s) castor oil-based polyester polyether polyol(s). [0030] 14 Castor oil is a light yellow, viscous non-drying oil obtained from seeds of castor-oil plant in the Euphorbiaceae family. Approximately 90% of the fatty acids in castor oil is ricinoleic acid, which has hydroxyl groups, a double bond and 5 an ester bond in the molecule. This is why castor oil shows unique characteristics which distinguish the oil from other plant oils and fats, such as outstanding stability, flexibility, electrical insulating properties, water resistance and impact resistance. By containing a castor oil polyol generated from 10 castor oil having such characteristics, the present material can form cured products which are not only resistant to mechanical stress such as friction and impact, but also have excellent properties such as heat resistance, hydrolysis resistance and acid resistance. 15 Further, by the use of a castor oil polyol, cured products that are obtained are less prone to thermal deformation and curing shrinkage. [0031] The castor oil polyols are not particularly limited. 20 Examples thereof include transesterification products of at least one of castor oil and castor oil-alkylene oxide adducts, with at least one of alcohols, polyester polyols and polyether polyols; ester compounds formed between a castor oil fatty acid (a fatty acid that is obtained from castor oil and is usually 15 a mixture of ricinoleic acid, oleic acid and so on) and at least one of alcohols, polyester polyols and polyether polyols; partially dehydrated or partially acylated products of castor oil diol; hydrogenated products of the above 5 transesterification products, ester compounds and partially dehydrated or partially acylated products; and compounds obtained by polymerizing castor oil into polymerized castor oil, and reacting a transesterification product of the polymerized castor oil with caprolactone. 10 A compound with a functionality of more than 2 that is selected from the above compounds may be used as the component (A) . [0032] Examples of the polyether polyols include those polyols 15 that are obtained by adding, for example, an alkylene oxide such as ethylene oxide, propylene oxide, butylene oxide or polyoxytetramethylene oxide to a starting compound having at least 3 or more active hydrogen groups, for example, a polyhydric alcohol such as glycerol, trimethylolpropane, 20 pentaerythritol, sorbitol or sucrose, or an aliphatic amine compound such as diethylenetriamine. [0033] Examples of the polyester polyols include those polyester polyols that are obtained by condensing a trihydric or 16 polyhydric alcohol such as glycerol, diglycerol, trimethylolpropane, pentaerythritol, sorbitol or sucrose, with a dibasic acid such as glutaric acid,, succinic acid, oxalic acid, terephthalic acid, isophthalic acid, adipic acid, 5 azelaic acid or sebacic acid. [0034] The hydroxyl value of the component (A) is not particularly limited. The lower limit of the hydroxyl value is preferably 40 mg KOH/g and more preferably 140 mg KOH/g, 10 and the upper limit of the hydroxyl value is preferably 500 mg KOH/g and more preferably 400 mg KOH/g for reasons such as that the present material exhibits a prescribed viscosity and attains more excellent filling properties, slab track repairing easiness and low-temperature curability. 15 [0035] The viscosity of the component (A) is not particularly limited. For reasons such as that the present material attains more excellent filling properties and slab track repairing easiness, the viscosity measured with an Ubbelohde viscometer 20 at 25°C in accordance with JIS Z8803:2011 is preferably 200 to 10,000 mPa-s, more preferably 500 to 6,500 mPa-s, and particularly preferably 500 to 2,000 mPa-s. [0036] The number average molecular weight (Mn) of the component 17 (A), although not particularly limited, is preferably 400 to 3,000, and more preferably 700 to 1,100 for reasons such as that the present material exhibits a prescribed viscosity and attains more excellent filling properties, slab track 5 repairing easiness and low-temperature curability. [0037] The component (A) may be one synthesized in accordance with a known method or may be a commercial product. Examples of such commercial products include URIC H-30, URIC H-52, URIC 10 H-57, URIC K-73X, URIC H-81, URICH-102, URICH-420, URICH-854, URICH-870, URICH-1824, URICH-368, POLYCASTOR #10, POLYCASTOR #30, URIC Y-406, URIC AC-009, URIC F-15, URIC F-25, URIC F-40, URIC F-60 (all manufactured by ITOH OIL CHEMICALS CO., LTD.), TLM, LAV, LM-R, ELA-DR, HS 3P-255, HS PPE-12H, HS 6G-160, HS 15 CM-025P, HS CM-075P, HS 3G-100M, HS 3G-500B, HS 2T-1208 (all manufactured by HOKOKU Co., Ltd.) and EXCENOL 410NE (manufactured by ASAHI GLASS CO., LTD.). [0038] The content of the component (A) relative to the present 20 material (in terms of solid) is preferably 20 to 40 mass% for reasons such as that the present material exhibits a prescribed viscosity and attains more excellent filling properties and slab track repairing easiness, and that cured products with a high Young's modulus can be obtained easily. In particular, 18 the content is more preferably 27 to 34 mass% for reasons such as that cured products having a similar Young's modulus as CA mortars can be obtained easily. [0039] 5 The content of the component (A) per 100 parts by mass of the difunctional polyol (B) is preferably not less than 150 parts by mass for reasons such as that the present material exhibits a prescribed viscosity and attains more excellent filling properties and slab track repairing easiness, and that 10 cured products with a high Young's modulus can be obtained easily. In particular,, the content is more preferably not less than 170 parts by mass, still more preferably not less than 190 parts by mass, and particularly preferably not less than 230 parts by mass for reasons such as that cured products having 15 a similar Young' s modulus as CA mortars can be obtained easily. If the content of the component (A) is less than above range, there is a risk that the Young's modulus of the obtainable cured products may be lowered. The content of the component (A) is preferably not more than 550 parts by mass, and more preferably 20 not more than 450 parts by mass per 100 parts by mass of the component (B). [0040] (Difunctional polyols (B)> The difunctional polyol (B) (hereinafter, also written 19 as the "component (B)") is not particularly limited as long as the polyol has two hydroxyl groups in the molecule. The component (B) serves as a reactive diluent to control the viscosity of the present material, and thereby enhances 5 the workability (filling properties) in the repairing of slab tracks. The component (B) is also advantageous in that it is cured by being reacted with an isocyanate compound (C) and does not bleed out from the cured product unlike conventional plasticizers. 10 A single, or two or more kinds of the components (B) may be used. [0041] Specific examples of the components (B) include castor oil polyols, polyether polyols and polyester polyols. Here, 15 the castor oil polyols include castor oil polyether polyols having a polyether structure, castor oil polyester polyols having a polyester structure, and castor oil polyester polyether polyols having a polyether structure and a polyester structure. 20 For reasons such as that the present material attains excellent low-temperature curability, high curing rate and low environmental loads and can give cured products having a higher Young's modulus, the component (B) is preferably a castor oil polyol, and more preferably a castor oil polyester polyol or 20 a castor oil polyester polyether polyol. [0042] Specific examples of the castor oil polyols include those castor oil polyols mentioned in the section of the components 5 (A) . A difunctional compound that is selected from those compounds may be used as the component (B). [0043] Examples of the polyether polyols include those polyols that are obtained by adding, for example, an alkylene oxide 10 such as ethylene oxide, propylene oxide, butylene oxide or polyoxytetramethylene oxide to a starting compound, for example, a dihydric alcohol such as propylene glycol or ethylene glycol. [0044] 15 Examples of the polyester polyols include those polyester polyols that are obtained by condensing a diol such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, dipropylene glycol, polypropylene glycol, neopentyl glycol, 20 1,5-pentanediol, 1,6-hexanediol, 3-methyl-l,5-pentanediol, 2-methyl-l,3-propanediol, 2,2-diethyl-l,3-propanediol or 2-butyl-2-ethyl-l,3-propanediol, with a dibasic acid such as glutaric acid, succinic acid, oxalic acid, terephthalic acid, isophthalic acid, adipic acid, azelaic acid or sebacic acid. 21 [0045] The hydroxyl value of the component (B), although not particularly limited, is preferably 20 to 1,000 mg KOH/g, and more preferably 120 to 200 mg KOH/g for reasons such as that 5 the present material exhibits a prescribed viscosity and attains more excellent filling properties and slab track repairing easiness. [0046] The viscosity of the component (B) is not particularly 10 limited. For reasons such as that the present material exhibits a prescribed viscosity and attains more excellent filling properties and slab track repairing easiness, the viscosity measured with an Ubbelohde viscometer at 25°C in accordance with J IS Z8803:2011 is preferably 150 to 5,000 mPa -s, 15 more preferably 150 to 3, 000 mPa *s, and particularly preferably 150 to 1., 000 mPa -s_. [0047] The Mn of the component (B), although not particularly limited, is preferably 400 to 10,000, more preferably 500 to 20 3,000, and particularly preferably 500 to 1,200 for reasons such as that the present material exhibits a prescribed viscosity and attains more excellent filling properties and slab track repairing easiness. [0048] 22 The difunctional polyol (B) may be one synthesized in accordance with a known method or may be a commercial product. Examples of such commercial products include "URIC Y-403", "URIC Y-202", "URIC Y-332", "URIC H-62" (all manufactured by 5 -ITOH OIL CHEMICALS CO., LTD.), "HS 2G-120", "HS 2G-160R", "HS 2G-270B", "HS 2B-5500" and "HS KA-001" (all manufactured by HOKOKU Co., Ltd.). [0049] The content of the component (B) relative to the present 10 material (in terms of solid) is preferably 5 to 25 mass% for reasons such as that the present material exhibits a prescribed viscosity and attains more excellent filling properties and slab track repairing easiness, and that cured products with a high Young's modulus can be obtained easily. In particular, 15 the content is more preferably 8 to 18 mass% for reasons such as that cured products having a similar Young's modulus as CA mortars can be obtained easily. [0050] (Isocyanate compounds (C)> 20 The isocyanate compound (C) (hereinafter, also written as the "component (C)") is not particularly limited as long as the compound has an isocyanate group and can be cured by reacting with the components (A) and (B). A single, or two or more kinds of the components (C) may be used. [0051] Examples of the components (C) include aromatic polyisocyanates such as diphenylmethane diisocyanate (hereinafter, abbreviated as "MDI", [e.g., 2,2'-MDI, 2,4'-MDI and 4,4'-MDI]), polymeric MDI (crude MDI), tolylene diisocyanate (hereinafter, abbreviated as "TDI", [e.g., 2,4-TDI and 2,6-TDI]) and naphthalene diisocyanate, araliphatic polyisocyanates such as xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate and isophorone diisocyanate, carbodiimide-modified products of the above polyisocyanates, and polyurethane prepolymers obtained by reacting isocyanate compounds with, for example, low-molecular weight polyols. [0052] In particular, aromatic polyisocyanates or araliphatic polyisocyanates are preferable, and diphenylmethane diisocyanate and polymeric MDI are more preferable because these compounds have good storage stability, the pot life of a mixture of the compounds with the main agent components can be controlled appropriately, the slab track repairing material exhibits outstanding workability and low-temperature curability, and the compounds are inexpensive and economically efficient. [0053] Examples of the commercial products of the components (C) include "Lupranate M 20 S" (manufactured by BASF INOAC Polyurethanes Ltd., crude MDI), "MILLIONATE MR-200" (manufactured by TOSOH CORPORATION, crude MDI), "COSMONATE T-80" (manufactured by Mitsui Chemicals, Inc., TDI) and "MILLIONATE MTL" (manufactured by TOSOH CORPORATION, carbodiimide-modified MDI). [0054] In the present material, the component (C) is preferably added so that the equivalent ratio of the isocyanate groups in the component to the total of the hydroxyl groups in the components (A) and (B) will be NCO/OH = 0.8 to 1.2, or more preferably 1.0 to 1.1. This equivalent ratio is advantageous in that curing failures, foaming, cracking and expansion are unlikely to occur. [0055] (Inorganic pigments (D)> For reasons such as that the curing shrinkage is reduced and cured products with a higher Young' s modulus can be obtained easily, the present material preferably includes an inorganic pigment (D) (hereinafter, also written as the "component (D)"). Because of its containing the components (A) and (B), the present material, even when containing the component (D), 25 exhibits sufficient fluidity and attains great easiness in the repairing of slab tracks. Further, economic advantages may be obtained by using the component (D) because the component (D) is less expensive than the resin components such as the 5 components (A) and (B). In the case where the present material is a two-part composition, the component (D) may be added to the curing agent but is preferably added to the main agent for reasons such as that cured products with uniform properties can be obtained 10 easily. A single, or two or more kinds of the components (D) may be used. [0056] Examples of the components (D) include silica, calcium 15 carbonate, quartz sand, mica, potassium feldspar, wollastonite, kaolin, clay, bentonite, titanium oxide, zinc oxide, magnesium carbonate and barium sulfate. In particular, silica or calcium carbonate is preferable for reasons such as that the present material attains excellent storage stability and economic 20 efficiency and that cured products having a similar Young's modulus as CA mortars can be obtained easily. Silica is more preferable because the pot life of the repairing material can be extended and cured products with less residual stress can be obtained. [0057] The weight average particle size of the component 50 x 100 mm cured product using a compressometer at room temperature 36 of 23°C and a displacement rate of 0.5 mm/min. Specifically, the graph in the range of stress degree of 0 to 0.1 N/mm2 is a nearly linear quadratic curve, and the slope of the tangent line at 0.1 N/mm2 on the quadratic curve was adopted as the 5 Young's modulus. [0079] To attain a high Young's modulus, the cured products preferably have a Young's modulus of 700 to 2,700 N/mm2, and more preferably 1,400 to 2,700 N/mm2. To attain a Young's 10 modulus similar to that of CA mortars, the cured products more preferably have a Young's modulus of 1,600 to 2,400 N/mm2, and particularly preferably 1,800 to 2,000 N/mm2. If the Young's modulus is below these ranges, the cured products may fail to support track slabs sufficiently. Any Young's modulus 15 exceeding the above ranges is so high that there is a risk that the load applied from a track slab will be concentrated to the repaired site and the track slab may be damaged or broken. When the Young' s modulus is similar to that of CA mortars, the cured products attain a high effect in preventing a dynamic 20 displacement during the running of a train, offering a more comfortable ride. [0080] {Slab track repairing methods) A slab track repairing method according to the present 37 invention includes a step of applying the present material to fill a defective site of a filling layer disposed between a track slab and a roadbed structure, and curing the present material to form a cured product. 5 [0081] The present material may be applied to fill a defective site in a filling layer by any known method without limitation. For example, the frame repairing method may be adopted in which a degraded portion of a filling layer is removed beforehand, 10 a formwork is arranged so as to enclose the cleared area, and the present material is poured into the formwork to fill the defective site. Besides the frame repairing method, for example, a bag made of a nonwoven fabric or the like may be arranged at a repair 15 site and the present material may be applied to fill the bag and then may be cured. Alternatively, a formwork made of a foam or the like may be implanted into a repair site, and the present material may be applied to fill the inside of the formwork and then may be cured. Still alternatively, a self-adhesive sheet 20 may be attached to the outside face of a repair site so as to cover the lateral opening of the repair site, and the present material may be applied to fill the space inside the sheet and then may be cured. [0082] (Slab tracks) A slab track according to the present invention includes a roadbed structure, a track slab, a filling layer disposed between the roadbed structure and the track slab, and a track rail installed on the track slab. At least part of the filling layer is a cured product of the present material. For example, such a slab track may be produced by the same method as the slab track repairing method described hereinabove. That is, the slab track may be a repaired slab track in which at least part of the filling layer, specifically, at least part of an outer peripheral portion of the filling layer is a cured product of the present material. [0083] Examples of the roadbed structures include elevated structures, underground structures and bridges made of such a material as concrete. Examples of the track slabs include those track slabs made of such a material as concrete. [0084] Specifically, the slab track is illustrated in Fig. 1. As illustrated, a track slab 24 is disposed on the top surface of a roadbed structure 20 via a filling layer 22 which is at least partly composed of a cured product of the present material. Further, a pair of track rails 30, 30 are installed, preferably fastened, on the top surface of the track slab 24, The track slab 24 has notches 26, 26 at its both ends. The notches 26 of the track slab 24 are aligned with projections 28 disposed on the roadbed structure 20 at prescribed intervals. EXAMPLES [0085] Next, the present invention will be described in further detail based on Examples without limiting the scope of the invention to such Examples. [0086] The following are the raw materials used. [0087] [Polyfunctional polyol (A) having functionality of more than 2] "URIC H-102": (manufactured by ITOH OIL CHEMICALS CO., LTD., penta functional castor oil polyester polyether polyol, hydroxyl value: 320 mg KOH/g, viscosity: 1,100 mPa-s, number average molecular weight: 877) "EXCENOL 410NE": (manufactured by ASAHI GLASS CO., LTD., tetra functional polyether polyol (pentaerythritol-alkylene oxide adduct), hydroxyl value: 410 mg KOH/g, viscosity: 1,800 mPa-s, number average molecular weight: 55 0) [Difunctional polyol (B)] "URIC Y-403": (manufactured by ITOH OIL CHEMICALS CO., LTD., difunctional castor oil polyester polyol, hydroxyl value: 160 WHAT IS CLAIMED IS: 1. A slab track repairing material comprising: a polyfunctional polyol (A) having a functionality of more than 2, a difunctional polyol (3)F and an isocyanate compound (C). 2. The repairing material according to Claim 1, wherein the polyfunctional polyol (A) is a tetra or higher functional polyol. 3. The repairing material according to Claim 1 or 2, wherein the content of the polyfunctional polyol (A) is not less than 150 parts by mass per 100 parts by mass of the difunctional polyol (B). 4. The repairing material according to any one of Claims 1 to 3, further comprising an inorganic pigment (D). 5. The repairing material according to Claim 4, wherein the content of the inorganic pigment (D) is not more than 450 parts by mass per 100 parts by mass of the difunctional polyol (B) . 6. The repairing material according to any one of Claims 1 to 5, which satisfies the following requirement: Requirement: The Young's modulus of a cured product of the repairing material is 700 to 2,700 N/mm2. 7. The repairing material according to any one of Claims 1 to 6, wherein the polyfunctional polyol (A) is a castor oil polyol having a functionality of more than 2. 8. The repairing material according to any one of Claims 1 to If wherein the difunctional polyol (B) is a difunctional castor oil polyol. 9. The repairing material according to any one of Claims 4 to 8, wherein the inorganic pigment (D) comprises at least one selected from silica and calcium carbonate. 10 . The repairing material according to any one of Claims 1 to 9, wherein the isocyanate compound (C) comprises at least one selected from an aromatic polyisocyanate and an araliphatic polyisocyanate. 11. A cured product of the repairing material described in any one of Claims 1 to 10. 12. A slab track repairing method comprising a step of applying the repairing material described in any one of Claims 1 to 10 to fill a defective site of a filling layer disposed between a track slab and a roadbed structure, and curing the repairing material to form a cured product. ': 13. A slab track comprising: a roadbed structure, a track slabr a filling layer disposed between the roadbed structure and the track slab, and a track rail installed on the track slab, at least part of the filling layer being a cured product of the repairing material described in any one of Claims 1 to 10. 14. A resin composition comprising: a polyfunctional polyol (A) having a functionality of more than 2, a difunctional polyol (B)r and an isocyanate compound (C).