WO2010107134A1

WO2010107134A1 - Asphalt modifier, asphalt composition, asphalt mixture, and methods for producing them

Info

Publication number: WO2010107134A1
Application number: PCT/JP2010/055151
Authority: WO
Inventors: Hiromitsu Nakanishi; Shinichi Takei; Koji Goto
Original assignee: Taiyu Kensetsu Co., Ltd.; Mitsubishi Corporation
Priority date: 2009-03-18
Filing date: 2010-03-17
Publication date: 2010-09-23

Abstract

An asphalt modifier prepared by mixing a vinyl aromatic hydrocarbon-conjugated diene block copolymer having a molecular weight in the range of from 100,000 to 400,000, a tackifying resin, and a process oil in a mixing ratio of from 25 to 70% by mass, from 15 to 50% by mass, and from 10 to 50% by mass, respectively, can provide an asphalt composition and asphalt mixture improved in both high-temperature and low-temperature properties, and this asphalt modifier is suitable for producing a composition and a mixture by a plant mixing method. In addition, various properties of the composition and mixture can be improved by using an asphalt modifier comprising a block copolymer obtained by mixing a plurality of vinyl aromatic hydrocarbon-conjugated diene block copolymers so that they have an average molecular weight in the range of from 100,000 to 400,000.

Description

Title of Invention: ASPHALT MODIFIER, ASPHALT COMPOSITION, ASPHALT MIXTURE, AND METHODS FOR PRODUCING THEM Technical Field

[0001] The present invention relates to an asphalt modifier and an asphalt composition and an asphalt mixture containing the same, and more particularly to an asphalt modifier suitably used for high-performance pavements such as open-graded pavements. Background Art

[0002] A pavement body made of an asphalt mixture using conventional straight asphalt as a binder shows a significant change in properties due to temperature, which has provided a problem in durability such as rutting due to softening and flow at high temperatures and development of a thermal stress crack due to embrittlement at low temperatures. For this reason, various methods have been employed for improving asphalt properties to improve an asphalt mixture and an asphalt pavement body.

[0003] As an example, asphalt containing rubber or a thermoplastic elastomer is produced by mixing a thermoplastic elastomer such as rubber or a vinyl aromatic hydrocarbon-conjugated diene block copolymer with straight asphalt. Since the asphalt containing rubber or a thermoplastic elastomer shows an increase in viscosity at 60⁰C, toughness, tenacity, and the like, it has been used as a high viscosity modified asphalt for wear resistance pavements, rutting resistance pavements, and drainage pavements.

[0004] As another example, oxidized asphalt such as semi-blown asphalt is produced from straight asphalt by blowing air at a high temperature to improve temperature sensitivity and enhance viscosity at 60⁰C up to l,000±200 Pa-s. Since the oxidized asphalt has a three to ten times higher viscosity at 60⁰C as compared with straight asphalt, it is hardly softened even at a high temperature and used as a rutting resistant binder.

[0005] However, while the asphalt containing rubber or a thermoplastic elastomer is relatively good in low-temperature properties, it is a little inferior to oxidized asphalt in high-temperature properties such as rutting resistance. On the other hand, oxidized asphalt is a little inferior in low-temperature properties such as a thermal stress crack, and there is concern about development of a crack at a relatively early stage in a cold district.

[0006] In order to obtain asphalt excellent in both high-temperature properties and low-temperature properties, the oxidized asphalt may be mixed with rubber or a thermoplastic elastomer.

[0007] However, when it is intended to mix and homogenize rubber or a thermoplastic elastomer in the oxidized asphalt having high viscosity, it is necessary to perform a step of mixing and homogenization at high temperatures for a long time. In addition, there has been a problem in that, depending on the combination of the oxidized asphalt and rubber or a thermoplastic elastomer to be mixed and homogenized, homogenization is not sufficiently achieved, and desired high-temperature and low-temperature properties cannot be obtained. Citation List Non Patent Literature

[0008] [NPL 1] "Hosou Chousa-Sikenhou Binran (Pavement Investigation and Test Method Handbook) (2nd separate volume)"

[NPL 2:] "Hosou Chousa-Sikenhou Binran (Pavement Investigation and Test Method Handbook) (3rd separate volume)" Summary of Invention

[0009] The present invention has been made in view of such a problem, and an object of the present invention is to provide an asphalt composition and an asphalt mixture in which both the high-temperature properties such as rutting resistance and low-temperature properties such as a thermal stress crack have been improved.

[0010] In order to solve the problem as described above, the present invention provides an asphalt modifier comprising a block copolymer, a tackifying resin, and a process oil, wherein the block copolymer comprises a vinyl aromatic hydrocarbon-conjugated diene block copolymer which has a polymer block A comprising a vinyl aromatic hydrocarbon as a main component and a polymer block B comprising a conjugated diene as a main component and has a molecular weight in the range of from 100,000 to 400,000; and wherein the asphalt modifier is obtained by mixing the vinyl aromatic hydrocarbon- conjugated diene block copolymer, the tackifying resin, and the process oil in a mixing ratio of from 25 to 70% by mass, from 15 to 50% by mass, and from 10 to 50% by mass, respectively.

[0011] The block copolymer contained in the asphalt modifier may be obtained by mixing a plurality of vinyl aromatic hydrocarbon-conjugated diene block copolymers, wherein the plurality of vinyl aromatic hydrocarbon-conjugated diene block copolymers are mixed so that the average molecular weight thereof is in the range of from 100,000 to 400,000.

[0012] The vinyl aromatic hydrocarbon-conjugated diene block copolymer is any of a styrene-butadiene-styrene block copolymer (SBS), a styrene-isoprene- styrene block copolymer (SIS), and a styrene-ethylene-butylene-styrene block copolymer (SEBS).

[0013] The asphalt modifier is preferably in the shape of a pellet having a diameter of from 0.5 to 50 mm.

[0014] The asphalt composition of the present invention is obtained by mixing the above-mentioned asphalt modifier with asphalt. In addition, the mixing is preferably performed by a plant mixing method.

[0015] In this case, the asphalt is preferably oxidized asphalt. The effect of improving low-temperature properties of asphalt by the asphalt modifier according to the present invention is particularly remarkably exhibited when the asphalt is oxidized asphalt.

[0016] In addition, the mixing ratio of the asphalt modifier in the asphalt composition is preferably from 3 to 30% by mass.

[0017] An asphalt mixture of the present invention is obtained by mixing the above-mentioned asphalt composition with an aggregate. In addition, the mixing is preferably performed by a plant mixing method.

[0018] A method for producing an asphalt modifier comprising a block copolymer, a tackifying resin, and a process oil of the present invention comprises the following steps A and B: a step A of preparing a vinyl aromatic hydrocarbon-conjugated diene block copolymer comprising a single vinyl aromatic hydrocarbon-conjugated diene block copolymer or a plurality of vinyl aromatic hydrocarbon-conjugated diene block copolymers, the copolymer or the copolymers each having a polymer block A comprising a vinyl aromatic hydrocarbon as a main component and a polymer block B comprising a conjugated diene as a main component, and the copolymer or the copolymers having a molecular weight or an average molecular weight, respectively, in the range of from 100,000 to 400,000; and a step B of heating and mixing the vinyl aromatic hydrocarbon-conjugated diene block copolymer, the tackifying resin, and the process oil in a ratio of from 25 to 70% by mass, from 15 to 50% by mass, and from 10 to 50% by mass, respectively, to homogenize the mixture.

[0019] The method for producing the asphalt modifier may comprise a step C of processing the mixture of the vinyl aromatic hydrocarbon-conjugated diene block copolymer, the tackifying resin, and the process oil which are homogenized in the step B into a pellet having a diameter of from 0.5 to 50 mm.

[0020] The method for producing the asphalt composition of the present invention comprises a step of mixing the asphalt modifier obtained by the above- mentioned method with asphalt composition in a mixing ratio of from 3 to 30% by mass, by a plant mixing method.

[0021] Note that it is preferred to use oxidized asphalt as the asphalt for the reason mentioned above.

[0022] Another aspect of the method for producing the asphalt composition of the present invention comprises a step of blowing heated air into straight asphalt heated to a temperature of from 180 to 300°C to oxidize, dehydrogenate, and polycondense an asphalt component in the straight asphalt to obtain oxidized asphalt; and a step of mixing the asphalt modifier obtained by the above- mentioned method with the oxidized asphalt composition in a mixing ratio of from 3 to 30% by mass by a plant mixing method.

[0023] A method for producing an asphalt mixture of the present invention comprises a step of mixing asphalt, an asphalt modifier obtained by the above-mentioned method, and an aggregate by a plant mixing method, wherein the asphalt modifier is mixed in a mixing ratio of from 3 to 30% by mass relative to the asphalt composition. [0024] Also in this case, it is preferred to use oxidized asphalt as the asphalt for the reason mentioned above.

[0025] In addition, another aspect of the method for producing an asphalt mixture of the present invention comprises a step of blowing heated air into straight asphalt heated to a temperature of from 180 to 300°C to oxidize, dehydrogenate, and polycondense the same to obtain oxidized asphalt; and a step of mixing the oxidized asphalt, the asphalt modifier obtained by the above-mentioned method, and an aggregate by a plant mixing method, wherein the asphalt modifier is mixed in a mixing ratio of from 3 to 30% by mass relative to the oxidized asphalt composition.

[0026] The asphalt modifier of the present invention is optimized in terms of the molecular weight of a vinyl aromatic hydrocarbon-conjugated diene block copolymer and the mixing ratio of a vinyl aromatic hydrocarbon-conjugated diene block copolymer, a tackifying resin, and a process oil. For this reason, when the asphalt modifier of the present invention is mixed with asphalt to produce an asphalt composition and an asphalt mixture, both of the high- temperature properties such as rutting resistance and low-temperature properties such as a thermal stress crack thereof are greatly improved as compared with conventional asphalt compositions and mixtures, respectively.

[0027] This effect of improving properties will become more remarkable by using a mixed-block copolymer composed of a plurality of vinyl aromatic hydrocarbon-conjugated diene block copolymers as a block copolymer.

[0028] Further, the asphalt modifier is formed into pellets. This allows easy handling and storage, higher melting rate in asphalt, and easy mixing operation.

[0029] Furthermore, the mixing operation for obtaining an asphalt mixture is preferably performed by a plant mixing method. This method allows us to easily set the mixing ratio of the modifier in asphalt and to produce an asphalt mixture which provides high modification effect according to the difference in the type or properties of the targeted asphalt mixture. Brief Description of Drawings [0030] [fig. 1] Fig. 1 (Table 1) shows the vinyl aromatic hydrocarbon-conjugated diene block copolymers (A-E) used in the present Examples and Comparative

Examples.

[fig. 2A] Fig. 2A (Table 2A) summarizes the block copolymer type of each asphalt modifier, the mixing ratio in the block copolymer, processability, and storage properties.

[fig. 2B] Fig. 2B (Table 2B) summarizes the block copolymer type of each asphalt modifier, the mixing ratio in the block copolymer, processability, and storage properties.

[fig. 3] Fig. 3 (Table 3) summarizes the properties of each asphalt mixture (I to VI).

Description of Embodiments

[0031] When the asphalt modifier of the present invention is mixed with asphalt to produce an asphalt composition and an asphalt mixture, in order to improve both of the high-temperature properties such as rutting resistance and low- temperature properties such as a thermal stress crack thereof as compared with conventional asphalt compositions and mixtures, respectively, the asphalt modifier comprises a block copolymer (vinyl aromatic hydrocarbon- conjugated diene block copolymer) which has a polymer block A comprising a vinyl aromatic hydrocarbon as a main component and a polymer block B comprising a conjugated diene as a main component and has a molecular weight in the range of from 100,000 to 400,000. The asphalt modifier comprises from 25 to 70% by mass of a vinyl aromatic hydrocarbon- conjugated diene block copolymer, from 15 to 50% by mass of a tackifying resin, and from 10 to 50% by mass of a process oil in order to optimize the mixing ratio in the asphalt modifier.

[0032] Here, the polymer block A comprising a vinyl aromatic hydrocarbon as a main component is a polymer block which comprises a vinyl aromatic hydrocarbon in an amount of more than 50% by weight, preferably from 60 to 100% by weight, more preferably from 70 to 100% by weight, further preferably from 80 to 100% by weight, wherein the polymer block is a homopolymer of a vinyl aromatic hydrocarbon or a polymer block of a vinyl aromatic hydrocarbon and a conjugated diene. Note that the distribution of the conjugated diene in the polymer block A may be random, tapered, partially block, or any combination thereof.

[0033] Further, the polymer block B comprising a conjugated diene as a main component is a polymer block which comprises a conjugated diene in an amount of more than 50% by weight, preferably from 60 to 100% by weight, more preferably from 70 to 100% by weight, further preferably from 80 to 100% by weight, wherein the polymer block is a homopolymer of a conjugated diene or a polymer block of a conjugated diene and a vinyl aromatic hydrocarbon. Note that the distribution of the vinyl aromatic hydrocarbon in the polymer block B may also be random, tapered, partially block, or any combination thereof.

[0034] The block copolymer (vinyl aromatic hydrocarbon-conjugated diene block copolymer) as described above may have a linear or branched structure, but preferably has a structure represented by any of the following general formulas (i) to (vii):

(i) (A-B)m,

(ii) (A-B)n-A,

(iii) (B-A)m-B,

(iv) ((A-B)_n)P-X,

(v) ((B-A)m)p-X,

(vi) ((A-B)n-A)p-X, and

(vii) ((B-A)n-B)p-X, wherein A represents a polymer block A mainly comprising a vinyl aromatic hydrocarbon; B represents a polymer block B mainly comprising a conjugated diene; X represents the residue of a polyfunctional coupling agent or the residue of a polyfunctional initiator; m is an integer of 1 or more, preferably 2 or more, more preferably from 2 to 6; n is an integer of 1 or more, preferably from 1 to 6, more preferably 1; and p is an integer of from 2 to 6. [0035] The composition ratio of the vinyl aromatic hydrocarbon to the conjugated diene in the block copolymer is, but not limited to, in the range of generally from 5:95 to 95:5, preferably from 10:90 to 50:50, more preferably from 15:85 to 45:55, by weight. [0036] The amount of vinyl bonds in the conjugated diene part of the block copolymer is, but not limited to, in the range of generally 90% or less, preferably 1 to 60%, more preferably from 5 to 30%.

[0037] The molecular weight of the block copolymer used for the asphalt modifier of the present invention is in the range of from 100,000 to 400,000 as the weight-average molecular weight in terms of polystyrene measured by GPC. The molecular weight of the vinyl aromatic hydrocarbon-conjugated diene block copolymer within the range as described above significantly improves both high-temperature and low-temperature properties of an asphalt composition or an asphalt mixture obtained using the above asphalt modifier, as compared with conventional compositions and mixtures, respectively.

[0038] The above-mentioned block copolymer is preferably produced by mixing a plurality of vinyl aromatic hydrocarbon-conjugated diene block copolymers, wherein the plurality of vinyl aromatic hydrocarbon-conjugated diene block copolymers are mixed so that the average molecular weight thereof is in the range of from 100,000 to 400,000.

[0039] Mixing a plurality of vinyl aromatic hydrocarbon-conjugated diene block copolymers facilitates the stabilization of the quality of the resulting asphalt modifier even when the plurality of block copolymers have a lot-to-lot variation, and this brings about an advantage also in cost. The average molecular weight after mixing a plurality of block copolymers is in the range of from 100,000 to 400,000, which is the same as the molecular weight range at the time of using a single block copolymer, but the grading range is relatively wider. When the resulting block copolymer has a wider grading range, the solubility thereof in asphalt will be higher, and it is easier to obtain a more homogeneous asphalt composition. As a result, various properties of the resulting asphalt composition or asphalt mixture are also improved.

[0040] Examples of the vinyl aromatic hydrocarbon-conjugated diene block copolymer include a styrene-butadiene-styrene block copolymer (SBS), a styrene-isoprene-styrene block copolymer (SIS), and a styrene-ethylene- butylene-styrene block copolymer (SEBS). SBS is preferred because of availability. [0041] When the asphalt modifier is produced from a single block copolymer, the dissolution rate thereof in asphalt will be low, which can often cause trouble, especially when the mixing is performed by a plant mixing method. For this reason, a block copolymer, a tackif ying resin, and a process oil are mixed and melted into the asphalt modifier of the present invention.

[0042] A process oil is aromatic, paraffinic, or naphthenic, but the process oil used in the present invention is not particularly limited as long as it is industrially usable.

[0043] The tackifying resin used in the present invention is also not particularly limited as long as it is industrially usable. Examples of the tackifying resin include a coumarone-indene resin, a phenol resin, a p-t-butylphenol- acetylene resin, a phenol-formaldehyde resin, a terpene-phenol resin, a polyterpene resin, a xylene-formaldehyde resin, a C5-based petroleum resin, a C9-based petroleum resin, a dicyclopentadiene-based resin, polybutene, and rosin, and a hydrogenated product thereof, and a modified product thereof with maleic anhydride or the like. Among others, a C5-based petroleum resin, a C9-based petroleum resin, and a dicyclopentadiene-based resin are preferred, and a C9-based petroleum resin is particularly preferred. These tackifying resins can be used independently or in combination. [0044] It is preferred to produce the asphalt modifier by mixing the vinyl aromatic hydrocarbon-conjugated diene block copolymer, the tackifying resin, and the process oil in a mixing ratio of from 25 to 70% by mass, from 15 to 50% by mass, and from 10 to 50% by mass, respectively.

[0045] If the amount of the process oil used is excessively small, the resulting asphalt modifier will have poor properties such as solubility in asphalt and ductility. On the contrary, if the amount of the process oil used is excessively large, the resulting asphalt modifier will have poor properties such as softening point and toughness.

[0046] Further, if the amount of the tackifying resin used is excessively small, the resulting asphalt modifier will have poor properties such as softening point, viscosity at 60⁰C, and dynamic stability. On the contrary, if the amount of the tackifying resin used is excessively large, the resulting asphalt modifier will have poor properties such as ductility and toughness. [0047] The asphalt modifier of the present invention optionally comprises a blocking resistant agent. The blocking resistant agent is not particularly limited as long as it is generally used industrially and may be organic or inorganic. An inorganic blocking resistant agent is preferred.

[0048] Examples of the inorganic blocking resistant agent include silica, calcium carbonate, magnesium carbonate, calcium sulfate, aluminum hydroxide, zinc oxide, talc, and clay.

[0049] In addition, examples of the organic blocking resistant agent include the following: a higher fatty acid monoamide such as stearamide, oleamide, lauramide, palmitamide, erucamide, and behenamide; a higher fatty acid bisamide such as methylene bis-stearamide, ethylene bis-stearamide, ethylene bis-oleamide, and ethylene bis-lauramide; a composite higher fatty acid amide such as N-stearyl oleamide, N-stearyl erucamide, N-stearyl stearamide, N-oleyl stearamide, and distearyl adipamide; a higher fatty acid salt such as a lithium salt, a sodium salt, a potassium salt, a magnesium salt, a calcium salt, a barium salt, a zinc salt, an aluminum salt, and an iron salt of lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, behenic acid, oleic acid, linoleic acid, α-eleostearic acid, β- eleostearic acid, and α-linolenic acid; and a resin compound such as polyacrylamide, polyvinyl chloride, polystyrene, polyolefines such as high density polyethylene, polymethyl methacrylate, polycarbonate, and a styrene-acrylonitrile copolymer.

[0050] These blocking resistant agents can be used independently or in combination, and the amount of the blocking resistant agent used is generally from 0 to 50 parts by weight, preferably 0.1 to 10 parts by weight, more preferably from 0.5 to 5 parts by weight, per 100 parts by weight of the modifier.

[0051] The asphalt modifier of the present invention optionally further comprises the following: an antioxidant such as hindered phenolic, sulfur-based, and phosphate- based; an ultraviolet absorber such as benzophenone-based; a light stabilizer such as hindered amine-based; rubber such as natural rubber, polyisoprene rubber, polybutadiene rubber, random styrene-butadiene rubber, nitrile-based rubber, ethylene-propylene rubber, chloroprene rubber, acrylic rubber, and isoprene-isobutyl rubber; a thermoplastic elastomer such as a block copolymer other than the vinyl aromatic hydrocarbon-conjugated diene block copolymer mentioned above; a thermoplastic resin such as polyolefin resins such as an ethylene-ethyl acrylate copolymer and an ethylene- vinyl acetate copolymer, a polystyrene- based resin, and a polyvinyl chloride-based resin; and an inorganic filler such as glass beads, silica, and carbon black. [0052] The method for producing the asphalt modifier of the present invention may be a known general procedure. For example, the components as described above are mixed with each other using a mixer such as a heat melting kettle, a roll mill, a single screw extruder, a twin screw extruder, or a Henschel mixer, followed by processing the resulting mixture using a press, a pelletizer, an extruder, a processing machine, or the like.

[0053] Mixing methods of each component may include a method of melt mixing and a method of dissolving and mixing in a solvent. For example, the following methods can be illustrated:

(a) a method in which three components, a block copolymer, a process oil, and a tackifying resin, are heated and mixed with each other by means of a heat melting kettle, a roll mill, or the like;

(b) a method in which the above three components are premixed without heating and then heated and mixed with each other in a single screw extruder, or the like;

(c) a method in which a tackifying resin is crushed, continuously mixed with a block copolymer, and finally heated and mixed with a process oil, in a mixer such as a Henschel mixer;

(d) a method in which a block copolymer and a process oil are premixed and then heated and mixed with a tackifying resin; and (e) a method in which a mixed block copolymer and a tackifying resin are heated and mixed with each other in a twin screw extruder, followed by side- feeding a process oil to be mixed with the above heated mixture.

[0054] Among the above methods, the methods of (c), (d), and (e) are particularly preferred for significantly improving the solubility of the resulting mixture in asphalt.

[0055] Note that these components are heated and mixed at a temperature in the range of from 50 to 250⁰C, preferably from 100 to 200⁰C.

[0056] The shape of the asphalt modifier of the present invention is not particularly limited, but may be of any shape (such as pellet-shape, strand- shape, plate-shape, and block-shape). A pellet-shape is preferred from a viewpoint of the solubility in asphalt.

[0057] The components mentioned above are mixed with each other, extruded in an extruder or the like into a strand-shape, cooled with cold water, and shredded with a pelletizer or the like to yield pellets of the asphalt modifier.

[0058] Note that coating the strands before entering the pelletizer with a blocking resistant agent is suitable because the shredding processability is improved.

[0059] Further, it is suitable to produce pellets each having a size of from 0.5 to 50 mm, preferably from 1 to 20 mm, more preferably from 2 to 10 mm because the solubility thereof in asphalt is significantly improved.

[0060] The asphalt composition of the present invention is obtained by mixing the above-mentioned asphalt modifier with asphalt.

[0061] Although the asphalt used for the composition may be common asphalt such as straight asphalt, the asphalt modifier of the present invention has a remarkable modification effect on oxidized asphalt.

[0062] Oxidized asphalt is obtained by subjecting, for example, heated straight asphalt (180 to 300⁰C) to a slight blowing operation (heated air is blown) to oxidize, dehydrogenize, and polycondense the asphalt component with oxygen in air. Oxidized asphalt has an advantage that the high-temperature properties of straight asphalt or the like is improved. That is, oxidized asphalt can be said to be a modified straight asphalt. Therefore, mixing of the asphalt modifier of the present invention with the oxidized asphalt is equivalent to performing "secondary modification".

[0063] Properties of oxidized asphalt differ by the properties of straight asphalt as a raw material, treatment temperature, and treatment time. For this reason, the degree of the effect of the "secondary modification" may also be different by the type of oxidized asphalt.

[0064] The method for preparing an asphalt composition is not particularly limited. For example, each component of the composition can be heated, melted, and kneaded by means of a heat-melting kettle, a wet mill, a high shear mixer, a roll, a kneader, a Banbury mixer, an extruder, and the like.

[0065] In the present invention, in order to greatly improve both high-temperature properties such as rutting resistance and low-temperature properties such as a thermal stress crack as compared with conventional compositions, the mixing ratio of asphalt to an asphalt modifier is set at a ratio of 97 to 70% by mass of asphalt to 3 to 30% by mass of the asphalt modifier.

[0066] The asphalt composition can be used not only as a binder for road pavement but for a wide variety of applications such as a roofing material, a sealing material, and a coating material.

[0067] When the asphalt composition of the present invention is used as a binder for road pavement, it is usually used as an "asphalt mixture" in which the asphalt composition is mixed with an aggregate (such as crushed stone, crushed gravel, gravel, sand, and recycled aggregate) and a filler (such as mineral powder, talc, and calcium carbonate). Note that, in the present specification, aggregate and filler are generically called as "aggregates."

[0068] The aggregates are used for impermeable asphalt mixtures such as dense graded, coarse graded, and fine graded mixtures and stone mastic mixtures, which are used for general road pavements, or used for open-graded mixtures used for permeable pavements, drainage pavements, sound-absorbing pavements, and the like.

[0069] Asphalt mixtures generally comprise aggregates in an amount of from 98 to 85% by mass and an asphalt composition in an amount of from 2 to 15% by mass. An asphalt modifier is generally mixed with asphalt in the mixing ratio mentioned above (3 to 30% by mass). In particular, in the case of a drainage pavement mixture, it is preferred to mix the present asphalt modifier with asphalt in a mixing ratio of 10 to 30% by mass of the modifier to 90 to 70% by mass of asphalt.

[0070] A method for obtaining an asphalt mixture includes:

(i) a premix method in which the asphalt composition prepared by mixing the present asphalt modifier with asphalt beforehand is mixed with aggregates; and (ii) a plant mixing method in which the asphalt modifier, asphalt, and aggregates are mixed in an asphalt plant. The feature of the present invention such as a quick dissolution rate of the modifier can be utilized more effectively in a plant mixing method.

[0071] Examples of the plant mixing method include:

(a) a method in which heated aggregates and heated asphalt are mixed and then the resulting mixture is mixed with the asphalt modifier;

(b) a method in which heated aggregates, heated asphalt, and the asphalt modifier are simultaneously mixed; and

(c) a method in which heated aggregates and asphalt modifier are mixed and then the resulting mixture is mixed with heated asphalt.

[0072] The asphalt composition and asphalt mixture of the present invention may be mixed with additives other than the aggregates as mentioned above, such as antistripping agents such as slaked lime, amines, and amides, fiber reinforcing materials such as methyl cellulose and polyvinyl alcohol, an elasticity improver, a viscosity-reducing agent, a viscosity improver, a filler, a pigment, a softener, an antioxidant, an ultraviolet absorber, a light stabilizer, rubber, and other thermoplastic elastomers and thermoplastics.

[0073] Hereinafter, the asphalt modifier, the composition, and the mixture of the present invention will be described more specifically with reference to Examples. (Block copolymer, tackifying resin, process oil, and asphalt)

[0074] Table 1 shows the vinyl aromatic hydrocarbon-conjugated diene block copolymers (A-E) used in the present Examples and Comparative Examples.

[0075] A styrene-butadiene-styrene block copolymer (SBS), a styrene-isoprene- styrene block copolymer (SIS), and a styrene-ethylene-butylene-styrene block copolymer (SEBS) can be used as a vinyl aromatic hydrocarbon-conjugated diene block copolymer in the present invention as described above, but a styrene-butadiene-styrene block copolymer (SBS) was used in the present Examples and Comparative Examples.

[0076] Block polymers A to C are each composed of a single SBS block copolymer, and block polymers D and E are obtained by mixing two types of SBS block copolymers at a mixing ratio of 1:1. Note that the average molecular weight was measured as the molecular weight in terms of standard polystyrene in accordance with a GPC method.

[0077] The tackifying resin, process oil, and asphalt which were used in the present Examples and Comparative Examples are a C9-based petroleum resin, an aromatic process oil, and oxidized asphalt (manufactured in Kazakhstan), respectively.

[0078] (Asphalt modifier)

Table 2A and Table 2B summarize the block copolymer type of each asphalt modifier, the mixing ratio in the block copolymer, processability, and storage properties.

[0079] These asphalt modifiers are obtained in the following procedure.

[0080] The tackifying resin was first put into a 200 liter Henschel mixer and stirred for 5 minutes at a low speed (25 Hz). Subsequently, the block copolymer was added to the tackifying resin and stirred for 1 minute. Then, the process oil was gradually added to the resulting mixture and stirred for 9 minutes at high speed (35 Hz). The resulting mixture had a temperature of 52°C. This mixture was cooled to 42°C in a ribbon blender, bagged, and cured for two days. The cured mixture was extruded into a strand-shape using a 65 mmφ single screw extruder, cooled in a cooling trough having a water temperature of 15°C, coated with 1% by weight of calcium carbonate, and cut by means of a water-cooled pelletizer provided with a rotary cutter into a 3 mmφx4 mm pellet.

[0081] The processability of the resulting asphalt modifier was evaluated by the three-stage criterion (O, Δ, x) by visually observing the adhesion of the modifier to the rotary cutter after operating the above-mentioned pelletizer for 10 minutes. In Table 2A and Table 2B, "O" represents "no adhesion is not observed"; "Δ" represents "adhesion of some pellets to the rotary cutter is observed, but it was possible to operate the pelletizer for 10 minutes "; and "x" represents "the pelletizer was stopped before completing the 10-minute- operation because the strand coiled around the cutter".

[0082] The storage properties of the asphalt modifier was evaluated by the three- stage criterion (O, Δ, x) on the state after 120 g of the above-mentioned modifier pellets were put in a 7x10 cm plastic bag, applied with 50 g/cm of load, and left standing still in an oven at 90°C for 3 hours. In Table 2A and Table 2B, "O" represents "no mutual adhesion"; "Δ" represents "the whole is mutually adhered, but it collapses shortly after being pushed with a finger"; and "x" represents "the whole is mutually adhered, and it does not collapse even when pushed with a finger".

[0083] (Asphalt composition)

Table 2A and Table 2B summarize the properties (binder properties) of each asphalt composition (1 to 7 and (1) to (5)).

[0084] These asphalt compositions were obtained by the following procedure.

[0085] In a 1 liter glass container, the above-mentioned modifier pellet is first added to the oxidized asphalt heated to 180⁰C at each mixing ratio shown in Table 2A and Table 2B, followed by continuously stirring the resulting mixture until the pellet is completely dissolved therein, to prepare the binder. Note that Table 2A and Table 2B also show the mixing ratio of the modifier to asphalt and the time until the modifier dissolves in asphalt.

[0086] Note that the evaluation conditions of the above-mentioned "time until the modifier dissolves in asphalt" are pursuant to "Method of Preparing Modified Asphalt" described in the "Hosou Chousa-Sikenhou Binran (Pavement Investigation and Test Method Handbook)" (2nd separate volume) published by the Japan Road Association.

[0087] The "penetration" (1/10 mm) as binder properties of an asphalt composition was measured according to JIS K2207.

[0088] The "softening point(°C)" was measured according to JIS K2207. The higher the softening point, the higher the resistance to high temperatures.

[0089] The "viscosity at 60°C" (Pa-s) was measured according to "A051 Method of Test for viscosity of Asphalt at 60⁰C" described in the "Hosou Chousa- Sikenhou Binran (Pavement Investigation and Test Method Handbook) (2nd separate volume)" edited by the Japan Road Association. The higher the viscosity at 60°C, the higher the rutting resistance at high temperatures.

[0090] The "bending work" (kPa) and "bending stiffness" (MPa) were measured according to the "A063T Method of Bending Test for Modified Asphalt" described in the "Hosou Chousa-Sikenhou Binran (Pavement Investigation and Test Method Handbook) (2nd separate volume)" edited by the Japan Road Association. The bending test of an asphalt composition was performed at -20⁰C to measure a maximum bending stress and a maximum bending strain (the amount of strain at the maximum bending stress). The maximum bending stress is multiplied by the maximum bending strain to yield the bending work, and the maximum bending stress is divided by the maximum bending strain to yield the bending stiffness. The larger the bending work or the smaller the bending stiffness, the higher the bending resistance of an asphalt composition at low temperatures.

[0091] The "Fraass breaking point (⁰C)" was measured according to JIS K2207.

The Fraass breaking point shows the flexibility of asphalt at low temperatures. The lower the Fraass breaking point, the lower the brittle fracture temperature, that is, the higher the resistance at low temperatures.

[0092] (Asphalt mixture)

Table 3 summarizes the properties of each asphalt mixture (I to VI).

[0093] These asphalt mixtures are obtained by the following procedure.

[0094] First, 95.0 parts of aggregates for open-graded asphalt mixtures

(composition: 85% by weight of crushed stone No. 6, 10% by weight of sand, 5% by weight of mineral powder) previously heated to 190⁰C were subjected to dry mixing for 30 seconds in a pug mill mixer, and then thereto was charged oxidized asphalt which was previously heated to 170⁰C, followed by mixing for one minute. Then, each modifier was charged to the mixture, followed by further mixing for one minute.

[0095] Note that the total amount of oxidized asphalt and the modifier is 5.0 parts, and the mixing ratio of the modifier to asphalt and the mixing ratio of the modifier are shown in Table 3. [0096] The "porosity" (%) of the asphalt mixture was measured according to a method of using a slide caliper described in the supplementary article of the Japan Highway Public Corporation test method "JHS217-1992". The temperature of the mixture obtained by the method mentioned above was adjusted to 16O⁰C, and a Marshall specimen fabrication device was used to prepare a specimen by compacting both sides of the specimen 50 times for each side.

[0097] The "dynamic stability" (times/mm) was calculated by performing a wheel tracking test according to the method described in the "Hosou Chousa- Sikenhou Binran (Pavement Investigation and Test Method Handbook) (3rd separate volume)" edited by the Japan Road Association. The higher the value of the dynamic stability, the higher the rutting resistance at high temperatures. Specifically, the mixture at 180⁰C obtained by the above- mentioned method was immediately put into a mold and compacted by reciprocating a roller compactor 25 times (50 times in total) at a linear pressure of 29.4 kN/m to prepare a specimen. The resulting specimen was subjected to a wheel tracking test.

[0098] The "Cantabro scattering loss" (%) at ordinary temperatures and low temperatures was measured according to the Japan Highway Public Corporation test method "JHS231-1992". The "ordinary temperatures" mean 20±l°C, and the "low temperatures" mean -20±l°C. The lower the Cantabro scattering loss, the higher the scattering resistance at ordinary temperatures or low temperatures. The specimen used in this measurement is the same as that used for measuring porosity.

[0099] The "workability" (applicability) was evaluated by using a mixture prepared by the following procedure. First, heated aggregate was mixed for 5 seconds in an 800 kg mixer, and then a modifier mixture was charged in the mixer and mixed for further 5 seconds. Next, asphalt was sprayed to the resulting mixture followed by mixing for 40 seconds. Note that the prepared mixture had a temperature of 180⁰C.

[0100] The "workability" of the mixture thus obtained was comprehensively evaluated by the adhesion to a dump truck bed and the adhesion to a roller. [0101] Specifically, the above-mentioned mixture was first loaded on a dump truck, covered with cloth for thermal insulation, carried to a construction site in 30 minutes, and transferred to an asphalt finisher by inclining the dump- truck bed. The adhesion of the mixture to the dump truck bed was evaluated. Next, the mixture was laid down and leveled by the asphalt finisher so that it had a thickness of 5 cm and was compacted by reciprocating a macadam roller 5 times. The adhesion of the mixture to the roller after the compaction was evaluated. The surface temperature at the first compaction was 165°C.

[0102] As shown in Table 3, the "workability" was evaluated by the three-stage criterion (O, Δ, x). Here, "O" represents "no adhesion to a dump truck bed (stained with asphalt without adhesion of aggregate) and no adhesion to a roller"; "Δ" represents "no adhesion to a dump truck bed, but some adhesion to a roller (a lump of the mixture is observed)", or "some adhesion to a dump truck bed (aggregate is adhering and the lump thereof is observed) and no adhesion to a roller"; and "x" represents "some adhesion to a dump truck bed and some adhesion to a roller".

[0103] The results shown in Table 2A and Table 2B show that all of the asphalt modifiers used in Examples 1 to 7 are excellent in processability and storage properties. It is also shown that the dissolution time of these modifiers in asphalt is less than the standard value (20 minutes), and these modifiers are suitable for producing the composition and mixture by a plant mixing method.

[0104] Further, it can be verified that the asphalt compositions in Examples 1 to 7 (No.l to 7) meet the standard values for all of the properties thereof.

[0105] In particular, when these asphalt compositions are compared with the asphalt composition in Comparative Example (1) in which no modifier is mixed, a significant difference can be verified in the viscosity at 60⁰C properties. The increase in the viscosity at 60⁰C of these asphalt compositions means a significant improvement in the high-temperature properties because of the addition of the asphalt modifier of the present invention.

[0106] The increase in the bending work, reduction in the bending stiffness, and reduction in the Fraass breaking point mean improvement in the low- temperature properties because of the addition of the asphalt modifier of the present invention. In particular, it is of interest to note that, when the asphalt modifier according to the present invention is added to oxidized asphalt, a significant improvement in the low-temperature properties, a weak point of oxidized asphalt, will be observed.

[0107] On the other hand, all of the asphalt modifiers used in Comparative

Examples (1) to (5) were found to be poor in any of the processability, storage properties, and the solubility in asphalt, or in the properties of the asphalt compositions prepared by using these asphalt modifiers.

[0108] That is, it is possible to understand from Table 2A and Table 2B that the asphalt modifier prepared by mixing the vinyl aromatic hydrocarbon- conjugated diene block copolymer having a molecular weight in the range of from 100,000 to 400,000, the tackifying resin, and the process oil in a mixing ratio of from 25 to 70% by mass, from 15 to 50% by mass, and from 10 to 50% by mass, respectively, can provide the asphalt composition and asphalt mixture improved in both high-temperature and low-temperature properties, and that this asphalt modifier is suitable for producing the composition and mixture by a plant mixing method.

[0109] From the results shown in Table 3, it can also be verified that the workability of the asphalt mixtures in Examples (I to VI) is generally excellent. Further, as compared with the asphalt mixtures in Comparative Examples ((I) to (III)), improvement in high temperature properties of the asphalt mixtures in Examples can be verified from the fact that the dynamic stability is improved, and improvement in the properties in ordinary temperatures and low temperatures can be verified from the fact that the Cantabro scattering loss is reduced.

[0110] Furthermore, by comparing various properties of the asphalt compositions in Examples 1 and 2 with various properties of the asphalt compositions in Examples 3 and 4, and by comparing various properties of the asphalt mixtures in Examples I and II with various properties of the asphalt mixtures in Examples III and IV, it can be verified that various properties of the compositions and mixtures can be improved by using the asphalt modifiers of the present invention comprising a block copolymer obtained by mixing a plurality of vinyl aromatic hydrocarbon-conjugated diene block copolymers so that they have an average molecular weight in the range of from 100,000 to 400,000.

[0111] As described above, the present invention can provide an asphalt composition and an asphalt mixture in which both high-temperature properties such as rutting resistance and low-temperature properties such as a thermal stress crack have been improved.

[0112] Particularly, when the asphalt modifier according to the present invention is added to oxidized asphalt, the low-temperature properties, which are a weak point of the oxidized asphalt, will be significantly improved.

[0113] The asphalt modifier, composition, and mixture of the present invention have been described with reference to Examples. However, the above Examples are only for executing the present invention, and the present invention is not limited to these. Various modifications of these Examples are within the scope of the present invention, and it is apparent from the above description that other various Examples are possible within the scope of the present invention.

[0114] The present invention can provide an asphalt composition and an asphalt mixture in which both high-temperature properties such as rutting resistance and low-temperature properties such as a thermal stress crack have been improved.

Claims

[Claim 1] An asphalt modifier comprising a block copolymer, a tackifying resin, and a process oil, wherein the block copolymer comprises a single vinyl aromatic hydrocarbon-conjugated diene block copolymer having a polymer block A comprising a vinyl aromatic hydrocarbon as a main component and a polymer block B comprising a conjugated diene as a main component and has a molecular weight in the range of from 100,000 to 400,000; and wherein the asphalt modifier is obtained by mixing the vinyl aromatic hydrocarbon-conjugated diene block copolymer, the tackifying resin, and the process oil in a mixing ratio of from 25 to 70% by mass, from 15 to 50% by mass, and from 10 to 50% by mass, respectively.

[Claim 2] An asphalt modifier comprising a block copolymer, a tackifying resin, and a process oil, wherein the block copolymer is obtained by mixing a plurality of vinyl aromatic hydrocarbon-conjugated diene block copolymers each having a polymer block A comprising a vinyl aromatic hydrocarbon as a main component and a polymer block B comprising a conjugated diene as a main component, wherein the plurality of vinyl aromatic hydrocarbon-conjugated diene block copolymers are mixed so that the average molecular weight thereof is in the range of from 100,000 to 400,000; and wherein the asphalt modifier is obtained by mixing the vinyl aromatic hydrocarbon-conjugated diene block copolymer, the tackifying resin, and the process oil in a mixing ratio of from 25 to 70% by mass, from 15 to 50% by mass, and from 10 to 50% by mass, respectively.

[Claim 3] The asphalt modifier according to claim 1 or 2, wherein the vinyl aromatic hydrocarbon-conjugated diene block copolymer is any of a styrene-butadiene-styrene block copolymer (SBS), a styrene- isoprene-styrene block copolymer (SIS), and a styrene-ethylene- butylene-styrene block copolymer (SEBS).

[Claim 4] The asphalt modifier according to claim 1 or 2, wherein the asphalt modifier is in the shape of a pellet having a diameter of from 0.5 to 50 mm.

[Claim 5] An asphalt composition produced by mixing an asphalt modifier according to claim 1 or 2 with asphalt.

[Claim 6] The asphalt composition according to claim 5, wherein the mixing is performed by a plant mixing method.

[Claim 7] The asphalt composition according to claim 5, wherein the asphalt is oxidized asphalt.

[Claim 8] The asphalt composition according to claim 5, wherein the mixing ratio of the asphalt modifier in the asphalt composition is from 3 to 30% by mass.

[Claim 9] An asphalt mixture produced by mixing an asphalt composition according to claim 5 with an aggregate.

[Claim 10] The asphalt mixture according to claim 9, wherein the mixing is performed by a plant mixing method.

[Claim 11] A method for producing an asphalt modifier comprising a block copolymer, a tackifying resin, and a process oil, comprising: a step A of preparing, as the block copolymer, a single vinyl aromatic hydrocarbon-conjugated diene block copolymer which has a polymer block A comprising a vinyl aromatic hydrocarbon as a main component and a polymer block B comprising a conjugated diene as a main component and has a molecular weight in the range of from 100,000 to 400,000; and a step B of heating and mixing the vinyl aromatic hydrocarbon- conjugated diene block copolymer, the tackifying resin, and the process oil in a ratio of from 25 to 70% by mass, from 15 to 50% by mass, and from 10 to 50% by mass, respectively, to homogenize the mixture.

[Claim 12] A method for producing an asphalt modifier comprising a block copolymer, a tackifying resin, and a process oil, comprising: a step A of preparing, as the block copolymer, a vinyl aromatic hydrocarbon-conjugated diene block copolymer which is obtained by mixing a plurality of vinyl aromatic hydrocarbon- conjugated diene block copolymers each having a polymer block A comprising a vinyl aromatic hydrocarbon as a main component and a polymer block B comprising a conjugated diene as a main component and has an average molecular weight in the range of from 100,000 to 400,000; and a step B of heating and mixing the vinyl aromatic hydrocarbon- conjugated diene block copolymer, the tackifying resin, and the process oil in a ratio of from 25 to 70% by mass, from 15 to 50% by mass, and from 10 to 50% by mass, respectively, to homogenize the mixture.

[Claim 13] The method for producing an asphalt modifier according to claim

11 or 12, further comprising a step C of processing the mixture of the vinyl aromatic hydrocarbon-conjugated diene block copolymer, the tackifying resin, and the process oil which has been homogenized in the step B into a pellet having a diameter of from 0.5 to 50 mm.

[Claim 14] A method for producing an asphalt composition, comprising a step of mixing an asphalt modifier obtained by a method according to claim 11 or 12 with asphalt composition in a mixing ratio of from 3 to 30% by mass, by a plant mixing method.

[Claim 15] The method for producing the asphalt composition according to claim 14, wherein oxidized asphalt is used as the asphalt.

[Claim 16] A method for producing an asphalt mixture, comprising a step of mixing asphalt, an asphalt modifier obtained by a method according to claim 11 or 12, and an aggregate by a plant mixing method, wherein the asphalt modifier is mixed in a mixing ratio of from 3 to 30% by mass relative to the asphalt composition.

[Claim 17] The method for producing the asphalt mixture according to claim

16, wherein oxidized asphalt is used as the asphalt.

[Claim 18] A method for producing an asphalt composition, comprising: a step of blowing heated air into straight asphalt heated to a temperature of from 180 to 300⁰C to oxidize, dehydrogenate, and polycondense an asphalt component in the straight asphalt to obtain oxidized asphalt; and a step of mixing an asphalt modifier obtained by a method according to claim 11 or 12 with the oxidized asphalt composition in a mixing ratio of from 3 to 30% by mass by a plant mixing method. [Claim 19] A method for producing an asphalt mixture, comprising: a step of blowing heated air into straight asphalt heated to a temperature of from 180 to 300⁰C to oxidize, dehydrogenate, and polycondense an asphalt component in the straight asphalt to obtain oxidized asphalt; and a step of mixing the oxidized asphalt, an asphalt modifier obtained by a method according to claim 11 or 12, and an aggregate by a plant mixing method, wherein the asphalt modifier is mixed in a mixing ratio of from 3 to 30% by mass relative to the oxidized asphalt composition.