Asphalt mixture for pavement and block for pavement

Abstract

Provided is an asphalt mixture for pavement, the asphalt mixture being obtained by effectively reutilizing discarded electrical wiring and enabling pavement having excellent dynamic stability. The asphalt mixture for pavement comprises aggregate and an asphalt binder. The aggregate contains crosslinked polyethylene recovered from discarded electrical wiring. The asphalt binder contains straight asphalt and a polyolefinic resin.

Description

Asphalt mixture for paving and paving blocks

[0001] FIELD OF THE DISCLOSURE This disclosure relates to asphalt mixtures for paving and paving blocks.

[0002] Conventional asphalt mixtures used for paving contain at least aggregates such as crushed stone and an asphalt binder. Polymer-modified asphalt, to which an elastomer such as styrene-butadiene-styrene block copolymer (SBS) is added, is known as an asphalt binder. In recent years, waste plastics, which are industrial waste, have been recycled and used as raw materials (aggregates, etc.) for asphalt mixtures for paving (see Patent Documents 1 and 2 below).

[0003] JP 2000-273808 A International Publication No. 2023 / 032609

[0004] An electric wire (e.g., a power cable for underground power transmission) is composed of a conductor (e.g., a bundle of multiple copper wires) located at the center of the wire, an insulating covering (a tubular insulator) that covers the conductor, and a corrosion-resistant covering (e.g., a tubular vinyl film) that covers the covering. Cross-linked polyethylene is often used as a covering material that can withstand high-voltage transmission. Power cables that use cross-linked polyethylene as a covering are called CV cables. The useful life of an electric wire is 20 to 30 years, and in recent years, as existing electric wires begin to reach the end of their lifespan, a rapid increase in discarded electric wires is expected. Although a thorough recycling system has been established to recover valuable conductors (copper) from discarded electric wires, it is also desirable to promote the reuse of not only the conductor but also the covering (cross-linked polyethylene).

[0005] Cross-linked polyethylene is a polymer (plastic) composed of multiple (numerous) linear polyethylene molecules (molecular chains) that are cross-linked with each other. In other words, cross-linked polyethylene has a three-dimensional cross-linked structure (mesh structure). Due to this high degree of cross-linking, cross-linked polyethylene has excellent heat resistance and creep resistance (creep resistance), making it suitable for use as a coating material. On the other hand, cross-linked polyethylene, which has excellent heat resistance and creep resistance, is difficult to process. Therefore, it is not easy to recycle cross-linked polyethylene recovered from discarded electric wires. For the above reasons, cross-linked polyethylene recovered from discarded electric wires is currently mainly reused as thermal recycling or landfill material.

[0006] The inventors discovered that cross-linked polyethylene, which has excellent heat resistance due to its high degree of cross-linking, is suitable as an aggregate for use in paving asphalt mixtures. However, even when using existing high-performance asphalt binders (e.g., polymer-modified asphalt type II or polymer-modified asphalt type H), pavements using aggregate made from plastics such as cross-linked polyethylene are unlikely to have sufficient durability against heavy loads. The reasons for this are as follows.

[0007] Conventional aggregates, such as crushed stone, sand, and gravel, have irregular shapes, uneven aggregate sizes (particle size), and rough aggregate surfaces. As a result, in pavements formed from conventional asphalt mixtures, aggregate tends to be packed tightly together, and physical interference (interlocking and friction) between aggregates tends to inhibit aggregate movement. However, because aggregates alone lack adhesive strength, their placement within the pavement is easily disrupted by external forces, and the structural strength of the pavement due to physical interference between aggregates cannot be maintained. Therefore, the adhesive properties of asphalt binders play a role in fixing the placement of aggregates within the pavement, supporting the structural strength of the pavement due to physical interference between aggregates, thereby enabling the pavement to demonstrate its structural strength.

[0008] In contrast, aggregates made from plastics such as waste plastics (plastic aggregates) are lighter than conventional aggregates. Furthermore, the surfaces of plastic aggregates are smoother than conventional aggregates. When plastic aggregates have curved surfaces, such as cylindrical pellets or spherical particles, point or line contact between the plastic aggregates may occur, but interlocking and friction between the plastic aggregates is unlikely. In other words, even if the asphalt binder fixes the aggregate placement, physical interference between the aggregates cannot be expected, resulting in a significant decrease in the structural strength of the pavement. As a result, pavements formed from conventional asphalt mixtures containing plastic aggregates must primarily rely on the adhesive strength of the asphalt binder to exert their structural strength, making it difficult to achieve sufficiently high dynamic stability (unit: turns / mm). Dynamic stability is a value measured by a wheel tracking test (Standard Number: Pavement Survey and Testing Method Handbook B003). The greater the dynamic stability, the more the aggregate placement is prevented from collapsing due to the load from the wheels (solid rubber tires), and the less likely ruts will form in the pavement due to the collapse of the aggregate placement. In other words, it is preferable for the pavement to have a high dynamic stability.

[0009] For the above reasons, in order to improve the dynamic stability of pavements using aggregates containing cross-linked polyethylene, a special asphalt binder different from existing polymer-modified asphalt is required.

[0010] An object of one aspect of the present invention is to provide an asphalt mixture for paving and paving blocks that allow for the effective reuse of discarded electric wires and that enable paving with excellent dynamic stability.

[0011] One aspect of the present invention relates to the following asphalt paving mixture and paving block.

[0012] [1] An asphalt mixture for paving, comprising: aggregate; and an asphalt binder, wherein the aggregate comprises cross-linked polyethylene recovered from discarded electric wires; and the asphalt binder comprises straight asphalt and a polyolefin resin.

[0013] [2] The asphalt mixture for paving according to [1], wherein at least a portion of the polyolefin resin is at least one polyolefin selected from the group consisting of low-density polyethylene, linear polyethylene, and high-density polyethylene.

[0014] [3] The asphalt mixture for paving according to [1] or [2], wherein the content of the polyolefin resin in the asphalt binder is 15% by mass or more.

[0015] [4] The asphalt mixture for paving according to any one of [1] to [3], wherein the polyolefin resin is melted in the straight asphalt.

[0016] [5] The asphalt mixture for paving according to any one of [1] to [4], wherein the content of asphalt binder in the asphalt mixture for paving is 10% by mass or more and 40% by mass or less.

[0017] [6] At least a portion of the aggregate is crushed coating material from discarded electric wires, and the coating material contains cross-linked polyethylene. The asphalt mixture for paving described in any one of [1] to [5].

[0018] [7] A paving block comprising the asphalt paving mixture according to any one of [1] to [6].

[0019] According to one aspect of the present invention, there are provided an asphalt paving mixture and paving blocks that allow for the effective reuse of discarded electric wires and enable paving with excellent dynamic stability.

[0020] Preferred embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments.

[0021] The asphalt paving mixture according to this embodiment includes aggregate and an asphalt binder. The aggregate includes cross-linked polyethylene recovered from discarded electric wires. For example, a coating material containing cross-linked polyethylene is recovered from components constituting discarded electric wires. By crushing this coating material, aggregate having the desired shape and dimensions can be obtained. The coating material and the aggregate may each consist solely of cross-linked polyethylene. The aggregate may further contain other components derived from the electric wire in addition to cross-linked polyethylene. For example, the aggregate may contain components derived from the corrosion prevention material (e.g., vinyl film) that forms the surface of the electric wire. Cross-linked polyethylene recovered from discarded electric wires has excellent heat resistance due to its high degree of cross-linking, and therefore, cross-linked polyethylene recovered from discarded electric wires can be effectively reused as aggregate that requires heat resistance. The aggregates made from crushed discarded electric wire coating (coating material containing cross-linked polyethylene) are irregular in shape and have a moderately rough surface. When mixed with asphalt binder in the asphalt mixture for paving, this enhances the structural strength of the pavement (suppressing the collapse of the aggregate arrangement due to external forces) and contributes to improving the dynamic stability of the pavement.

[0022] The asphalt binder includes straight asphalt and a polyolefin-based resin. The asphalt binder may consist solely of straight asphalt and a polyolefin-based resin. The thermoplastic elastomer contained in conventional polymer-modified asphalt is excluded from the polyolefin-based resin. For example, the thermoplastic elastomer contained in conventional polymer-modified asphalt is at least one thermoplastic elastomer selected from the group consisting of styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), and styrene-ethylene-butylene-styrene block copolymer (SEBS). The asphalt binder does not need to include the thermoplastic elastomer contained in conventional polymer-modified asphalt. However, the asphalt binder may further include one or more thermoplastic elastomers in addition to straight asphalt and a polyolefin-based resin.

[0023] Straight asphalt is a bituminous material obtained by vacuum distillation of crude oil. In other words, straight asphalt may be the remainder (vacuum residue) of crude oil excluding light fractions. The quality of straight asphalt is specified by Japanese Industrial Standards (JIS K2207). For example, the straight asphalt may be at least one type of asphalt selected from the group consisting of straight asphalt 40-60, straight asphalt 60-80, straight asphalt 80-100, and straight asphalt 150-200.

[0024] Because the paving asphalt mixture according to this embodiment contains cross-linked polyethylene, a type of plastic aggregate, and a polyolefin resin, the pavement formed from the paving asphalt mixture can have high dynamic stability. For example, a pavement using the paving asphalt mixture according to this embodiment can have high dynamic stability compared to pavements using conventional polymer-modified asphalt and plastic aggregate. Furthermore, according to this embodiment, bleeding of the asphalt binder from the asphalt mixture is suppressed. The inventors speculate that the pavement has high dynamic stability and bleeding of the asphalt binder from the paving asphalt mixture is suppressed due to the following mechanism.

[0025] Like plastic aggregates, polyolefin resins are organic substances, and thus have a chemical affinity for plastic aggregates. Furthermore, the polyolefin resins contained in asphalt binders tend to entangle adjacent aggregates as fine fibers fused or dissolved in straight asphalt. As a result, the aggregates are fixed together via the polyolefin resin. Furthermore, the straight asphalt clings to the polyolefin resin entangled with the aggregates. As a result, the aggregates are firmly fixed together via the polyolefin resin and straight asphalt, improving the dynamic stability of pavements containing plastic aggregates. Furthermore, the inclusion of polyolefin resins increases the viscosity of the asphalt binder, thereby suppressing its leaching from the asphalt mixture. In contrast, conventional asphalt mixtures containing non-plastic aggregates, such as crushed stone, contain stone powder (filler), which enhances the mechanical strength of pavements formed from these mixtures. However, stone powder, being an inorganic substance, does not have a chemical affinity for plastic aggregate. Furthermore, because stone powder is particulate, it cannot bind to adjacent aggregates. Therefore, it is difficult to increase the dynamic stability of pavements containing plastic aggregates using conventional stone powder alone, and it is difficult to prevent asphalt binder seepage from the asphalt mixture.

[0026] The above mechanism is hypothetical, and the technical scope of the present invention is not limited by the above mechanism.

[0027] The polyolefin resin contained in the asphalt binder is not limited. For example, the polyolefin resin may be at least one polyolefin selected from the group consisting of polyethylene, polypropylene, polybutene, polybutadiene, polystyrene, polyvinyl chloride, polyvinylidene chloride, and ABS resin (a copolymer of acrylonitrile, butadiene, and styrene). The polyolefin resin may preferably be at least one polyolefin selected from the group consisting of polyethylene, polypropylene, polybutene, and polybutadiene.

[0028] At least a portion of the polyolefin resin contained in the asphalt binder may be at least one polyolefin selected from the group consisting of low-density polyethylene, linear polyethylene, and high-density polyethylene. All of the polyolefin resins contained in the asphalt binder may be at least one polyolefin selected from the group consisting of low-density polyethylene, linear polyethylene, and high-density polyethylene. When the polyolefin resin is at least one polyolefin selected from the group consisting of low-density polyethylene, linear polyethylene, and high-density polyethylene, the dynamic stability of pavements containing plastic aggregate is likely to be increased and the exudation of asphalt binder from the asphalt mixture is likely to be suppressed. When the polyolefin resin is at least one polyolefin selected from the group consisting of low-density polyethylene, linear polyethylene, and high-density polyethylene, the low-density polyethylene, linear polyethylene, and high-density polyethylene are likely to melt in straight asphalt, making the above mechanism more likely to occur. Of low-density polyethylene, linear polyethylene, and high-density polyethylene, it is preferable that the polyolefin resin contain at least one of low-density polyethylene and linear polyethylene, since this tends to increase the dynamic stability of pavements containing plastic aggregate and tends to suppress the leaching of asphalt binder from the asphalt mixture. Low-density polyethylene (LDPE) is a crystalline polyethylene with random branches. The density (specific gravity) of the low-density polyethylene may be 0.910 or more and less than 0.930. Linear polyethylene (Linear Low-Density Polyethylene; L-LDPE) is a linear polyethylene copolymer that is a copolymer of the repeating unit ethylene and an α-olefin. The linear polyethylene may be polyethylene as defined by the Japanese Industrial Standard (JIS K6899-1:2000). That is, the linear polyethylene may be a linear polyethylene copolymer having a density (specific gravity) of 0.910 or more and 0.925 or less. Linear polyethylene may be rephrased as linear low-density polyethylene.High density polyethylene (HDPE) is a crystalline linear polyethylene. The density (specific gravity) of high density polyethylene may be 0.942 or more. High density polyethylene may also be called rigid polyethylene.

[0029] The asphalt binder may contain only one type of polyolefin-based resin as the polyolefin-based resin. The asphalt binder may also contain multiple types of polyolefin-based resins. In other words, multiple types of polyolefin-based resins may be mixed in the asphalt binder. When multiple types of polyolefin-based resins are mixed, the types of polyolefin-based resins may be selected and their mixing ratios may be adjusted in the process of producing the asphalt mixture (the process of mixing the asphalt binder and aggregate) so that the viscosity of the asphalt mixture during mixing falls within an appropriate range.

[0030] The content of polyolefin resin in the asphalt binder may be 15% by mass or more. When the asphalt binder contains multiple types of polyolefin resins, the content of polyolefin resin is the total content of the multiple types of polyolefin resins. As the content of polyolefin resin increases, the dynamic stability of the pavement tends to increase. When the content of polyolefin resin in the asphalt binder is 15% by mass or more, the dynamic stability tends to increase. As the content of polyolefin resin increases, the viscosity of the asphalt binder increases, and bleeding of the asphalt binder from the asphalt mixture tends to be suppressed. In other words, as the content of polyolefin resin decreases, the original properties of the straight asphalt become more pronounced, the viscosity of the asphalt binder decreases, and the asphalt binder tends to leak out of the asphalt mixture. When the content of the polyolefin resin in the asphalt binder is 15 mass % or more, the leaching of the asphalt binder from the asphalt mixture is sufficiently suppressed.

[0031] Because the viscosity of the paving asphalt mixture is not too high and workability is good, the content of the polyolefin resin in the asphalt binder is preferably 70% by mass or less, more preferably 50% by mass or less, and most preferably 30% by mass or less. In terms of the mixing ability, kneading and dropping, compaction, and surface finish of the paving asphalt mixture, a paving asphalt mixture having a polyolefin resin content of 30% by mass in the asphalt binder is superior to a paving asphalt mixture having a polyolefin resin content of 40% or 50% by mass in the asphalt binder. For example, the content of straight asphalt in the asphalt binder may be preferably 30% by mass or more and 85% by mass or less, more preferably 50% by mass or more and 85% by mass or less, and most preferably 70% by mass or more and 85% by mass or less.

[0032] At least a portion of the polyolefin resin may be melted or dissolved in the straight asphalt. All of the polyolefin resin may be melted or dissolved in the straight asphalt. When the polyolefin resin is melted or dissolved in the straight asphalt, the dynamic stability of the pavement containing plastic aggregate is likely to increase, and the bleeding of the asphalt binder from the asphalt mixture is likely to be suppressed. When the polyolefin resin is melted or dissolved in the straight asphalt, the above mechanism may be more likely to occur.

[0033] The aggregate contained in the paving asphalt mixture may be solely aggregate containing cross-linked polyethylene recovered from discarded electric wires. The paving asphalt mixture may also contain multiple aggregates with different compositions. For example, the paving asphalt mixture may further contain another plastic aggregate in addition to the aggregate containing cross-linked polyethylene. The aggregate contained in the paving asphalt mixture may be solely plastic aggregate. The paving asphalt mixture may further contain aggregate made of a material other than plastic (non-plastic aggregate) in addition to the aggregate containing cross-linked polyethylene. The paving asphalt mixture may contain both plastic aggregate and non-plastic aggregate.

[0034] The alternative plastic aggregate may be at least one plastic selected from the group consisting of polystyrene, polyolefin (such as polypropylene, polybutene, and polybutadiene), polyethylene terephthalate, polyamide, polycarbonate, polyurethane, ABS resin, polyurethane foam, unsaturated polyester resin, and epoxy resin. The shape of the plastic aggregate is not limited. For example, the plastic aggregate may be cylindrical pellets or spherical particles. The plastic aggregate may also be irregular particles. The size of the plastic aggregate is not particularly limited. The plastic aggregate may have a single particle size (e.g., a particle size within the range of 3 to 9 mm or 3 to 5 mm). The plastic aggregate may have a particle size distribution suitable for paving, like conventional aggregates. According to this embodiment, the dynamic stability of the pavement can be increased even when the plastic aggregate does not have a particle size distribution suitable for paving.

[0035] When the paving asphalt mixture further contains another plastic aggregate in addition to the aggregate containing cross-linked polyethylene, the other plastic aggregate may also be waste plastic, as with the aggregate containing cross-linked polyethylene. Some or all of the plastic aggregate contained in the paving asphalt mixture may be waste plastic. By recycling waste plastic as an aggregate for the paving asphalt mixture, the cost of paving can be reduced.

[0036] The proportion of plastic in the aggregate may be greater than 0% by mass and less than 100% by mass, 50% by mass to 100% by mass, 85% by mass to 100% by mass, or 90% by mass to 100% by mass. In other words, the proportion of plastic aggregate in the paving asphalt mixture may be greater than 0% by mass and less than 100% by mass, 50% by mass to 100% by mass, 85% by mass to 100% by mass, or 90% by mass to 100% by mass, relative to the total mass of all aggregates contained in the paving asphalt mixture. When using a conventional asphalt binder that does not contain polyolefin resin, the higher the proportion of plastic in the aggregate, the more difficult it is to achieve high dynamic stability for the pavement. For example, when using a conventional asphalt binder that does not contain polyolefin resin, it is difficult to achieve high dynamic stability for a pavement with a plastic aggregate proportion of 85% by mass or more. On the other hand, according to this embodiment, a pavement with a plastic aggregate proportion of 85% by mass or more can achieve high dynamic stability. Therefore, the paving asphalt mixture according to this embodiment can contain a larger amount of plastic aggregate than conventional paving asphalt mixtures without impairing the dynamic stability of the pavement, and as a result, a larger amount of waste plastic can be used as aggregate in the paving asphalt mixture than conventionally.

[0037] For example, the non-plastic aggregate may be at least one type of aggregate selected from the group consisting of crushed stone, stone powder, lime, sand, gravel, and steel slag. The proportion of non-plastic aggregate in the aggregate may be 0% by mass or more and less than 100% by mass, 0% by mass or more and 50% by mass or less, or 0% by mass or more and 15% by mass or less. In other words, the proportion of non-plastic aggregate in the paving asphalt mixture may be 0% by mass or more and less than 100% by mass, 0% by mass or more and 50% by mass or less, or 0% by mass or more and 15% by mass or less, relative to the total mass of all aggregates contained in the paving asphalt mixture.

[0038] The content of asphalt binder in the paving asphalt mixture may preferably be 10% by mass or more and 40% by mass or less, more preferably 15% by mass or more and 35% by mass or less, and even more preferably 15% by mass or more and 30% by mass or less. The content of aggregate in the paving asphalt mixture may preferably be 60% by mass or more and 90% by mass or less, more preferably 65% ​​by mass or more and 85% by mass or less, and even more preferably 70% by mass or more and 85% by mass or less. When the contents of each component in the paving asphalt mixture are within the above ranges, the pavement is likely to have high dynamic stability, and leaching of asphalt binder from the asphalt mixture is likely to be suppressed.

[0039] The asphalt binder may be produced by mixing the above components, such as straight asphalt and polyolefin resin, while heating at 160 to 240° C. Mixing at the above temperature makes it easier for the polyolefin resin to melt in the straight asphalt, and can suppress combustion of light oil remaining in the asphalt binder.

[0040] Paving asphalt mixtures may be produced by mixing the above-mentioned components, such as an asphalt binder and a plastic aggregate containing cross-linked polyethylene, while heating at a temperature that results in a viscosity suitable for mixing (e.g., 200°C or less). When mixing non-cross-linked plastic aggregate with an asphalt binder, mixing must be performed at a temperature below the melting point of the non-cross-linked plastic (e.g., 130-160°C), limiting the asphalt binder to a viscosity that is compatible with that temperature. On the other hand, aggregates made from cross-linked polyethylene have high heat resistance and do not melt or deform even at temperatures above the melting point of the non-cross-linked plastic. Therefore, they can be mixed with high-viscosity asphalt binders by lowering the viscosity at high temperatures (e.g., 160-200°C). Furthermore, paving asphalt mixtures produced by mixing cross-linked polyethylene aggregate with an asphalt binder offer better workability than paving asphalt mixtures produced by mixing non-cross-linked plastic aggregate with an asphalt binder, because their viscosity can be lowered by heating to a high temperature during paving construction.

[0041] The paving blocks according to this embodiment include the paving asphalt mixture described above. For example, the paving asphalt mixture is heated and molded to form a molded body, and the molded body is cooled to form the paving blocks. The temperature of the paving asphalt mixture during molding may be below the melting point of the plastic aggregate. The paving blocks may also be referred to as paving panels. Interlocking block paving may be constructed using the paving blocks. In other words, paving may be constructed by laying multiple paving blocks on the surface to be paved. In the case of paving using a conventional kneading method, cracks or gaps may form in the paving due to thermal contraction of the cross-linked polyethylene (aggregate) associated with heating and cooling of the paving asphalt mixture. However, since the cross-linked polyethylene contained in the paving blocks has already shrunk sufficiently during the manufacturing process of the paving blocks, thermal contraction of the cross-linked polyethylene contained in the paving blocks is unlikely to occur during the construction of the interlocking block paving. Therefore, interlocking block paving using paving blocks suppresses the formation of cracks and gaps in the paving. Paving blocks using aggregate containing cross-linked polyethylene are lighter than conventional paving blocks using non-plastic aggregate, making them easier to transport and pavement construction. The dimensions of the paving blocks may be those of typical paving blocks. For example, the paving blocks may be square plates (rectangular parallelepipeds) with faces parallel to the road surface (surface to be paved). For example, the length of one side of the paving block in a direction parallel to the road surface may be 5 to 110 cm, preferably 25 to 90 cm. The thickness of the paving block in a direction perpendicular to the road surface may be 3 to 8 cm. Naturally, the dimensions of the paving blocks may be adjusted within the range that allows molding and construction depending on the conditions of the road surface and the installation location of the paving blocks. For example, the length and thickness of one side of the paving block may be adjusted to values ​​outside the above ranges. The dimensions of the paving blocks can be adjusted appropriately to ensure efficient manufacturing and construction. The shape of the surface parallel to the road surface is not limited to a square, but may be rectangular, diamond, trapezoidal, or fan-shaped, etc.Furthermore, during construction, multiple types of paving blocks with different sizes or shapes may be combined.

[0042] The present invention is not necessarily limited to the above-described embodiments. Various modifications of the present invention are possible without departing from the spirit of the present invention, and these modifications are also included in the present invention.

[0043] The present invention will be described in detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples.

[0044] Example 1 The asphalt binder of Example 1 was prepared by mixing low-density polyethylene (LDPE) containing linear polyethylene (L-LDPE) with straight asphalt. Straight asphalt 60-80 was used as the straight asphalt. The LDPE content (unit: mass%) in the asphalt binder was adjusted to the value shown in Table 1 below.

[0045] A coating material made of cross-linked polyethylene was recovered from discarded electric wires. The particles obtained by crushing the coating material and passing through a 9 mm mesh were used as aggregate.

[0046] The above aggregate made of cross-linked polyethylene was mixed with the above asphalt binder to prepare the paving asphalt mixture of Example 1. The content (unit: mass %) of the asphalt binder in the paving asphalt mixture was adjusted to the value shown in Table 1 below.

[0047] (Examples 2 and 3) The asphalt binder content in each of the asphalt paving mixtures of Examples 2 and 3 was adjusted to the value shown in the following Table 1. The asphalt paving mixtures of Examples 2 and 3 were prepared in the same manner as in Example 1, except for the above-mentioned points.

[0048] (Examples 4 to 7) The LDPE content in the asphalt binder of each of Examples 4 to 7 was adjusted to the value shown in the following Table 1. The asphalt binder content in the paving asphalt mixture of each of Examples 4 to 7 was adjusted to the value shown in the following Table 1. The paving asphalt mixture of each of Examples 4 to 7 was prepared in the same manner as in Example 1, except for the above-mentioned points.

[0049] (Comparative Examples 1 and 2) Polymer-modified asphalt type H was used as the asphalt binder for each of Comparative Examples 1 and 2. The composition of polymer-modified asphalt type H is specified by the Pavement Design and Construction Guidelines. The Pavement Design and Construction Guidelines are published by the Japan Road Association. Polymer-modified asphalt type H is an asphalt binder containing a styrene-butadiene-styrene block copolymer (SBS copolymer) as a modifier and does not contain LDPE. The asphalt binder content in the paving asphalt mixtures for each of Comparative Examples 1 and 2 was adjusted to the values ​​shown in Table 1 below. The paving asphalt mixtures for each of Comparative Examples 1 and 2 were prepared in the same manner as in Example 1, except for the above-mentioned details.

[0050] <Wheel Tracking Test (Standard Number: Pavement Survey and Test Method Handbook B003)> The paving asphalt mixtures of Examples 1 to 7 and Comparative Examples 1 and 2 were evaluated by the following wheel tracking test. A pavement (flat sample) was formed from the paving asphalt mixture. A load (0.63 MPa) was applied to the surface of the sample by pressing a solid rubber tire against the flat surface of the sample. While the load was applied to the surface of the sample, the tire was moved back and forth in the front and rear direction at a speed of 42 ± 1 times per minute. The tire was moved back and forth repeatedly for 60 minutes while the temperature of the sample was maintained at 60°C. The depth Di (unit: mm) of the ruts formed on the surface of the sample was measured at a time Ti, 45 minutes after the tire started moving back and forth. The depth Df of the ruts formed on the surface of the sample was measured at time Tf, 60 minutes after the start of the tire's reciprocating motion. Dynamic stability S was calculated using the following equation 1. N in equation 1 is the number of times (unit: times) the tire made reciprocating motion from time Ti to time Tf. S=N / (Df-Di) (1) The dynamic stability (unit: times / mm) for each of Examples 1 to 7 and Comparative Examples 1 and 2 is shown in Table 1 below. The higher the dynamic stability, the more the flow of the pavement caused by vehicle traffic is suppressed, and the less likely ruts are to form. Therefore, a high dynamic stability is preferable.

[0051] Marshall Stability Test (Standard Number: Pavement Survey and Test Method Handbook B001) The paving asphalt mixtures of Examples 2, 5, and 7 and Comparative Examples 1 and 2 were evaluated using the Marshall Stability Test described below. Cylindrical samples were formed from the paving asphalt mixtures. The diameter of the samples was 101.6 mm. The thickness of the samples was 63.5 mm. The sides (outer surfaces) of the samples were sandwiched between a pair of arc-shaped loading heads. A load was applied to the samples at a specified loading rate by the pair of loading heads. The temperature of the samples to which the load was applied was maintained at 60°C. The maximum load (stability) at which the samples broke was measured. The stability (unit: kN) of Examples 2, 5, and 7 and Comparative Examples 1 and 2 is shown in Table 1 below. The higher the stability, the less likely the pavement is to collapse.

[0052] <Cantabro Test (Standard Number: Pavement Survey and Test Method Handbook B010)> The paving asphalt mixtures of Examples 2, 5, and 7 and Comparative Examples 1 and 2 were evaluated using the Cantabro test described below. Cylindrical samples were formed from the paving asphalt mixtures. The mass Mi of the sample was measured. After measuring the mass Mi, the sample was placed in a Los Angeles tester (a rotatable drum). The Los Angeles tester containing the sample was rotated 300 times at room temperature. The rotation speed of the Los Angeles tester was adjusted to 30 to 33 revolutions per minute. After the Los Angeles tester had rotated 300 times, the mass Mf of the sample removed from the Los Angeles tester was measured. The Cantabro loss ratio R was calculated using the following equation 2: R = 100 × (Mi - Mf) / Mi (2) The Cantabro loss ratios (unit: %) of Examples 2, 5, and 7 and Comparative Examples 1 and 2 are shown in Table 1 below. The stronger the force with which the asphalt binder binds aggregates together, the more the aggregate is prevented from falling off the sample when the Los Angeles tester rotates, and the less the sample's mass is reduced. In other words, the stronger the force with which the asphalt binder binds aggregates together, the smaller the Cantablo loss rate. The smaller the Cantablo loss rate, the less likely aggregate will fall off the pavement when vehicles pass by. Therefore, a small Cantablo loss rate is preferable.

[0053]

[0054] For example, an asphalt paving mixture according to one aspect of the present invention may be used to pave road surfaces.

Claims

1. An asphalt mixture for paving comprising an aggregate and an asphalt binder, the aggregate containing cross-linked polyethylene recovered from discarded electric wires, and the asphalt binder containing straight asphalt and a polyolefin resin.

2. The asphalt paving mixture according to claim 1, wherein at least a portion of said polyolefin resin is at least one polyolefin selected from the group consisting of low density polyethylene, linear polyethylene, and high density polyethylene.

3. The paving asphalt mixture according to claim 1, wherein the content of the polyolefin resin in the asphalt binder is 15 mass% or more.

4. The asphalt paving mixture according to claim 1, wherein the polyolefin resin is melted in the straight asphalt.

5. The paving asphalt mixture according to claim 1, wherein the content of the asphalt binder in the paving asphalt mixture is 10% by mass or more and 40% by mass or less.

6. The asphalt paving mixture according to claim 1, wherein at least a portion of the aggregate is crushed covering material of discarded electric wires, and the covering material contains the cross-linked polyethylene.

7. A paving block comprising the asphalt paving mixture according to any one of claims 1 to 6.