Paving mixes and paving binders

Abstract

The present invention addresses the problem of providing: a pavement mixture which can be easily handled at normal temperature or lower and which develops excellent strength in a relatively short time after being laid; and a pavement binder which can be used in this type of pavement mixture. This problem can be solved by providing: a pavement binder which is obtained by being mixed with an aggregate and which is characterized by containing a polysaccharide that forms a gel upon contact with a divalent or higher metal ion; and a pavement mixture which contains an aggregate and the pavement binder.

Description

[Technical Field]

[0001] The present invention relates to paving mixtures and paving binders. [Background technology]

[0002] Asphalt pavement is the most widely used type of pavement and is typically constructed by spreading and compacting a hot asphalt mixture, which is obtained by heating and mixing aggregate and asphalt. When the temperature of the hot asphalt mixture drops after paving, the viscosity of the asphalt contained in the hot asphalt mixture increases, firmly bonding the aggregates together, and forming a pavement with excellent strength. Asphalt pavement is constructed in this way by cleverly utilizing the temperature-dependent adhesive behavior of asphalt. However, because asphalt's viscosity increases significantly with temperature, handling of hot asphalt mixtures becomes significantly more difficult when temperatures drop below 100°C. Therefore, when using hot asphalt mixtures for construction, the hot asphalt mixture produced in the asphalt plant must be transported to the construction site while still hot, or it must be reheated at the construction site before use, which requires considerable effort and cost.

[0003] Meanwhile, cold-mix asphalt mixtures using cutback asphalt have been proposed as asphalt mixtures that can be applied at temperatures below 100°C. Cutback asphalt is a liquid asphalt made by mixing asphalt with a cutback agent, a volatile oil (e.g., gasoline, kerosene, heavy oil, etc.), and has the advantage of being easy to apply even at room temperature. However, pavements constructed using cold-mix asphalt mixtures have the disadvantage of being inferior in strength immediately after construction compared to heated asphalt mixtures, because they cannot achieve sufficient strength unless the cutback agent, a diluting component of asphalt, has sufficiently volatilized. However, in real-world construction sites where early reopening to traffic is required, ensuring sufficient curing time after construction is not always easy.

[0004] In response to this, various cold asphalt mixtures have been developed to quickly develop sufficient strength. For example, Patent Document 1 discloses a cold asphalt mixture containing aggregate, asphalt, and kerosene and 1-bromopropane as cutback agents. According to Patent Document 1, the addition of 1-bromopropane improves the volatility of the cutback agent, allowing the cold asphalt mixture to quickly develop sufficient strength. However, the cold asphalt mixture described in Patent Document 1 requires a relatively long period of time to develop strength, and it is difficult to say that its hardening rate is sufficient.

[0005] Furthermore, as mentioned above, asphalt viscosity increases as the temperature decreases. Therefore, cold asphalt mixtures that use asphalt as the main component of the binder that bonds the aggregates have the drawback of exhibiting a significant increase in viscosity in environments even colder than room temperature, such as in winter or cold regions, resulting in poor workability. Attempts have been made to increase the fluidity of cold asphalt mixtures by adding more cutback agents, but the greater the amount of cutback agent, the longer the volatilization time required. To the inventors' knowledge, no paving mixtures are known that exhibit excellent workability even at temperatures lower than room temperature and that demonstrate sufficient strength in a short time after application. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-74919 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made to overcome the disadvantages of the prior art as described above, and aims to provide a paving mixture that is easy to work even at room temperature or lower and that exhibits excellent strength within a relatively short time after work, as well as a paving binder to be used in such a paving mixture. [Means for solving the problem]

[0008] While various binders are known that exhibit the property of binding materials together, as far as the applicant is aware, almost no binder other than asphalt is known that can bind aggregates used in pavements together and produce pavements with extremely high strength sufficient to withstand the traffic loads of cars and trucks. In the course of intensive research efforts to solve this problem, the inventors discovered that an aqueous solution of a polysaccharide that forms a gel upon contact with divalent or higher metal ions can be easily mixed with aggregates even at room temperature or below, and that spraying an aqueous solution containing divalent or higher metal ions that gel the polysaccharide onto a mixture obtained by mixing the aqueous solution of the polysaccharide with aggregate rapidly binds the aggregates together, resulting in a molded product with high strength. Surprisingly, the molded product exhibited strength equal to or greater than that of molded products obtained from cold asphalt mixes using cutback asphalt, which is widely used in the art. This finding led to the completion of the present invention.

[0009] In one aspect, the present invention solves the above-mentioned problems by providing a paving mixture comprising aggregate and a binder, the binder including a polysaccharide that forms a gel upon contact with divalent or higher metal ions. In a preferred embodiment, the polysaccharide is contained in the binder in the form of an aqueous solution.

[0010] In another aspect, the present invention solves the above-mentioned problems by providing a paving binder for use in a paving mixture, the paving binder comprising a polysaccharide that forms a gel upon contact with divalent or higher metal ions. In a preferred embodiment, the polysaccharide is contained in the paving binder in the form of an aqueous solution. [Effects of the Invention]

[0011] According to the present invention, a paving mixture that has excellent workability even at room temperature or lower and that exhibits excellent strength within a relatively short time after application, and a paving binder for use in such a paving mixture, can be obtained. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a photograph of a specimen formed using a paving mixture according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in more detail below.

[0014] The paving binder of the present invention is a paving binder used in paving mixtures, characterized in that it contains a polysaccharide that forms a gel when in contact with divalent or higher metal ions.

[0015] Binders are the components that bind the aggregates that make up the pavement together and solidify the pavement. The binder acts to bond the aggregates together, resulting in a strong pavement.

[0016] As described above, the paving binder of the present invention contains a polysaccharide that forms a gel upon contact with divalent or higher metal ions. In a preferred embodiment, the polysaccharide is contained in the paving binder in the form of an aqueous solution. Here, "a polysaccharide aqueous solution" refers to a liquid in which the polysaccharide is dissolved in a water-based solvent, i.e., a polysaccharide solution in which the solvent is primarily water. "The binder contains a polysaccharide in the form of an aqueous solution" refers to a binder containing a polysaccharide aqueous solution. In this specification, "the solvent is primarily water" means that the solvent is more than 50 vol% by volume, preferably 75 vol% or more, more preferably 90 vol% or more, even more preferably 95 vol% or more, and even more preferably 100 vol%. Paving binders according to one embodiment of the present invention, which use a polysaccharide aqueous solution containing water as the primary solvent, have the advantage of exhibiting minimal increase in viscosity with decreasing temperature, resulting in excellent workability even at low temperatures.

[0017] On the other hand, polysaccharides are substances with a structure in which many monosaccharide molecules are polymerized. The polysaccharides used in the paving binder of the present invention are those that form a gel upon contact with divalent or higher metal ions. A polysaccharide that forms a gel upon contact with divalent or higher metal ions means that an aqueous solution containing the polysaccharide is in a liquid state (sol state) before contact with the divalent or higher metal ions, but after contact with the divalent or higher metal ions, for example, when the aqueous solution is mixed with a solution containing divalent or higher metal ions and the divalent or higher metal ions are brought into contact with the polysaccharide, an insoluble gel is formed. A polysaccharide aqueous solution with such properties is liquid before the addition of the divalent or higher metal ions that function as a hardener, making it easy to mix with aggregate. However, upon contact with the divalent or higher metal ions that function as a hardener, it gels, quickly and firmly bonding the aggregates together. Therefore, by mixing a paving binder according to one embodiment of the present invention, which contains such polysaccharides, preferably in the form of an aqueous solution, with aggregate to form a paving mixture, the timing of the onset of hardening of the paving mixture can be controlled by controlling the timing of contact with the divalent or higher metal ions that function as hardeners, thereby simultaneously achieving both excellent workability at low temperatures and early strength development.

[0018] The polysaccharides that can be used in the paving binder of the present invention are not particularly limited as long as they form a gel upon contact with divalent or higher metal ions. Suitable examples include alginic acid, low-methoxylated pectin (LM pectin), carboxymethylcellulose (CMC), gellan gum, and derivatives thereof. Alginic acid and low-methoxylated pectin (LM pectin) are more suitable, and alginic acid is even more suitable. These polysaccharides may be used alone or in combination. Furthermore, these polysaccharides may be used in the form of their salts, if necessary. For example, monovalent cation salts of polysaccharides (such as sodium salts, potassium salts, and ammonium salts) are highly soluble in water and are therefore suitable for preparing aqueous polysaccharide solutions.

[0019] Incidentally, alginic acid is a natural polysaccharide that is abundantly contained in brown algae such as kelp and wakame seaweed, and has a structure formed by the polymerization of mannuronic acid and guluronic acid. An aqueous solution of alginic acid is liquid at room temperature, but forms an insoluble gel when it comes into contact with divalent or higher metal ions. In other words, alginic acid is a polysaccharide that forms a gel when it comes into contact with divalent or higher metal ions, and when alginic acid is used as the polysaccharide, divalent or higher metal ions can be used as the hardening agent. There are no particular restrictions on the type of divalent or higher metal ion that can be used as a hardening agent for alginic acid, but for example, calcium ions (Ca 2+ ), magnesium ions (Mg 2+ ), barium ions (Ba 2+ ), aluminum ions (Al 3+ ), strontium ions (Sr 3+ ), iron ions (Fe 3+ ) are preferably used. These metal ions may be used alone or in combination of two or more.

[0020] Low methoxylated pectin (LM pectin) is a polysaccharide extracted primarily from fruits such as lemons, oranges, grapefruits, and apples. It is a type of pectin with a polymerized structure of galacturonic acid and its methyl ester, methylated galacturonic acid. LM pectin refers to pectins with a degree of esterification of 50% or less, in other words, pectins in which the proportion of methylated galacturonic acid is less than 50% of the total galacturonic acid that constitutes the pectin. While an aqueous solution of LM pectin is liquid at room temperature, it forms an insoluble gel when it comes into contact with divalent or higher metal ions. In other words, LM pectin is a polysaccharide that forms a gel when it comes into contact with divalent or higher metal ions. When LM pectin is used as a polysaccharide, divalent or higher metal ions can be used as a hardening agent. There are no particular limitations on the type of divalent or higher metal ion that can be used as a hardening agent for LM pectin, but calcium ions (Ca 2+ ) and magnesium ions (Mg 2+These metal ions may be used alone or in combination of two or more.

[0021] Gellan gum is a polysaccharide produced by microorganisms of the genera Pseudomonas and Sphingomonas, and has a structure with a repeating tetrasaccharide unit of D-glucose, D-glucuronic acid, D-glucose, and L-rhamnose as the basic unit. Like alginic acid and LM pectin, an aqueous solution of gellan gum is liquid at room temperature, but forms an insoluble gel when it comes into contact with divalent or higher metal ions. In other words, gellan gum is a polysaccharide that forms a gel when it comes into contact with divalent or higher metal ions, and when gellan gum is used as a polysaccharide, divalent or higher metal ions can be used as a hardening agent. There are no particular restrictions on the type of divalent or higher metal ion that can be used as a hardening agent for gellan gum, but for example, calcium ions (Ca 2+ ) and magnesium ions (Mg 2+ These metal ions may be used alone or in combination of two or more.

[0022] Carboxymethyl cellulose (CMC) is a polysaccharide produced from cellulose as a raw material, and has a structure in which some of the hydroxy groups of the glucopyranose that constitutes the cellulose skeleton are carboxymethylated. An aqueous solution of carboxymethyl cellulose is liquid at room temperature, but forms an insoluble gel when it comes into contact with divalent or higher metal ions. That is, carboxymethyl cellulose is a polysaccharide that forms a gel when it comes into contact with divalent or higher metal ions, and when carboxymethyl cellulose is used as the polysaccharide, divalent or higher metal ions can be used as the hardening agent. There are no particular restrictions on the type of divalent or higher metal ion that can be used as the hardening agent for carboxymethyl cellulose, but for example, calcium ions (Ca 2+ ) and aluminum ions (Al 3+ These metal ions may be used alone or in combination of two or more.

[0023] As described above, alginic acid, LM pectin, gellan gum, and carboxymethyl cellulose are all polysaccharides that form gels when they come into contact with divalent or higher metal ions. According to the findings of the present inventors, when an aqueous solution of these polysaccharides is mixed with aggregate and then brought into contact with a solution containing divalent or higher metal ions, the aggregates are firmly bonded together, resulting in a pavement with excellent strength.

[0024] In a preferred embodiment, there is no particular limitation on the concentration of polysaccharides in the aqueous solution of polysaccharides contained in the binder. However, from the viewpoint of sufficiently covering the periphery of the aggregate and obtaining the desired adhesive strength, the aqueous solution of polysaccharides preferably contains 0.1 to 20% by mass of polysaccharides, more preferably 0.5 to 15% by mass of polysaccharides, and even more preferably 1 to 10% by mass of polysaccharides. If the polysaccharide content in the aqueous solution is less than 0.1% by mass, it may be difficult to sufficiently cover the surface of the aggregate and exert sufficient bonding strength. On the other hand, if the polysaccharide content in the aqueous solution exceeds 20% by mass, the viscosity of the aqueous solution containing the polysaccharides itself becomes too high, which causes the inconvenience of making it difficult to mix with the aggregate. Similarly, from the viewpoint of sufficiently coating the periphery of the aggregate and obtaining the desired adhesive strength, the viscosity of such an aqueous polysaccharide solution at 20° C. is preferably 300 to 120,000 cp, more preferably 750 to 90,000 cp, even more preferably 1500 to 60,000 cp, and even more preferably 3000 to 30,000 cp, but is not limited to these. If the viscosity of the aqueous polysaccharide solution is too low, the adhesion to the aggregate will be poor, while if the viscosity of the aqueous polysaccharide solution is too high, it will be difficult to mix with the aggregate.

[0025] In a preferred embodiment, the paving binder of the present invention may contain one or more modifying components such as asphalt emulsion, modified asphalt emulsion, thermoplastic resin, or rubber, as necessary, from the viewpoint of improving adhesion to aggregate and improving the plastic deformation resistance, abrasion resistance, flexibility, etc. of the resulting pavement.

[0026] There are no particular limitations on the type of thermoplastic resin that can be incorporated into the paving binder of the present invention, but examples include styrene-based resins such as styrene-butadiene block copolymer (SBS) and styrene-isoprene block copolymer (SIS), ethylene-based resins such as ethylene-acrylic acid copolymer (EAA), ethylene-vinyl acetate copolymer (EVA), and ethylene-ethyl acrylate copolymer (EEA), polyester-based resins, nylon-based resins, and acrylic resins. These thermoplastic resins may be used alone or in combination. Furthermore, all or part of these thermoplastic resins may be incorporated into the paving binder of the present invention as emulsions.

[0027] On the other hand, there are no particular limitations on the type of rubber that can be blended into the paving binder of the present invention, but examples include natural rubber, Guttavirture, cyclized rubber, styrene-butadiene rubber, styrene-isoprene rubber, polyisoprene rubber, butadiene rubber, chloroprene rubber, butyl rubber, halogenated butyl rubber, chlorinated polyethylene, chlorosulfonated polyethylene, ethylene-propylene rubber, EPT rubber, Alfin rubber, styrene-butadiene block polymer rubber, and styrene-isoprene block polymer rubber. Any one of these rubbers may be used alone, or two or more may be used in combination. Furthermore, all or part of these rubbers may be blended into the paving binder of the present invention as an emulsion.

[0028] <Paving mixture> The paving mixture of the present invention can be produced by mixing the paving binder of the present invention as described above with aggregate. The paving mixture is a mixture of aggregate, binder, etc. in a predetermined mixing ratio, and is used for constructing the surface or base layer of a pavement.

[0029] The aggregate contained in the paving mixture of the present invention primarily refers to sand, gravel, crushed sand, crushed stone, etc., used in paving. However, there are no particular limitations on the type of aggregate that can be used in the paving mixture of the present invention; an appropriate aggregate can be selected depending on the construction site and construction method. For example, with regard to aggregate particle size, if the paving layer to be constructed is relatively thin, aggregate with a maximum particle size of No. 7 crushed stone (maximum particle size 5 mm) may be used. On the other hand, if the paving layer to be constructed is relatively thick, aggregate with a maximum particle size of No. 6 crushed stone (maximum particle size 13 mm) or No. 5 crushed stone (maximum particle size 20 mm) may be used. In addition to sand, gravel, crushed sand, crushed stone, etc., the aggregate may also contain filler components. Examples of such filler components include stone powder, clay, talc, fly ash, rubber powder, cork powder, wood powder, resin powder, inorganic fiber, pulp, synthetic fiber, carbon fiber, etc.

[0030] In the paving mixture of the present invention, there is no particular limitation on the content of the polysaccharide that forms a gel upon contact with divalent or higher metal ions, but from the perspective of obtaining a pavement with excellent strength, the content is preferably 0.125 parts by mass or more per 100 parts by mass of the total mass of aggregate contained in the paving mixture, more preferably more than 0.125 parts by mass, even more preferably 0.20 parts by mass or more, and even more preferably 0.25 parts by mass or more. If the amount of polysaccharide mixed per 100 parts by mass of aggregate is less than 0.125 parts by mass, the aggregate may not be sufficiently coated with the polysaccharide, which may result in a decrease in the adhesive strength of the aggregate.

[0031] In a preferred embodiment, the content of the aqueous solution of polysaccharides that form a gel upon contact with divalent or higher metal ions contained in the paving mixture of the present invention is not particularly limited. However, from the perspective of obtaining a pavement exhibiting excellent strength, the content is preferably 2.5 parts by weight or more, more preferably 3.5 parts by weight or more, and even more preferably 4.5 parts by weight or more, calculated as the amount of water contained in the aqueous solution per 100 parts by weight of the total aggregate contained in the paving mixture. In other words, when the polysaccharide is contained in the paving mixture of the present invention in the form of an aqueous solution, the content of water derived from the aqueous solution in the paving mixture is preferably 2.5 parts by weight or more, more preferably 3.5 parts by weight or more, and even more preferably 4.5 parts by weight or more, calculated as the amount of water contained in the aqueous solution per 100 parts by weight of the total aggregate. If the content of the aqueous solution is less than 2.5 parts by weight, calculated as the amount of water contained in the aqueous solution, the aggregates may not be sufficiently coated with the aqueous solution containing the polysaccharide, resulting in reduced adhesive strength between the aggregates.

[0032] On the other hand, from the viewpoint of obtaining a pavement exhibiting similarly excellent strength, the content of the aqueous solution is preferably 20 parts by weight or less, more preferably 15 parts by weight or less, even more preferably 12 parts by weight or less, and even more preferably 10 parts by weight or less, based on the amount of water contained in the aqueous solution per 100 parts by weight of aggregate contained in the paving mixture. In other words, when the polysaccharide is contained in the paving mixture of the present invention in the form of an aqueous solution, the content of water derived from the aqueous solution in the paving mixture is preferably 20 parts by weight or less, more preferably 15 parts by weight or less, even more preferably 12 parts by weight or less, and even more preferably 10 parts by weight or less, based on the total mass of aggregate per 100 parts by weight. As will be shown in the experimental examples described below, the inventors' findings indicate that if the content of the aqueous solution in the paving mixture is too high, based on the amount of water contained in the aqueous solution, the strength of the resulting pavement tends to be reduced. Although the reason for this is not entirely clear, it is presumed that if the water content of the aqueous solution contained in the paving mixture is too high, the amount of water contained in the paving mixture will be correspondingly high, and even if a curing agent containing divalent or higher metal ions is sprayed on the paving mixture after it has been spread and compacted, the sprayed divalent or higher metal ions will have difficulty penetrating into the paving mixture, resulting in insufficient adhesion of the aggregate within the paving mixture. In other words, it is not desirable for the amount of water contained in the paving mixture of the present invention to be too high, and it is preferable that the amount of water contained be 20 parts by weight or less, more preferably 15 parts by weight or less, even more preferably 12 parts by weight or less, and even more preferably 10 parts by weight or less, per 100 parts by weight of aggregate.

[0033] If necessary, the paving mixture of the present invention may be colored to a desired color by adding an appropriate pigment, such as titanium oxide, carbon black, zinc oxide, white lead, graphite, cadmium red, molybdenum orange, ferric hydroxide, iron oxide yellow, lead yellow, chromium oxide, chrome green, ultramarine, Prussian blue, cobalt blue, manganese violet, etc.

[0034] Furthermore, heat-shielding pigments and hollow particles can be added to the paving mixture of the present invention as needed. Any heat-shielding pigments used for paving can be used as the heat-shielding pigment. For example, those with a solar reflectance of 10% or more and an L* value of 80 or less in the CIE 1976 L*a*b* color space are preferred. When a heat-shielding pigment is incorporated into the paving mixture of the present invention, the resulting pavement effectively blocks radiant heat from the sun, effectively suppressing the heat island phenomenon, particularly in the summer. Furthermore, hollow particles can be used, such as ceramic balloons, glass balloons, shirasu balloons, and balloons made of resins such as polystyrene, with particle sizes of 10 to 125 μm, preferably 25 to 80 μm. The incorporation of these hollow particles into the paving mixture of the present invention offers the advantage of improving the heat-shielding effect of the resulting pavement due to their high thermal insulation, reflectivity, and irradiance.

[0035] <Pavement construction method> To construct a pavement using the paving mixture of the present invention, first thoroughly clean the road surface where the construction will be carried out. Then, the paving mixture of the present invention is spread evenly on the road surface by hand or machine, compacted, and then, at an appropriate time, a predetermined amount of hardener, i.e., a solution containing divalent or higher metal ions, is sprayed. The spraying of the solution containing divalent or higher metal ions hardens the binder, resulting in a hardened paving mixture layer. While there are no particular limitations on the thickness of the paving mixture layer, when fine aggregate is used as the aggregate, a layer thickness of 1 to 20 mm is generally preferred. Of course, thicker layers may be formed, in which case coarse aggregate with a larger particle size can be used. There are no particular restrictions on the amount of solution containing the hardener to be sprayed. For example, when using alginic acid as the polysaccharide and a 10% by mass aqueous solution of calcium chloride as the aqueous solution containing divalent or higher metal ions, it is preferable to use 10 to 1000 g, more preferably 20 to 500 g, and even more preferably 50 to 200 g per kg of aggregate in the paving mixture.

[0036] The paving mixture of the present invention quickly exhibits excellent strength after spraying the aqueous solution containing divalent or higher metal ions as a curing agent, making it particularly suitable for repairing road surfaces where early reopening to traffic is required, but it can also be used in a wide range of road construction projects, both new construction and repair. While the paving mixture of the present invention is of course applicable to general roads, it is not limited to general roads; it can also be used to pave roads such as expressways, campus roads, park roads, walking paths, bicycle paths, sports fields, parking lots, airports, port facilities, plazas and sidewalks attached to public halls, etc.

[0037] The paving binder and paving mixture of the present invention will be described in more detail below using experimental examples, but it goes without saying that the present invention is in no way limited by the following experimental examples.

[0038] <Experiment 1. Preparation of paving mixture> Sodium alginate (viscosity 200 cp or less, sold by Kouhara, Maikon Co., Ltd.) was dissolved in water at room temperature to prepare an alginic acid aqueous solution with an alginic acid concentration of 5% by mass. The resulting alginic acid aqueous solution exhibited moderate viscosity, making it easy to mix with aggregate and exhibiting good adhesion to the aggregate. The viscosity of the alginic acid aqueous solution was measured using a B-type viscometer (product name "Digital Viscometer DV-3T," manufactured by AMETEK Brookfield) according to standard methods, and was found to be 15,000 cp at 20°C. Next, No. 7 crushed stone (produced in Kasama City, Ibaraki Prefecture), fine sand (produced in Kasama City, Ibaraki Prefecture), and stone powder (calcium carbonate, sold by Ryoko Sekki Kogyo Co., Ltd.) were mixed according to the proportions shown in Table 1 below. To 100 parts by weight of the resulting mixture, 2.5 parts by weight, 5 parts by weight, 7.5 parts by weight, 10 parts by weight, 12.5 parts by weight, 15 parts by weight, or 20 parts by weight of the 5% by weight aqueous alginic acid solution prepared previously was added according to the blending amounts shown in Table 1, and the mixture was thoroughly mixed until the aggregate was sufficiently coated with the aqueous alginic acid solution, thereby obtaining paving mixtures (Test Samples 1 to 7) each containing a different amount of aqueous alginic acid solution. All of the above operations were performed at room temperature (approximately 20°C). In the following experiments, a cold asphalt mixture (product name "Rescue Patch (registered trademark)", sold by Nichireki Co., Ltd.) (hereinafter sometimes referred to as "Control Sample 1") using conventional cutback asphalt as a binder was used as a comparison.

[0039] [Table 1]

[0040] <Experiment 2. Marshall Stability Test - Part 1> Test specimens were prepared using the paving mixtures (test samples 1 to 7) obtained in Experiment 1, and their Marshall stability was measured. The Marshall stability was measured as follows, with some modifications to the Marshall stability test method described in the "Pavement Survey and Test Method Handbook," 2019 edition, pages 5 to 16 (Japan Road Association).

[0041] According to a conventional method, predetermined amounts of test samples 1 to 7 were placed into a mold and compacted a predetermined number of times using a Marshall hammer. Next, a 10% by mass aqueous solution of calcium chloride was sprayed onto the molded specimens of test samples 1 to 7 in the mold using a sprayer, with the amount of 100 g per kg of aggregate. Test samples 1 to 7 were removed from the mold, cured for three days, and then used as specimens for Marshall stability measurements. An example of a specimen obtained in this manner is shown in Figure 1. All of the above procedures were performed at room temperature (approximately 20°C). Incidentally, a specimen of control sample 1 was prepared in the same manner as above, except that the procedure of spraying calcium chloride aqueous solution after compaction was not performed.

[0042] The specimen obtained in this manner was placed on the lower of a pair of cylindrical loading heads with its cylindrical side horizontal, and then the upper loading head was placed on top and the specimen was set into the loading device. The specimen was sandwiched between the upper and lower loading heads and a load was applied in the diameter direction of the specimen, and the maximum load (kN) measured before the load began to decrease was taken as the Marshall stability. The results are shown in Table 2.

[0043] [Table 2]

[0044] As shown in Table 2, the Marshall stability of the specimens obtained from the paving mixtures (test samples 2 to 7) containing 5 parts by mass, 7.5 parts by mass, 10 parts by mass, 12.5 parts by mass, 15 parts by mass, or 20 parts by mass of 5% by mass alginic acid aqueous solution per 100 parts by mass of aggregate was 10.2 kN, 15.1 kN, 16.8 kN, 15.1 kN, 14.2 kN, or 11.9 kN, respectively. This was significantly higher than the Marshall stability of 2.8 kN for the control sample 1, a conventional cold asphalt mixture using cutback asphalt. On the other hand, the Marshall stability of the specimen obtained from the paving mixture (test sample 1) containing 2.5 parts by mass of 5% by mass alginic acid aqueous solution per 100 parts by mass of aggregate was only 0.6 kN, significantly lower than the Marshall stability of 2.8 kN for the specimen obtained from the control sample 1. The above results show that specimens obtained from paving mixtures containing 5 parts or more of a 5% by mass aqueous solution of alginic acid per 100 parts by mass of aggregate, in other words, 0.25 parts by mass (= 5 parts by mass x 0.05) or more of alginic acid, exhibit superior strength compared to specimens obtained from conventional cold asphalt mixtures.

[0045] On the other hand, when comparing the Marshall stabilities of the specimens obtained from test samples 2 to 7, the specimens obtained from test samples 3 to 6, in which the amount of 5% by mass alginic acid aqueous solution per 100 parts by mass of aggregate is 7.5 to 15 parts by mass, have a Marshall stability of 14 kN or more, and among them, the specimens obtained from test samples 3 to 5, in which the amount of 5% by mass alginic acid aqueous solution per 100 parts by mass of aggregate is 7.5 to 12.5 parts by mass, have a Marshall stability of 15 kN or more, and in particular, the specimen obtained from test sample 4, in which the amount of 5% by mass alginic acid aqueous solution per 100 parts by mass of aggregate is 10 parts by mass, has a Marshall stability of 16.8 kN, which is the largest. In other words, it shows that excellent Marshall stability can be obtained when the amount of 5% by mass alginic acid aqueous solution per 100 parts by mass of aggregate is preferably 7.5 to 15 parts by mass, more preferably 7.5 to 12.5 parts by mass. The amount of 5% by weight alginic acid aqueous solution per 100 parts by weight of aggregate is 7.5 parts by weight to 15 parts by weight, which corresponds to 0.375 parts by weight (= 7.5 parts by weight × 0.05) to 0.75 parts by weight (= 15 parts by weight × 0.05) or less, and 7.5 parts by weight to 12.5 parts by weight corresponds to 0.375 parts by weight (= 7.5 parts by weight × 0.05) to 0.625 parts by weight (= 12.5 parts by weight × 0.05) or less. Therefore, the above results, in other words, show that excellent Marshall stability can be obtained when the amount of alginic acid per 100 parts by weight of aggregate is preferably 0.375 parts by weight to 0.75 parts by weight, more preferably 0.375 parts by weight to 0.625 parts by weight.

[0046] These results were surprising to the inventors. If alginic acid were simply considered to function as a binder, increasing the amount of alginic acid aqueous solution in the paving mixture would increase the amount of alginic acid functioning as a binder, leading to stronger adhesion of the aggregates. However, the results shown in Table 2 indicate that the strength of the hardened paving mixture actually decreases when the amount of alginic acid exceeds a certain level. To investigate the cause of these results, we performed Marshall stability tests and then observed the interior of test specimens obtained using Test Sample 7. Surprisingly, in test specimens obtained using Test Sample 7, which contained a high amount of alginic acid aqueous solution, the aggregates were strongly bonded near the surface, but the adhesion of the aggregates was relatively weaker in the interior of the specimens. The reason for this difference in adhesive strength across locations is thought to be that the alginate contained in the binder quickly came into contact with the sprayed divalent or higher metal ions near the surface of the test specimen, causing rapid gelation, whereas the sprayed divalent or higher metal ions had difficulty penetrating into the interior of the test specimen, preventing complete gelation of the alginate. However, considering that the test specimens obtained using test samples 3 to 5, which contained a lower amount of alginate aqueous solution, the sprayed divalent or higher metal ions penetrated deep into the specimen and were fully hardened, it is believed that the moisture content of the test specimen itself is what is preventing the divalent or higher metal ions from fully penetrating into the specimen. In other words, if the amount of alginate aqueous solution relative to the aggregate contained in the paving mixture is too high, resulting in too much moisture in the paving mixture, the sprayed divalent or higher metal ions may not fully penetrate the interior of the test specimen, preventing the alginate from fully gelling and resulting in insufficient hardening.Considering this reasonably reasonable assumption, and the fact that the specimen obtained using test sample 7 also had a Marshall stability of over 10 kN, greater than that of control sample 1, it is concluded that the amount of moisture contained in the paving mixture should preferably be 19 parts by mass or less per 100 parts by mass of aggregate, which is the moisture content of the paving mixture for test sample 7, and more preferably 15 parts by mass or less, which includes the moisture content of 14.25 parts by mass of the paving mixture for test sample 6.

[0047] <Experiment 3. Marshall Stability Test - Part 2> Next, in order to obtain information on the strength immediately after construction of pavements constructed using the paving mixture according to one embodiment of the present invention, a Marshall stability test was conducted in the same manner as in Experiment 2, except that the curing time was changed from 3 days to 30 minutes. The results are shown in Table 3.

[0048] [Table 3]

[0049] As shown in Table 3, the Marshall stability of the specimens obtained from the paving mixtures (test samples 2 to 7) containing 5 parts by weight, 7.5 parts by weight, 10 parts by weight, 12.5 parts by weight, 15 parts by weight, or 20 parts by weight of 5% by weight alginic acid aqueous solution per 100 parts by weight of aggregate was already increased to 9.0 kN, 13.0 kN, 7.4 kN, 4.6 kN, 4.4 kN, or 3.3 kN after 30 minutes of curing. This was significantly higher than the Marshall stability of the specimen obtained from control sample 1, which was a conventional room temperature asphalt mixture using cutback asphalt, at 0.9 kN, and was also higher than the Marshall stability of the specimen obtained from control sample 1, which was 2.8 kN after 3 days of curing (Table 2). These results, just as with the case of three-day curing, show that specimens obtained from paving mixtures containing 5 parts or more of a 5% by mass aqueous solution of alginic acid per 100 parts by mass of aggregate, in other words, 0.25 parts by mass (= 5 parts by mass x 0.05) or more of alginic acid, exhibit the desired strength at a speed far exceeding that of specimens obtained from conventional room-temperature asphalt mixtures.

[0050] Furthermore, considering that the Marshall stability of the specimen obtained from Test Sample 3, which contained 7.5 parts by weight of 5% alginic acid aqueous solution per 100 parts by weight of aggregate, peaked at 13.0 and gradually decreased as the amount of alginic acid aqueous solution was increased, it is clear that, for the same reasons as discussed in Experiment 2, there is an optimum moisture content for the paving mixture, even when the curing period is relatively short (30 minutes).The results in Table 3 indicate that the upper limit of moisture content for the paving mixture is preferably 19 parts by weight or less, which is the moisture content of Test Sample 7, more preferably 15 parts by weight or less, which includes the moisture content of Test Sample 6 (14.25 parts by weight), more preferably 12 parts by weight or less, which includes the moisture content of Test Sample 5 (11.875 parts by weight), and even more preferably 10 parts by weight or less, which includes the moisture content of Test Sample 4 (9.5 parts by weight). On the other hand, from the results of Table 3, it is determined that the lower limit of the moisture content in the paving mixture is preferably 2.5 parts by mass or more per 100 parts by mass of aggregate, which is higher than the moisture content of the paving mixture of test sample 1, which is 2.375 parts by mass, more preferably 3.5 parts by mass or more, and even more preferably 4.5 parts by mass or more, which includes the moisture content of the paving mixture of test sample 2, which is 4.75 parts by mass.

[0051] <Experiment 4. Examination of polysaccharides other than alginic acid> LM pectin (product name: UNIPECTIN) is a polysaccharide that is generally used as a gelling agent instead of alginic acid as a binder. It forms a gel when it comes into contact with divalent or higher metal ions, just like alginic acid. TM OF 100C" sold by Unitec Foods Co., Ltd.), or carrageenan (kappa type) (product name "SATIAGEL"), which is also a polysaccharide commonly used as a gelling agent but which, in contrast to alginic acid and LM pectin, exhibits the property of forming a temperature-dependent gel. TMTest Sample 8 and Comparative Sample 1 were prepared in the same manner as Test Sample 3 in Experiment 1, except that "ME22" (sold by Unitec Foods Co., Ltd.) was used. Using the obtained Test Sample 8 and Comparative Sample 1, a 10% by mass aqueous solution of calcium chloride was sprayed onto the molded products of Test Sample 8 to Comparative Sample 1 in the same manner as described in Experiment 2, using a spray bottle, at a rate of 100 g per kg of aggregate, to prepare test specimens, and their Marshall stability was evaluated. The results are shown in Table 4. For comparison, Table 4 also shows the Marshall stability of the test specimens obtained using Test Sample 8 and Comparative Sample 1, along with the Marshall stability of the test specimen obtained using Comparative Sample 1, as transcribed from Table 2.

[0052] [Table 4]

[0053] As shown in Table 4, the Marshall stability of the specimen obtained from test sample 8, which used an LM pectin aqueous solution as the binder, was 3.8 kN after three days of curing, which was significantly greater than the 2.8 kN Marshall stability of the specimen obtained from a conventional cold asphalt mixture using cutback asphalt as the binder. This result demonstrates that even when using LM pectin, which is a polysaccharide that, like alginic acid, has the property of gelling when it comes into contact with divalent or higher metal ions, it is possible to obtain excellent Marshall stability that is equal to or better than that of conventional cold asphalt mixtures.

[0054] In contrast, the Marshall stability of the specimen obtained using Comparative Sample 1, which used an aqueous carrageenan solution as the binder, was 0.0 kN, and its strength was extremely low. This result is presumably due to the fact that when carrageenan, which has the property of gelling temperature-dependently, i.e., when temperature drops, is used as the binder, when the mixture and specimen are prepared at room temperature, as reproduced in this experiment, the carrageenan binder gels before the aggregate and binder are sufficiently mixed together, and the aggregate is not sufficiently bonded.

[0055] <Experiment 5. Evaluation of workability - Part 1> Next, the following test was conducted to obtain information regarding the workability of paving mixtures according to one embodiment of the present invention. First, 1000 g of any of test samples 2 to 4 prepared in Experiment 1 was placed in a cylindrical container (product name "Small Tenkirikan" manufactured by Kondo Can Co., Ltd.) with a diameter of 8.5 cm and a depth of 10.8 cm and cured at 20°C. Then, using a push-pull gauge (product name "RX-50" manufactured by Aiko Engineering Co., Ltd.), a needle was pierced vertically into the paving mixture in the container for 2 to 3 cm at a speed of approximately 1 cm / 5 s. The measured penetration resistance (N) was defined as the penetration rate. A high penetration rate means that a large force is required to pierce the paving mixture, which means that a large force is required to handle the paving mixture, i.e., poor workability. On the other hand, a low penetration rate means that a small force is required to pierce the paving mixture, which means that a small force is required to handle the paving mixture, which means good workability. The penetration values ​​obtained are shown in Table 5.

[0056] [Table 5]

[0057] As shown in Table 5, at a temperature of 20°C, the penetration strengths of the paving mixtures (test samples 2 to 4) containing 5 parts, 7.5 parts, or 10 parts by weight of 5% by weight alginic acid aqueous solution per 100 parts by weight of aggregate were 11.8N, 11.8N, and 10.8N, respectively. These were significantly smaller than the penetration strength of 29.4N of control sample 1, a conventional cold asphalt mixture using cutback asphalt as a binder. These results demonstrate that paving mixtures using polysaccharides, such as alginic acid, as a binder, which gel when in contact with divalent or higher metal ions, have excellent workability at room temperature of around 20°C.

[0058] <Experiment 6. Evaluation of workability - Part 2> Next, to evaluate the workability of the paving mixture according to one embodiment of the present invention at even lower temperatures, the penetration of test samples 2 to 4 and control sample 1 was measured in the same manner as in Experiment 5, except that the curing temperature was changed from 20°C to 0°C. The results are shown in Table 6.

[0059] [Table 6]

[0060] As shown in Table 6, the penetration strengths at 0°C of paving mixtures (test samples 2 to 4) containing 5, 7.5, or 10 parts by weight of 5% alginic acid aqueous solution per 100 parts by weight of aggregate were 9.8N, 7.8N, or 9.8N, respectively, which were almost unchanged from the penetration strengths at 20°C. These results indicate that paving mixtures using polysaccharides, such as alginic acid, as binders, which gel upon contact with divalent or higher metal ions, have excellent workability even at low temperatures of around 0°C. In contrast, the penetration strength at 0°C of a conventional cold asphalt mixture using cutback asphalt as a binder was 83.3N, approximately three times higher than the penetration strength at 20°C. These results indicate that conventional cold asphalt mixtures using cutback asphalt as a binder exhibit a significant deterioration in workability at low temperatures of around 0°C.

[0061] As described above, paving mixtures that use polysaccharides, such as alginic acid, as binders that have the property of gelling when they come into contact with divalent or higher metal ions are not only easy to apply at temperatures of around 20°C, but also have excellent workability even in low-temperature environments such as those expected in winter or cold regions. [Industrial Applicability]

[0062] The paving binder or paving mixture of the present invention can be applied at room temperature or lower, which offers the advantage of greatly facilitating application in winter or cold regions. Furthermore, the paving binder or paving mixture of the present invention can produce pavements that exhibit excellent strength in a relatively short time after application, thereby shortening the time from application to opening to traffic, making the present invention highly applicable industrially. Furthermore, the paving binder or paving mixture of the present invention uses natural polysaccharides as the main binder component, enabling the construction of pavements that exhibit excellent strength without the need for petroleum resources, and is therefore believed to contribute greatly to the creation of a sustainable society.

Claims

1. 1. A paving mix comprising aggregate and a binder, The binder does not contain asphalt and contains a polysaccharide that forms a gel when it comes into contact with divalent or higher metal ions, and the polysaccharide is one or more selected from alginic acid, low-methoxylated pectin, gellan gum, carboxymethylcellulose, and derivatives thereof.

2. 2. The paving mixture according to claim 1, wherein the content of said polysaccharides per 100 parts by mass of said aggregate is 0.125 parts by mass or more.

3. 3. A paving mixture according to claim 1 or 2, characterized in that the polysaccharide is contained in the form of an aqueous solution.

4. 4. The paving mixture according to claim 3, wherein the content of said aqueous solution is 20 parts by mass or less in terms of the water content of said aqueous solution per 100 parts by mass of said aggregate.

5. A paving binder for use in paving mixtures, which does not contain asphalt and contains a polysaccharide that forms a gel when it comes into contact with a divalent or higher metal ion, wherein the polysaccharide is one or more selected from the group consisting of alginic acid, low-methoxylated pectin, gellan gum, carboxymethylcellulose, and derivatives thereof.

6. 6. The paving binder of claim 5, wherein the polysaccharide is contained in the form of an aqueous solution.

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