JPS6126944B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an asphalt mixture for paving, particularly an asphalt mixture for road paving, which has excellent flow resistance and water resistance. Roads paved with conventional heated paving mixtures consisting of crushed stone, sand, filler, and straight asphalt are prone to plastic flow and ruts caused by vehicle traffic, especially during periods of high road surface temperature. It had the disadvantage of being easy. On roads where ruts have occurred, the steering wheel is easily removed while the vehicle is running, and rainwater tends to accumulate, causing slips and handroplaning, reducing traffic safety.
Furthermore, there is a problem of water splashing onto roadside passersby and houses, so there is a desire for an asphalt mixture for paving that is less likely to cause ruts, that is, has greater flow resistance. In addition, in recent years, permeable asphalt mixtures have been used to secure underground water sources and protect vegetation, and open-grained asphalt mixtures have been used to prevent vehicles from slipping. These mixtures have many voids and are easy to contact with water. Additionally, mixtures on roads with poor drainage often come into contact with water. Conventional straight asphalt mixtures tend to cause delamination between the aggregate and asphalt when they come into contact with water.
As a result, roads are damaged. Therefore, it is also desired to improve the water resistance of asphalt mixtures for paving. In order to improve these drawbacks, modified asphalt mixtures to which various synthetic resins are added have been proposed. These modified asphalts are classified into premix type and plant mix type depending on the method of adding resin. The premix type refers to the poor compatibility between asphalt and resin, so a mixed solution of these is prepared in advance in special equipment or a dedicated factory, and then this is done on the premises of a paving mixture plant to mix aggregate and asphalt. It is supplied to a dedicated tank and the final mixture is produced in this paving mixture plant. The plant mix type is one in which when producing an asphalt mixture in a pavement mixing plant, a modified resin is added directly into the mixer to produce the modified asphalt mixture. This plant mix type does not require the above-mentioned dedicated tank in a pavement mixture plant, and can be stored with just the modifier, so it can be stored for a relatively long period of time. Furthermore, it has the advantage that the amount added can be adjusted according to the specifications of each pavement site, and that it is well suited for small-scale construction work, such as when using a modified asphalt mixture only at intersections. However, the modified resin used in this method must have good compatibility with asphalt and must be able to be mixed uniformly in a short time in the mixer of a paving mix plant. In order to increase the flow resistance of asphalt mixtures for pavement, thermoplastic resins such as ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), and styrene-butadiene rubber (SBR) are added to asphalt. However, since these methods add already polymerized materials, they have poor compatibility with asphalt, and a premix type must be used.
In order to use these as a plant mix type, it was necessary to take steps such as emulsifying the resin or pulverizing the resin and pre-mixing the filler. Instead of adding the above-mentioned resins, several methods of adding urethane resins have been attempted. For example, there is a method (Japanese Patent Publication No. 51-41135) that uses a polybutadiene-based urethane oligomer that has good compatibility with asphalt. In this method, the resin molecules simply exist in the asphalt in a dispersed state, and no crosslinking reaction occurs between the asphalt and the resin molecules, and the modification principle and modification effect are comparable to those of the thermoplastic resin described above. . A method of adding a thermosetting urethane prepolymer has also been proposed (Japanese Patent Application Laid-Open No. 57-38853, Japanese Patent Publication No. 43-22319). These methods use a prebutadiene urethane polymer containing an isocyanate group at the end or a polydiene urethane elastomer that is mixed with asphalt in a partially cured state.
mix in an actual paving mix plant.
When producing at a high temperature such as 140 to 170°C, there is a problem that the usable time of the produced mixture is shortened. In other words, during normal road paving, the plant
It takes 2 to 4 hours to produce a mixture at 140 to 170°C, transport it by truck while still at high temperature, pave it on site, and complete compaction. During this time, if the asphalt, which is the binder of the mixture, and the added resin react and thicken significantly, the workability during paving will be affected, making it impossible to obtain a flat road surface, and insufficient compaction through rolling work. There are disadvantages such as the road becoming less durable. The present inventors have found that the flow resistance at high temperatures is high, yet the brittleness and flexibility at low temperatures are not impaired, the adhesion between the aggregate and the binder is good, and the water resistance is good. The purpose of the present invention is to provide a modified asphalt mixture that satisfies the requirements such as being a plant mix type that can be directly added in a pavement mixture plant, and has workability equivalent to that of a heated asphalt mixture for pavement using conventional straight asphalt. As a result of intensive research aimed at achieving this goal, we have arrived at the present invention. The asphalt mixture for pavement of the present invention is an asphalt mixture in which a urethane prepolymer formed from a polyol and a diisocyanate and having an isocyanate group at the end of a branched structure molecule is added, and the raw material polyol is a polyoxyalkylene polyol and A mixed polyol containing polybutadiene polyol is used, and the mixing ratio of polyoxyalkylene polyol and polybutadiene polyol is within a range of 20 to 80% by weight of the polyoxyalkylene polyol in the raw material polyol, and the hydroxyl value of the mixed polyol is 20
The range is from 250 mmHgKOH/g,
The present invention is characterized in that methylene bisphenyl diisocyanate, tolylene diisocyanate, or a mixture thereof is used as the raw material isocyanate. The polyoxyalkylene polyol in the raw material polyol is ethylene glycol, propylene glycol, glycerin, trimethylolpropane, bisphenol A, which has two or more active hydrogen groups.
etc., by adding ethylene oxide, propylene oxide, etc. as alkylene oxide,
These include ethylene oxide additives and propylene oxide additives having two or more hydroxyl groups. Polybutadiene polyol is a polybutadiene having two or more hydroxyl groups at the end of the molecule, and specific examples include polyBDR-45HT and polyBD-
CS-15 (all made by ARCO), NISSO-PB
There are G1000, G2000, G3000 (all manufactured by Nippon Soda), etc. Unlike conventional asphalt mixtures in which resins are simply mixed, the present invention combines a urethane prepolymer, which is a modifier, with asphalt, thereby exhibiting excellent effects not previously available. be. That is, the urethane prepolymer used in the present invention has an isocyanato group at the end of a branched structure molecule, and this isocyanato group is a group having active hydrogen present in asphalt, such as a hydroxyl group, an amino group, and a carboxyl group. , reacts with functional groups such as phenolic hydroxyl groups. The molecules in asphalt have a complex skeletal structure, and the above functional groups present as terminals or side chains react with the isocyanato groups in the urethane prepolymer to form urethane bonds, creating a three-dimensional network structure. urethane resinized asphalt is produced. The urethane prepolymer becomes a thermosetting molecule through the above reaction, and because of this structure, the modified asphalt is resistant to plastic deformation and has elastic properties. The urethane prepolymer used in the present invention uses a mixture of polyoxyalkylene polyol and polybutadiene polyol as the raw material polyol, and has a hydroxyl value of 20 to 240 mgKOH/g as the raw material polyol that is the combination of the above two types of polyols.
Blend so that If the hydroxyl value of the raw material polyol is less than this, the strength of the modified binder will be low and the effect of improving rutting will be small. If the amount is more than this, the modified binder becomes too hard and becomes brittle at low temperatures. Therefore, when added to an asphalt mixture, the mixture has a low cold bending strength, does not go below the brittle point, and becomes a road that is susceptible to cracking. Furthermore, when mixed with asphalt, the viscosity increases significantly, resulting in a mixture with poor workability on site. As the raw material diisocyanate, methylene bisphenyl diisocyanate, tolylene diisocyanate, or a mixture thereof is used, and the urethane prepolymer is blended so that the terminal isocyanate group is usually contained in an amount of 1 to 20% by weight, preferably 3 to 15% by weight. . That is, the raw material diisocyanate is blended so that the number of isocyanato groups is greater than the number of hydroxyl groups in the raw material polyol, so that unreacted isoyanato groups remain in the polymer produced after the polymerization reaction. Therefore, the blending ratio of the raw material polyol and the raw material diisocyanate is determined so that the content of isocyanate groups in the produced urethane prepolymer falls within the above range. If the number of isocyanato groups is less than the above range, the amount of bonding with asphalt molecules will be insufficient and the formation of a network structure will not be sufficient, so that the flow resistance will not be sufficiently improved. If the number of isocyanato groups is more than this, the flow resistance becomes too high and workability during paving work becomes poor. The amount of urethane prepolymer added to asphalt is usually in the range of 1 to 10% by weight, and if it is less than this, it is difficult to mix the additive uniformly with a mixer in a conventional pavement mix plant due to its mixing performance. No effect is obtained, and even if a larger amount is added, it is meaningless since the flow resistance is already sufficiently high. In general, increasing flow resistance impairs brittleness and flexibility, making cracks more likely to occur at low temperatures. The present inventors conducted various studies to solve this problem, and as a result, discovered that the brittleness and flexibility of modified asphalt at low temperatures could be improved by using polyoxyalkylene polyol as the raw material polyol, and Furthermore, it has been found that the increase in viscosity of the asphalt mixture due to the reaction of the prepolymer at high temperatures can be appropriately suppressed, and workability during paving can also be improved. However, when a polyoxyalkylene polyol is used alone, the compatibility between the produced urethane prepolymer and asphalt is low, and there is a problem in creating a plant mix type in which a modifier is added in an existing pavement mixture plant. Therefore, as a result of further studies, it was discovered that compatibility can be improved by using polybutadiene polyol as a raw material polyol, and that it can be uniformly dissolved in a short time even in existing pavement mixture plants. By using a mixture of preoxyalkylene polyol and polybutadiene polyol as the raw material polyol, it was possible to further improve the water resistance of the modified asphalt. Conventional asphalt mixtures, especially when using hydrophilic aggregates,
Since asphalt molecules are hydrophobic, they are difficult to adhere to the hydrophilic aggregate surface, and water easily enters and adsorbs to the interface between the aggregate and asphalt, causing a peeling phenomenon. Since hydrophilic polyoxyalkylene polyol and lipophilic polybutadiene polyol are present in the urethane prepolymer used in the present invention,
The polyoxyalkylene polyol molecule side is oriented to the aggregate and strongly adheres to it, and the polybutadiene polyol molecule side is oriented to asphalt, and the terminal isocyanate groups react sterically to form a strong urethane-resinated asphalt on the surface of the aggregate. It is thought that the formation of a film makes it difficult for water to penetrate into the surface of the aggregate, thereby preventing peeling and improving water resistance. The ratio of polyoxyalkylene polyol to polybutadiene polyol is usually in the range of 20 to 80% by weight of polyoxyalkylene polyol in the raw material polyol. If the amount is less than this, the brittleness and flexibility at low temperatures will not be sufficiently improved, and the reaction rate will be rapid and the viscosity will increase significantly when used at high temperatures, impairing the workability of a mixture using this as a binder. If the amount is more than this, the compatibility between the urethane prepolymer and asphalt will deteriorate. Also,
Outside this range, the effect of improving water resistance decreases. The raw material diisocyanate for the urethane prepolymer used in the present invention is methylene bisphenyl diisocyanate, tolylene diisocyanate, or a mixture thereof, and the urethane prepolymer made from these materials has a moderate amount of asphalt under conventional heated asphalt mixture production conditions. It has a high reaction rate. The heated asphalt mixture is mixed with molten asphalt and aggregate in a paving mix plant, and is transported to the paving site and applied after up to 3 to 4 hours. The modified asphalt mixture produced in the paving mixture plant must therefore maintain its workability over this period. As mentioned above, this workability is improved by using polyoxyalkylene polyol as the raw material polyol, but the reaction rate between asphalt and urethane prepolymer also differs depending on the type of raw material diisocyanate, and in the case of the above diisocyanate. At the normal asphalt mixture heating temperature, the reaction with asphalt proceeds gradually, the modified asphalt mixture does not harden rapidly or increase in viscosity, and the inherent workability of asphalt is not impaired. Therefore, the modified asphalt mixture of the present invention can be paved in the same manner as conventional heated asphalt mixtures without requiring special paving techniques. In order to cause the urethane prepolymer and asphalt to react, it is desirable to hold the temperature at 100°C or higher for 30 minutes or more, but asphalt mixtures for paving
Except for emulsionized or cut-back cold paving asphalt mixtures, always
It is manufactured by heating the asphalt above ℃ and is applied before it cools down in a molten state, and the urethane prepolymer as a modifier is added at least at the time of mixing in the pavement mixture plant or before that, so the above-mentioned The conditions are necessarily met and no special new heating operation is required to produce the modified asphalt mixture for paving according to the invention. Typically, mixing in paving mix plants is between 120 and 180°C.
It is carried out within the range of This is because asphalt has low fluidity at temperatures below this, and asphalt thermally decomposes at temperatures above this. The urethane prepolymer used in the present invention has good compatibility with asphalt, so it can be used as a plant mix type, but since it does not harden rapidly or increase in viscosity after being added, it can be used as a premix type, which is mixed with asphalt in advance. You can also. Examples of the present invention are shown below. Example 1 Polypropylene glycol (PPG) (average molecular weight approximately 3000, hydroxyl value 37.5 mgKOH/g) and polybutadiene polyol (polyBD) (average molecular weight approximately
2800, hydroxyl value 46.6mgKOH/g) mixing ratio 50 pairs
50 (weight ratio) of polyol and methylene bisphenyl diisocyanate (MDI) or tolylene diisocyanate (TDI) and having 3 to 15% by weight of terminal isocyanate groups, 1 to 10% by weight of asphalt. %
A doped paving asphalt mixture was produced. The aggregate particle size of the mixture is "20 mm dense particle size Ascon" as shown in the Asphalt Pavement Guidelines (Japan Road Association). First, crushed stone, sand, and filler mixed to this particle size are heated to 175 °C and then penetrated. A heated asphalt mixture for pavement was prepared by adding 60 to 80 grade straight asphalt and further adding and mixing the various urethane prepolymers described above. The amount of binder in each mixture was 5.0% by weight. In order to investigate the flow resistance of this mixture, test specimens were prepared by compacting with a roller compactor and heated to 60°C.
A foil tracking test was conducted. For comparison, a straight asphalt mixture with no added wood and SBR, which is currently commonly used.
Similar tests were conducted on mixtures with added latex. The results are shown in Table 1. In addition,
The amount of binder in each mixture was 5.0% by weight. These results show that the mixture containing urethane prepolymer had smaller foil tracking deformation and deformation rate, increased dynamic stability, and clearly improved flow resistance compared to the comparative mixture. I understand. Further, the workability of the mixture to which the urethane prepolymer was added was no different from that of the straight asphalt mixture. Example 2 Polypropylene glycol (PPG) (average molecular weight approximately 3000, hydroxyl value 37.5 mgKOH/g) and polybutadiene polyol (polyBD) (average molecular weight approximately 3000, hydroxyl value 37.5 mgKOH/g)
2800, hydroxyl value 46.6 mgKOH/g) and a polyol with a mixing ratio (weight ratio) of 100:0 to 0:100 and methylene bisphenyl diisocyanate (MDI) or tolylene diisocyanate (TDI). 1 to 10% by weight of urethane prepolymer to asphalt.
A paving asphalt mixture with wt.% loading was prepared. The aggregate particle size of the mixture and the method for preparing the heated asphalt mixture for pavement are the same as in Example 1. In order to examine the brittleness and flexibility of this mixture at low temperatures, a test specimen was prepared using a roller compactor in the same manner as in Example 1, and was
It was cut to 300 mm and subjected to a bending test from -10°C to +20°C using a central loading method with a span of 230 mm. Prior to this, in order to investigate the compatibility of various urethane prepolymers with asphalt, the mixing situation after addition of the urethane prepolymers was observed. For comparison, a bending test was also conducted on a straight asphalt mixture (mixture number 19). The results are shown in Table 2. Note that the amount of binder in each mixture was 5.0% by weight. From this result, when the mixing ratio of polypropylene glycol and polybutadiene polyol in the raw material polyol is 80:20 to 20:80 by weight, and the amount of urethane prepolymer added is 1% or more, the bending strength and breaking strain increase. However, it is clear that the embrittlement point is lowered. In other words, it can be said that a mixture to which a urethane prepolymer is added is less likely to become brittle than a straight asphalt mixture, and can maintain flexibility even at low temperatures. In addition, a mixture that does not contain polypropylene glycol and contains only polybutadiene polyol (mixture number 18) has normal workability immediately after production, but assuming the actual on-site construction time, it was stored at 150°C for 3 hours. Otherwise, the mixture will harden and workability will deteriorate significantly. In addition, the adhesiveness of the binder is low, resulting in poor rolling effect and resulting in a specimen with low density. On the other hand, the workability of the composition of the present invention and the finish of the specimen under the same conditions were as good as when no urethane prepolymer was added (mixture number 19). Example 3 Polypropylene glycol (PPG) (average molecular weight approximately 3000, hydroxyl value 37.5 mgKOH/g) and polybutadiene polyol (polyBD) (average molecular weight approximately
2800, hydroxyl value 46.6mgKOH/g) mixing ratio 50 pairs
An asphalt mixture for paving is prepared by adding 1 to 10% by weight of a urethane prepolymer having 10% by weight of terminal isocyanate groups, which is produced from a polyol of 50 (weight ratio) and methylene bisphenyl diisocyanate (MDI), to the asphalt. Example 1
Manufactured in a similar manner. The aggregate particle size of the mixture in this example was set to ``13 mm open particle size Ascon'' as indicated in the asphalt pavement guidelines, which has many voids and is easily affected by water. The amount of binder (straight asphalt + resin) is
The amount added was determined so that the voids in the mixture would be 8%. In order to investigate the peeling resistance and water resistance of this mixture, a standard marshall stability test and a water immersion marshall stability test were conducted. For comparison purposes, similar tests were conducted on a straight asphalt mixture to which no resin was added and a mixture to which SBR latex, which is commonly used at present, was added. This result is shown in Table 3.
It was shown to. Note that the amount of binder in each mixture was 4.2% by weight. From these results, it is clear that the mixture to which the urethane prepolymer was added has increased residual stability as well as increased mechanical stability and flow, and has improved water resistance, compared to the comparative mixture. The reason why the residual stability of mixtures No. 21 and 22 in Table 3 exceeds 100% is because unreacted isocyanate groups remain in the asphalt even after specimen preparation, and these react and polymerize during 48 hours of water immersion. , it is thought that the stability increased as a result of it becoming a stronger binder. This also shows that the urethane prepolymer and asphalt react gradually and do not suddenly harden upon addition. Example 4 A urethane prepolymer having 7.0% by weight of terminal isocyanate groups produced from polyoxyalkylene polyols with various hydroxyl values, polybutadiene polyol (polyBD), and tolylene diisocyanate (TDI) was added to asphalt in an amount of 5% by weight. A paving asphalt mixture was produced. This mixture is
After storing at 150°C for 3 hours, foil tracking specimens and bending test specimens were prepared. Table 4 shows the workability, foil tracking test results, and bending test results of this mixture. From this result, the hydroxyl value of the polyol is 20 mg.
The mixture containing urethane prepolymer of KOH/g or less (mixture number 25) is sticky during operation, has poor workability, and has low flow resistance. In addition, mixtures containing urethane prepolymers with a hydroxyl value of 250 mgKOH/g or more have the drawbacks of high binder viscosity, difficulty in working at normal temperatures, small increase in density due to compaction work, and high brittleness points, making them prone to cracking. It turns out that it has. In addition, each test method in the examples is based on the asphalt pavement guidelines.

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Claims (1)

[Scope of Claims] 1. An asphalt mixture in which a urethane prepolymer formed from a polyol and a diisocyanate and having an isocyanate group at the end of a branched structure molecule is added, wherein the raw material polyol is a polyoxyalkylene polyol and a polybutadiene polyol. using a mixed polyol in which the mixing ratio of polyoxyalkylene polyol and polybutadiene polyol is in the range of 20 to 80% by weight of the polyoxyalkylene polyol in the mixed polyol, and the hydroxyl value of the mixed polyol is 20 to 80%.
250 mgKOH/g, asphalt mixture for paving, characterized in that methylene bisphenyl diisocyanate, tolylene diisocyanate, or a mixture thereof is used as the raw material diisocyanate. 2. The asphalt mixture for paving according to claim 1, wherein the urethane prepolymer is added to a heated mixture of asphalt and aggregate. 3. The asphalt mixture for paving according to claim 1, wherein the urethane prepolymer is added to asphalt in advance and mixed with heated aggregate. 4. The asphalt mixture for paving according to any one of claims 1 to 3, wherein the urethane prepolymer is added in an amount of 1 to 10% by weight of asphalt as a binder. 5. The asphalt mixture for paving according to any one of claims 1 to 4, wherein the urethane prepolymer has 3 to 15% by weight of isocyanate groups at the ends of branched structure molecules. 6. The asphalt mixture for paving according to any one of claims 1 to 5, wherein the temperature of the mixture is 100°C or higher.