ASPHALT COMPOSITION

Field of the Invention

This invention relates to an asphalt composition that is well-suited to applications such as road

pavement, waterproof materials, and adhesives, and is particularly well-suited to improving stability and strength .

Background of the Invention

Asphalt is conventionally used in a wide range of fields, including road pavement and waterproofing. This asphalt often uses styrene-butadiene-styrene copolymer

(SBS) as a reinforcing material. However, SBS loses stability when distributed in the asphalt. Particularly with regard to the storage temperatures associated with industrial applications (150°C to 180°C) , there are problems with the SBS rapidly separating from the asphalt and rising to the surface.

Because of this situation, when SBS is mixed into asphalt as a reinforcing material, stabilisers have been added in order to stabilise the SBS within the asphalt. Conventionally such stabilisers have included substances such as, for example, ^' sulphur, polyoxyethylene

nonylphenol, peroxide, carbon black, and aromatic oil.

However, the addition of sulphur as a stabiliser is associated with the risk of generating hydrogen sulphide. Polyoxyethylene nonylphenol is an environmental hormone the use of which should be avoided (for example, see JP 2000-53865) , and the handling of organic peroxides at high temperatures is associated with the risk of

degradation and explosion. Carbon black is expensive in comparison to asphalt, and its use poses a stumbling block in supplying asphalt products for the market (for example, see JP 10-237309) . The addition of aromatic oil can improve stability by dissolving styrene blocks in SBS, but this means the loss of desirable improvements in elasticity that could come from the presence of those styrene blocks, and that in turn makes it difficult to obtain the anticipated level of strength in asphalt products .

For some time, there has been increasing demand for technology that would improve both the stability and the strength of asphalt compositions.

The present invention was conceived in response to the problems described above, and its objective is to provide an asphalt composition that is suitable for use in substances such as road pavement, waterproof

materials, and adhesives, and particularly an asphalt composition that can offer both improved stability and improved strength.

Summary of the Invention

Accordingly, the present invention provides an asphalt composition comprising a styrene-butadiene- styrene copolymer (SBS) and a 20-carbon polycyclic diterpene having a carboxyl group, with the remainder of the composition consisting of asphalt, wherein after storage stability testing, the difference absolute value between upper-level softening temperature and lower-level softening temperature does not exceed 3°C, and the DS value is 6300 or above.

By providing an asphalt composition that contains a styrene-butadiene-styrene copolymer (SBS) and a 20-carbon polycyclic diterpene having a carboxyl group, with this asphalt composition showing a difference absolute value between upper-level softening temperature and lower-level softening temperature of no more than 3°C after storage stability testing, the present invention makes it

possible to simultaneously achieve improved storage stability and improved strength (DS value of 6300 or above) .

Brief description of the Drawings

Figure 1 illustrates the relationship between the modulus of elasticity G* for the wavelength angular frequency ω of this asphalt composition and the loss tangent (tanδ) .

Figure 2 shows a schematic perspective view of the measurement portion of the dynamic viscoelasticity tester.

Figure 3 is provided to explain the details of the method for measuring DS values.

Figure 4 shows an example of the settlement (mm) seen for testing time (minutes) , using the starting time for DS value measurement testing as the reference point. Detailed description of the Invention

Below will be provided a detailed explanation of the asphalt composition and its manufacturing method to provide optimal morphological characteristics for the implementation of this invention.

The authors of the present invention experimented earnestly in their research to produce an asphalt composition that would resolve the problems described above and provide the desired level of stability and strength. As a result, these researchers found that through the addition to asphalt of styrene-butadiene- styrene copolymer (SBS) and a 20-carbon polycyclic diterpene with carboxyl group (resin acid) , it was possible to stabilize the product, with no separation of asphalt and SBS, and ^' also to improve the strength of the asphalt composition. Specifically, with the mixture of SBS and resin acid, it was discovered that bonding can occur between a 20-carbon polycyclic diterpene having a carboxyl group and a double bond comprising a butadiene block. This releases any mutual aggregation among styrene blocks, making it possible to improve the stability of the asphalt composition.

That is to say, the asphalt composition of this invention preferably comprises from 2 wt% to 8 wt% of styrene-butadiene-styrene copolymer (SBS) and preferably comprises from 0.3 wt% to 3 wt% of 20-carbon polycyclic diterpene having a carboxyl group (resin acid) , where the weight percentages are based upon the weight of the asphalt composition. The remainder of the asphalt

composition of this invention consists of asphalt. Here the term "asphalt" indicates one element of the asphalt composition of this invention, and that is first formed into the asphalt composition of this invention through the addition of SBS and resin acid.

The styrene-butadiene-styrene copolymer (SBS) is added to the asphalt as a thermoplastic elastomer. This SBS shows little loss of physical strength in areas such as kinematic viscosity and in coefficient for storage elastic shear modulus for degradation of the asphalt composition at manufacturing temperatures, utilization temperatures, and processing temperatures (150°C to 210°C) , and is an inexpensive elastomer in comparison to hydrogenated thermoplastic elastomers that will be described later. SBS has a chemical structure in which a butadiene block is sandwiched between styrene blocks, and to the double bond constituting this butadiene block is added a 20-carbon polycyclic diterpene having a carboxyl group {resin acid) , making it possible to stabilize the SBS within the asphalt composition so that the SBS will not tend to separate and rise up from within the asphalt, and also improving the performance of the asphalt

composition.

Under the present invention, by controlling the ratio of SBS to be mixed into the asphalt, properties of the asphalt composition of this invention will be

optimized.

The physical properties of asphalt vary greatly with changes in temperature. That is to say, asphalt is highly temperature-sensitive. Thus, when forming materials to be used at ambient temperature, this substance can be liquefied by heating to a temperature of approximately 100°C to 200°C, and then formed into the desired shape while in its liquid state. However, even though this asphalt is to be used at ambient temperatures, the temperature during use may change depending on factors such as the location of use and the season, so the properties of the asphalt may change, and the product may fail to deliver its prescribed performance.

For this reason, in the asphalt composition of this invention, the inventors have worked to minimise the changes in physical properties due to variations in temperature, that is to say, to reduce the temperature sensitivity of asphalt by the admixture of SBS, which has lower temperature sensitivity than asphalt. In addition, this SBS provides greater elasticity than asphalt at ambient temperatures, so the admixture of SBS under the present invention also serves to improve the physical strength of the product.

However, if the asphalt composition of this

invention contains less than 2 wt% of SBS, problems can arise because the improvement in temperature sensitivity and physical strength resulting from SBS addition may be insufficient for practical purposes. Improvement in the physical properties and temperature dependence of the asphalt may not be attained, and it may be difficult to achieve properties that are appropriate for a wide temperature range. If the SBS content exceeds 8 wt%, the viscosity of the final asphalt composition may be too high, and there may be markedly decreased operability when actually applying this composition to the road.

Also, if the SBS content exceeds 8 wt%, the final asphalt composition may show worsening thermal stability and storage stability, and a uniform composition may not be obtained. Thus, the SBS content is preferably in the range of from 2 wt% to 8 wt%.

The 20-carbon polycyclic diterpene containing a carboxyl group (resin acid) can be a substance such as, for example, abietic acid, dehydroabietic acid,

neoabietic acid, pimaric acid, isopimaric acid, and palustric acid, although it is not limited to these acids, but can also include any resin acid under the definition of a 20-carbon polycyclic diterpene having a carboxyl group. These 20-carbon polycyclic diterpenes having a carboxyl group generally include rosins.

The term rosin as used here includes gum rosin, wood rosin, and tall oil rosin. These rosins can be classified into categories such as gum rosin or wood rosin, as described above, according to differences in location of origin, raw materials, and method of harvesting, but all share the common point of being obtained as a residue of the steam distillation of pine resin. These rosins are mixtures containing ingredients including abietic acid, palustric acid, neoabietic acid, dehydroabietic acid, plmaric acid, sandacopimaric acid, and isopimaric acid. These rosins generally soften at approximately 80°C, and melt at approximately 90°C to 100°C. A variety of rosin acids can be included within rosins, including abietic acid, dehydroabietic acid, dihydroabietic acid,

tetrahydroabietic acid, palustric acid, neoabietic acid, and levopimaric acid, but these rosin acids can also be purified and used alone.

Under the present invention, the following examples are offered as an explanation when gum rosins are used as the 20-carbon polycyclic diterpene having a carboxyl group (resin acid) . This gum rosin is produced by

filtering the raw pine resin after it is harvested and removing impurities from it, and then distilling the resin to remove low-boiling-point oil of turpentine. This gum rosin generally contains abietic acid 20 wt% to 40 wt%, neoabietic acid 15 wt% to 25 wt%, palustric acid 20 wt% to 30 wt%, pimaric acid 3 wt% to 8 wt¾, isopimaric acid 10 wt% to 20 wt%, and dehydroabietic acid 3 wt% to 8 wt%.

In addition, rather than using the unmodified rosin, it is acceptable simply to add one or more of the

following categories of material: abietic acid,

dehydroabietic acid, neoabietic acid, pimaric acid, isopimaric acid, palustric acid etc.

This 20-carbon polycyclic diterpene having a

carboxyl group (resin acid) preferably makes up from 0.3 wt% to 3 wt% of the asphalt composition of this

invention. However, if the asphalt composition of this invention contains less than 0.3 wt% of this resin acid, the addition of the 20-carbon polycyclic diterpene having a carboxyl group (such as abietic acid, dehydroabietic acid, neoabietic acid, pimaric acid, isopimaric acid, palustric acid, or pimaric acid) is likely to be

insufficient, and improved stability of the asphalt composition may not be achieved. If the content of this resin acid exceeds 3 wt%, not only is there likely to be a problem with the effect of improved stability reaching its upper limit, but there is likely to be a dramatic rise in the cost of raw materials because of the

increased addition of expensive resin acid. That is to say, the addition of resin acid exceeding 3 wt% is not accompanied by a commensurately large improvement in stability, and is impractical from the perspective of raw material costs.

It is more desirable for the asphalt composition to comprise 0.3 wt% to 1 wt% of the 20-carbon polycyclic diterpene having a carboxyl group (resin acid) . By placing the upper limit of resin acid content at 1 wt%, it is possible to hold down increases in the cost of raw materials while improving the stability of the asphalt composition of this invention, providing improved cost- effectiveness.

Asphalt is comprised of straight asphalt that is obtained as a residual oil from the vacuum distillation of crude oil, depropanated asphalt that is obtained by removing substances such as propane from residual oil following the vacuum distillation of crude oil, and substances such as extracts that are obtained from solvent-extracted oil that was in turn obtained by removing substances such as propane from residual oil following the vacuum distillation of crude oil. It can also be comprised of aromatic oils in place of these extracts. These aromatic oils are to be as specified in JISK6200, aromatic hydrocarbons containing at least 35 mass% of hydrocarbon process oil. Asphalt is prepared by the vacuum distillation method described above, by a blowing method (involving the blowing of air) , or by a mixing method (blending method) . This asphalt can contain one or more types of depropanated asphalt, straight asphalt, and/or extracts.

Depropanated asphalt is obtained from the vacuum- distilled residual oil through a removal process using propane or propane and butane intermixed substances as solvents, yielding a desolvented asphalt. In addition to this depropanated asphalt, it is also acceptable to use any other form of asphalt, for example straight asphalt or blown asphalt.

An example of this depropanated asphalt that can be used would be a product that, under JISK2207, shows needle penetration of 8 (1/10 mm) at 25°C, softening point of 66.5°C, and density at 15°C of 1028 kg/m ³ .

For the straight asphalt it is acceptable to use, for example, a product having needle penetration at 25°C of 65 (1/10 mm), softening point of 48.5°C, and density at 15°C of 1034 kg/m ³ .

Extracts are extracted oils that are obtained from solvent-extracted oils. Those solvent-extracted oils were obtained by removal using substances such as propane from residual oil following the vacuum distillation of crude oil, and the extracts are obtained by further solvent extraction using polar solvents, to yield heavy lube stock as a refined oil. The substance used as an extract can have a kinematic viscosity of 61.2 mm2/s at 100 °C, a kinematic viscosity of 3970 mm2/s at 40°C, and a density of 976.4 kg/m3 at 15°C. In this regard, it is desirable for this extract to constitute no more than 5 wt% of the asphalt composition of this invention. This is because if the content of the extract exceeds 5 wt%, the strength of the resulting asphalt composition of this invention may not reach a level considered sufficient for asphalt applications .

To actually produce the asphalt composition of this invention, first prepare the asphalt described above.

This asphalt is a preferably a mixture of one or more of the categories of straight asphalt, depropanated asphalt, and extract. The asphalt may be held at a temperature of approximately 195 °C, and SBS, preferably from 2 wt% to 8 wt% is added, resin acid, preferably from 0.3 wt% to 3 wt%, is also added, and the ingredients are mixed and stirred, e.g. at a temperature of 190°C to 210°C and at a speed of 1500 to 6000 rpm for 2 to 3 hours. In this regard, it is acceptable for the mixing time to deviate from the 2 to 3 hour range.

It is preferred that the mixing temperature is from 190°C to 210°C. If the mixing temperature is below 190°C, it will be difficult to add the 20-carbon polycyclic diterpene having a carboxyl group (resin acid) at the double bond that constitutes this butadiene block within the SBS. It thus may not be possible to stabilize the SBS within the asphalt composition and improve properties so that the SBS will not tend to separate and rise up within the asphalt, and as a result the SBS may separate from the asphalt.

If the mixing temperature exceeds 210 ºC, the SBS may degrade and deteriorate, and it may not be possible to achieve the improved strength and reduced temperature sensitivity (improved temperature sensitivity) that were to be expressed as a result of adding SBS to asphalt. As a result, it is preferable to limit the mixing

temperature to the temperature range described above.

Figure 1 illustrates the relationship between the modulus of elasticity G* for the wavelength angular frequency ω of this asphalt composition and the loss tangent (tanδ) . Sine wave oscillations are applied as a uniform distortion to the asphalt composition, the angular frequency ω is gradually increased and the modulus of elasticity G* and the loss tangent (tanδ) are measured in relation to that angular frequency.

The modulus of elasticity G* specified for this invention can be measured using a dynamic viscoelasticity tester. Specifically, as shown in Figure 2, asphalt binder (1) is pressed between two parallel plates (2a and 2b) . A predetermined sine wave distortion is applied to one of these plates (2a) , and the sine stress σ that is transmitted through the asphalt binder (1) to the other plate (2b) is measured. Those conditions of measurement are to be as follows: diameter of the plates (2a and 2b) 25 mm, thickness of the asphalt binder (1) 1 mm, strain level 10%. Based on those measured results, the modulus of elasticity G* is determined from the following formula (1). Here, γ in the following formula (1) is the maximum strain applied to the plate.

The loss tangent (tanδ) is an index indicating the magnitude of energy that is lost within the asphalt composition when the sine wave distortion γ is applied to the asphalt composition.

A large loss tangent (tanδ) indicates that a large amount of energy is lost when strain is applied, which is to say that the substance is easily deformed, and that it does not return to its original shape when the applied strain is released. A small loss tangent (tanδ) indicates that a small amount of energy is lost when strain is applied, which is to say that the substance is not easily deformed, and that it is prone to return to its original shape when the applied strain is released.

When the modulus of elasticity G* is measured as described above, the loss tangent (tanδ) is calculated from the phase difference δ between the sine wave

distortion γ for the designated angular frequency applied to one plate and the sine stress σ transmitted through the asphalt composition to the other plate.

The modulus of elasticity G* and loss tangent (tanδ) as described above may also be measured on the basis of the method described in "Pavement Review and Test Method Handbook" (edited by the Japan Road Association) under the title "A062 dynamic shear rheometer test method."

In this regard, the example in Figure 1 shows the modulus of elasticity G* and the loss tangent (tanδ) exhibited by an asphalt composition consisting of SBS 4.5 wt%, gum rosin 0.75 wt%, and the remainder asphalt, at 60°C with the application of 10% sine wave distortion. The samples of asphalt composition for use were prepared at various mixing temperatures (180°C, 185°C, and 190°C) .

Particularly in the case of road pavement in a setting of actual use, the asphalt composition is spread on the road with aggregate {gravel, sand, etc.). It is then necessary to smooth the paved surface with heavy equipment and human labour in order to provide an

improved ride for traffic on the road, to prevent

stumbling by pedestrians, and to prevent water

accumulating in puddles. To smooth the pavement surface, a large force is applied slowly to the paved surface in a process much like ironing.

Since at that point the asphalt composition receives vibrations at a low angular frequency to, the higher the tanδ for the low angular frequency ω, the easier it will be to deform the asphalt composition, and the lower the restoration force will be.

In comparison to the other samples, those prepared at a mixing temperature of 190 °C tended to have a higher tanδ for low angular frequency ω. In contrast, the samples prepared at a mixing temperature of 185°C tended to have a low tanδ for low angular frequency ω. Thus we see that a mixing temperature of 190°C or above is desirable from the perspective of workability.

It is also desirable to have a low modulus of elasticity G* for the low angular frequency ω range. In particular, when compacting and smoothing the asphalt composition, a load is placed on that asphalt composition in a low angular frequency ω range, and at this point workability is improved by having the composition be as soft as possible, or in other words having the lowest possible level of elasticity. From the perspective of modulus of elasticity, also, the sample prepared at a mixing temperature of 190 °C tended to show a lower modulus of elasticity G* at low angular frequency ω than was the case with other samples. For mixing temperatures of 185°C and below, the modulus of elasticity G* at low angular frequency ω was higher, and the workability of samples tended to be worse. Thus we see that a mixing temperature of 190°C or above is desirable from the perspective of workability.

The asphalt composition of this invention, obtained by the manufacturing method described above, can provide stable properties with no separation of SBS from asphalt. The styrene blocks that comprise SBS characteristically aggregate with other SBS styrene blocks, but under the present invention a 20-carbon polycyclic diterpene having a carboxyl group (resin acid) can be attached at the double bond comprising the butadiene block. In

particular, by attaching a resin acid in the vicinity of a styrene block, the bulky resin acid acts on the styrene block, making it possible to release the aggregation among the styrene blocks. Because of the release of this aggregation of styrene blocks, there is no separation between the SBS and the asphalt, and satisfactory

stability can be assured.

In this regard, it is possible to determine whether or not this asphalt composition is stable by conducting a storage stability test. This storage stability test was conducted using an aluminium tube having an inner

diameter of 5.2 cm and a height of 13 cm, filled to a depth of 12 cm with the asphalt composition of this invention (approximately 250 g) , and heating the sample at 170°C for 48 hours. Stability was confirmed by then measuring the upper-level softening point and the lower- level softening point for the asphalt composition in the aluminium tube. In this context, the upper-level

softening point means the softening point within the upper 4 cm, and "within the upper 4 cm" means 0 to 4 cm from the upper surface when the aluminium tube is filled to a depth of 12 cm with the asphalt composition, or in other words, material collected in a range from 8 to 12 cm from the bottom of the asphalt composition. In this context, the lower-level softening point means the softening point within the lower 4 cm, and "within the lower 4 cm" means 0 to 4 cm from the bottom when the aluminium tube is filled to a depth of 12 cm with the asphalt composition, or in other words, material

collected in a range from 8 to 12 cm from the surface of the asphalt composition.

The measurement of the softening point can be based on the method shown in JISK2207. Also, the difference absolute value between the upper-level softening point and the lower-level softening point can be used to determine stability. In cases where storage stability is considered satisfactory if the difference absolute value between these softening points is 3.0°C or less, the asphalt composition of this invention makes it possible to keep the softening point difference absolute value within 3.0°C.

Under JISK2207, if softening point repeatability shows a softening point of 80 °C or below, the softening point difference absolute value should not exceed 1.0 °C, and if the softening point is above 80 °C the softening point difference absolute value should not exceed 2.0°C. Here, the term softening point repeatability indicates the tolerance for measurements performed in the same place by the same operator on the same sample. With regard to stability, a general standard is that a

softening point difference absolute value within 2°C to 3°C indicates nearly complete stability, and a softening point difference absolute value in excess of 5°C

indicates instability. Here, with a perfectly uniform sample showing satisfactory storage stability, if the softening point is measured within the upper 4 cm and the lower 4 cm, and the respective softening points are considered to be the upper limit and the lower limit, then the difference will be as follows. The test error alone is 2.0°C (at a softening point of 80°C or below, the upper limit component is 1°C and the lower limit component is 1°C, for a total of 2°C) or 4.0ºC (at a softening point above 80°C, the upper limit component is 2°C and the lower limit component is 2°C, for a total of 4°C) .

From the above, in order to limit the softening point difference absolute value to 3°C or below,

stability will be considered satisfactory if the actual difference is no more than 1°C in comparison to the test error (= 2.0°C) for a softening point of 80°C or below, while for a softening point of 80°C or above the

precision will be at or below the test error (= 4.0°C), and so this can be considered as the same softening point. Because of this, the threshold for the softening point difference absolute value under this invention is 3°C or less. Further, it is desirable to have a softening point difference absolute value of 2.5°C or less, which provides even more satisfactory storage stability. In addition, if the softening point difference absolute value is 2.0°C or less, a product can be produced that has even greater storage stability.

It is also possible to increase the strength of the asphalt composition of this invention, produced through the manufacturing method described above. The strength of this asphalt composition can be judged based on DS

(Dynamic Stability) values from a wheel tracking test as described in the "Pavement Review and Test Method

Handbook" (edited by the Japan Road Association) .

Although this DS value can be used exclusively as an indicator for the measurement of road pavement strength, the asphalt composition of this invention is also well- suited to applications such as waterproof materials and adhesives, and there are cases in which improvements in strength are observed in those applications, so the evaluation of such substances by DS value can also be considered. Therefore, even if the DS value is used as an indicator for evaluation in this regard, this substance can still be used for a variety of applications such as waterproof materials and adhesives, as well as for road pavement .

Below, the method for measuring this DS value is explained. The DS value {dynamic stability} , an indicator for evaluating the fluidity resistance (difficulty of forming ruts) of an asphalt composition at high

temperatures, is measured using the wheel tracking test. The wheel tracking test is conducted at a temperature of 60°C, the presumed temperature of a road surface in the summer. Test samples of the asphalt composition mixed with aggregate (crushed gravel) , controlled to a

specified degree of granularity as described below in Table 1, are maintained at a temperature of 60°C for at least 5 hours, and wheels are run on the samples for 1 hour. For example, Sample 5 measuring 30 x 30 x 5 cm was prepared as shown in Figure 3. After the test sample has been prepared, there are no particular limitations on the time elapsing before the measurement of DS value is initiated, but if the sample is maintained at a high temperature for prolonged period, there may be some change in the sample's properties. Thus, generally after preparing 1.8 kg of the asphalt composition of this invention, the product is poured into a steel can having a diameter of 16 cm, a height of 17 cm, and a plate thickness of 1 mm, and cooled to room temperature. Within

48 hours of the completion of preparation of the asphalt composition, the sample, still in the steel can, is placed in an air convection oven that is kept at 175°C, and heated for 3 hours.

Next, a downward load of 686 N (70 kgf, or 70 kg weight) is applied through a wheel 11, and the wheel is run back and forth in the direction of the arrow marked on the figure, at a rate of 42 times/minute . In this regard, the wheel 11 is run along a specific path, without deviating or slipping from that path.

Figure 4 shows an example of the settlement (mm) seen for testing time (minutes) , using the starting time for DS value measurement testing as the reference point.

Using the starting time for testing as the reference point, and thus increasing the testing time, causes an increase in the settlement due to running the wheel 11 back and forth. This settlement is the settlement depth (mm) as measured downwards from the surface of Sample 5.

When measuring the DS value, the settlement

occurring up to 45 minutes after the start of initial testing is not taken into consideration. This is because the changes that determine settlement depth in the first 45 minutes after the start of initial testing are

basically caused by factors such as engagement with the aggregate that was added, and thus are essentially unusable for the evaluation of fluidity resistance.

Using the starting time for testing as the reference point when measuring the DS value, the focus is placed on the deformation d (mm) occurring during the 15-rninute interval from 45 minutes after the starting point to 60 minutes after that starting point. This d is calculated by using the starting time for testing as the reference point and determining the difference between the amount of settlement 45 minutes after the reference point and 60 minutes after that reference point. The DS value can be determined from Formula (2) below.

If the round-trip frequency for the wheel 11 is 42 (times/min), then Formula (2) can be modified as follows to produce (2) ' .

DS value (times/mm) = 630 (times) / d (mm)

(2) '

The numerator in Formula (2) ' is 42 (times/min) x 15 (min) = 630 (times) . That is to say, this DS value can be determined from the number of tire passes in 15 minutes in relation to d (mm) . The higher the DS value, the less deformation there will be in the asphalt composition itself, which means that the composition is strong and resists rutting.

DS values are not used simply for testing asphalt compositions, but also are used to measure test samples of mixtures of asphalt composition and aggregate (crushed rock, limestone filler) adjusted to an appropriate level of graininess, mixed together under specific conditions described below and similar to actual road pavement.

For the asphalt composition of this invention, in particular, the content of extract is kept below 5%, so it is possible to prepare a dense granular mixture

(aggregate maximum particle size 13 mm) , for use in ordinary road pavement that will have a DS value as described above of at least 6300 (times/mm) . In this regard, if the DS value is 6000 (times/mm) or above, there will be almost no problems with the surface

strength of the asphalt composition, according to the "Pavement Review and Test Method Handbook" (edited by the Japan Road Association) . If the DS value is 7000 or above, the surface strength will be even greater, for use on roads where travel by large vehicles is anticipated, and this strength can be further improved at values of 7800 or above.

Thus, the present invention offers two-pronged improvement; storage stability can be improved by

reducing the softening point difference to below 3.0°C, and strength can be improved by increasing the DS value to 6300 (times/mm) or above.

Below is shown the specific method for measuring the DS value using the asphalt composition of this invention.

The test sample is prepared using crushed rock from hard sandstone as the aggregate, and rock powder from crushed limestone for preparation of the fine fraction (constituent ingredients of small particle diameter). Materials other than the crushed rock and rock powder described above, including sea sand and recovered dust, can cause variation in the DS value, and are not to be used .

In order to adjust the degree of granularity of the aggregate, the limestone to be used is crushed into rock powder in conformance with JISA5008 "Limestone powder for use in pavement," where the percentage by weight passing through a 600 μm sieve is 100%, through a 150 μm sieve is 90% to 100%, and through a 75 μm sieve is 70% to 100%, and where the water content does not exceed 1%.

For aggregate other than rock powder, crushed rock from hard sandstone is used, to satisfy the properties listed in (1) through (6) below.

(1} Water absorption rate less than 1.5%, and preferably less than 1.0%. (JISA1110)

Here crushed rock having a water absorption rate of 0.64% is used. If the aggregate has a high water

absorption rate, it will absorb the asphalt that covers it, resulting in a composition having a lower ratio of asphalt within the mixture. Also, when using aggregate that has a high water absorption rate, the amount of asphalt absorption will differ greatly depending on the humidity and the surface moisture at the time of use, resulting in variations in the amount of asphalt within the mixture.

Thus, in order to maintain a constant amount of asphalt within the mixture, a water absorption rate of less than 1.5%, and preferably less than 1.0%, is

required.

(2) Apparent density between 2.60 g/cm3 and 2.70 g/cm.3 (JISA1110) .

Here crushed rock having an apparent density of 2.66 g/cm3 was used.

(3} Stability not to exceed 6%, and preferably not to exceed 3% (JISA1122) .

Here crushed rock having stability of 2.4% was used. Stability here means stability specifications with regard to freezing and thawing. A lower stability value

indicates less aggregate damage on freezing and thawing. Guidelines for pavement design and construction specify a stability value of no more than 12%, but in order to control for variation in aggregate properties, the values from those guidelines are halved.

(4) Abrasion loss not to exceed 20%, and preferably not to exceed 15% (JISA1121) .

Here, crushed rock having abrasion loss of 12.6% was used. The abrasion loss test evaluates the hardness of the aggregate and its resistance to abrasion loss, or in other words the durability of the aggregate. If abrasion loss exceeds 20%, major rutting will occur (see Tsuchiya, Iwata, "Analysis of actual road surface characteristics on high-speed expressways," High-Speed Expressways and Automobiles, Express Highway Research Foundation of

Japan, p. 27 (July 1986)), so here abrasion loss has been specified not to exceed 20%, and preferably not to exceed 15%.

(5) Content of soft particles not to exceed 5.0%, and preferably not to exceed 3.0% (JISA1126) .

Here crushed rock having a content of soft particles of 2.5% was used. The content of soft particles is determined by whether a brass rod (Mohs' hardness 3 to 4) makes scratches on the aggregate, showing whether the aggregate is harder or softer than the brass rod. Like the abrasion loss test, the content of soft particles test evaluates the hardness of the aggregate and its resistance to abrasion loss, or in other words the durability of the aggregate. It is generally necessary for the content of soft particles not to exceed 5%. (See "Pavement Review and Test Method Handbook A008")

(6) The content of long, thin rock fragments and/or flat rock fragments is to be no more than 10.0%, and

preferably no more than 5.0% (pavement design and

construction guidelines (specified values) and "Pavement Review and Test Method Handbook A008" (test methods) ) .

Here, crushed rock containing 2.8% long, thin rock fragments and/or flat rock fragments was used. Here, rock pieces having a long axis/short axis ratio of 3 or above are generally considered to be long, thin rock fragments or flat rock fragments. When long, thin rock fragments and/or flat rock fragments are included in the mix, the pavement or test sample may deform readily when load is applied from a certain direction. That is to say, with the admixture of large amounts of long, thin rock

fragments or flat rock fragments, those fragments may orient unidirectionally, and then deformation of the composition will be more likely to occur when a load is applied parallel to that direction than when a

perpendicular load is applied.

Consequently, when measuring the resistance to rutting (the DS value) , there can be considerable

variation in the measured values unless limitations are placed on the admixture of long, thin rock fragments and/or flat rock fragments.

Crushed rock powder and crushed rock that satisfied these properties was used as the aggregate, and the aggregate composition was adjusted as shown in Table 1, to prepare the test samples under the conditions shown in

Table 2.

The actual preparation of the test samples was divided into broad categories of mixtures of asphalt composition and aggregate, and rolling compaction was performed in two steps. For mixing, 604 g of asphalt composition previously heated to 175°C is subsequently heated to 185°C while 10176 g of aggregate with

granularity as described above is prepared {below, that controlled granularity is termed "formulated

granularity").

First, the aggregate was placed in a mixer and the aggregate alone was mixed for 60 seconds to make uniform. The mixing was temporarily stopped, 604 g of asphalt composition was introduced into the mixer, and the asphalt composition and aggregate were mixed together for 120 seconds.

When the mixing was completed, the asphalt

composition and aggregate was placed in a wheel tracking test frame (internal dimensions 30.0 cm long, 30.0 cm wide, and 5.0 cm deep), and rolling compaction was performed.

Rolling compaction was conducted at the rolling compaction temperature shown in Table 2 below, using a cylindrical roller having a radius of 460 mm to apply the rolling compaction load to the mixed asphalt. This rolling compaction was applied two stages: the primary rolling compaction and the secondary rolling compaction. Next, the mixture was dried for 8 hours.

The void ratio and compactness of the sample after mixing were as shown in Table 2 below.

(Table 2)

Of course the asphalt composition of this invention is not limited to applications for use in road pavement, but can also be used in applications such as waterproof materials and adhesives.

Examples

The invention will now be described by reference to examples which are not intended to be limiting of the invention .

As Table 3 shows, asphalt consisting of one or more types of straight asphalt, depropanated asphalt (PDA), or extract was heated to 195°C and held at that temperature while SBS 4.5 wt% was added.

The SBS used was a styrene-butadiene-styrene copolymer having a bromine value of 220 (g/100 g,

JISK0070), molecular weight of approximately 150000, styrene content of 30 mass%, and styrene block copolymer content at both ends of the elastomer molecule of 16 mass% .

In this regard, asphalt compositions were prepared with admixture of Acid A { straight-chain) , as shown in Comparative Examples 1 to 6, and asphalt compositions of this invention were prepared with admixture of Rosin B a shown in Examples 1 to 5, with admixture of Rosin C as shown in Example 6, with admixture of abietic acid as shown in Example 7, and with admixture of dehydroabietic acid as shown in Example 8. For these Examples and comparative examples, the asphalt compositions are prepared with a mixing ratio of straight asphalt, depropanated asphalt (PDA) , and extract to provide needl penetration of 40 to 50.

Here, Acid A has an acid value of 190 (mg KOH/g, JISK0070) and an iodine value of 110 {g/100 g, JISK0070) , being a mixture of 7 wt% straight-chain monomer acid with a carbon number of 18, 76 wt% dimer acid with a carbon number of 36, and 7 wt% trimer acid with a carbon number of 54, and has a mean molecular weight of approximately 590. Rosin B is an unhomogenized gum resin having an acid value of 156 (mg KOH/g, JISK0070) and a softening point of 77.0°C (JISK2207) . Rosin C is a tall oil rosin having an acid value of 170 (mg KOH/g, JISK0070) and a

saponification value of 178 (mg KOH/g, JISK0070), with a softening point of 77.0°C (JISK2207).

For the ingredients shown in Table 3, all numerical values in the table are wt%.

In Comparative Example 1, the extract makes up 12 wt% of the asphalt, in Comparative Example 2 the extract makes up 8 wt% of the asphalt, in Comparative Example 3 the extract makes up 6 wt% of the asphalt, and in

Comparative Examples 4 to 6, the extract makes up 4 wt% of the asphalt. In Comparative Examples 1 to 4, Acid A (straight chain) makes up 0.3 wt%, in Comparative Example 5 Acid A (straight chain) makes up 0 wt%, and in

Comparative Example 6 Acid A (straight chain) makes up 0.5 wt% of the mixture. In Examples 1 to 5, Rosin B was added instead of the Acid A (straight chain) that was mixed into Comparative Examples 1 to 6. The content of Rosin B varied among these Examples 1 to 5. Example 6 contained 0.75 wt% of Rosin C, Example 7 contained 0.75 wt% of abietic acid, and Example 8 contained 0.75 wt% of dehydroabietic acid.

The following manufacturing conditions were applied to all compositions. The substances were mixed and agitated at 195°C in a homogenizer at a speed of 3500 rpm for approximately 2 hours. In each case, 1.8 kg of sample was prepared.

Properties were measured for each manufactured comparative example and Example. The results of those measurements are shown in Table 3. The following

properties were measured: needle penetration (1/10 mm), softening point ( ° C ) , viscosity at 180°C (mPa.s), storage stability, DS value. Needle penetration data was for measurements performed at 25°C in accordance with

JISK2207. Softening point was also measured under

JISK2207 conditions. Viscosity was measured under the conditions specified in JPI-5S-54-99 "Viscosity

determination of asphalt using rotational viscometer, " at a measurement temperature of 180°C, using an SC4-21 spindle at a spindle speed of 20 rpm.

For storage stability, an aluminium tube having an inner diameter of 5.2 cm and a height of 13 cm was filled to a depth of 12 cm with the asphalt composition of this invention (approximately 250 g) , and the sample was sealed and heated at 170°C for 48 hours. Next, in

accordance with JISK2207, softening points were measured within the upper 4 cm and the lower 4 cm of the asphalt composition within that aluminum tube. Table 3 shows this upper softening point and the absolute difference between the upper softening point and the lower softening point, that is to say, the softening point difference absolute value .

The DS value was measured using the wheel tracking test. This DS value was obtained for various combinations of asphalt composition and aggregate composed of dense- graded asphalt mixture (13) , with the asphalt composition making up 5.6 wt%, formed into a sheet-shaped test sample 30 cm long, 30 cm wide, and 5 cm deep, using the method defined in "Pavement Review and Test Method Handbook" (edited by the Japan Road Association) . Japanese roads have been confirmed to reach temperatures of

approximately 60 ºC in the summer. When vehicles travel on roads at these temperatures, flow deformation and

conditions such as rutting will develop. The wheel tracking test was conceived as a way to experimentally confirm the extent of such rutting. It is conducted in order to evaluate dynamic stability, which is an

indicator of fluidity resistance in pavement materials. A tire was used to apply a specific load to a test sample for 1 hour within a constant-temperature chamber held at 60°C, and the amount of deformation was measured. Based on the above formula (2), the DS value was calculated from the amount of deformation detected during the 15- minute period from 45 minutes to 60 minutes after the start of the test.

In Table 3 above, the trends seen in Comparative Examples 1 through 4 indicate that DS values rose as the amount of extract decreased. However, when the amount of extract decreased, the difference absolute value tended to increase between the softening points for the upper and lower sections. For Comparative Example 4, in

particular, when the extract was decreased to 4 wt% the DS value increased to 7875 {times/mm) , but the softening point difference absolute value worsened to 19.9°C.

As can be seen with Comparative Examples 5 and 6, when the extract was reduced to 4 wt%, storage stability could not be improved even by increasing the content of Acid A, that is to say, carboxylic acid.

In Example 1, the extract content was 4 wt% and Rosin B was 0.3 wt%, but it was still possible to raise the DS value to 7000 (times/mm) or above while making the softening point difference absolute value extremely small. This provided improvements both in strength and in storage stability. In the same way, Examples 2 through 5 contained Rosin B 0.6 wt%, 0.75 wt%, 1 wt%, and 1.5 wt% respectively, making it possible to maintain DS values of 7000 (times/mm) or above, to hold the softening point difference absolute value to 1.3°C or below, and to achieve improvements in both strength and storage

stability. However, with regard to this storage

stability, it became clear that the softening point difference absolute value was not greatly changed by further increases in the content of Rosin B. It would seem that, even if Rosin B was added to exceed 3 wt%, there would be very little change in this softening point difference absolute value.

In Example 6, the extract was reduced to 4 wt% and Rosin C 0.75 wt% was added. This also provided similarly favorable DS value and softening point difference

absolute value. In Example 7, where abietic acid was added as the only resin acid, and in Example 8, where dehydroabietic acid was added as the only resin acid, again similarly favorable DS values and softening point difference absolute values were obtained. The results from Examples 6 through 8 indicate that even when the type of resin acid is changed, it is possible to maintain a high standard with regard to DS value through the addition of abietic acid and/or dehydroabietic acid, while also obtaining improved storage stability.

In this way, based on the results from Table 3, we see that improvements in both DS value and softening point difference absolute value can be implemented by using no more than 5 wt% extract and adding resin acid in a range of 0.3 wt% to 3 wt%. The results from Table 3 additionally show that, for identical SBS content, those asphalt compositions having lower softening points after the completion of

preparation also have higher stability. This can be considered to occur because, for systems containing identical compositions of the same thermoplastic

elastomer, the lower the softening point after the production of the asphalt composition is completed, the greater the improvement in stability from the addition of a 20-carbon polycyclic diterpene having a carboxyl group to a double bond comprising a butadiene block within the SBS.

Table 4 shows the results of a validation

experiment, performed by replacing SBS with styrene- ethylene-butylene-styrene (SEBS) or styrene-isoprene- styrene {SIS) and determining whether the expected effects of the present invention were demonstrated. In this validation experiment, the production conditions for the asphalt composition were the same as described above in Table 3. SBS, SEBS, and SIS were all added in

quantities of 4.3 wt%, and needle penetration, softening point, and viscosity at 150°C and 180°C (mPa.s) were measured.

The samples R1 and R2 in Table 4 were both created using SBS . Sample R1 was prepared without the addition of gum rosin, and is a Comparative Example differing in composition from the present invention. In contrast, 0.75 wt% gum rosin was added to Sample R2, making this sample an example of the present invention. In comparing the properties of Samples R1 and R2, the softening point of Sample R2 was much lower than that of Sample Rl, with stability improved by the addition of gum rosin, so that Sample R2 provides the effects expected from this invention.

In Samples S1 and S2, SEBS was substituted for SBS, so these samples are examples of the use of SEBS.

The styrene-ethylene-butylene-styrene block

copolymer (SEBS) used here has a hydrogen atom added to the double bond in the SBS butadiene block, resulting in a single bond, with a bromine value of 5 (g/100 g,

JISK0070) , molecular weight of approximately 150000, styrene content of 32 raassl, and styrene block copolymer content at both ends of the elastomer molecule of 15 mass% .

Sample SI was prepared without the addition of gum rosin, and 1 wt% gum rosin was added to Sample R2. A comparison of the properties of Samples SI and S2 show almost no change in softening point, and no apparent increase in stabilization effects associated with the addition of gum rosin.

In Samples Pi through P6, SIS has been added in place of SBS.

The SIS used was a styrene-isoprene-styrene

copolymer having a bromine value of 220 (g/100 g,

JISK0070) , molecular weight of approximately 220000, styrene content of 15 mass%, and styrene block copolymer content at both ends of the elastomer molecule of 7.5 mass% .

Pi through P3 are examples in which gum rosin was added. Almost no change in softening point was observed, regardless of whether or how much gum rosin was added. P4 through P6 are examples in which tall rosin was added. Almost no change in softening point was observed,

regardless of whether or how much tall rosin was added. It thus appears that the addition of rosin is not

associated with the development of improved stabilizing effects for this SIS.

That is to say, this invention shows improved stabilization effects with the addition of SBS, but these expected results cannot be obtained when SEBS or SIS is substituted for SBS. This improvement in stability can be achieved with SBS, which has a chemical structure with a butadiene block sandwiched between styrene blocks and a resin acid attached to the double bond constituting this butadiene block, but when SEBS or SIS is used, the resin acid cannot be attached and this improvement in stability cannot be obtained.