JP7680296B2 - Asphalt pavement structures and asphalt reinforcement materials - Google Patents

Description

The present invention relates to an asphalt pavement structure and an asphalt reinforcing material for reinforcing an asphalt pavement structure.

Generally, an asphalt pavement structure comprises a layer of crushed stone constructed above the roadbed and a layer of asphalt constructed above the crushed stone layer.

Immediately after construction of an asphalt pavement structure, the top surface of the crushed stone layer and the bottom surface of the asphalt layer are in close contact, but there are cases where the asphalt layer peels off from the crushed stone layer. In such cases, the asphalt layer is the only layer that bears the load of the asphalt pavement structure, reducing the thickness of the asphalt pavement structure and decreasing the strength of the asphalt pavement structure. Furthermore, peeling of the asphalt layer from the crushed stone layer can cause the asphalt layer to turn into soil. Therefore, peeling of the asphalt layer from the crushed stone layer is thought to be one of the factors that shorten the lifespan of asphalt pavement structures.

If the asphalt layer peels off from the crushed stone layer and the strength of the asphalt pavement structure is reduced, cracks are likely to occur on the underside of the asphalt layer due to loads acting on the upper surface of the asphalt layer (for example, wheel loads when vehicles pass by).

When cracks occur on the underside of the asphalt layer, groundwater in the crushed stone layer seeps into the cracks in the asphalt layer, causing the fine particles in the asphalt layer to flow out. This causes the cracks in the asphalt layer to extend further toward the top of the asphalt layer. These types of cracks in the asphalt layer are also cited as a factor that shortens the lifespan of asphalt pavement structures.

In addition, when rainwater seeps through the joints in the asphalt layer and reaches the crushed stone layer, the crushed stone layer becomes wet and deforms, which shortens the lifespan of the asphalt pavement structure.

Therefore, various techniques have been put into practice to extend the lifespan of asphalt pavement structures. For example, the following Patent Document 1 discloses a technique for reinforcing asphalt pavement structures by laying sheet-like reinforcing material in the asphalt layer.

Japanese Patent Application Publication No. 6-248609

However, conventional reinforcement techniques are not sufficient to extend the service life of asphalt pavement structures, and there is a demand for further extending the service life of asphalt pavement structures.

In light of the above, the objective of the present invention is to provide an asphalt pavement structure and asphalt reinforcement material that can increase the resistance of the asphalt layer to peeling off from the crushed stone layer, prevent cracks from occurring on the underside of the asphalt layer, and suppress deformation of the crushed stone layer due to wetting.

According to the present invention, there is provided the following asphalt pavement structure that solves the above-mentioned problems: That is, there is provided an asphalt pavement structure comprising a crushed stone layer constructed above a roadbed, an asphalt layer constructed above the crushed stone layer, and an asphalt reinforcing material embedded between the crushed stone layer and the asphalt layer, the asphalt reinforcing material including a sheet that absorbs and retains asphalt emulsion spread between the crushed stone layer and the asphalt layer and has a thickness that follows the unevenness of the upper surface of the crushed stone layer , and a geogrid that is overlaid on the sheet, the sheet and the geogrid being previously bonded or welded to each other .

In the asphalt pavement structure of the present invention, it is preferable that the geogrid is a mesh having multiple openings, the sheet is placed on the crushed stone layer side, and the geogrid is placed on the asphalt layer side. It is preferable that the sheet or the geogrid is made of a material that softens or melts at the material temperature of the asphalt layer when the asphalt layer is constructed. It is preferable that the sheet is made of a nonwoven fabric.

The present invention also provides the following asphalt reinforcing material that solves the above-mentioned problems: That is, an asphalt reinforcing material for reinforcing an asphalt pavement structure that includes a crushed stone layer constructed above a roadbed and an asphalt layer constructed above the crushed stone layer, the asphalt reinforcing material includes a sheet that absorbs and retains asphalt emulsion that is spread between the crushed stone layer and the asphalt layer and has a thickness that follows the irregularities on the upper surface of the crushed stone layer, and a geogrid that is overlaid on the sheet, the sheet and the geogrid being bonded or welded to each other, and the asphalt reinforcing material is embedded between the crushed stone layer and the asphalt layer.

In the asphalt reinforcement material of the present invention, the geogrid is preferably a mesh having multiple openings, the sheet being placed on the crushed stone layer side, and the geogrid being placed on the asphalt layer side. It is convenient for the sheet or the geogrid to be made of a material that softens or melts at the material temperature of the asphalt layer when the asphalt layer is constructed. It is desirable for the sheet to be made of a nonwoven fabric.

According to the present invention, the sheet absorbs and retains the asphalt emulsion, so that the crushed stone layer and the asphalt layer are strongly bonded by the sheet retaining the asphalt emulsion, and the peeling resistance of the asphalt layer from the crushed stone layer can be increased. Furthermore, since the sheet has a thickness that follows the unevenness of the upper surface of the crushed stone layer, when the sheet is laid on the upper surface of the crushed stone layer, the lower surface of the sheet deforms along the unevenness of the upper surface of the crushed stone layer. This increases the contact area between the lower surface of the sheet that absorbs and retains the asphalt emulsion and the upper surface of the crushed stone layer. Therefore, according to the present invention, the adhesion between the crushed stone layer and the asphalt layer can be increased, and the peeling resistance of the asphalt layer from the crushed stone layer can be further increased.

The present invention can increase the resistance of the asphalt layer to peeling off from the crushed stone layer, suppressing a decrease in the layer thickness (reduction in strength) of the asphalt pavement structure, and dispersing the load acting on the asphalt pavement structure (for example, the wheel load when vehicles are passing) by the geogrid. Therefore, the present invention can prevent cracks from occurring on the underside of the asphalt layer.

In the present invention, the sheet absorbs and retains the asphalt emulsion, so the sheet retaining the asphalt emulsion exerts a waterproofing function and suppresses the flow of water between the crushed stone layer and the asphalt layer. This prevents rainwater and the like that seeps in through the joints of the asphalt layer from reaching the crushed stone layer, suppressing deformation of the crushed stone layer due to wetting. Furthermore, the nonwoven fabric retaining the asphalt emulsion also prevents groundwater present in the crushed stone layer from penetrating into the asphalt layer (capillary water rise), suppressing the outflow of fine particles from the asphalt layer.

1 is a cross-sectional view of an asphalt pavement structure constructed in accordance with the present invention (wherein the subbase is included in the asphalt layer). 2 is a cross-sectional view of another asphalt pavement structure constructed in accordance with the present invention, where the subbase is included in a crushed stone layer. FIG. 2 is a plan view of the geogrid shown in FIG. 1 . A plan view of a geogrid with triangular openings. 1 is a cross-sectional view of another asphalt pavement structure constructed in accordance with the present invention (one asphalt layer, two crushed stone layers: upper subgrade, lower subgrade). 1 is a cross-sectional view of another asphalt pavement structure constructed in accordance with the present invention (one asphalt layer, one crushed stone layer: subbase).

Below, preferred embodiments of the asphalt pavement structure and asphalt reinforcement material of the present invention will be described with reference to the drawings.

Referring to FIG. 1, the asphalt pavement structure 2 comprises a crushed stone layer 6 constructed above the roadbed 4, an asphalt layer 8 constructed above the crushed stone layer 6, and an asphalt reinforcement material 10 embedded between the crushed stone layer 6 and the asphalt layer 8.

The crushed stone layer 6 shown in FIG. 1 is mainly composed of a lower roadbed 12. The lower roadbed 12 is made of crushed run, crushed run steel slag, recycled crushed run, cut gravel, mountain gravel, sand, etc.

The asphalt layer 8 shown in FIG. 1 includes an upper subgrade 14 constructed above a lower subgrade 12, a base layer 16 constructed above the upper subgrade 14, and a surface layer 18 constructed above the base layer 16.

The upper roadbed 14 shown in FIG. 1 is made of a stabilized roadbed material. When the upper roadbed 14 is made of a stabilized roadbed material, the upper roadbed 14 is included in the asphalt layer 8. On the other hand, when the upper roadbed 14 is not made of a stabilized roadbed material, the upper roadbed 14 is included in the crushed stone layer 6, and the asphalt layer 8 is mainly composed of a base layer 16 and a surface layer 18 (see FIG. 2).

For example, a stabilized roadbed material can be one that is manufactured by adding bituminous materials such as straight asphalt to suitable aggregate and mixing it with heat. The aggregate can be a mixture of single-grained crushed stone, sand, etc., or crushed run or locally produced materials to which supplementary materials such as crushed stone, gravel, steel slag, sand, etc. have been added as necessary. Stabilized roadbed materials can also be ones in which cement, lime, or cement and bituminous materials have been added to aggregate.

When included in the crushed stone layer 6, the upper roadbed 14 (see FIG. 2) can be formed from size-adjusted crushed stone, size-adjusted steel slag, recycled size-adjusted crushed stone, hydraulic size-adjusted steel slag, etc.

The base layer 16 and the surface layer 18 may both be composed of an asphalt mixture. However, the aggregate used in the base layer 16 may have a different particle size from that used in the surface layer 18. The asphalt mixture that constitutes the base layer 16 and the surface layer 18 may be a room temperature asphalt mixture, but is preferably a heated asphalt mixture, which has better durability than a room temperature asphalt mixture.

Continuing the explanation with reference to Figure 1, the asphalt reinforcement material 10 includes a sheet 20 that absorbs and retains the asphalt emulsion E that is spread between the crushed stone layer 6 and the asphalt layer 8, and has a thickness that conforms to the unevenness of the upper surface of the crushed stone layer 6, and a geogrid 22 that is layered on the sheet 20.

The sheet 20 and the geogrid 22 are embedded between the crushed stone layer 6 and the asphalt layer 8. Specifically, when the upper roadbed 14 is made of a stabilized roadbed material, the upper roadbed 14 is included in the asphalt layer 8, and therefore the sheet 20 and the geogrid 22 are embedded between the upper surface of the lower roadbed 12 and the lower surface of the upper roadbed 14, as shown in FIG. 1. On the other hand, when the upper roadbed 14 is not made of a stabilized roadbed material, the upper roadbed 14 is included in the crushed stone layer 6, and therefore the sheet 20 and the geogrid 22 are embedded between the upper surface of the upper roadbed 14 and the lower surface of the base layer 16, as shown in FIG. 2.

In the embodiment shown in FIG. 1, the sheet 20 is arranged on the crushed stone layer 6 side (lower side) and the geogrid 22 is arranged on the asphalt layer 8 side (upper side), but the geogrid 22 may be arranged on the crushed stone layer 6 side (lower side) and the sheet 20 on the asphalt layer 8 side (upper side). In addition, the sheet 20 and the geogrid 22 may each be a single layer, but as shown in FIG. 2, the sheet 20 may be arranged above and below the geogrid 22.

The sheet 20 is preferably made of nonwoven fabric. The sheet 20 may be made of either short or long fibers, but is preferably made of short fibers that can absorb and retain more asphalt emulsion E compared to long fibers. A sheet 20 that absorbs and retains more asphalt emulsion E will increase the adhesion between the crushed stone layer 6 and the asphalt layer 8 and will provide better waterproofing.

The sheet 20 has a thickness that conforms to the unevenness of the upper surface of the crushed stone layer 6, so when the sheet 20 is laid on the upper surface of the crushed stone layer 6, the lower surface of the sheet 20 deforms to conform to the unevenness of the upper surface of the crushed stone layer 6. This increases the contact area between the lower surface of the sheet 20, which has absorbed and retained the asphalt emulsion E, and the upper surface of the crushed stone layer 6.

The sheet 20 may be formed from an appropriate synthetic resin, such as polypropylene, polyethylene, or acrylic. Of the synthetic resins, it is preferable that the sheet 20 be formed from a thermoplastic synthetic resin that softens or melts at the material temperature of the asphalt layer 8 when the asphalt layer 8 is constructed.

When constructing the asphalt layer 8, the temperature of the stabilized roadbed material (material of the upper roadbed 14) produced by the hot mixing method and the temperature of the heated asphalt mixture (material of the base layer 16 and surface layer 18) are high, for example, around 110 to 170°C. To give a more specific example, the material temperature of the asphalt layer 8 when it arrives at the site is around 160 to 170°C, the material temperature of the asphalt layer 8 when it is laid is around 120 to 150°C, and the material temperature of the asphalt layer 8 during the first compaction is around 110 to 140°C.

Therefore, if the sheet 20 is made of a thermoplastic synthetic resin (such as polypropylene) that softens or melts at such temperatures (for example, 110 to 170°C), when the asphalt layer 8 is constructed, the sheet 20 will soften or melt due to the temperature of the material of the asphalt layer 8, and then the sheet 20 will cool and solidify. As a result, the effect of bonding the upper surface of the crushed stone layer 6 and the lower surface of the asphalt layer 8 is exerted not only by the asphalt emulsion E absorbed in the sheet 20, but also by the sheet 20 itself.

The geogrid 22 in the illustrated embodiment is a mesh having a plurality of openings 24, as shown in FIG. 3. Therefore, when the geogrid 22 is placed on the asphalt layer 8 side (upper side) as in the embodiment shown in FIG. 1, the aggregate of the asphalt layer 8 enters the openings 24 of the geogrid 22, thereby firmly connecting the geogrid 22 and the asphalt layer 8. Note that, although the shape of the openings 24 is rectangular in the illustrated embodiment, it is not limited to a rectangular shape, and various shapes (for example, a triangular shape as shown in FIG. 4, or a tortoiseshell shape or a circular shape, not shown) can be adopted.

The geogrid 22, like the sheet 20, can be made of an appropriate synthetic resin such as polyolefin (e.g., polypropylene, polyethylene). However, it does not have to be made of the same material as the sheet 20.

The geogrid 22, like the sheet 20, is advantageously made of a thermoplastic synthetic resin that softens or melts at the material temperature of the asphalt layer 8 when the asphalt layer 8 is constructed. In this case, the geogrid 22 also exerts the effect of bonding the upper surface of the crushed stone layer 6 and the lower surface of the asphalt layer 8.

Next, we will explain the construction method for the asphalt pavement structure 2 as described above.

When constructing the asphalt pavement structure 2, first the roadbed 4 and crushed stone layer 6 are constructed. A known method can be used to construct the roadbed 4 and crushed stone layer 6. For example, the roadbed 4 can be constructed by excavating the existing ground to a predetermined depth using an excavating machine such as a hydraulic excavator, then leveling the top surface of the roadbed 4 using a leveling vehicle such as a bulldozer, and then compacting the surface of the roadbed 4 with a compacting vehicle such as a tire roller.

Once the roadbed 4 has been constructed, the roadbed material brought in by dump truck is spread on the top surface of the roadbed 4 using a leveling vehicle such as a motor grader, and then compacted using a rolling vehicle to flatten the top surface of the crushed stone layer 6.

As described above, the crushed stone layer 6 shown in FIG. 1 is mainly composed of the lower roadbed 12, so when constructing the crushed stone layer 6 shown in FIG. 1, it is sufficient to carry out the process of constructing the lower roadbed 12. On the other hand, the crushed stone layer 6 shown in FIG. 2 includes the lower roadbed 12 and the upper roadbed 14, so when constructing the crushed stone layer 6 shown in FIG. 2, the process of constructing the lower roadbed 12 and the process of constructing the upper roadbed 14 are carried out.

After constructing the crushed stone layer 6, asphalt emulsion E is sprayed on the top surface of the crushed stone layer 6 and asphalt reinforcement material 10 is laid. FIG. 1 shows an example in which asphalt emulsion E is sprayed on the top surface of the crushed stone layer 6 and then asphalt reinforcement material 10 is laid, but asphalt emulsion E may be sprayed after asphalt reinforcement material 10 is laid. That is, asphalt emulsion E may be sprayed directly on the top surface of the crushed stone layer 6, or asphalt emulsion E may be sprayed on the top surface of the crushed stone layer 6 via asphalt reinforcement material 10 that has been laid previously.

Alternatively, as shown in Figure 2, half of the prescribed amount of asphalt emulsion E may be directly spread on the top surface of the crushed stone layer 6, and then the asphalt reinforcement material 10 may be laid in the order of sheet 20, geogrid 22, and sheet 20, and the remaining asphalt emulsion E may be spread on top of the asphalt reinforcement material 10.

It is preferable to bond or weld the sheet 20 and the geogrid 22 together before laying the asphalt reinforcement 10, as this will facilitate construction.

After laying the asphalt reinforcement material 10, the asphalt layer 8 is constructed. In the asphalt layer 8 shown in Figure 1, the upper roadbed 14, the base layer 16, and the surface layer 18 are constructed in that order. On the other hand, in the asphalt layer 8 shown in Figure 2, the base layer 16 and the surface layer 18 are constructed in that order.

The upper roadbed 14 can be constructed, for example, by spreading stabilized roadbed material heated to about 150-170°C and compacting it uniformly. The base layer 16 and surface layer 18 are also constructed in a similar manner to the upper roadbed 14, for example, by spreading a heated asphalt mixture heated to about 150-170°C and compacting it uniformly. In this manner, the asphalt pavement structure 2 is constructed.

In addition, asphalt emulsion E is sprayed between each layer that constitutes the asphalt layer 8. Specifically, in the embodiment shown in FIG. 1, asphalt emulsion E is sprayed on the upper surface of the upper roadbed 14 and the upper surface of the base layer 16, and in the embodiment shown in FIG. 2, asphalt emulsion E is sprayed on the upper surface of the base layer 16.

As described above, in the illustrated embodiment, the sheet 20 absorbs and retains the asphalt emulsion E, so that the crushed stone layer 6 and the asphalt layer 8 are strongly bonded by the sheet 20 retaining the asphalt emulsion E, and the peeling resistance of the asphalt layer 8 from the crushed stone layer 6 can be increased. Furthermore, since the sheet 20 has a thickness that follows the unevenness of the upper surface of the crushed stone layer 6, when the sheet 20 is laid on the upper surface of the crushed stone layer 6, the lower surface of the sheet 20 deforms along the unevenness of the upper surface of the crushed stone layer 6. Therefore, the contact area between the lower surface of the sheet 20 that absorbs and retains the asphalt emulsion E and the upper surface of the crushed stone layer 6 is increased. Therefore, the adhesion between the crushed stone layer 6 and the asphalt layer 8 is increased, and the peeling resistance of the asphalt layer 8 from the crushed stone layer 6 is further increased.

In addition, the asphalt emulsion is absorbed by the sheet 20, reducing uneven distribution of the asphalt emulsion E and promoting the evaporation of the water contained in the asphalt emulsion E, thereby shortening the construction time.

In the form shown in Figure 1, when laying the asphalt reinforcement material 10, the sheet 20 is placed on the crushed stone layer 6 side (lower side), and the geogrid 22 with multiple openings 24 is placed on the upper roadbed 14 side (upper side) of the asphalt layer 8. Therefore, when the upper roadbed 14 is constructed, the aggregate of the upper roadbed 14 enters the openings 24 of the geogrid 22, firmly connecting the geogrid 22 and the upper roadbed 14.

In addition, if at least one of the sheet 20 or the geogrid 22 is made of a material that softens or melts at the material temperature of the asphalt layer 8 when the asphalt layer 8 is constructed, the sheet 20 itself or the geogrid 22 itself will have the effect of bonding the upper surface of the crushed stone layer 6 and the lower surface of the asphalt layer 8.

In this manner, in the illustrated embodiment, the resistance to peeling of the asphalt layer 8 from the crushed stone layer 6 can be increased, suppressing a decrease in the layer thickness (reduction in strength) of the asphalt pavement structure 2, and dispersing the load acting on the asphalt pavement structure 2 (for example, the wheel load when vehicles are passing) by the geogrid 22. Therefore, according to the illustrated embodiment, it is possible to prevent cracks from occurring on the underside of the asphalt layer 8.

In the illustrated embodiment, the sheet 20 absorbs and retains the asphalt emulsion E, so that the sheet 20 retaining the asphalt emulsion E exhibits a waterproofing function and suppresses the flow of water between the crushed stone layer 6 and the asphalt layer 8. This prevents rainwater and the like that seeps in through the joints of the asphalt layer 8 from reaching the crushed stone layer 6, suppressing deformation of the crushed stone layer 6 due to wetting. Furthermore, the sheet 20 retaining the asphalt emulsion E also prevents groundwater present in the crushed stone layer 6 from penetrating into the asphalt layer 8 (capillary water rise), suppressing the outflow of fine particles from the asphalt layer 8.

In the above explanation, an example in which the asphalt layer 8 has three layers, the upper roadbed 14, the base layer 16, and the surface layer 18 (the form shown in FIG. 1), and an example in which the asphalt layer 8 has two layers, the base layer 16 and the surface layer 18 (the form shown in FIG. 2), are given, but the asphalt layer 8 may be a single layer instead of multiple layers.

For example, on general roads with low traffic volume, asphalt reinforcement material 10 may be buried between crushed stone layer 6 including lower roadbed 12 and upper roadbed 14, and single asphalt layer 8, as shown in FIG. 5. Also, on simple pavements and farm roads, asphalt reinforcement material 10 may be buried between crushed stone layer 6 consisting of lower roadbed 12, and single asphalt layer 8, as shown in FIG. 6.

2: Asphalt pavement structure 4: Subgrade 6: Crushed stone layer 8: Asphalt layer 10: Asphalt reinforcement 12: Lower roadbed 14: Upper roadbed 16: Base layer 18: Surface layer 20: Sheet 22: Geogrid 24: Opening E: Asphalt emulsion

Claims (8)

The roadbed comprises a crushed stone layer constructed above the roadbed, an asphalt layer constructed above the crushed stone layer, and an asphalt reinforcement material buried between the crushed stone layer and the asphalt layer;
The asphalt reinforcement material comprises a sheet that absorbs and retains asphalt emulsion spread between the crushed stone layer and the asphalt layer and has a thickness that conforms to the unevenness of the upper surface of the crushed stone layer, and a geogrid overlaid on the sheet , wherein the sheet and the geogrid are previously bonded or welded to each other to form an asphalt pavement structure. The geogrid is a mesh having a plurality of openings,
The asphalt pavement structure according to claim 1 , wherein the sheet is disposed on the crushed stone layer side, and the geogrid is disposed on the asphalt layer side. The asphalt pavement structure according to claim 1 or 2, wherein the sheet or the geogrid is made of a material that softens or melts at the material temperature of the asphalt layer when the asphalt layer is constructed. An asphalt pavement structure according to any one of claims 1 to 3, wherein the sheet is formed from a nonwoven fabric. An asphalt reinforcing material for reinforcing an asphalt pavement structure comprising a crushed stone layer constructed above a roadbed and an asphalt layer constructed above the crushed stone layer,
The sheet absorbs and retains the asphalt emulsion spread between the crushed stone layer and the asphalt layer and has a thickness that follows the unevenness of the upper surface of the crushed stone layer, and a geogrid is superimposed on the sheet;
The sheet and the geogrid are bonded or welded to each other, and are embedded between the crushed stone layer and the asphalt layer to form an asphalt reinforcement material. The geogrid is a mesh having a plurality of openings,
The asphalt reinforcement material according to claim 5 , wherein the sheet is placed on the crushed stone layer side and the geogrid is placed on the asphalt layer side. The asphalt reinforcing material according to claim 5 or 6 , wherein the sheet or the geogrid is formed from a material that softens or melts at the material temperature of the asphalt layer when the asphalt layer is constructed. The asphalt reinforcement according to any one of claims 5 to 7 , wherein the sheet is formed from a nonwoven fabric.

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