Asphalt mixture additive and asphalt mixture containing said additive

Abstract

The present invention provides an asphalt mixture additive and an asphalt mixture containing said additive that make it possible to achieve longevity of pavement by improving flow resistance (rutting resistance) and improving crack resistance. An asphalt mixture additive according to an embodiment of the present invention contains polyethylene and ethylene vinyl acetate. The polyethylene is characterized by being low-density polyethylene. An asphalt mixture according to an embodiment of the present invention is characterized by being obtained by mixing an aggregate, asphalt, and an asphalt mixture additive comprising polyethylene and ethylene vinyl acetate.

Description

Additive for Asphalt Mixture and Asphalt Mixture Containing the Additive

[0001] Embodiments of the present invention relate to an additive for an asphalt mixture and an asphalt mixture containing the additive.

[0002] Conventionally, for example, modified asphalt has been developed to address the generation of road surface unevenness due to the softening of asphalt at high temperatures and the occurrence of cracks at low temperatures. Further, in Patent Document 1 shown below, a modified asphalt obtained by mixing waste plastic and an additive having compatibility with asphalt and showing affinity for the waste plastic is disclosed.

[0003] Patent No. 4046290

[0004] Thus, the modified asphalt shown in Patent Document 1 combines waste plastic and waste oil. Regarding the waste plastic, at least one of waste polystyrene, waste polypropylene, and waste polyethylene is the main component, but for any plastic, there are doubts about the resistance of asphalt, particularly to cracking.

[0005] Further, waste oil is used as an additive showing affinity for waste plastic, but the waste oil is only used for the purpose of melting the waste plastic. Therefore, no particular strength is required for the waste oil itself. Thus, it is also unlikely that the waste oil has any effect on, for example, cracking in the asphalt mixture produced by mixing.

[0006] That is, in the case of the modified asphalt disclosed in Patent Document 1, although it is thought to be inexpensive and of excellent quality that can be produced at a temperature near the existing asphalt production temperature, it is not sufficient in dealing with road surface unevenness and cracking.

[0007] Therefore, an object of the present invention is to provide an additive for an asphalt mixture and an asphalt mixture containing the additive that can extend the service life of the pavement by improving the flow resistance (resistance to rutting) and the crack resistance.

[0008] The additive for asphalt mixtures in the embodiments of the present invention contains polyethylene and ethylene vinyl acetate. Furthermore, the polyethylene is characterized by being low-density polyethylene.

[0009] Furthermore, in the embodiments of the present invention, the additive for asphalt mixtures has a mixing ratio of polyethylene and ethylene vinyl acetate of 20% to 80% polyethylene and 80% to 20% ethylene vinyl acetate.

[0010] Furthermore, the mixing ratio of polyethylene and ethylene vinyl acetate in the additives for asphalt mixtures is 40% to 60% polyethylene and 60% to 40% ethylene vinyl acetate.

[0011] In the embodiment of the present invention, the additive for asphalt mixtures is formed into pellets after kneading polyethylene and ethylene vinyl acetate.

[0012] The asphalt mixture in the embodiment of the present invention is characterized by being a mixture of aggregate, asphalt, polyethylene, and an additive for asphalt mixtures consisting of ethylene vinyl acetate.

[0013] Thus, by using the above-mentioned additives for asphalt mixtures in the asphalt mixture according to the embodiment of the present invention, it is possible to improve the flow resistance (rutting resistance) and crack resistance, thereby extending the lifespan of the pavement.

[0014] This graph shows the results of a bending fatigue test performed on specimens prepared by varying the ratio of polyethylene and ethylene vinyl acetate constituting the asphalt mixture additive according to an embodiment of the present invention. This graph shows the results of a Marshall stability test performed on specimens prepared by varying the ratio of polyethylene and ethylene vinyl acetate constituting the asphalt mixture additive according to an embodiment of the present invention. This table shows the test results shown in Figures 1 and 2 for multiple ratios of polyethylene and ethylene vinyl acetate constituting the asphalt mixture additive according to an embodiment of the present invention. This graph shows the results of a wheel tracking test performed on specimens prepared by varying the ratio of polyethylene and ethylene vinyl acetate constituting the asphalt mixture additive according to an embodiment of the present invention.

[0015] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0016] The asphalt mixture according to the embodiment of the present invention is a mixture of aggregate, asphalt, and an additive for asphalt mixtures. The additive for asphalt mixture according to the embodiment of the present invention contains at least polyethylene and ethylene vinyl acetate.

[0017] While several types of polyethylene exist depending on their density and manufacturing method, low-density polyethylene (LDPE) is preferably used, for example. More preferably, linear low-density polyethylene (LLDPE) may also be used.

[0018] However, polyethylene alone makes it difficult to ensure crack resistance when an asphalt mixture is laid on a road. In this case, the modified asphalt described in Patent Document 1 above contains a mixture of waste plastics such as waste polystyrene, waste polypropylene, and waste polyethylene.

[0019] Thus, when asphalt mixtures are manufactured by mixing plastics such as waste polystyrene, waste polypropylene, and waste polyethylene with aggregates and asphalt, they tend to be harder and more prone to cracking compared to asphalt mixtures that do not contain plastics. This tendency to crack in such asphalt mixtures makes them more susceptible to cracking in pavements subjected to heavy loads, leading to a decrease in crack resistance.

[0020] Furthermore, due to the properties of polyethylene, even when mixed as an additive into an asphalt mixture, it may not be compatible with the asphalt and may not spread evenly throughout the mixture.

[0021] Therefore, the additive for asphalt mixtures used in the embodiments of the present invention includes not only polyethylene but also ethylene vinyl acetate (EVA). This ethylene vinyl acetate is a copolymer of ethylene and vinyl acetate.

[0022] By adding ethylene vinyl acetate as an additive to asphalt mixtures, polyethylene's poor compatibility with asphalt can be mitigated, and its solubility can be improved. Furthermore, because ethylene vinyl acetate is flexible, it can improve the crack resistance of the mixed asphalt mixture.

[0023] Furthermore, since the additive for asphalt mixtures in the embodiments of the present invention contains polyethylene, it is possible to improve its resistance to flow (resistance to rutting). And, by improving both resistance to flow and resistance to cracking, it is ultimately possible to extend the lifespan of the pavement.

[0024] As described above, the additive for asphalt mixtures in the embodiments of the present invention contains polyethylene and ethylene vinyl acetate. Regarding the mixing ratio of the two, it can be confirmed that the optimal ratio yields the best results.

[0025] First, several test specimens were prepared with varying mixing ratios of polyethylene and ethylene vinyl acetate. That is, the proportions of aggregate and asphalt constituting the test specimens (asphalt mixtures) were kept the same, while the mixing ratio of polyethylene and ethylene vinyl acetate added as an additive to the asphalt mixture was varied.

[0026] Specifically, there are six types: (1) polyethylene:ethylene vinyl acetate = 100:0, (2) polyethylene:ethylene vinyl acetate = 80:20, (3) polyethylene:ethylene vinyl acetate = 60:40, (4) polyethylene:ethylene vinyl acetate = 40:60, (5) polyethylene:ethylene vinyl acetate = 20:80, and (6) polyethylene:ethylene vinyl acetate = 0:100.

[0027] Linear low-density polyethylene (LLDPE) was used as the polyethylene contained in the asphalt mixture additive used in the test specimens. Therefore, the test results used in the following explanation are all examples of cases where an asphalt mixture additive containing linear low-density polyethylene was used.

[0028] However, the additive used in asphalt mixtures does not necessarily have to be linear low-density polyethylene. In other words, simple low-density polyethylene or high-density polyethylene can also be used.

[0029] Furthermore, while there are multiple types of additives for asphalt mixtures, the other components of the asphalt mixture, such as aggregates and asphalt, can be anything.

[0030] Figure 1 is a graph showing the results of bending fatigue tests conducted on specimens prepared by varying the ratio of polyethylene and ethylene vinyl acetate constituting the asphalt mixture additive according to an embodiment of the present invention. The bending fatigue tests were conducted in accordance with the Pavement Survey and Testing Methods Handbook issued by the Japan Road Association.

[0031] As mentioned above, the test specimens used in the experiment were all made from the same materials, except for the different proportions of polyethylene and ethylene vinyl acetate in the additives used for the asphalt mixture. The conditions for preparing the test specimens were a mixing temperature of 185°C for the aggregate, asphalt, and asphalt additives, and a compaction temperature of 165°C. The dimensions of the prepared test specimens were 40 mm x 400 mm x 40 mm (length x width x height).

[0032] Furthermore, the additive for the asphalt mixture was added externally at a concentration of 0.4% to the mixture consisting of aggregate and asphalt.

[0033] Furthermore, the test conditions for the bending fatigue test were as follows: loading method: "two-point loading with both ends fixed", span length: "300 mm", test method: "strain control", test temperature: "+20°C", frequency and waveform: "5 Hz, sine wave", and strain: "600 μm".

[0034] In the test results shown in Figure 1, the horizontal axis shows the six test specimens (1) through (6) described above. In these six test specimens, linear low-density polyethylene is represented as "LLDPE," and ethylene vinyl acetate is represented as "EVA."

[0035] On the other hand, the vertical axis shows the number of cycles from the start of the test until the specimen fractures. In the graph shown in Figure 1, to make it easier to understand the number of cycles, parallel lines are shown on the vertical axis at intervals of 5,000 cycles from 0 to 20,000 cycles.

[0036] Looking at the bending fatigue test results in Figure 1, it can be seen that the results for specimens (3) and (4) are superior to those for the other specimens.

[0037] Next, let's discuss the Marshall stability test. In the Marshall stability test, a cylindrical specimen is cured under specified conditions, then sandwiched between two arc-shaped loading plates, and a load is applied in the diametrical direction of the specimen. The maximum load (stability: kN) until the specimen breaks is measured. This Marshall stability test is also conducted in accordance with the Pavement Survey and Testing Methods Handbook issued by the Japan Road Association.

[0038] The asphalt mixture used as the test specimen here is basically the same as the asphalt mixture prepared for the bending fatigue test described above. That is, the proportions of aggregate and asphalt constituting the test specimen are the same, but the difference lies in the mixing ratio of polyethylene and ethylene vinyl acetate added as additives to the asphalt mixture.

[0039] The test specimens prepared in this manner have different mixing ratios of polyethylene and ethylene vinyl acetate, and are the same as the test specimens described in (1) to (6) above. However, the shape of the test specimen used in the Marshall stability test differs from that of the bending fatigue test; it is cylindrical, and the thickness of the test specimen is 63.5 cm ± 1.3 mm.

[0040] Furthermore, the mixing temperature of the aggregate, asphalt, and asphalt mixture additive was 185°C, and the compaction temperature was 165°C. Compaction was performed 75 times on each side, and both sides were compacted. The asphalt mixture additive was added externally at a concentration of 0.4% to the mixture consisting of aggregate and asphalt.

[0041] Then, after curing the prepared specimens in water at 60°C for 30 minutes, a Marshall stability test was performed on the specimens at a loading rate of 50 ± 5 mm / min.

[0042] Figure 2 is a graph showing the results of a Marshall stability test conducted on test specimens prepared by varying the ratio of polyethylene and ethylene vinyl acetate that constitute the additive for asphalt mixtures according to an embodiment of the present invention.

[0043] In the test results shown in Fig. 2, the six specimens from (1) to (6) described above are shown on the horizontal axis. Also, the vertical axis indicates the Marshall stability (kN). Looking at Fig. 2, it can be seen that the results of the specimens (4), (6), and (3) are superior to those of the other specimens.

[0044] Fig. 3 is a table showing the results of the tests shown in Fig. 1 and Fig. 2 for multiple ratios of polyethylene and ethylene vinyl acetate that constitute the additive for asphalt mixtures according to the embodiment of the present invention. That is, it is a summary of the test results of the bending fatigue test and the Marshall stability test for each of the specimens from (1) to (6) described above.

[0045] That is, in the table shown in Fig. 3, the mixing ratios of polyethylene (linear low-density polyethylene: LLDPE) and ethylene vinyl acetate (EVA) in the specimens from (1) to (6) are shown on the horizontal axis. And the bending fatigue test and the Marshall stability test are shown on the vertical axis.

[0046] And the results of each test are indicated by three symbols: "◎", "○", and "△". Here, these symbols are a simple indication of the test results. "◎" represents very good, "○" represents good, and "△" represents ordinary.

[0047] Looking at the results shown in Fig. 3, for the additive for asphalt mixtures, the mixing ratio of polyethylene and ethylene vinyl acetate is preferably such that polyethylene is 20% to 80% and ethylene vinyl acetate is 80% to 20%. And a more suitable mixing ratio in the additive for asphalt mixtures is such that polyethylene is 40% to 60% and ethylene vinyl acetate is 60% to 40%.

[0048] The reason for such results can be considered as follows. First, when examining the properties of polyethylene and ethylene vinyl acetate that constitute the additive for asphalt mixtures in the embodiments of the present invention, polyethylene has a higher melting point and higher strength at room temperature than ethylene vinyl acetate. On the other hand, ethylene vinyl acetate has a lower melting point and lower strength at room temperature compared to polyethylene. However, ethylene vinyl acetate has better compatibility with asphalt than polyethylene.

[0049] First, when considering the case of using the additive for asphalt mixtures of "LLDPE:EVA = 100:0" which is the specimen of (1), since the mixing ratio of EVA is "0", the additive for asphalt mixtures contains only polyethylene.

[0050] In this case, as described above, since the melting point of polyethylene is higher than that of ethylene vinyl acetate, its compatibility with asphalt is poor and it is difficult to disperse uniformly in the mixture. Therefore, it is considered that the Marshall stability is low and the number of bending cycles is low in the bending fatigue test.

[0051] The test results also agree with the pointed-out fact that the modified asphalt disclosed in Patent Document 1 above, which contains polyethylene and does not contain ethylene vinyl acetate in the asphalt mixture, has low crack resistance.

[0052] Next, when considering the additive for asphalt mixtures of "LLDPE:EVA = 0:100" which is the specimen of (6), since the mixing ratio of LLDPE is "0", the additive for asphalt mixtures contains only ethylene vinyl acetate.

[0053] Regarding the results for the specimen of (6), since the strength of ethylene vinyl acetate is low, the Marshall stability is slightly low. Also, in the bending fatigue test, since the amount of deflection becomes too large, it is considered that the number of bending cycles is low.

[0054] In contrast, in the case of asphalt mixtures to which additives for asphalt mixtures in embodiments of the present invention have been added, as in the test specimens (2) to (5), polyethylene and ethylene vinyl acetate are mixed. This is thought to improve the asphalt compatibility of polyethylene and to reinforce the softness of ethylene vinyl acetate with polyethylene. As a result, good results were obtained in bending fatigue tests and Marshall stability tests.

[0055] Next, we will examine the results based on the wheel tracking test. Figure 4 is a graph showing the results of a wheel tracking test performed on test specimens prepared by varying the ratio of polyethylene and ethylene vinyl acetate that constitute the additive for asphalt mixtures according to the embodiment of the present invention.

[0056] For example, the passage of many vehicles causes plastic deformation (flow deformation) in the asphalt mixture, resulting in rutting. Therefore, the asphalt mixture needs to have resistance to flowability, which is the resistance to plastic deformation caused by vehicle loads. The wheel tracking test is conducted to verify the quality of this flowability.

[0057] First, the wheel tracking test was conducted in accordance with the Pavement Survey and Testing Methods Handbook, Volume 3, published by the Japan Road Association. As mentioned above, the test specimens used in the test were all made from the same materials, except for the difference in the proportions of polyethylene and ethylene vinyl acetate in the additives used for the asphalt mixture.

[0058] The conditions for preparing the specimens were as follows: the mixing temperature of the aggregate, asphalt, and asphalt mixture additives was 185°C, and the compaction temperature was 165°C. Compaction was performed using a roller compactor, and the test wheel load was 686 ± 10 N. The dimensions of the prepared specimens were 300 mm x 300 mm x 50 mm (length x width x height).

[0059] Furthermore, the additive for the asphalt mixture was added externally at a concentration of 0.4% to the mixture consisting of aggregate and asphalt.

[0060] Furthermore, as for the test conditions in the wheel tracking test, the test specimen was first cured in a constant temperature room maintained at 60°C ± 2°C for at least 5 hours before the start of the test. During the test, the test wheel traveled back and forth over the central part of the test specimen at a speed of 42 ± 1 times / min. The distance traveled by the test wheel was 230 ± 10 mm.

[0061] In the test results shown in Figure 4, the six test specimens (1) through (6) described above are shown on the horizontal axis, similar to Figures 1 and 2. In these six test specimens, linear low-density polyethylene is represented as "LLDPE" and ethylene vinyl acetate as "EVA," respectively.

[0062] The vertical axis represents dynamic stability (cycles / mm). In wheel tracking tests, a higher value for dynamic stability indicates better results. In other words, a higher value indicates superior fluidity, which is the resistance to plastic deformation caused by the vehicle's load.

[0063] As can be seen from the test results in Figure 4, all test specimens showed values ​​of 6,000 cycles / mm or higher, which is considered to be a sufficient value for dynamic stability. Furthermore, test specimen (1), which does not contain ethylene vinyl acetate, showed the best results, while conversely, test specimen (6), which does not contain polyethylene, showed the lowest value. And given the properties of polyethylene and ethylene vinyl acetate explained above, the results shown by test specimens (1) and (6) can be said to be reasonable.

[0064] In other words, for example, with the mixing ratio of polyethylene and ethylene vinyl acetate shown in specimens (2) to (5), it was possible to improve the crack resistance as described above, and also obtain sufficiently good results regarding flow resistance. Therefore, with the additive for asphalt mixtures and the asphalt mixture containing the additive in the embodiment of the present invention, it is possible to extend the lifespan of the pavement by improving flow resistance (rutting resistance) and crack resistance.

[0065] Furthermore, regarding the additive for asphalt mixtures in the embodiments of the present invention, for example, when manufacturing an asphalt mixture, the additive for asphalt mixtures, formed in pellet form, can be mixed with aggregate and asphalt.

[0066] In other words, for example, polyethylene and ethylene vinyl acetate are melted and kneaded using a so-called kneading extruder, and then extruded into a "string" or "rod" shape. At this time, the extruded additive may be cooled and then cut into pellets, or it may be cut with a cutter immediately after extrusion without cooling to form pellets.

[0067] As explained above, by using an additive for asphalt mixtures containing polyethylene and ethylene vinyl acetate, it is possible to improve the flow resistance (rutting resistance) and crack resistance, and as a result, the lifespan of the pavement can be extended.

[0068] It should be noted that this invention is not limited to the embodiments described above, but rather represents an example of the present invention. In the implementation stage, the components can be modified and materialized without departing from the spirit of the invention, and various changes or improvements can be made to the above embodiments. Furthermore, various inventions can be formed by appropriately combining the multiple components disclosed in the above embodiments.

[0069] For example, some components may be removed from all the components shown in the embodiment. Furthermore, components from different embodiments may be combined as appropriate, and such modified or improved forms may also be included in the present invention. These embodiments and their variations are included in the scope and essence of the invention, as well as in the claims of the invention and its equivalents.

[0070] In the preparation of the specimens for the bending fatigue tests and Marshall stability tests described above, new materials were used in all cases. However, the polyethylene and ethylene vinyl acetate contained in the asphalt mixture additives do not necessarily need to be new.

[0071] In other words, for example, used agricultural polyolefin special films (agricultural PO) can be processed into pellets using the method described above and used as an additive for asphalt mixtures.

[0072] The additives for asphalt mixtures were explained assuming they would be processed into pellets and then mixed with other components of the asphalt mixture. However, it is also possible to use them without necessarily forming them into pellets.

[0073] Furthermore, the following configurations may be adopted for the technology described in the embodiments of the present invention: (1) An additive for asphalt mixtures characterized by containing polyethylene and ethylene vinyl acetate. (2) The additive for asphalt mixtures according to (1) above, characterized in that the polyethylene is low-density polyethylene. (3) The additive for asphalt mixtures according to (1) or (2) above, characterized in that the mixing ratio of the polyethylene and ethylene vinyl acetate in the additive for asphalt mixtures is 20% to 80% polyethylene and 80% to 20% ethylene vinyl acetate. (4) The additive for asphalt mixtures according to any one of (1) to (3) above, characterized in that the mixing ratio of the polyethylene and ethylene vinyl acetate in the additive for asphalt mixtures is 40% to 60% polyethylene and 60% to 40% ethylene vinyl acetate. (5) The additive for asphalt mixtures according to any one of (1) to (4) above, characterized in that the additive for asphalt mixtures is formed into pellets after kneading the polyethylene and ethylene vinyl acetate. (6) An asphalt mixture characterized by being a mixture of aggregate, asphalt, and an additive for asphalt mixtures described in any of (1) to (5) above.

Claims

1. An additive for asphalt mixtures, characterized by containing polyethylene and ethylene vinyl acetate.

2. The additive for asphalt mixtures according to claim 1, characterized in that the polyethylene is low-density polyethylene.

3. The additive for asphalt mixtures according to claim 1, characterized in that the mixing ratio of polyethylene and ethylene vinyl acetate in the additive for asphalt mixtures is 20% to 80% polyethylene and 80% to 20% ethylene vinyl acetate.

4. The additive for asphalt mixtures according to claim 1, characterized in that the mixing ratio of polyethylene and ethylene vinyl acetate in the additive for asphalt mixtures is 40% to 60% polyethylene and 60% to 40% ethylene vinyl acetate.

5. The additive for asphalt mixture according to claim 1, characterized in that the additive for asphalt mixture is formed into pellets after kneading the polyethylene and the ethylene vinyl acetate.

6. An asphalt mixture characterized by being a mixture of aggregate, asphalt, and an additive for asphalt mixtures according to any one of claims 1 to 5.

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