Temperature stress test method for asphalt mixture considering full restraint

Abstract

To provide a test method capable of evaluating low-temperature crack resistance of asphalt pavement.SOLUTION: A test device in which a specimen made of an asphalt mixture whose both ends are grasped by a pair of jigs is placed inside a constant-temperature bath, a temperature of the constant-temperature bath is varied and which evaluates temperature stress acting on the specimen, includes: a strain gauge that is attached to the specimen; and a control mechanism that controls operations of the pair of jigs. The control mechanism acquires the strain of the specimen detected by the strain gauge for each prescribed time, and controls the operations of the pair of jigs so that the strain of the specimen detected by the strain gauge remains within a predetermined range on the basis of the acquired strain.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present disclosure relates to a temperature stress test method, and more particularly to a temperature stress test method for a specimen made of an asphalt mixture, and a method for evaluating the low-temperature crack resistance of an asphalt mixture layer using the same. [Background technology]

[0002] In winter, cracks called "low-temperature cracks" may occur in asphalt pavements in cold regions such as Hokkaido. Low-temperature cracks are typically cracks that occur at roughly equal intervals across the road, and are also called low-temperature cracks or temperature stress cracks. When low-temperature cracks occur, they can cause the destruction of the asphalt pavement to progress, or rainwater can seep in through the low-temperature cracks, reducing the bearing capacity of the roadbed and subgrade, leading to the destruction of the asphalt pavement. Therefore, it is extremely important to properly evaluate the low-temperature crack resistance of asphalt pavements used in cold regions.

[0003] To the best of the inventors' knowledge, no method has been established for predicting the occurrence of low-temperature cracks or evaluating the low-temperature crack resistance of asphalt pavement. At the research level, for example, Non-Patent Document 1 discloses a method using a compression test, which reports that a correlation was found between the compression strength when a cylindrical specimen taken from a low-temperature crack occurrence site was broken by a tensile stress generated in a direction perpendicular to the compression direction and the amount of low-temperature cracks. However, as seen in Non-Patent Document 2, for example, it has also been reported that the compression strength does not correlate with the frequency of crack occurrence in cold regions, and the current situation is that the compression test is not generally adopted.

[0004] Also, as seen in Non-Patent Document 2, for example, there are reports that the bending strain at the time of bending failure correlates with the frequency of occurrence of low-temperature cracks, but this is not generally adopted at present. In asphalt pavement, the asphalt mixture layer is firmly adhered to the layers above and below it, and its movement is restricted by its own weight, so it is difficult to imagine that low-temperature cracks would occur due to the bending deformation assumed in the bending test, and it is difficult to say that the bending test reflects the situation occurring in the asphalt mixture layer of asphalt pavement. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Kimio Maruyama, Hideto Takemoto, "Study on Various Test Values ​​and Low-Temperature Crack Generation Rate Using Field Cores", 57th Annual Academic Conference of the Japan Society of Civil Engineers, Presentation Date: 2002 / 09 / 25~ 2002 / 09 / 27 [Non-Patent Document 2] Manabu Oguri, Morito Takahashi, Yasuyoshi Ebiko, "Selection of asphalt for suppressing low-temperature cracking", Civil Engineering Research Institute Monthly Report No. 542, July 1998 [Non-Patent Document 3] Akihiro Moriyoshi, Takashi Mizusawa, "Fundamental Study on Thermal Stress Testing of Asphalt Mixtures", Journal of the Japan Society of Civil Engineers, Vol. 384 / V-7, August 1987 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made to solve the problems of the prior art as described above, and in one aspect, it is an object of the present invention to provide a test method capable of evaluating the low-temperature crack resistance of asphalt pavement. [Means for solving the problem]

[0007] As can be inferred from the fact that low-temperature cracks are also called temperature stress cracks, it is believed that the occurrence of low-temperature cracks is related to temperature stress caused by temperature contraction of the asphalt mixture due to a sudden drop in temperature. A temperature stress test is known as a method for evaluating the temperature stress characteristics of an asphalt mixture, and typically, the asphalt mixture is fixed to a pair of jigs, the surrounding temperature is changed, the asphalt mixture is caused to shrink and deform, and the temperature stress generated in the asphalt mixture is evaluated using a strain gauge or load measuring instrument attached to the jigs or test equipment (Non-Patent Document 3, Figure 5 (B)). The temperature stress test makes it possible to find the relationship between temperature and temperature stress generated by the shrinkage and deformation of the asphalt mixture due to a drop in temperature.

[0008] The temperature stress characteristics of asphalt mixtures are sometimes evaluated as characteristics related to low-temperature cracks. However, it has been difficult to evaluate the breakage of asphalt mixtures due to a drop in environmental temperature, i.e., the occurrence of low-temperature cracks, by conventional temperature stress tests such as those shown in Non-Patent Document 3. Rather, according to the findings of the present inventors, in conventional temperature stress tests, even when the asphalt mixture is exposed to low temperatures assumed in cold regions where low-temperature cracks occur, the asphalt mixture almost never breaks. This result seems to be clearly inconsistent with the occurrence of low-temperature cracks in cold regions, suggesting that the test conditions of conventional temperature stress tests are different from the conditions in which the asphalt mixture layer is placed in asphalt pavement in cold regions.

[0009] Therefore, reconsidering the mechanism of low-temperature cracking, it was generally believed that low-temperature cracking occurs because asphalt pavement exposed to cold weather shrinks relatively freely. In accordance with this idea, in conventional temperature stress tests, as shown in Non-Patent Document 3, for example, a specimen made of an asphalt mixture is subjected to shrinkage deformation, and the resulting stress is measured by a strain gauge or load measuring device attached to a jig that holds the specimen or a test device.

[0010] In contrast, when we look at asphalt pavement at the site, the asphalt mixture layer that constitutes the asphalt pavement is firmly attached to the other layers above and below it, such as the roadbed, base layer, and surface layer, and is in a restrained state that makes it difficult to shrink. For this reason, even when exposed to a cold climate and the temperature drops, the asphalt mixture layer is hardly able to shrink at all, and rather, tensile stress acts on the asphalt mixture layer in a direction that suppresses its shrinkage, and it was thought that this tensile stress was the cause of the low-temperature cracks.

[0011] Having obtained the above findings, the inventors attached strain gauges to a specimen made of an asphalt mixture and attempted to control the strain of the specimen so that the strain measured by the strain gauges would fall within a predetermined range in order to faithfully reproduce the restraint state of the asphalt mixture layer at the paving site. By controlling the strain of the specimen, the inventors reproduced the restraint state of the asphalt mixture layer at the paving site, placed the specimen in a thermostatic chamber, lowered the temperature, and exposed the specimen to low temperatures. To their surprise, they found that they could perfectly reproduce the fracture of the specimen, as seen in the occurrence of low-temperature cracks in cold regions, and thus completed the present invention.

[0012] That is, in one aspect, the present invention provides A test apparatus in which a test specimen made of an asphalt mixture with both ends held by a pair of jigs is placed in a thermostatic chamber, the temperature of the thermostatic chamber is changed, and the temperature stress acting on the test specimen is evaluated, A strain gauge attached to the specimen; A control mechanism for controlling the operation of the pair of jigs; Equipped with The control mechanism acquires the strain of the specimen detected by the strain gauge at predetermined time intervals, and controls the operation of the pair of jigs based on the acquired strain so that the strain of the specimen detected by the strain gauge falls within a predetermined range. The present invention solves the above problems by providing a test device characterized by the above features.

[0013] As described above, in the testing device according to one aspect of the present invention, the strain generated in the specimen is measured by a strain gauge directly attached to the specimen, and the operation of the jig that holds the specimen is controlled so that the strain falls within a predetermined range. This makes it possible to reproduce the restrained state of the asphalt mixture layer at the paving site.

[0014] According to the findings of the present inventors, the above-mentioned configuration in which a strain gauge is attached to the specimen and the strain generated in the specimen is directly measured is very important in reproducing the constrained state of the asphalt mixture layer. In other words, when strain gauges are attached to other members constituting the test layer, such as a jig that holds both ends of the specimen or a frame to which the jig is attached, it is difficult to avoid the effects of shrinkage deformation of the member itself due to a decrease in the temperature of the thermostatic bath and elongation deformation due to an increase in temperature stress generated in the specimen, making it difficult to accurately evaluate the strain of the specimen made of asphalt mixture. In contrast, according to the above-mentioned test device according to one aspect of the present invention, the strain generated in the specimen is directly measured by the strain gauge attached to the specimen, and the movement of the jig is controlled so that the strain falls within a predetermined range, so that the constrained state of the asphalt mixture layer can be reproduced with higher accuracy. In this way, the above-described testing device according to one aspect of the present invention, which directly measures the strain of the test specimen and controls it to fall within a predetermined range, makes it possible to clearly observe the phenomenon of fracture of the asphalt mixture accompanying a decrease in temperature, such as the occurrence of low-temperature cracks, as shown in the experimental examples described below. Effect of the Invention

[0015] According to one aspect of the present invention, the test device can evaluate the temperature stress characteristics of an asphalt mixture that reflects the restraint state of an asphalt mixture layer in an asphalt pavement. For example, by using this test device to evaluate the temperature stress characteristics of an asphalt mixture under predetermined conditions that simulate a cold region, it is possible to evaluate the low-temperature crack resistance of an asphalt mixture layer made of the asphalt mixture. [Brief description of the drawings]

[0016] [Figure 1] FIG. 2 is a diagram showing a system configuration of a strain control mechanism included in a testing device according to an embodiment of the present invention. [Diagram 2] FIG. 13 is a diagram showing a state in which strain is controlled by a testing device according to one embodiment of the present invention. [Diagram 3] FIG. 1 shows the results of a temperature-stress relationship measured by a temperature stress test using a test device according to one embodiment of the present invention, in which the strain of a specimen made of an asphalt mixture was controlled, in comparison with the results of a temperature-stress relationship measured by a temperature stress test using a test device according to one embodiment of the present invention, in which the strain of a specimen made of an asphalt mixture was not controlled. [Figure 4] 1 is a photograph showing a typical state of a specimen made of an asphalt mixture after a temperature stress test was conducted by controlling the strain of the specimen using a test device according to one embodiment of the present invention. [Diagram 5] 1A is a diagram showing a temperature stress testing method using the testing device of the present invention in comparison with a conventional temperature stress testing method; FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] <1. Test equipment> A test device according to one aspect of the present invention will be described in more detail below.

[0018] A test apparatus according to one aspect of the present invention is a test apparatus for evaluating temperature stress occurring in a specimen made of an asphalt mixture, and may also be referred to as a temperature stress test apparatus.

[0019] In this specification, the term "temperature stress" refers to the stress that occurs in a test specimen when the test specimen, which is restrained from freely expanding and contracting, is subjected to a temperature change. Asphalt, which is a component of asphalt mixtures, has the property of expanding and contracting due to temperature changes, when a test specimen made of an asphalt mixture is subjected to a temperature change, temperature stress occurs due to the temperature change.

[0020] An asphalt mixture is a mixture of aggregate, asphalt, filler, etc. in a predetermined mixing ratio, and is a paving material used for the surface or base layer of asphalt pavement, and is also called asphalt concrete or asphalt mixture. Various asphalt mixtures are known, such as heated asphalt mixtures that are used by heating, room temperature asphalt mixtures that are used at room temperature, and modified asphalt mixtures that contain modified asphalt.

[0021] The specimen made of the asphalt mixture may be any specimen made of any asphalt mixture as long as it is a specimen made of the asphalt mixture described above. There is also no particular limitation on the source of the specimen made of the asphalt mixture, and it may be, for example, a specimen cut out from an asphalt pavement that has already been constructed, or a specimen prepared for testing.

[0022] There is no particular limitation on the shape of the specimen, and specimens of any suitable shape can be used, but typically the specimen is columnar, more typically the specimen is prismatic, even more typically the specimen is square, and even more typically the specimen is regular square. There is no particular limitation on the dimensions of the specimen, but the total length of the specimen can be, for example, 100 mm to 400 mm, more typically 110 mm to 300 mm, even more typically 120 mm to 250 mm, and even more typically 140 mm to 200 mm. In addition, when the specimen is square, the length of one side of the bottom surface can be, for example, 10 mm to 150 mm, typically 40 mm to 100 mm.

[0023] A testing apparatus according to one aspect of the present invention is a testing apparatus for evaluating the temperature stress characteristics of a specimen made of the above-mentioned asphalt mixture, in which the specimen, both ends of which are held by a pair of jigs, is placed in a constant temperature bath, the temperature of the constant temperature bath is changed, and the temperature stress acting on the specimen is evaluated.To repeat some of the above, the testing apparatus comprises a pair of jigs which hold both ends of the specimen, a constant temperature bath capable of housing the specimen therein, a strain gauge which is attached to the specimen as a means of directly measuring the strain generated in the specimen, and a control mechanism which controls the operation of the pair of jigs.

[0024] The pair of jigs for holding both ends of the specimen may be basically any type as long as they can stably hold both ends of the specimen, but in a preferred embodiment, the jig is preferably a jig having a bottom surface that is bonded to the end face of the specimen and a side surface that is bonded to the periphery of the side of the specimen. In other words, it is preferable that the jig has a bottom surface that is bonded to the end face of the specimen via an adhesive layer and a side surface that is bonded to the periphery of the side of the specimen via an adhesive layer. There is no particular limit to the dimensions of the bottom surface and side surface, but the bottom surface has approximately the same shape as the end face of the specimen, and the height of the side surface is at least 5 mm or more, preferably 10 mm or more, more preferably 15 mm or more, and even more preferably 20 mm or more in order to ensure sufficient adhesion with the specimen. There is no particular limit to the type of adhesive constituting the adhesive layer, but an epoxy resin-based adhesive can be preferably used.

[0025] Conventionally, in a temperature stress test, a pair of jigs for holding a specimen is mostly used, which are bonded to only the end faces of the specimen via an adhesive layer. However, when a temperature stress test is performed using a test device according to one aspect of the present invention, which is equipped with a control mechanism for controlling the distortion of the specimen to fall within a predetermined range, a stronger tensile stress acts on the specimen and the jig for holding it in order to counteract the distortion, and therefore, when a jig that is bonded to only the end faces of the specimen is used, there is a problem that the specimen and the jig are often peeled off. In contrast, the above-mentioned jig has the advantage of being able to hold the specimen more firmly.

[0026] On the other hand, the strain gauge attached to the specimen is for measuring the strain of the specimen that occurs with temperature change. Basically, any type of strain gauge may be used as long as it is capable of measuring the strain of the specimen that occurs with temperature change, and for example, a commercially available strain gauge may be used. The number of strain gauges attached to the specimen may be one, or may be two or more. There is no particular restriction on the attachment position of the strain gauge, but it is preferable to attach it to a position where the longitudinal strain of the specimen can be measured, and it is preferable to attach it to the center position of the longitudinal direction of the outer surface of the specimen.

[0027] As mentioned above, attaching a strain gauge to the specimen, in other words, providing a means for directly measuring the strain generated in the specimen, is extremely important in accurately grasping the strain in the specimen and reproducing the restrained state of the asphalt mixture layer. If the strain gauge is attached to another member, for example, a jig that holds both ends of the specimen or another member of the testing equipment such as a frame to which the jig is attached, it is difficult to avoid the effects of shrinkage deformation of the member itself due to a drop in temperature and elongation deformation due to an increase in temperature stress generated in the specimen, making it difficult to accurately grasp the strain in the specimen made of asphalt mixture.

[0028] On the other hand, the control mechanism acquires the strain of the specimen detected by the strain gauge at predetermined time intervals, and controls the operation of the pair of jigs based on the acquired strain so that the strain of the specimen detected by the strain gauge falls within a predetermined range. The testing device according to one aspect of the present invention thus controls the strain generated in the specimen so that it falls within a predetermined range, thereby reproducing a state in which the deformation of the specimen is almost completely restrained, and performs a temperature stress test (FIG. 5(A)). In this respect, the testing device is different from a conventional temperature stress testing device (FIG. 5(B)) that measures the force associated with the shrinkage deformation of the specimen due to a temperature drop.

[0029] The control mechanism may be basically any mechanism as long as it can control the operation of the pair of jigs so that the strain of the specimen detected by the strain gauge falls within a predetermined range, and may include, for example, a loading device connected to the pair of jigs, a data logger that acquires the strain measured by the strain gauge, and a control device that acquires the strain from the data logger and can control the operation of the loading device. The control device may be, for example, an electronic calculator such as a personal computer or a smartphone, while the loading device may be a loading device that can apply a tensile load and / or a compressive load.

[0030] In addition, there are no particular limitations on the specific method of controlling the strain by the control mechanism, but when the control mechanism includes, as described above, a loading device connected to a pair of jigs, a data logger that acquires the strain measured by the strain gauge, and a control device that acquires the strain from the data logger and can control the operation of the loading device described above, the control mechanism may be configured, for example, to acquire the strain measured by the strain gauge by the data logger, and the strain acquired by the data logger by the control device, and the control device controls the operation of the loading device connected to the pair of jigs based on the acquired strain.

[0031] There is no particular limitation on the method of controlling the operation of the loading device. For example, the load applied by the loading device may be increased or decreased so that the stress applied to the specimen increases or decreases by an amount equivalent to the strain measured by the strain gauge. For example, if the strain measured by the strain gauge at a certain point in time is the measured strain (Δε), the stress acting on the specimen via a pair of jigs may be increased or decreased by an amount equivalent to this Δε. The increase or decrease in stress (Δσ) equivalent to the measured strain (Δε) may be expressed, for example, as Δσ=E×Δε, where E is the elastic modulus of the asphalt mixture. The elastic modulus E of the asphalt mixture may be a literature value or may be determined by testing.

[0032] On the other hand, the positions of the pair of jigs may be displaced in a direction that cancels the strain measured by the strain gauge by an amount equivalent to the strain measured by the strain gauge. In this case, the positions of the pair of jigs may be displaced by an amount equivalent to the measured strain (Δε) measured by the strain gauge. The displacement (ΔL) equivalent to the measured strain (Δε) can be expressed, for example, as ΔL = L × Δε, where L is the longitudinal length of the specimen made of asphalt mixture.

[0033] In the testing apparatus according to one aspect of the present invention, the control mechanism controls the operation of the pair of jigs so that the strain of the specimen detected by the strain gauge attached to the specimen falls within a predetermined range. There is no particular limit to the predetermined range, but it is preferable that the operation of the pair of jigs is controlled so that the strain of the specimen detected by the strain gauge falls within ±10μ, preferably ±8μ, more preferably ±7μ, even more preferably ±6μ, and even more preferably ±5μ, for example.

[0034] The control of the strain by the control mechanism is performed at predetermined time intervals during the test. There is no particular limit to the predetermined time, and it may be an appropriate time depending on the performance of the control device, the rate of temperature increase or decrease, etc., but it may be, for example, 10 second intervals, 5 second intervals, 4 second intervals, 3 second intervals, 2 second intervals, or 1 second intervals.

[0035] In a preferred embodiment, the test apparatus according to one aspect of the present invention may be configured such that a load cell configured to measure the stress applied to the pair of jigs by the control mechanism is attached to either or both of the pair of jigs. When the test apparatus according to one aspect of the present invention has such a configuration, it is extremely convenient because the temperature stress acting on the specimen can be evaluated based on the stress measured by the load cell. However, the method of evaluating the temperature stress acting on the specimen is not limited to this, and a person skilled in the art may use an appropriate method for evaluating the temperature stress acting on the specimen.

[0036] <2. Temperature stress test method> The test device according to one aspect of the present invention can be particularly suitably used for evaluating the temperature stress characteristics of a specimen made of an asphalt mixture. That is, in another aspect of the present invention, A temperature stress testing method comprising placing a test specimen made of an asphalt mixture with both ends held by a pair of jigs in a thermostatic chamber, changing the temperature of the thermostatic chamber, and obtaining a temperature stress acting on the test specimen, During the test, the strain generated in the specimen is detected at predetermined time intervals by a strain gauge attached to the specimen, and the operation of the pair of jigs is controlled based on the detected strain so that the strain of the specimen detected by the strain gauge falls within a predetermined range. The present invention provides a temperature stress test method characterized by the above. The temperature stress test method has already been described in the description of the test device, so a detailed description thereof will be omitted here.

[0037] <3. Evaluation method for low-temperature crack resistance> The temperature stress test method according to one aspect of the present invention can be particularly suitably used for evaluating the low-temperature crack resistance of an asphalt mixture layer. When evaluating the low-temperature crack resistance of an asphalt mixture layer using the temperature stress test method according to one aspect of the present invention, In the temperature stress test method according to one aspect of the present invention described above, a test specimen made of an asphalt mixture constituting an asphalt mixture layer to be evaluated is used, The temperature of the thermostatic chamber is changed according to predetermined conditions, and the low-temperature crack resistance of the asphalt mixture layer is evaluated based on the presence or absence of fracture of the test specimen, the fracture stress, and / or the fracture temperature at that time.

[0038] The test specimen made of the asphalt mixture constituting the asphalt mixture layer to be evaluated for low-temperature crack resistance does not necessarily mean a test specimen taken from the pavement site to be evaluated for low-temperature crack resistance, but may be a test specimen made from an asphalt mixture of the same composition as the asphalt mixture that has been constructed or is to be constructed at the pavement site to be evaluated. The asphalt mixture layer to be evaluated may be a surface layer or a base layer, but since low-temperature cracks mainly occur in the surface layer, it is particularly preferable that it is the surface layer. The surface layer means the layer on the surface or the top of the asphalt pavement.

[0039] When evaluating low-temperature crack resistance using the temperature stress test method according to one aspect of the present invention, the above-mentioned test specimen made of the asphalt mixture constituting the asphalt mixture layer to be evaluated is placed in a thermostatic chamber, and the temperature of the thermostatic chamber is changed according to a predetermined condition. The predetermined condition may basically be any condition, but typically may be a condition that reproduces or reflects the change in road surface temperature or air temperature over a predetermined period at a paving site in a cold region. The predetermined period may be, for example, half a day, a day, a week, or a month.

[0040] The above-mentioned predetermined condition that can be used in the temperature stress test method according to one aspect of the present invention typically includes a temperature decreasing step of decreasing the temperature to a predetermined temperature. The condition including a temperature decreasing step of decreasing the temperature to a predetermined temperature can be, for example, a condition in which the temperature is decreased at a predetermined temperature decreasing rate from a predetermined start temperature to a predetermined end temperature, and is typically, for example, a condition in which the temperature is decreased at a predetermined temperature decreasing rate from the maximum road surface temperature or maximum air temperature of a day to the minimum road surface temperature or minimum air temperature of a day. Such a condition can be said to be a condition that reproduces or reflects the change in road surface temperature or air temperature of a day in a cold region.

[0041] On the other hand, the above-mentioned predetermined condition that can be used in the temperature stress test method according to one aspect of the present invention may include two or more temperature-reducing steps for reducing the temperature to a predetermined temperature. The condition including two or more temperature-reducing steps for reducing the temperature to a predetermined temperature may be, for example, a condition in which a temperature-reducing step for reducing the temperature from a predetermined start temperature to a predetermined end temperature at a predetermined temperature-reducing rate and a temperature-rising step for increasing the temperature from the predetermined end temperature to the predetermined start temperature at a predetermined temperature-rising rate are set as one cycle, and this cycle is repeated multiple times. Such a condition can be said to be a condition that reproduces or reflects the change in road surface temperature or air temperature in a predetermined period, such as one week, two weeks, or one month, in a cold region.

[0042] The temperature drop rate in the temperature drop step is not particularly limited, and a person skilled in the art can use an appropriate temperature drop rate, but typically, for example, the temperature drop rate is within the range of -20°C / h to -1°C / h, or within the range of -10°C / h to -5°C / h. The same is true for the temperature rise rate in the temperature rise step, which is not particularly limited, but may be, for example, within the range of 1°C / h to 20°C / h, or within the range of 5°C / h to 10°C / h.

[0043] The above-mentioned predetermined conditions may also include a temperature maintenance step of maintaining the temperature at a predetermined temperature. For example, during the night in a cold region, a predetermined minimum temperature may be maintained for a certain period of time, during which the asphalt mixture layer may undergo creep deformation. When the above-mentioned predetermined conditions include a temperature maintenance step of maintaining the temperature at a predetermined temperature, there is an advantage in that the temperature stress characteristics of the specimen can be evaluated taking into account creep deformation at the predetermined temperature.

[0044] In a method for evaluating low-temperature crack resistance according to one aspect of the present invention, the temperature of the thermostatic chamber is changed according to the specified conditions as described above, and the low-temperature crack resistance of an asphalt mixture layer constructed using the asphalt mixture constituting the test specimen is evaluated based on the presence or absence of fracture, fracture stress, and / or fracture temperature of the test specimen at this time.

[0045] In this specification, when the low-temperature crack resistance of an asphalt mixture layer is evaluated, unless otherwise specified, both absolute evaluation and relative evaluation of the low-temperature crack resistance may be included. For example, as described below, it may be an evaluation that predicts whether or not low-temperature cracks will occur when the asphalt mixture layer to be evaluated is used in a specified environment, or the magnitude of the low-temperature crack resistance of the asphalt mixture layer may be evaluated in comparison with a specified standard.

[0046] The fracture of a specimen means that the specimen breaks into two or more parts when a tensile load is applied in the longitudinal direction of the specimen, and the presence or absence of fracture literally means whether or not fracture of the specimen is observed.

[0047] When the temperature of the thermostatic chamber is changed according to a specified condition, the fact that a specimen placed in the thermostatic chamber breaks means that the specimen is highly likely to break if exposed to the specified conditions. Therefore, the presence or absence of breakage of the specimen when the temperature of the thermostatic chamber is changed according to the above-mentioned specified conditions that reproduce or reflect the change in road surface temperature or air temperature over a specified period at a paving site in a cold region can be an indicator of the low-temperature crack resistance of the asphalt mixture layer constructed using the asphalt mixture constituting the specimen. For example, when a specimen made of an asphalt mixture constituting a certain asphalt mixture layer is used and the temperature of the thermostatic chamber is lowered from the maximum road surface temperature or maximum air temperature of a day at the paving site where the asphalt mixture layer is constructed to the minimum road surface temperature or minimum air temperature of a day at the paving site, if the specimen breaks, it is determined that there is a high possibility of low-temperature cracks occurring when the asphalt mixture layer is applied to the paving site.

[0048] On the other hand, in this specification, the breaking temperature means the temperature of the thermostatic chamber when the specimen breaks, and preferably can be the temperature of the thermostatic chamber when the specimen breaks when the temperature of the thermostatic chamber is lowered in one direction from a predetermined start temperature to a predetermined end temperature. When the temperature of the thermostatic chamber is lowered from a predetermined start temperature to a predetermined end temperature, a tensile stress acts on the specimen placed in the thermostatic chamber due to the suppression of the shrinkage deformation of the asphalt mixture accompanying the temperature drop. The fact that the specimen breaks when the temperature of the thermostatic chamber is lowered to a certain temperature indicates that when the air temperature at the paving site drops to around that temperature, the asphalt mixture layer composed of the same asphalt mixture as the specimen is likely to break. Therefore, based on the breaking temperature, the low-temperature crack resistance of the asphalt mixture layer can be evaluated.

[0049] When evaluating the low-temperature crack resistance of an asphalt mixture layer based on the fracture temperature of a test specimen, for example, a test specimen made of the asphalt mixture constituting the asphalt mixture layer is used, the temperature of the thermostatic chamber is lowered from a start temperature such as the maximum road surface temperature, maximum air temperature or a temperature higher than that of the day at the paving site where the asphalt mixture layer is used, to an end temperature such as the minimum road surface temperature, minimum air temperature or a temperature lower than that of the day at the paving site, the fracture temperature at that time is obtained, and the magnitude of the fracture temperature is compared with the minimum road surface temperature or minimum air temperature at the paving site. If the fracture temperature exceeds the minimum road surface temperature and / or minimum air temperature at the paving site, it is judged that there is a high possibility of low-temperature cracking occurring when the asphalt mixture layer is applied to the paving site. On the other hand, if the fracture temperature is lower than the minimum road surface temperature and / or minimum air temperature at the paving site, it is judged that there is a low possibility of low-temperature cracking occurring even when the asphalt mixture is applied to the paving site.

[0050] In addition, when evaluating the low-temperature crack resistance of an asphalt mixture layer based on the fracture temperature of a test specimen, the fracture temperatures obtained for a test specimen made of an asphalt mixture constituting the asphalt mixture layer in question may be compared with those obtained for a test specimen made of an asphalt mixture constituting another asphalt mixture layer, to compare the low-temperature crack resistance of two or more asphalt mixture layers. In this case, the lower the fracture temperature, the higher the low-temperature crack resistance.

[0051] On the other hand, the breaking stress means the stress at which the specimen breaks. When the temperature of the thermostatic chamber is lowered from a specified start temperature to a specified end temperature, a tensile stress acts on the specimen placed in the thermostatic chamber due to the suppression of shrinkage deformation caused by the temperature drop. The fact that the specimen breaks when the temperature of the thermostatic chamber is lowered to a specified temperature and a certain tensile stress acts on it indicates that if the tensile stress acts on an asphalt mixture layer made of the same asphalt mixture as the specimen at the paving site, the asphalt mixture layer is likely to break.

[0052] When evaluating the low-temperature crack resistance of an asphalt mixture layer based on the breaking stress of a specimen, for example, a specimen made of the asphalt mixture constituting the asphalt mixture layer is used, the breaking stress is obtained, and the magnitude of the breaking stress is compared with an estimated value of the stress predicted to occur in the asphalt mixture layer at the site where the asphalt mixture layer is used. For example, if the estimated value of the stress predicted to occur at the site exceeds the breaking stress obtained by the temperature stress test method according to one aspect of the present invention, it can be determined that the asphalt mixture layer is likely to break and low-temperature cracks to occur.

[0053] There are no particular limitations on the method for estimating the stress generated in the asphalt mixture layer at the site where the asphalt mixture layer is used, but the stress may be estimated based on the temperature change at the site. More specifically, for example, the stress may be estimated based on the amount of temperature change in the asphalt mixture layer per day at the site and the linear expansion coefficient of the asphalt mixture layer, based on the following formula.

[0054]

number

[0055] In the above formula, σt is the estimated stress value, E is the elastic modulus of the asphalt mixture layer (unit: N / mm 2), α is the linear expansion coefficient of the asphalt mixture layer (unit: 1 / ℃), and Δt is the temperature change of the asphalt mixture layer per day (unit: ℃). The elastic modulus and linear expansion coefficient of the asphalt mixture layer may be obtained experimentally, or values ​​from literature may be used.

[0056] The temperature change amount of the asphalt mixture layer per day means the difference between the maximum temperature and the minimum temperature of the asphalt mixture layer in a day. For example, when the asphalt mixture layer is a surface layer, the difference between the maximum road surface temperature and the minimum road surface temperature in a day can be used as the temperature change amount of the asphalt mixture layer per day. The temperature change amount of the asphalt mixture layer per day does not necessarily have to be an actual measured value, but may be an estimated value. For example, an estimated value predicted from past road surface temperature data or asphalt mixture layer temperature data, or an estimated value predicted from past air temperature data may be used. Since it is known that the air temperature and the temperature of the asphalt mixture layer are correlated, a person skilled in the art can estimate the temperature of the asphalt mixture layer based on air temperature data, etc.

[0057] When comparing the magnitude relationship between the estimated stress value predicted to occur at the site and the breaking stress obtained by the temperature stress test method, a predetermined coefficient considering the fatigue, deterioration over time, etc. of the asphalt mixture layer may be taken into consideration. This has the advantage of making it possible to evaluate the low-temperature crack resistance over a medium to long term period, such as several years or several decades. As the predetermined coefficient considering the fatigue, deterioration over time, etc. of the asphalt mixture layer, an appropriate one can be used depending on the performance required for the asphalt pavement at each site.

[0058] <4. Experimental Example> The present invention will now be described in more detail with reference to experimental examples.

[0059] <4.1. Preparation of test specimen> A specimen was prepared from a porous asphalt mixture containing 4.9% by mass of polymer-modified asphalt (H-type) as asphalt. Specifically, the asphalt mixture was filled into a mold measuring 300 mm wide x 400 mm long and 60 mm deep, and compacted using a roller compactor. The mold was then removed and cut into a specified shape. The specimen was in the shape of a roughly regular square prism, with the length of one side of the base being 50 mm and the height being 300 mm.

[0060] <4.2. Temperature stress test> A pair of jigs made of Invar steel were fixed to both ends of the specimen prepared as described above so that the centers of the jigs and the specimen were aligned. The jig used was a box-shaped jig with a roughly square bottom surface that was bonded to the end surface of the specimen and four sides that were bonded to the side periphery of the specimen, and its inner dimensions, i.e., the dimensions of the bonding surface that was bonded to the specimen, were 54 mm long per side of the bottom surface and 25 mm deep per side. On the other hand, its outer dimensions were 90 mm long per side of the bottom surface and 55 mm high per side. An epoxy resin adhesive was used to bond the jig and the specimen. The specimen with the above-mentioned jigs attached was attached to a frame made of Invar steel and placed in a thermostatic chamber equipped in the test device.

[0061] The temperature stress test was carried out using a test device constructed by incorporating the strain control mechanism shown in Figure 1 into a commercially available temperature stress test device (Intesco Co., Ltd.). As shown in Figure 1, during the test, the strain (measured strain: ε m ) was detected by a data logger (TDS-630, Tokyo Measuring Instruments Laboratory Co., Ltd.), and the control device recorded the measured strain (ε mThe operation of the loading device is controlled so that the load stress (T) becomes zero. The loading device is connected to a jig fixed to the end of the specimen, and applies a specified load to the jig according to instructions from the control device. The load applied to the specimen via the jig is detected by a load cell connected to the jig, and the temperature stress generated in the specimen due to temperature change can be calculated from the load detected by the load cell.

[0062] The temperature change conditions of the thermostatic chamber were set to simulate winter temperature changes in cold regions, with a starting temperature of approximately 3°C and a final temperature of approximately -38°C. The temperature drop rate was set to -10°C / h. During the test, strain was controlled by the strain control mechanism at 1 second intervals. Prior investigations showed that the strain control range under these conditions was within ±5μ (Fig. 2).

[0063] The relationship between the temperature inside the thermostatic chamber and the stress calculated from the load detected by the load cell is shown in Fig. 3. Also, a photograph showing a typical state of the specimen after the test is shown in Fig. 4.

[0064] As shown in Figure 3, when the strain detected by the strain gauge attached to the test specimen was controlled, an increase in temperature stress was confirmed as the temperature in the thermostatic chamber decreased, and a rapid decrease in temperature stress was confirmed when the temperature in the thermostatic chamber reached -25°C. The rapid decrease in temperature stress at -25°C indicates that the test specimen made of the asphalt mixture broke. This result indicates that, for example, if the asphalt mixture is applied to the surface layer of an asphalt pavement, there is a risk that the surface layer made of the asphalt mixture will break if the road surface temperature reaches -25°C.

[0065] On the other hand, when a similar test was conducted without controlling the strain detected by the strain gauge attached to the specimen, an increase in temperature stress due to a decrease in the temperature in the thermostatic chamber was confirmed, but the measured temperature stress tended to be smaller than when the amount of strain detected by the strain gauge was controlled. In addition, the temperature stress plateaued at about 1.5 MPa, and no further increase in temperature stress was observed, and no fracture of the specimen made of asphalt mixture was confirmed, even when the temperature in the thermostatic chamber was lowered to nearly -40°C. In this way, the fracture behavior of the asphalt mixture due to a decrease in temperature could not be found by conventional temperature stress tests that do not control the amount of strain detected by the strain gauge attached to the specimen within ±5μ. [Industrial Applicability]

[0066] According to the present invention, it is possible to evaluate and measure the temperature stress characteristics of asphalt mixtures that reflect the restraint state of the asphalt mixture layer in asphalt pavement. In particular, according to the temperature stress characteristics under predetermined conditions that reflect the weather conditions of cold regions, it is possible to evaluate the low-temperature crack resistance of asphalt pavement, so it is possible to predict the occurrence of low-temperature cracks in cold regions and to efficiently select and design asphalt mixtures suitable for cold regions. Thus, the present invention has great industrial applicability.

Claims

1. A test apparatus in which a test specimen made of an asphalt mixture with both ends held by a pair of jigs is placed in a thermostatic chamber, the temperature of the thermostatic chamber is changed, and the temperature stress acting on the test specimen is evaluated, A strain gauge attached to the specimen; A control mechanism for controlling the operation of the pair of jigs; Equipped with The control mechanism acquires the strain of the specimen detected by the strain gauge at predetermined time intervals, and controls the operation of the pair of jigs based on the acquired strain so that the strain of the specimen detected by the strain gauge falls within a predetermined range. A test device comprising:

2. a load cell is attached to one or both of the pair of jigs and configured to measure a stress applied to the jig by the control mechanism; 2. The testing apparatus according to claim 1, wherein a temperature stress acting on the specimen is evaluated based on the stress measured by the load cell.

3. A temperature stress testing method comprising placing a test specimen made of an asphalt mixture with both ends held by a pair of jigs in a thermostatic chamber, changing the temperature of the thermostatic chamber, and evaluating the temperature stress acting on the test specimen, During the test, the strain generated in the specimen is detected at predetermined time intervals by a strain gauge attached to the specimen, and the operation of the pair of jigs is controlled based on the detected strain so that the strain of the specimen detected by the strain gauge falls within a predetermined range. A method comprising:

4. The method according to claim 3, characterized in that the stress applied to one or both of the pair of jigs is measured by a load cell attached to the jig, and the temperature stress acting on the specimen is evaluated based on the measured stress.

5. A method for evaluating low-temperature crack resistance of an asphalt mixture layer, comprising: The temperature stress testing method according to claim 3 or 4, As a test specimen, a test specimen made of the asphalt mixture constituting the asphalt mixture layer is used, A method for evaluating the low-temperature crack resistance of the asphalt mixture layer based on the presence or absence of fracture, fracture temperature, and / or fracture stress of the test specimen when the temperature of the thermostatic chamber is changed according to specified conditions.

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