JP2001141624A - Method and device for measuring asphalt strength - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and device for measuring asphalt strength that can measure the displacement of a sample caused by press deformation even in liquid such as an antifreeze solution, has a wide measurement range, cannot be easily damaged, and can be easily adjusted. SOLUTION: When a cylindrical asphalt mixture sample TP is pressed in a vertical direction for measuring displacement (deformation) in horizontal and vertical directions, gap detectors 4VT and 4HR that can detect the amount of displacement according to change in inductance or charge while a measuring probe being made of a magnetic body is displaced in a magnetic filed being formed by a coil are used and provided in the vertical and horizontal directions, and measuring probes 10VT and 10HR made of iron are provided at the tip of probe tip parts 5VT and 5HR. Also, a measuring probe-retaining device 11 for retaining the measuring probe 10VT in the vertical direction being pressed is equipped with a retreat mechanism by a spring 16, thus preventing deformation and damage while both escape each other even if the device 11 collides with the gap detector 4VT when the sample is broken.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring the strength of an asphalt mixture obtained by kneading asphalt and gravel, and particularly to measuring the strength of a soft asphalt mixture used for water works such as dam construction. It is suitable for doing.

[0002]

2. Description of the Related Art For example, a dam for power generation is generally located in a mountainous highland, has a low temperature and is exposed to cold water, and therefore uses a soft asphalt mixture. On the other hand, there is no standard in Japan for measuring the strength of such asphalt mixtures. Therefore, if you want to measure and specify the strength of asphalt mixture, for example, AMERICAN ASSOCIATION
OFSTATE HIGHWAY AND TRANSPORTATION OFFICIALS (AASH
TO) issued by AASHTO Provisional Standard "Standa
rd Test Method for Determining the Creep Complianc
e and Strength of Hot Mix Asphalt (HMA) Using the I
ndirect Tensile Test Device "is used to measure asphalt strength in accordance with the so-called TP9-94. This strength measurement method is, for example, as shown in FIG.
mm × t38 ~ 50mm to form a cylindrical specimen,
When this is pressed in the diametric direction, the amount of deformation in the pressing direction and the direction perpendicular to the two bottom surfaces (here, a circular plane excluding the outer peripheral surface is referred to as the bottom surface) is measured, and the asphalt mixture is measured at each deformation amount. Is used to measure the strength of the sample.

The amount of deformation of the two bottom surfaces of the cylindrical specimen in two orthogonal directions is measured using, for example, a measuring device as shown in FIG. This measuring device is also specified in the TP9-94, and has an LVDT (linear variable differential transd
ucers). This displacement meter
For example, as shown in FIG. 7, a brass pipe Y having an outer diameter of 1.6 mm is protruded from a fixed portion (CORE ASSEMBLY) Z provided at one end of the displacement direction to be measured, and is provided at the tip thereof. The probe (LVDT CORE) X is moved to the movable part (COIL ASSEMB
LY) Insert into W scale tube (SUB-MINIATURE LVDT) U. For example, in the case of FIG. 7, the test piece extends in the direction of arrow b in the direction perpendicular to the pressing direction a and is deformed, so that the tracing stylus X is displaced in the direction c coming out of the scale tube U. In this scale tube U, there is a magnetic field generated by a coil in the movable portion W. Therefore, when the tracing stylus X protruding from the fixed portion Z is displaced in the axis direction of the tube U in the scale tube U, the magnetic field is generated. Is generated, and from that state, it is possible to detect where the tracing stylus X is located, that is, how much the tracing stylus X has been displaced from the position of this place. Then, each of the fixed part and the movable part is attached to a brass cylindrical body attached with an adhesive at a position 1 inch (25.4 mm) from the center of the bottom surface in the direction in which the displacement is to be measured, and pressed. Measurement of displacement during deformation, that is, measurement of strength of asphalt mixture. In addition, the displacement of the two bottom surfaces of the cylindrical asphalt mixture specimen in the same direction, that is, for example, the displacement in the vertical direction or the horizontal direction is averaged and used for strength measurement.

[0004]

The displacement that can be accurately measured by the LVDT is 0.25 mm or less. Since the TP9-94 is for measuring the strength of a relatively hard asphalt mixture used at room temperature, for example, on an interstate highway, the displacement measurement range may be about the LVDT. However, the above-mentioned asphalt mixture for waterworks is very soft, and the amount of deformation (displacement) to be measured needs to be at least several mm. In addition, asphalt mixtures for dam construction etc. are exposed to sub-zero temperatures, so strength measurements should also be made under such conditions, and how the amount of deformation changes with changes in temperature or water temperature, for example. It should be measured, and in order to easily change the temperature of the asphalt mixture specimen, it is preferable to perform the measurement in a liquid using an antifreeze, but in the LVDT, the scale tube and the measuring element are electrically connected by the antifreeze. , Can not measure. For the same reason, the scale tube of the LVDT and the measuring element must not come into contact with each other and must be separated from each other in a set state. However, the adjustment is very difficult and time-consuming. In particular, in the LDVT, a so-called calibration is required to set the initial position of the probe to zero, and when it takes a long time, the asphalt mixture specimen cooled in accordance with the use environment warms up during that time, and the It takes time to cool to the same temperature again.
In addition, the asphalt mixture for water works is soft and has a large deformation, and is significantly deformed when broken.
There is also a problem that the displacement gauge itself is deformed or damaged due to the contact or collision between the LVDT scale tube and the probe. Also, for example, a strain gauge or a laser photometric displacement meter having a large displacement measurement range cannot be used in consideration of liquid breakage or specimen breakage.

The present invention has been developed to solve the above-mentioned problems, and has a wide displacement measurement range, can cope with large deformation and breakage of a test sample, is easy to adjust, and can be used in a liquid. It is an object of the present invention to provide an asphalt strength measuring method and apparatus which can be used.

[0006]

According to a first aspect of the present invention, there is provided a method for measuring asphalt strength according to the present invention, comprising forming a test piece made of an asphalt mixture into a cylindrical shape, and forming the test piece on both bottom surfaces thereof. In the same direction, set two orthogonal directions, and attach a probe made of a conductor or magnetic material to one end of each of the two orthogonal directions on each bottom surface, and within the magnetic field generated by the coil, A gap detector for detecting a displacement amount of the measuring element based on a change in inductance or a change in electric charge of the coil when the measuring element made of a conductor or a magnetic material is displaced in a direction in which the measuring element moves away from or facing the measuring element. Then, disposed at the other end of each of the two orthogonal directions, in this state, the cylindrical asphalt mixture specimen is pressed in the diameter direction, the displacement amount of each measuring element detected by the gap detector Or It is characterized in measuring the intensity of the asphalt mixture specimen.

[0007] Further, according to a second aspect of the present invention, there is provided the asphalt strength measuring method according to the first aspect of the present invention.
The strength of the cylindrical asphalt mixture specimen is measured by averaging the displacement of the probe in the same direction on the two bottom surfaces of the cylindrical asphalt mixture specimen. In addition, the asphalt strength measuring device according to claim 3 of the present invention comprises a measuring element attached to one end of each of the bottom surfaces of the asphalt mixture test specimen formed in a columnar shape in two directions orthogonal to each other, and the respective measuring elements. The direction in which the measuring element made of a conductor or a magnetic material is disposed at the other end of each of two orthogonal directions of the bottom surface of the asphalt mixture specimen in opposition to the element, and in the magnetic field generated by the coil, the measuring element made of a conductor or a magnetic substance is separated A gap detector capable of detecting the amount of displacement of the probe based on a change in inductance or a change in charge of the coil when the coil is displaced, and each gap when the cylindrical asphalt mixture specimen is pressed in the diameter direction. And a measuring means for measuring the strength of the specimen from the displacement of the probe detected by the detector.

According to a fourth aspect of the present invention, there is provided an asphalt strength measuring apparatus according to the third aspect, wherein
Among the two bottom surfaces of the cylindrical asphalt mixture specimen, an averaging means for averaging the displacement of the tracing stylus in the same direction detected by each of the gap detectors and outputting the averaged displacement to the measuring means, Is what you do. The asphalt strength measuring device according to claim 5 of the present invention is the device according to claim 3 or 4, wherein at least when the columnar asphalt mixture specimen is pressed in the diameter direction, the measuring element and the gap detector And at least one of the tracing stylus and the gap detector in the direction in which the stylus and the gap detector are displaced in a direction approaching each other, comprising a holding mechanism that allows the tracing stylus or the gap detector to retreat in a direction away from each other. Is what you do.

[0009]

Embodiments of the present invention will be described below. FIG. 1 is a schematic configuration diagram of an asphalt strength measuring method and apparatus of the present embodiment. In the present embodiment, the asphalt mixture specimen TP formed into a columnar shape having the above-described size is erected so that the diameter direction is vertical, and the vertical direction, that is, the diametrical direction of the columnar asphalt mixture specimen TP is set. Is assumed to be pressed. Therefore, the deformation amount (displacement amount) of the asphalt mixture specimen TP to be measured is the vertical direction which is the pressing direction and the horizontal direction which is the orthogonal direction, and the two bottom surfaces BF of the specimen TP are changed to the left and right bottom surfaces. And a displacement meter (in the figure, a vertical sensor and a horizontal sensor, respectively) for measuring displacements in two orthogonal directions, a vertical direction and a vertical direction, respectively.
a to 1d are provided. Each of these displacement meters 1a to 1d is constituted by a gap detector described later, which is disposed at one end in each of the two orthogonal directions. As will be described later, each of these gap detectors has a direction to be measured by each of the displacement meters 1a to 1d,
In other words, the displacement of the tracing stylus made of a conductor or a magnetic material disposed at the other end in the vertical or horizontal direction is detected, and all the displacement detection values A to D are input to the averaging device 2. The averaging machine 2 adds and averages outputs A and B of the displacement meters 1a and 1b for detecting, for example, two vertical displacements among the displacements detected by the respective displacement meters 1a to 1d. The outputs C and D of the displacement meters 1c and 1d for detecting the displacement in the horizontal direction are added and averaged and output to the personal computer PC. In this personal computer PC, for example, an arithmetic processing such as an analysis method described in the TP9-94 is programmed and stored in advance, and by this arithmetic processing, the displacement meter 1a
The strength of the measured asphalt mixture specimen TP can be calculated using the average value of the outputs of 〜1d.

Next, details of the gap detector and a structure for attaching the gap detector to the asphalt mixture specimen TP will be described. The gap detector includes a coil therein, and when a measuring element made of, for example, a conductor or a magnetic material is displaced in a direction approaching or moving away from the gap detector in a magnetic field generated by the coil, the coil In this method, it is possible to detect in which direction the measuring element is displaced and how much the probe is displaced based on a change in inductance or a change in electric charge generated in, for example, “GAP-SENS”.
ER "(registered trademark: Electronic Application Co., Ltd.) Model AEC-55
05 and AEC-5509. Incidentally, in this gap detector, the tip for detecting the displacement of the tracing stylus is called a probe, and the probe is a completely molded type and has excellent vibration resistance, heat resistance, and water and oil resistance. Therefore, by using this gap detector, it is possible to detect the displacement of the tracing stylus even in the conductive antifreeze. In this gap detector, when the probe is made of a magnetic material such as iron, the size of the gap, that is, the displacement and the detected value are linear, but the probe is made of aluminum or the like. Are non-linear, both have non-linear (non-linear) characteristics.

The structure for attaching the gap detector and the probe to the asphalt mixture specimen TP is configured as shown in FIG. On each bottom surface BF of the specimen TP, the TP9-94
Similarly, in the vertical and horizontal directions, at a position 1 inch from the center, a φ8 mm × h3.2 mm brass cylindrical body 3 a
To 3d are attached with an adhesive. Then, the gap detector 4HR for measuring the displacement in the horizontal direction is moved so that the probe tip 5HR is directed leftward in FIG. 2A.
The L-shaped aluminum bracket 6a is attached to the vertical wall 7a of the bracket 6a, and the base 8a of the L-shaped bracket 6a facing the bottom surface BF of the asphalt mixture specimen TP is connected to the right column 3a in FIG. Fixed to. Specifically, the circular recess formed in the base portion 8a is
a of the screw 9a screwed into the screw hole formed from the side surface of the base portion 8a so as to be pressed against the outer peripheral surface of the columnar body 3a. It is to be fixed to the cylindrical body 3a. On the other hand, a base portion 8b of an individual L-shaped aluminum bracket 6b is put on the cylindrical body 3b on the left side in FIG. 2B and fixed similarly with screws 9b. The base portion 8b is used for measuring the horizontal displacement. The gap detector 4HR extends rightward in the figure to the vicinity of the probe tip 5HR, and a vertical wall 7b is provided upright at the extended tip. The vertical wall portion 7b is provided at a position facing the probe tip 5HR of the gap detector 4HR for measuring horizontal displacement.
A circular iron probe 10HR is embedded.

A bottom portion 8c of an individual L-shaped aluminum bracket 6c is provided on the lower cylindrical body 3c shown in FIG. 2a.
And fixed in the same manner with screws 9c.
c, a vertical displacement measuring gap detector 4VT is attached so that the probe tip 5VT faces upward in the figure. Here, the probe tip 5VT from the vertical wall 7c is attached.
The length of the VT protruding is made longer so that it is located further above the base 8b of the bracket 6b attached to the left column 3b shown in the figure. With this configuration, it is possible to make the height of the horizontal displacement measuring gap detector 4HR from the specimen bottom surface BF equal to the height of the vertical displacement measuring gap detector 4VT. . Also, a base portion 8 of an individual L-shaped aluminum bracket 6d is provided on the upper cylindrical body 3d in FIG. 2A.
d, and similarly fixed with screws 9d, and the tracing stylus holder 11 is attached to the vertical wall 7d. As shown in FIG. 2 a, the measuring element holding device 11 has a circular iron measuring element 10 VT embedded at the lower end of a rod 12 whose axis is oriented vertically, and a weight 13 at the upper end of the rod 12. Attached. Further, a piston 14 is formed at a central portion in the axial direction of the rod 12 and is housed in a cylinder body 15. The piston 14 is lowered downward in the figure by a spring 16 housed in the cylinder body 15. Pressed. Therefore, the stylus 1
The rod 12 in which the 0VT is embedded is pressed downward by the weight of the weight 13 and the elastic force of the spring 16, and in this state, the tracing stylus 10VT is attached to the probe tip dance VT of the vertical displacement measuring gap detector 4VT. , Facing each other with a little space between them. On the other hand, probe 1
When 0VT is pressed from below, the entire rod 12 including the weight 13 moves upward as shown by a two-dot chain line in FIG. 2 against the weight of the weight 13 and the elastic force of the spring 16. When the asphalt mixture specimen TP pressed in the vertical direction breaks, a deformation such as a large contraction occurs in the vertical direction, and the gap detector 4V for measuring the vertical displacement is used.
There is a large possibility that the probe tip 5VT of T collides with the tracing stylus 12. In such a case, the tracing stylus holding device 11
Of the probe 10VT
It is possible to prevent or prevent the gap detector 4VT from being deformed or damaged.

[0013] The linearity at various temperatures of the displacement amount of the gap detector and the iron tracing stylus thus configured and the detected value thereof and their respective correction coefficients were investigated. FIG.
At 0 ° C., −10 ° C., −20 ° C., and −30 ° C., the relationship between the amount of displacement given by the microphone meter and the detected value is shown. Is shown. From the figure, at various temperatures, the true displacement and the detected value show good linearity. Therefore, if an appropriate correction coefficient is set at each temperature, the detected value can be made closer to the true displacement amount as indicated by a black triangle.

Next, the asphalt measuring device was immersed in an antifreeze solution at -15 ° C. together with the columnar asphalt mixture specimen, and the results of a vertical pressing test are shown in FIG. The asphalt mixture specimen is a soft material called straight asphalt 60/80, and FIG. 4A shows the vertical displacement and FIG. 4B shows the horizontal displacement. The displacement in the vertical direction is in the negative direction on the number line, and the displacement in the horizontal direction is in the positive direction. Here, both are represented by absolute values. This measuring device itself has a displacement measuring range of at least several mm, but in an actual test, it was broken when a deformation (displacement) of about 0.05 mm in the vertical direction and about 0.04 mm in the horizontal direction occurred. (8se on the time axis
c.). As is clear from the figure, the asphalt measuring apparatus according to the present embodiment was able to measure displacement (deformation) even in antifreeze, and was able to accurately measure the process leading to destruction. In addition, the gap detector detects a change in the gap between the probe and the probe as a displacement on the basis of the attachment point, so that there is no need for so-called calibration, and for example, the apparatus is provided on an asphalt mixture specimen cooled to a required temperature. Since the pressing deformation can be measured immediately after mounting, there is also an advantage that the adjustment is easy. Of course, by the retreat mechanism of the tracing stylus holding device, the asphalt mixture specimen continues to be output even if destroyed,
Even large deformation or destruction does not cause deformation or damage.

On the other hand, FIG. 8 shows the results of a press deformation test of the same asphalt mixture specimen using the LVDT. This test was also performed on the same asphalt mixture specimen, and FIG. 8A shows the displacement in the vertical direction, and FIG. 8B shows the displacement in the horizontal direction. Can not be measured in antifreeze like
Therefore, the magnitude of the displacement is different from that of FIG. Also,
The time axis of the horizontal axis also differs greatly from the viewpoint of the measurement accuracy of the displacement meter. In fact, this displacement measurement cannot detect the destruction of the asphalt mixture specimen. The detection value is saturated at the vertical displacement amount shown in FIG. 8A because the measuring element has been caught in the scale tube.
Since then, no displacement has been measured. The reason why the detected value drops stepwise in the horizontal displacement amount shown in FIG. 8B is that the tracing stylus has fallen out of the scale tube, and thereafter, the displacement cannot be measured. As mentioned above, the range where displacement can be accurately measured by LVDT is 0.25
mm, the measurement result is a natural result and is not suitable for measuring the strength from the deformation of such a soft asphalt mixture. On the other hand, in the asphalt strength measurement of the present embodiment, not only the use in the antifreeze but also the displacement data up to the destruction can be accurately measured.

[0016]

As described above, according to the method and the apparatus for measuring asphalt strength of the present invention, when each of the two bottom surfaces of the cylindrical asphalt mixture specimen is pressed in the diameter direction, Deformation in two orthogonal directions,
Since the strength of the asphalt mixture specimen is measured by detecting the displacement of the probe made of a conductor or magnetic material in the direction of contact and separation from the gap sensor and the amount of displacement, the displacement measurement range is wide, and large deformation and It can cope with the destruction of the sample, and can be easily adjusted because the position where the gap sensor and the measuring element are attached is the zero position, and can be used even in a liquid such as antifreeze.

Further, since the strength of the cylindrical asphalt mixture specimen is measured by averaging the displacement of the probe in the same direction on the two bottoms of the cylindrical asphalt mixture specimen, the deformation occurring at the two bottoms of the specimen is considered. By correcting the deviation, the strength of the asphalt mixture can be measured more accurately. Further, when the cylindrical asphalt mixture specimen is pressed in the diameter direction, the probe or the gap detector approaching each other is provided with a holding mechanism that can retreat in a direction away from each other, for example, when the specimen is broken. When the tracing stylus and the gap detector collide with each other at a large displacement, the two escape to each other to prevent deformation and breakage.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an asphalt strength measuring method and apparatus of the present invention.

FIGS. 2A and 2B are explanatory views of a gap detector used in each displacement meter of FIG. 1 and a mounting structure thereof, wherein FIG. 2A is a front view and FIG.
Is a side view, (c) is a bottom view, and (d) is a side view of the separation diagram c.

FIG. 3 is an output characteristic diagram at various temperatures of a gap detector used in FIG. 2;

FIG. 4 is an explanatory diagram of a result of a press deformation test of an asphalt mixture specimen by the asphalt strength measuring device of FIG.

FIG. 5 is an explanatory diagram of strength measurement of an asphalt mixture specimen.

FIG. 6 is an explanatory diagram of asphalt strength measurement defined in TP9-94.

FIG. 7 is an explanatory diagram of a displacement meter in measuring asphalt strength specified in TP9-94.

FIG. 8 is an explanatory diagram of a result of a press deformation test of an asphalt mixture specimen by the asphalt strength measuring device of FIG.

[Explanation of symbols]

 1a to 1d are displacement gauges 2 are averaging machines 3a to 3d are cylinders 4HR, 4VT are gap detectors 5HR, 5VT are probe tips 10HR, 10VT are tracing styluses 11 are tracing styluses 12 rods 13 are weights 14 Is a piston 15 is a cylinder body 16 is a spring

Claims (5)

[Claims] 1. A specimen made of an asphalt mixture is formed into a cylindrical shape, and two orthogonal directions are set so as to be in the same direction on both of the two bottom surfaces. Attach a probe made of a conductor or a magnetic material to one end, and change the inductance or charge of the coil when the probe made of a conductor or a magnetic material is displaced in the magnetic field generated by the coil. On the basis of the change, a gap detector for detecting the displacement amount of the tracing stylus is disposed at the other end of each of the two orthogonal directions so as to face the tracing stylus, and in that state, the columnar asphalt is provided. An asphalt strength measuring method comprising: pressing a mixture specimen in a diameter direction; and measuring a strength of the asphalt mixture specimen from a displacement amount of each measuring element detected by the gap detector. 2. The asphalt strength measuring method according to claim 1, wherein the strength of the cylindrical asphalt mixture specimen is measured by averaging the displacement of a probe in the same direction on two bottom surfaces of the cylindrical asphalt mixture specimen. 3. A stylus attached to one end in each of two orthogonal directions of each bottom surface of a columnar shaped asphalt mixture specimen, and each of the asphalt mixture specimens opposed to the respective stylus. A change in inductance or electric charge of the coil when the measuring element made of a conductor or a magnetic body is displaced in a direction in which the probe is separated from and separated in the magnetic field generated by the coil, which is disposed at the other end of each of the two orthogonal directions on the bottom surface. Based on the change, the gap detector capable of detecting the displacement of the probe, and the displacement of the probe detected by each gap detector when the cylindrical asphalt mixture specimen is pressed in the diameter direction. An asphalt strength measuring device, comprising: a measuring means for measuring the strength of the specimen. 4. An averaging means for averaging displacement amounts of a tracing stylus in the same direction detected by each of the gap detectors and outputting to the measuring means among two bottom surfaces of the cylindrical asphalt mixture specimen. The asphalt strength measuring device according to claim 3, wherein: 5. At least one of the probe and the gap detector in a direction in which the probe and the gap detector are displaced in a direction approaching each other when the columnar asphalt mixture specimen is pressed in the diameter direction. The asphalt strength measuring device according to claim 3, wherein the measuring element or the gap detector includes a holding mechanism that can retreat in a direction away from each other.