Asphalt mixture core sample-based shrinkage coefficient calculation method

Abstract

The invention discloses a shrinkage coefficient calculation method based on an asphalt mixture core sample, which comprises the following steps: acquiring the asphalt mixture core sample, and cutting the asphalt mixture core sample into a disc test piece; measuring a calibration strain coefficient of the circular asphalt mixture shrinkage coefficient testing device; putting the disc test piece into a circular asphalt mixture shrinkage coefficient testing device, pasting a temperature sensor on the surface of the test piece, putting the testing device into an environment box, then carrying out a shrinkage coefficient test and calculating the shrinkage coefficient. The shrinkage coefficient calculation method based on the asphalt mixture core sample is simple and easy to implement, real and reliable in data and simple to operate, can effectively calculate the shrinkage coefficients of different asphalt mixture core samples, and is a shrinkage coefficient calculation method with relatively high innovativeness.

Description

Technical Field

[0001] The invention relates to the technical field of linear shrinkage coefficient test of asphalt mixture, and in particular to a shrinkage coefficient calculation method based on an asphalt mixture core sample. Background Art

[0002] Asphalt mixture is a temperature-sensitive material, and its mechanical properties and volume will change under the influence of temperature changes. The decrease in temperature will lead to a decrease in the deformation performance of asphalt mixture. Shrinkage cracking caused by rapid temperature drop has always been one of the main forms of early road damage. At the same time, its temperature sensitivity will cause microcracks to form on roads in areas with large temperature differences under the coupling of load and temperature stress. These microcracks will further develop into more serious diseases, thus affecting the normal use of the road.

[0003] The linear shrinkage coefficient of asphalt mixture is an important indicator for evaluating the low-temperature crack resistance of asphalt mixture. It is also a necessary parameter for calculating temperature stress. It is of great significance to improve the low-temperature shrinkage crack resistance of asphalt pavement. At present, the shrinkage coefficient of asphalt mixture is mainly obtained based on the method specified in the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" JTGE20-2011. However, this method has some disadvantages, which are reflected in:

[0004] 1. The test stipulates that the wheel plate specimen formed by the wheel rolling method is cut into a 200mm×20mm×20mm rectangular specimen, but the preparation of the specimen is time-consuming, the preparation process is complicated, and the specimen preparation efficiency is low;

[0005] 2. After the specimen reaches the specified temperature and remains constant, in order to prevent the specimen temperature from changing greatly and causing large measurement errors in the shrinkage coefficient, the specimen needs to be taken out of the constant temperature water bath and measured within 5 seconds. This process places high demands on the test personnel;

[0006] 3. During the test, the specimen will heat up and expand after contacting the air, causing human errors in the test results;

[0007] 4. In this test, the specimen is placed horizontally at the bottom of a constant temperature water tank. During the cooling and shrinking process of the specimen, the bottom of the tank has a large friction force on the specimen, which will cause errors in the test.

[0008] On the other hand, the shrinkage coefficient measured by the traditional shrinkage coefficient test has insufficient correlation with other low-temperature test parameters and has a certain variability. This is because the specimens used in the shrinkage coefficient test are difficult to continue other low-temperature tests, and new specimens must be re-molded for subsequent low-temperature tests.

[0009] Based on the above drawbacks, developing a method for calculating the shrinkage coefficient based on asphalt mixture core samples has important practical value. Summary of the invention

[0010] In order to overcome the shortcomings of the prior art, the purpose of the present invention is to provide a method for calculating the shrinkage coefficient based on asphalt mixture core samples, which can reduce the difficulty of testing the shrinkage coefficient of asphalt mixture, improve the test accuracy, and increase the correlation between the shrinkage coefficient and other low-temperature parameters, thereby achieving the effect of accurate calculation.

[0011] The purpose of the present invention is achieved by the following technical solutions:

[0012] According to an embodiment of the present disclosure, a method for calculating a shrinkage coefficient based on an asphalt mixture core sample is provided, comprising the following steps:

[0013] A. Obtain an asphalt mixture core sample and cut the asphalt mixture core sample into disc specimens;

[0014] B. Obtain a shrinkage coefficient test device; the shrinkage coefficient test device comprises a chassis, a specimen placement slot is provided on the chassis, and four displacement sensors are provided on the sides of the specimen placement slot on the chassis;

[0015] C. Determine the standard strain coefficient of the shrinkage coefficient test device in step B: obtain a cross-shaped Invar alloy; use the shrinkage coefficient test device to test the Invar alloy: use a displacement sensor to measure the slope of the Invar alloy after deformation with temperature change, and the slope is the standard strain coefficient of the shrinkage coefficient test device;

[0016] D. Place the disc specimen in step A into the shrinkage coefficient test device in step B, install a temperature sensor on the disc specimen, and then place the shrinkage coefficient test device with the disc specimen in an environmental chamber, perform continuous temperature change treatment on the interior of the environmental chamber, and read the data measured by the displacement sensor at different temperatures;

[0017] E. Calculate the shrinkage coefficient: Calculate using the following formula:

[0018] α=dε / dT=α g +(α1-α g )exp[(TT g ) / R] / {1+exp[(TT g ) / R]} (1)

[0019] In the formula,

[0020] α is the contraction coefficient;

[0021] ε is the strain caused by low temperature shrinkage;

[0022] α1 and α g are the shrinkage / expansion coefficients of the fluid and glassy states;

[0023] R is the distance between the two asymptotic foci and the curve, which can characterize the curvature of the curve;

[0024] T g is the glass transition temperature.

[0025] As a preferred embodiment, in step A, the specific steps of obtaining the asphalt mixture core sample are: taking the core sample drilled on site, or using a selective compactor with a controlled number of times to form a core sample with a diameter of 150 mm.

[0026] As a preferred embodiment, in step A, the specific steps of cutting the asphalt mixture core sample into disc specimens are: cutting the core sample drilled on site according to the layer to obtain the disc specimen, or obtaining the disc specimen with a thickness of 40 mm after cutting the specimen formed by rotary compaction.

[0027] As a preferred embodiment, in step C, the specific steps of obtaining the cross-shaped Invar alloy are: assembling two Invar alloy rods with a length of 150 mm and a cross section of 6.35 mm x 12.7 mm into a square cross.

[0028] As a preferred embodiment, in step D, before the shrinkage coefficient test device is placed in the environmental chamber, the starting temperature, cooling rate and final temperature on the environmental chamber are set first; wherein the starting temperature is set at 20°C, and if continuous temperature change is adopted, the minimum cooling rate is 5°C / h, and the maximum cooling rate is 20°C / h.

[0029] As a preferred embodiment, when the internal temperature of the environmental chamber changes, four displacement sensors perform four independent measurements of the dimensional changes of the specimen.

[0030] As a preferred embodiment, the specific operation of continuous temperature change is: after maintaining the initial temperature at 20°C for 4 hours, the temperature is cooled to -40°C at cooling rates of 5°C / h, 10°C / h, 15°C / h and 20°C / h respectively, and the data sampling frequency is 10 Hz.

[0031] As a preferred embodiment, the calibration strain of the disc specimen is determined by the following formula:

[0032] Calibrated strain = uncalibrated strain - device calibration gauge factor * drop temperature;

[0033] In the formula,

[0034] The uncalibrated strain is the average of the four displacement sensors;

[0035] The drop temperature is the temperature of the environmental chamber dropped from 20°C.

[0036] As a preferred embodiment, in step D, after cooling to a certain temperature, the temperature is kept at a certain time, and then a displacement sensor is used to measure and record data and calculate to measure the shrinkage coefficient in different temperature ranges.

[0037] In summary, compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. Compared with the traditional calculation method, the present application does not require the molding of rectangular specimens, which not only simplifies the specimen preparation process of the shrinkage coefficient test, but also expands the scope of application of the test and improves the data correlation; at the same time, there is no need to take out the specimen for rapid measurement, which not only eliminates the time limit for taking out the specimen, thereby reducing the probability of test failure, but also eliminates the influence of temperature changes on the measurement accuracy after taking out the specimen; the present device can measure the multi-directional shrinkage coefficient of the specimen in real time by setting multiple displacement sensors, taking into account the influence of the anisotropy of asphalt mixture, and solving the problems of poor micrometer accuracy and large manual reading errors in the existing shrinkage coefficient test;

[0039] 2. This application has compiled a fitting model formula considering the thermal strain of asphalt mixture:

[0040] α=dε / dT=α g +(α1-α g )exp[(TT g ) / R] / {1+exp[(TT g ) / R]} (1)

[0041] According to this formula, the data can be fitted by simply inputting the calibration strain collected during low-temperature shrinkage. By taking the first derivative of the fitted data, the relationship between the shrinkage coefficient and temperature can be output. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is an overall schematic diagram of the shrinkage coefficient test device of the present invention;

[0043] The numbers and letters in the figure represent the corresponding component names:

[0044] 1. Chassis; 2. Test piece prevention groove; 3. Displacement sensor. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] Example: Figure 1As shown, a method for calculating the shrinkage coefficient based on an asphalt mixture core sample comprises the following steps:

[0047] A. Obtain an asphalt mixture core sample and cut the asphalt mixture core sample into disc specimens;

[0048] B. Obtain a shrinkage coefficient test device; the shrinkage coefficient test device comprises a chassis 1, a specimen placement slot 2 is provided on the chassis 1, and four displacement sensors 3 are provided on the sides of the specimen placement slot 2 on the chassis 1;

[0049] C. Determine the standard strain coefficient of the shrinkage coefficient test device in step B: obtain a cross-shaped Invar alloy; use the shrinkage coefficient test device to test the Invar alloy: use the displacement sensor 3 to measure the slope of the Invar alloy after deformation with temperature change, and the slope is the standard strain coefficient of the shrinkage coefficient test device;

[0050] D. Place the disc specimen in step A into the shrinkage coefficient test device in step B, install a temperature sensor on the disc specimen, and then place the shrinkage coefficient test device with the disc specimen in an environmental chamber, perform continuous temperature change treatment on the interior of the environmental chamber, and read the data measured by the displacement sensor at different temperatures;

[0051] E. Calculate the shrinkage coefficient: Calculate using the following formula:

[0052] α=dε / dT=α g +(α1-α g )exp[(TT g ) / R] / {1+exp[(TT g ) / R]} (1)

[0053] In the formula,

[0054] α is the contraction coefficient;

[0055] ε is the strain caused by low temperature shrinkage;

[0056] α1 and α g are the shrinkage / expansion coefficients of the fluid and glassy states;

[0057] R is the distance between the two asymptotic foci and the curve, which can characterize the curvature of the curve;

[0058] T g is the glass transition temperature.

[0059] It should be noted that formula (1) is determined by the first-order derivative of the following formula (2):

[0060] ε=C+α g (TT g)+R(α1-α g )ln{1+exp[(TT g ) / R]} (2);

[0061] In the formula,

[0062] ε is the strain caused by low temperature shrinkage;

[0063] α1 and α g are the shrinkage / expansion coefficients of the fluid and glassy states;

[0064] R is the distance between the two asymptotic foci and the curve, which can characterize the curvature of the curve;

[0065] T g is the glass transition point temperature;

[0066] C is the y-intercept of the two asymptotic line foci, and the constant of curve fitting has no physical meaning.

[0067] Specifically, in step A, the specific steps for obtaining the asphalt mixture core sample are: taking the core sample drilled on site, or using a selective compactor with a controlled number of times to form a core sample with a diameter of 150 mm.

[0068] Specifically, in step A, the asphalt mixture core sample is cut into disc specimens by cutting the core sample drilled on site according to the layer to obtain the disc specimen, or the disc specimen with a thickness of 40 mm is obtained by cutting the rotary compacted specimen.

[0069] Specifically, in step C, the specific steps of obtaining the cross-shaped Invar alloy are as follows: assembling two Invar alloy rods (shrinkage coefficient = 1.2 με / ° C.) with a length of 150 mm and a cross section of 6.35 mm x 12.7 mm into a square cross.

[0070] Specifically, in step D, before the shrinkage coefficient test device is placed in the environmental chamber, the starting temperature, cooling rate, and final temperature on the environmental chamber are set first; wherein the starting temperature is set at 20°C, and if continuous temperature change is adopted, the minimum cooling rate is 5°C / h, and the maximum cooling rate is 20°C / h.

[0071] Specifically, when the internal temperature of the environmental chamber changes, four displacement sensors make four independent measurements of the dimensional changes of the specimen.

[0072] Specifically, the specific operation of continuous temperature change is: after maintaining the initial temperature at 20°C for 4 hours, the temperature is lowered to -40°C at cooling rates of 5°C / h, 10°C / h, 15°C / h and 20°C / h respectively, and the data sampling frequency is 10 Hz.

[0073] Specifically, the calibration strain of the disc specimen is determined by the following formula:

[0074] Calibrated strain = uncalibrated strain - device calibration gauge factor * drop temperature;

[0075] In the formula,

[0076] The uncalibrated strain is the average of the four displacement sensors;

[0077] The drop temperature is the temperature of the environmental chamber dropped from 20°C.

[0078] Specifically, in step D, after cooling to a certain temperature, the temperature is kept at a certain time, and then a displacement sensor is used to measure and record data and calculate to measure the shrinkage coefficient in different temperature ranges.

[0079] During implementation, a number of steel balls (not shown) are arranged in the test piece prevention groove 2, and the diameter of the steel balls is 2 mm. In this way, the test piece is placed in the groove with 2 mm diameter steel balls, and the steel balls can reduce the external constraints on the test piece during the shrinkage process.

[0080] During implementation, four displacement sensors 3 are evenly arranged around the test piece prevention groove 2 on the chassis 1, so that the angle between adjacent displacement sensors 3 is 90°, and the four displacement sensors 3 are on the same plane. In this way, the shrinkage of the core sample in different directions can be measured more accurately in real time.

[0081] During implementation, the displacement sensor is a linear displacement meter.

[0082] During implementation, the displacement sensor 3 is in a square shape, and the outer wall of the displacement sensor 3 facing the center of the specimen prevention groove 2 is flush with the inner wall of the specimen prevention groove 2 .

[0083] During implementation, the test piece prevention groove 2 is a circular groove.

[0084] During implementation, the chassis 1 is a component made of stainless steel. During implementation, the bottom plate is made of austenitic stainless steel, which has a small linear shrinkage coefficient, thereby avoiding affecting the shrinkage coefficient test of the core sample of the mixed material.

[0085] In this embodiment, the specimen will shrink to different degrees with temperature changes in a constant temperature environment. The purpose of the shrinkage coefficient test is to test the shrinkage degree of the specimen at different temperatures, and then analyze and judge the shrinkage performance of the asphalt mixture. The four displacement sensors installed on the chassis test the length of the specimen in each direction at different temperatures, and the shrinkage coefficient is obtained by analyzing the displacement (i.e., the length change).

[0086] The above embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which are equivalent modifications and improvements made to the above embodiments based on the essential technology of the present invention, and all of them belong to the protection scope of the present invention.

Claims

1. A method for calculating the shrinkage coefficient based on an asphalt mixture core sample, characterized in that: The following steps are involved: A. Obtain an asphalt mixture core sample and cut the asphalt mixture core sample into disc specimens; B. Obtain shrinkage coefficient test device; The shrinkage coefficient test device comprises a chassis, a test piece placement slot is provided on the chassis, and four displacement sensors are arranged on the sides of the test piece placement slot on the chassis; C. Determine the standard strain coefficient of the shrinkage coefficient test device in step B: obtain a cross-shaped Invar alloy; use the shrinkage coefficient test device to test the Invar alloy: use a displacement sensor to measure the slope of the Invar alloy after deformation with temperature change, and the slope is the standard strain coefficient of the shrinkage coefficient test device; D. Place the disc specimen in step A into the shrinkage coefficient test device in step B, install a temperature sensor on the disc specimen, and then place the shrinkage coefficient test device with the disc specimen in an environmental chamber, perform continuous temperature change treatment on the interior of the environmental chamber, and read the data measured by the displacement sensor at different temperatures; E. Calculate the shrinkage coefficient: Calculate using the following formula: α=dε / dT=α g +(α1-α g )exp[(T-T g ) / R] / {1+exp[(T-T g ) / R]} (1) In the formula, α is the contraction coefficient; ε is the strain caused by low temperature shrinkage; α1 and α g are the shrinkage / expansion coefficients of the fluid and glassy states; R is the distance between the two asymptotic foci and the curve, which can characterize the curvature of the curve; T g is the glass transition temperature.

2. A method for calculating shrinkage coefficient based on asphalt mixture core sample according to claim 1, characterized in that: In step A, the specific steps for obtaining the asphalt mixture core sample are: taking the core sample drilled on site, or using a selective compactor with a controlled number of times to form a core sample with a diameter of 150 mm.

3. A method for calculating shrinkage coefficient based on asphalt mixture core sample according to claim 2, characterized in that: In step A, the asphalt mixture core sample is cut into disc specimens. The specific steps are: the core sample drilled on site is cut according to the layer to obtain the disc specimen, or the disc specimen with a thickness of 40 mm is obtained by cutting the rotary compaction molded specimen.

4. The method for calculating shrinkage coefficient based on asphalt mixture core sample according to claim 1, characterized in that: In step C, the specific steps of obtaining a cross-shaped Invar alloy are as follows: assemble two Invar alloy rods with a length of 150 mm and a cross section of 6.35 mm x 12.7 mm into a square cross.

5. The method for calculating shrinkage coefficient based on asphalt mixture core sample according to claim 1, characterized in that: In step D, before the shrinkage coefficient test device is placed in the environmental chamber, the starting temperature, cooling rate, and final temperature on the environmental chamber are set first; wherein the starting temperature is set at 20°C, and if continuous temperature change is adopted, the minimum cooling rate is 5°C / h, and the maximum cooling rate is 20°C / h.

6. A method for calculating shrinkage coefficient based on asphalt mixture core sample according to claim 5, characterized in that: When the internal temperature of the environmental chamber changes, four displacement sensors make four independent measurements of the dimensional change of the specimen.

7. A method for calculating shrinkage coefficient based on asphalt mixture core sample according to claim 6, characterized in that: The specific operation of continuous temperature change is: after maintaining the initial temperature at 20°C for 4 hours, the temperature is lowered to -40°C at cooling rates of 5°C / h, 10°C / h, 15°C / h and 20°C / h respectively, and the data sampling frequency is 10 Hz.

8. A method for calculating shrinkage coefficient based on asphalt mixture core sample according to claim 7, characterized in that: The calibration strain of the disk specimen is determined by the following formula: Calibrated strain = uncalibrated strain - device calibration gauge factor * drop temperature; In the formula, The uncalibrated strain is the average of the four displacement sensors; The drop temperature is the temperature of the environmental chamber dropped from 20°C.

9. The method for calculating shrinkage coefficient based on asphalt mixture core sample according to claim 1, characterized in that: In step D, after cooling to a certain temperature, the temperature is kept at a certain time, and then a displacement sensor is used to measure and record data and calculate to measure the shrinkage coefficient in different temperature ranges.

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