CN108693053A - A kind of test method of asphalt residual intensity - Google Patents

Abstract

The invention discloses a method for testing the residual strength of asphalt mixture, which comprises the following steps: 1) preparing a sample of asphalt mixture, performing a fatigue test to determine the law of fatigue development; Stop loading the specimen during the failure stage; 3) Immediately test the tensile strength of the specimen that stopped loading; 4) Repeat steps 2) and 3) to determine the tensile strength of the material under different fatigue levels; 5) Fit different Residual strength under the fatigue state, obtain the relation of residual strength-damage fatigue; The present invention has determined the ultimate tensile strength of asphalt mixture different fatigue stages with the material fatigue damage by the mode that fatigue test and tensile strength test carry out synchronously The law of decay is of great significance to the design of pavement and the formulation of traffic control schemes in the whole life cycle of pavement.

Description

A test method for residual strength of asphalt mixture

technical field

The invention relates to the technical field of road engineering, in particular to a method for testing the residual strength of asphalt mixture.

Background technique

Asphalt pavement has the characteristics of smooth road surface, low noise, short construction period, and convenient maintenance in the later stage, so it has been widely used in road engineering. With the maturity of asphalt mixture and pavement construction technology, early failure forms such as loose mixture and roadbed subsidence have become less and less. Instead, long-term diseases such as fatigue have gradually become the main factors affecting the service life of asphalt pavement.

The fatigue development of asphalt mixture is accompanied by the deterioration of various mechanical properties of the material. With the fatigue development of the material, the ultimate bearing capacity of the material will gradually decrease. The current pavement design method is based on the strength of the non-damaged asphalt mixture material. With the increase of the service life of the pavement, the remaining strength of the pavement material will gradually decrease, and the pavement may exceed the bearing capacity of the structure within the design load range, resulting in pavement acceleration. phenomenon of destruction. Therefore, determining the law between the residual strength and fatigue development of pavement materials is of great significance for pavement design and the formulation of traffic control schemes in the pavement life cycle.

Contents of the invention

In view of the above-mentioned problems, the purpose of the present invention is to provide a test method for the residual strength of asphalt mixture, by carrying out fatigue test and tensile strength test to multiple groups of test pieces simultaneously, to obtain the tensile strength of asphalt mixture with fatigue development. The law of decay provides a corresponding mechanical basis for further road design and maintenance management.

In order to achieve the above object, the technical scheme adopted in the present invention is as follows: a method for testing the residual strength of asphalt mixture, comprising the steps:

1) Prepare the mixture specimen according to the test requirements, conduct the first set of fatigue tests, and determine the fatigue life N _f , the fatigue damage variable D and the fatigue damage decay law f(D) of the current mixture specimen;

2) Under the same test conditions as the first group of fatigue tests, take the second group of mixture specimens for fatigue test loading, when the number of loading is α ₁ N _f , where 0≤α ₁ <1, stop the loading test;

3) Immediately carry out the asphalt mixture bending test to the mixture specimen after step 2) processing, obtain the bending tensile strength R _B1 of the specimen after experiencing fatigue loading;

4) Under the same test conditions, repeat step 2) and step 3), and when the loading times are α ₂ N _f , α ₃ N _f , ... α _n N _f , the corresponding flexural tensile strength is R _B2 , R _B3 , ... R _Bn ; repeated data should be at least 3 groups, and the obtained data should cover as wide a range as possible from the beginning of the fatigue test to the end of the fatigue life of the specimen.

5) From the fatigue decay law f(D) obtained in step 1) and the flexural tensile strength R _B2 , R _B3 , ... R _Bn of the material under different fatigue loading times, the remaining flexural tensile strength of the mixture specimen can be obtained The relationship between strength R _B and fatigue damage variable D:

R _B =aD ² +bD+c

Among them, a, b, c are parameters, which are obtained by fitting the experimental data.

The mixture test piece in the step 1) of the present invention is prepared according to the requirements of T 0739-2011 four-point bending fatigue life test of asphalt mixture in JTG E20-2011 highway engineering asphalt and asphalt mixture test regulations.

Step 1) of the present invention, the fatigue damage variable D of the mixture test piece is characterized by the stiffness of the test piece, and its relational expression is as follows:

Among them, D is the fatigue damage variable, E _i is the stiffness of the specimen when it is loaded cyclically, E ₀ is the initial stiffness of the specimen; the fatigue test is a repeated loading test, and the above Nf is the final loading times, this i is the loading number of a certain time in the test process.

Step 1 of the present invention) in, fatigue damage decay law f (D), its relational expression is as follows:

Among them, D is the variable of fatigue damage; N is the number of stress cycles; a ^* , p, q are all fatigue parameters, which are obtained by regression of test data.

In step 3) of the present invention, the tensile strength test method is based on T 0715-2011 asphalt mixture bending test in JTG E20-2011 road engineering asphalt and asphalt mixture test regulations.

The advantage of the present invention is that: the present invention provides a method for the decay law of the residual strength of asphalt mixture, which combines the four-point bending fatigue life test and bending test of asphalt mixture in the JTGE20-2011 road engineering asphalt and asphalt mixture test regulations Combined, the decay law of tensile strength of asphalt mixture with fatigue development is obtained, which provides a mechanical basis for road design and formulation of maintenance management plans for the later stages of road service life. At the same time, the statistical relationship between the residual strength of asphalt mixture and the failure critical condition of fatigue test can be used to determine the reliability of materials in different fatigue stages.

Description of drawings

Fig. 1 is the flowchart of the inventive method;

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

JTG E20-2011 in the description and examples of the present invention is the specification code for the asphalt mixture test, T0739-2011 is the code for the fatigue test of the asphalt mixture in the specification, and T 0715-2011 is the code for the bending test of the asphalt mixture in the specification; the present invention This test method mentioned in is not limited to any asphalt mixture, it can be any asphalt mixture that meets the requirements of the specification.

Embodiment 1: as shown in Figure 1, a kind of method for decay law of residual strength of asphalt mixture comprises the following steps:

1) Prepare matrix 70# asphalt AC-20 mixture according to T 0739-2011 four-point bending fatigue life test requirements of asphalt mixture in JTG E20-2011 highway engineering asphalt and asphalt mixture test regulations. The test temperature was 15°C, the loading frequency was 10 Hz, the controlled strain loading mode was adopted, and the loading level was 800 με. Carry out the first set of fatigue tests to obtain the fatigue life of the current mixture N _f =2400 times.

The fatigue damage of the material is characterized by the stiffness of the specimen, which takes the following form:

In the formula: D is the fatigue damage variable characterized by stiffness, E _i is the stiffness of the specimen when it is loaded in the i-th cycle, and E ₀ is the initial stiffness of the specimen before loading.

The fatigue test adopts controlled stress loading method. The law of fatigue damage decay adopts the following nonlinear fatigue damage model:

In the formula: D is the variable of fatigue damage; N is the number of stress cycles; a ^* , p, q are all fatigue parameters, which are related to temperature and stress loading level and obtained by regression of test data.

In this example, since the temperature and load level are kept constant, q=0 is set. According to the judgment rule of fatigue life under the control strain mode, when D=0.5, it is determined that the specimen is damaged, then the above formula can be expressed as:

0.5＝a ^* E ₀ ^p ε ^p N _f

Taking the natural logarithm on both sides of the formula, we get:

lnN _f ＝-lna ^* -pln(E ₀ ε)+ln0.5

Afterwards, the parameters a ^* and p can be linearly fitted by mathematical tools such as MATLAB. In this example, the fitting result is a ^* =3.2*10 ^-7 , p=3.8.

2) Under the same test conditions as the first group, take the second group of specimens for fatigue test loading, when the number of loading is α ₁ N _f (0≤α ₁ <1), stop loading. In this example, α ₁ =0 is taken, that is, the second group of specimens is not subjected to fatigue test loading.

3) According to T 0715-2011 asphalt mixture bending test in JTG E20-2011 highway engineering asphalt and asphalt mixture test regulations, conduct the bending and tensile strength test on the second group of specimens as soon as possible to determine the fatigue load. The bending and tensile strength R _B1 of the specimen.

4) Repeat steps 2) and 3) under the same test conditions to obtain the corresponding material flexural and tensile strengths R _B2 , R _B3 , and R _B4 when the loading times are 0.3N _f , 0.6N _f , and 0.9N _f .

5) From the fatigue decay law obtained in step 1) and the bending and tensile strength of the material under different fatigue loading times, the remaining bending and tensile strength-damage law of the material is fitted.

The decay law of the material residual strength R _B with the fatigue damage D of the material is as follows:

R _B =aD ² +bD+c

Where a, b, c are parameters. From the fatigue damage development law obtained in step 1), the damage degrees D ₁ , D ₂ , D ₃ , and D ₄ under loading times of 0, 0.3N _f , 0.6N _f , and 0.9N _f times can be obtained; D ₁ , D ₂ , D ₃ , D ₄ and the bending strength R _B1 , R _B2 , R _B3 , R _B4 use MATLAB and other mathematical software to perform least square fitting, and then the parameters a, b, c can be obtained.

It should be noted that the above are only preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Any combination or equivalent transformation made on the basis of the above embodiments belongs to the protection scope of the present invention.

Claims (6)

1. a method for testing the residual strength of asphalt mixture, is characterized in that, comprises the steps: 1) Prepare the mixture specimen according to the test requirements, conduct the first set of fatigue tests, and determine the fatigue life N _f , the fatigue damage variable D and the fatigue damage decay law f(D) of the current mixture specimen; 2) Under the same test conditions as the first group of fatigue tests, take the second group of mixture specimens for fatigue test loading, when the number of loading is α ₁ N _f , where 0≤α ₁ <1, stop the loading test; 3) Immediately carry out the asphalt mixture bending test to the mixture specimen after step 2) processing, obtain the bending tensile strength R _B1 of the specimen after experiencing fatigue loading; 4) Under the same test conditions, repeat step 2) and step 3), and when the loading times are α ₂ N _f , α ₃ N _f , ... α _n N _f , the corresponding flexural tensile strength is R _B2 , R _B3 , ... R _Bn ; 5) From the fatigue decay law f(D) obtained in step 1) and step 3), the bending and tensile strength R _B1 , R _B2 , R _B3 , ... R _Bn of the material under different fatigue loading times obtained in step 4) , the relationship between the residual flexural tensile strength R _B of the mixture specimen and the fatigue damage variable D is obtained: R _B =aD ² +bD+c Among them, a, b, c are parameters, which are obtained by fitting the experimental data. 2. the method for testing of asphalt mixture residual strength as claimed in claim 1, is characterized in that, in described step 1), mixture test piece is according to in JTG E20-2011 highway engineering asphalt and asphalt mixture test regulations T 0739-2011 Asphalt mixture prepared according to requirements of four-point bending fatigue life test. 3. the method for testing of asphalt mixture residual strength as claimed in claim 1, is characterized in that, in described step 1), the fatigue damage variable D of mixture specimen is characterized by the stiffness of specimen, and its relation as follows: Among them, D is the fatigue damage variable, E _i is the stiffness of the specimen during the i-th cyclic loading in the fatigue test, and E ₀ is the initial stiffness of the specimen. 4. the test method of asphalt mixture residual strength as claimed in claim 1 is characterized in that, in described step 1), fatigue damage decay law f (D), its relational expression is as follows: Among them, D is the variable of fatigue damage; N is the number of stress cycles; a ^* , p, q are all fatigue parameters, which are obtained by regression of test data. 5. the test method of asphalt mixture residual strength as claimed in claim 1, is characterized in that, described step 3) in, the flexural tensile strength test method of asphalt mixture is based on JTG E20-2011 road engineering asphalt It is implemented according to the requirements of T 0715-2011 Asphalt Mixture Bending Test in the Asphalt Mixture Test Regulations. 6. the method for testing of asphalt mixture residual strength as claimed in claim 1, is characterized in that, in described step 4), repeat step 2) and step 3) operation, the α _n N _f that obtains and R _Bn The number of groups is not less than 3 groups.