CN103487333B - Asphalt mixture self-healing capability evaluating method - Google Patents

Abstract

The invention discloses a method for evaluating the self-healing ability of asphalt mixture. Based on the four-point bending fatigue test of asphalt mixture, after the traditional fatigue test procedure, an intermission period is introduced, and the test piece is placed in a certain environment for curing. Then carry out the fatigue test to form the test mode of "fatigue-healing-re-fatigue". By comparing the stiffness modulus curves of the two fatigue tests, the healing index function is established, and the healing index HI is selected as the key index for evaluating the self-healing ability of asphalt mixture, which can effectively evaluate the self-healing ability of different types of asphalt mixture. It is also possible to test the influence of different factors such as self-healing time, self-healing temperature, and the degree of damage of the mixture before self-healing on the self-healing effect of asphalt mixture. Moreover, this method is simple, feasible, easy to operate, and the data is accurate and reliable. It is a performance-based The long-life design of asphalt pavement and the formulation of asphalt pavement maintenance planning for the whole life cycle provide technical index basis.

Description

A method for evaluating the self-healing ability of asphalt mixture

technical field

The invention belongs to the technical field of performance detection of highway asphalt pavement materials, and relates to an evaluation method for fatigue self-healing characteristics of asphalt mixture.

Background technique

The self-healing of asphalt mixture can be simply defined as the process of partial or complete healing of cracks in asphalt mixture due to repeated traffic loads. When an asphalt mixture fatigues, its hardness and strength decline. Many researchers have observed that during cyclic loading, asphalt mixtures go through three stages: microcrack initiation, growth, and finally macrocrack formation. Regarding the inner reason of healing behavior, there are currently two theories: physical theory and mechanical performance theory. The former refers to the slowing down of microscopic fatigue damage along with the repair of the chemical structure. It is related to the chemical composition and physicochemical properties of asphalt and asphalt mixture. In the latter case, healing behavior can be defined as the partial recovery of the material's own mechanical properties (such as strength and modulus) during the intermission.

Studies have shown that the mechanical properties of damaged asphalt mixtures can be restored to a large extent, but this recovery (healing) ability depends on many factors, including the composition of the asphalt mixture, the degree of damage, and the load, temperature, External conditions such as time (recovery period or length of rest period). Although the self-healing properties of asphalt materials have an important impact on the design of pavement life, in the design codes of various countries, there are few explicit considerations of the self-healing properties of mixtures, which directly causes the gap between the design life of the pavement and the actual service life. In the design method of individual countries, the indoor fatigue life is simply enlarged, and the amplification factor is from 4 to 100. It can be seen that the difference is very large.

To sum up, the self-healing performance of asphalt mixture has an important influence on its fatigue life. At present, there is no systematic and standardized evaluation method for the self-healing ability of asphalt mixture in China. The change rate of modulus before and after was used as the self-healing evaluation index. The specific calculation formula is as follows:

$\mathrm{<span\; class="notranslate">\; RSC</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; after</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; before</span>}}}{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; before</span>}}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 100</span>}<span\; class="notranslate">\; \%</span>$

In the formula: RSC - rate of change of stiffness modulus;

S _after - modulus of stiffness after the interval, in MPa;

S _before ——intermittent front stiffness modulus, unit MPa;

This evaluation index reveals the overall healing properties of asphalt mixtures, but it cannot distinguish between total healing and damage-related healing, i.e., does not remove the effects of space hardening and cooling in the healing data to determine the recovery of pure damage in the total healing. Corresponding to the factors that cause the stiffness modulus to decrease during the loading process: damage, space softening and heating, the factors that cause the stiffness modulus to increase during the healing process are: damage recovery, space hardening and cooling. Among them, steric softening and cooling will lead to an increase in the stiffness modulus, but from the damage point of view, the increase in the stiffness modulus has no physical meaning. Therefore, the accuracy of this evaluation index is not enough, and this index cannot reflect the recovery degree of asphalt mixture's ability to resist load.

Establishing a scientific and systematic evaluation method for the self-healing ability of asphalt mixture can effectively judge the self-healing ability of different types of mixture, thereby guiding engineering practice, optimizing the use of asphalt mixture, and prolonging the life of roads.

Contents of the invention

Technical problem: The purpose of this invention is to propose a method for evaluating self-healing ability of asphalt mixture with accurate and reliable data, simple and feasible test method, and easy to popularize.

Technical solution: The self-healing ability evaluation method of asphalt mixture of the present invention comprises the following steps:

1) Fatigue test:

According to the "Test Regulations for Asphalt and Mixtures in Highway Engineering" JTG E20-2011, the four-point bending fatigue test procedure for asphalt mixture was prepared, and the four-point bending fatigue test was carried out;

2) Healing of damaged specimens:

Place the beam specimen that has reached the termination condition of the fatigue test in step 1) on a hard glass plate or ceramic tile with a flat surface, and perform curing under the set conditions. The set conditions are the curing temperature set according to the needs of the test and maintenance time;

3) Carry out the fatigue test again:

The damaged beam specimens cured in step 2) were subjected to the four-point bending fatigue test of the damaged beam specimens again according to the four-point bending fatigue test procedures for asphalt mixtures in JTGE20-2011 "Test Regulations for Asphalt and Mixtures in Highway Engineering" test;

4) Summarize the test data obtained in steps 1) and 3), draw the relationship curve of the stiffness modulus with the loading time before and after the asphalt mixture is healed, and then calculate the damage rate D and the healing index HI, and the damage rate D is defined as the strength The slope of the attenuation curve of modulus with loading times, the specific calculation formula is as follows:

$\mathrm{<span\; class="notranslate">\; D.</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}}{\mathrm{<span\; class="notranslate">\; t</span>}}$

In the formula: D——the corresponding modulus damage rate when reaching the set fatigue damage ratio;

S _O ——initial stiffness modulus, in MPa;

S _t —— terminal stiffness modulus, in MPa;

t—the time required for the stiffness modulus to change from S _O to S _t , unit s;

The definition of the healing index HI is the ratio of the damage rate of the beam specimen before healing to the damage rate of the specimen after healing, and the specific calculation formula is as follows:

$\mathrm{<span\; class="notranslate">\; HI</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; before</span>}}}{{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; after</span>}}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 100</span>}<span\; class="notranslate">\; \%</span>$

In the formula: D _before - the damage rate of the specimen before healing;

_Daft —the damage rate of the specimen after healing;

5) The self-healing ability of the asphalt mixture is evaluated according to the healing index HI. The larger the healing index HI, the stronger the self-healing ability of the asphalt mixture.

In the data analysis of the present invention, under load, the relationship between stress and strain of the asphalt mixture is nonlinear, and the stiffness modulus can describe the mechanical properties of the asphalt mixture in the viscoelastic state. In order to evaluate the healing effect of the asphalt mixture after the "fatigue-healing-re-fatigue" test process, the change of the stiffness modulus before and after healing will be considered, and the healing effect of the asphalt mixture will be briefly characterized. Because there are many unstable factors in the test piece forming and test process, even the asphalt mixture beam specimens with the same asphalt material and the same gradation have different modulus and fatigue life, so it is not possible to compare them. The absolute value of the modulus. In order to more intuitively evaluate the self-healing effect (stiffness modulus recovery) of asphalt mixture from the perspective of mechanical properties, the damage rate index is used as a characterization index.

The larger the damage rate D value, the faster the stiffness modulus decay of the asphalt mixture. The change of the asphalt mixture fatigue curve before and after the interval can reflect the self-healing performance of the asphalt mixture. The closer the fatigue curve after the interval is to the curve before the interval, the stronger its self-healing ability is. Each stiffness modulus attenuation curve corresponds to a D value. Comparing the calculated D value with the original D value can directly evaluate the influence of different influencing factors on the self-healing ability of asphalt mixture. On this basis, the corresponding result index, that is, the healing index HI (Healing Index), can be used to characterize the reconstruction effect of asphalt mixture microstructure under the condition of given healing time.

To sum up, the evaluation index of self-healing performance of asphalt mixture is selected as the healing index HI. The larger the healing index, the better the self-healing performance of the asphalt mixture.

The method of the present invention includes two parts: test process and data analysis. The test adopts the four-point bending fatigue test of asphalt mixture, and the evaluation index is the healing index HI. It can evaluate the self-healing ability of different types of asphalt mixtures (such as different gradations, different asphalt binders, different asphalt contents, etc.) under different conditions (such as different curing temperatures, different curing times, etc.).

Beneficial effect: compared with the prior art, the present invention has the following advantages:

The evaluation index provided by the present invention, by comparing the closeness of the fatigue curve before and after the interval, the modulus increase due to space hardening and cooling during the healing process will be offset during the loading process of the fatigue test again, and there is no need to distinguish between the total healing and Damage-related healing is therefore more precise and can reflect the recovery capacity of asphalt mixtures against load action.

From the perspective of the mechanical properties of asphalt mixture, the present invention proposes the healing index HI as the evaluation index of asphalt mixture self-healing ability based on the change of asphalt mixture bending stiffness modulus, the test data is accurate and reliable, and the test method is simple and feasible , easy to promote.

Description of drawings

Figure 1 is a schematic diagram of the "fatigue-healing-re-fatigue" test process of the asphalt mixture trabecular specimen.

Figure 2 is a graph showing the relationship between stiffness modulus and loading time of AC-13 matrix asphalt mixture before and after healing.

Detailed ways

The present invention will be further described below in conjunction with specific examples, but the content of the present invention is not limited to the following examples.

Example 1:

As shown in Figure 2, under the test conditions of 15°C and 500 microstrain, the fatigue test was first carried out on the AC-13 matrix asphalt mixture, and the fatigue test was stopped immediately when the stiffness modulus decayed to 50% of the initial value. Introduce a lull that is healing time. After reaching the set time (2h in this example), the fatigue test starts immediately, that is, the fatigue test after the healing period. The black solid line in the figure indicates the damage rate corresponding to the stiffness modulus of the AC-13 matrix asphalt mixture specimen decaying to 50% of the initial modulus value before the introduction of the healing time; the arrow indicates the healing time after 2 h (15 °C Bottom), the restored stiffness modulus value of the specimen; the black dotted line indicates the corresponding damage rate when the stiffness modulus of the matrix asphalt mixture specimen decays to 50% of the initial modulus value after the introduction of healing time. The ratio of the two slopes is the healing index HI, which is the evaluation index of the self-healing ability of the selected asphalt mixture.

Example 2:

The summary of this example is: comparing the self-healing ability of AC-13 SBS modified asphalt mixture and PA-13 SBS modified asphalt mixture, the optimal asphalt ratio is 5.3% and 4.8% respectively.

(1) According to the "Test Regulations for Asphalt and Mixtures in Highway Engineering" JTG E20-2011, the four-point bending fatigue test procedures for asphalt mixtures were carried out respectively for AC-13 SBS modified asphalt mixtures (specimen code 1) and PA- Four-point bending fatigue test of Type 13 SBS modified asphalt mixture (specimen code 2). The test parameters are: the test temperature is 15°C, the loading frequency is 10 Hz, the loading waveform is partial sine wave, the control strain mode is adopted, and the strain level is 500 microstrain.

(2) Place specimen 1 and specimen 2 in a temperature-controlled box with a temperature of 15°C and cure for 2 hours. The specimens should be placed horizontally on a hard glass plate or ceramic tile with a flat surface and a certain rigidity to prevent the specimens from out of shape.

(3) Perform four-point bending fatigue tests on specimen 1 (denoted as specimen 1*) and specimen 2 (denoted as specimen 2*) after curing, using the same test parameters as in (1).

The test results are summarized in the table below.

Table 1 AC-13 and PA-13 SBS modified asphalt mixture "fatigue-healing-re-fatigue" test results

It can be seen from Table 1 that the healing index of PA-13 graded asphalt mixture is slightly higher than that of AC-13 type asphalt mixture under the same curing conditions of curing temperature of 15 °C and curing time of 2 h. It shows that PA-13 graded asphalt mixture has better self-healing effect than AC-13 type. AC-13 type asphalt mixture is a dense mixture with a large aggregate surface area, and the proportion of structural asphalt in the total amount of asphalt is relatively large, which can obtain greater particle adhesion and thus higher strength; correspondingly, free The proportion of asphalt in the total amount of asphalt is small, the porosity of the dense mixture is small, and the fluidity of the asphalt is poor. After fatigue damage, it cannot move well, fill the concrete pores, rebond the aggregate, and gain strength. PA-13 type asphalt mixture is just the opposite of AC-13. It has a large proportion of free asphalt and better fluidity. Therefore, after fatigue damage, it can better bond aggregates, regain strength, and have better performance. Self-healing ability. In summary, the self-healing ability evaluation method of asphalt mixture is accurate and effective.

Claims (2)

1. an asphalt self-healing capability evaluation method, comprises the steps:

1) torture test:

According to " highway engineering pitch and test mixture code " JTG E20-2011 Asphalt Mixture four-point bending torture test code, prepare test specimen and carry out four-point bending torture test;

2) impaired test specimen healing:

By described step 1) in reach torture test end condition the beam test specimen Bohemian glass plate that is placed on surfacing or ceramic tile on, carry out maintenance under conditions set, the condition of described setting is the curing temperature and the curing time that need setting according to test;

3) again torture test is carried out:

By described step 2) in impaired beam test specimen after maintenance according to " highway engineering pitch and test mixture code " JTG E20-2011 Asphalt Mixture four-point bending torture test code, again carry out the four-point bending torture test of impaired beam test specimen;

It is characterized in that, the method also comprises:

4) by described step 1) and 3) in gained test figure gather, draw the relation curve of asphalt healing front and back stiffness modulus with the load time, then damage rate D and healing index HI is calculated, described damage rate D is defined as stiffness modulus with the slope loading number of times die-away curve, and specific formula for calculation is as follows:

$D=\frac{S_0-S_t}{t}$

In formula: D---arrive modulus damage speed corresponding when setting fatigure failure ratio;

S ₀---initial stiffness modulus, units MPa;

S _t---stop stiffness modulus, units MPa;

T---stiffness modulus number is by S ₀change to S _tthe required time, unit s;

Described healing index HI is defined as the damage rate of beam test specimen before healing and test specimen damage rate ratio after healing, and specific formula for calculation is as follows:

$\mathrm{HI}=\frac{D_{\mathrm{before}}}{D_{\mathrm{after}}}\&times;100\%$

In formula: D _before---the damage rate of test specimen before healing;

D _after---test specimen damage rate after healing;

5) evaluate the self-healing capability of asphalt according to healing index HI, HI is larger for healing index, shows that asphalt self-healing capability is stronger.

2. asphalt self-healing capability evaluation method according to claim 1, it is characterized in that, described step 1) and step 3) torture test in, the selected test parameters measured is identical, and described test parameters comprises: test temperature, loading mode, Loaded contact analysis, loading frequency, stress/strain level.