CN104849154A - Identification method for fatigue failure of pitch under dynamic shear load effect - Google Patents

Abstract

The invention discloses a method for identifying fatigue failure of asphalt under the action of a dynamic shear load, which relates to a test method for testing the fatigue performance of road asphalt with a dynamic shear rheometer. It solves the problem of judging the critical point of fatigue failure in the current asphalt accelerated fatigue test, and improves the scientific validity of the test data analysis process. The present invention analyzes the accelerated fatigue test data of asphalt under virtual strain coordinates, quantitatively analyzes the occurrence and accumulation of fatigue damage by calculating the virtual strain energy stored in the material during the test, and finally proposes to use the peak point of stored virtual strain energy as the asphalt The critical point criterion for the occurrence of fatigue failure.

Description

Identification method of fatigue failure of asphalt under dynamic shear load

technical field

The invention belongs to the field of building materials, and relates to a recognition method for judging fatigue failure of road asphalt under the action of dynamic shear load.

Background technique

Fatigue cracks will occur on the asphalt pavement due to the repeated action of the wheel load, and the fatigue cracks on the pavement seriously affect the comfort and safety of road driving. The pros and cons of asphalt fatigue resistance have an important contribution to the ability of asphalt pavement to resist fatigue cracks, so it is necessary to evaluate and distinguish the fatigue resistance of different asphalt materials scientifically and effectively. The linear amplitude sweep test with controlled strain (i.e., linear strain sweep test) is currently a commonly used asphalt accelerated fatigue specification test method in the world ^[1] . The problem has been in the research state, and there are no good indicators and parameters to characterize and distinguish the pros and cons of different asphalt fatigue resistance.

Contents of the invention

The purpose of the present invention is to judge and identify the critical point of material fatigue failure during asphalt accelerated fatigue test, so as to quantitatively compare the fatigue life of different asphalt materials under dynamic shear load. The specific implementation process and analysis method of the present invention are as follows.

The method for identifying fatigue failure of asphalt under dynamic shear load is characterized in that a dynamic shear rheometer is used to complete a linear amplitude sweep test of controlled strain on a parallel plate asphalt sample at any temperature from 5°C to 30°C, The scanning range of the dynamic strain amplitude increases linearly from 0.1% to 30%, the dynamic loading frequency is 10Hz, and the scanning time is designed to be 5-15 minutes; then according to the shear stress τ and shear strain γ data collected in the test, Calculate the virtual shear strain γ ^R index and the virtual strain energy index W ^R _s stored in the material during the test; finally, the peak point of the stored virtual strain energy W ^R _s during the test is taken as the critical point of asphalt fatigue failure. The number of cyclic loading N corresponding to the point is the fatigue life N _f of asphalt at this temperature, loading frequency and loading rate.

Furthermore, by changing the scanning time of the linear strain scanning test to produce different loading rates, under the same strain scanning range, test temperature and loading frequency, the fatigue life of asphalt identified under different loading rates will also be different.

Further, the scanning time is designed to be 5 minutes.

Further, the scanning time is designed to be 10 minutes or 15 minutes.

More specifically:

(1) Apply dynamic shear rheometer to conduct linear strain scanning test on parallel plate asphalt samples. According to the specification requirements of the test ^[1] , the shear strain increases linearly from 0.1% to 30%, and the test loading frequency is fixed at 10Hz , The test temperature can be any temperature from 5°C to 30°C, and the scan time is designed to be 5 minutes.

(2) The dynamic shear loading rate applied in the test process can be changed by controlling the scanning time. Under the condition of keeping the strain scanning range, the test temperature and the loading frequency constant, the present invention has also carried out the scanning time as 10 minutes and 15-minute comparison test.

(2) After the test is completed, analyze the test data according to the following procedure;

i. Calculate the virtual shear strain (γ ^R ) index according to the formula (1) according to the shear strain (γ) data collected by the dynamic shear rheometer, where |G ^* | ₀ is at this specific temperature and loading frequency The linear viscoelastic dynamic shear modulus of the asphalt sample in the undamaged state can be obtained by a small-strain single-point dynamic test before the linear strain sweep test;

γ ^R ＝ γ·|G ^* | ₀

(1)

ii. The shear stress (τ) data collected by the dynamic shear rheometer is analyzed under the coordinates of the virtual shear strain (γ ^R ), as shown in accompanying drawing 1; according to formula (2) for each data point Calculate the virtual strain energy (W ^R _s ) index stored in the material during the test, that is, the area of the dotted line in Figure 1;

${{\mathrm{<span\; class="notranslate">\; W</span>}}^{\mathrm{<span\; class="notranslate">\; R</span>}}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}^{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

iii. Take the calculated stored virtual strain energy (W ^R _s ) value as the ordinate, and the number of cyclic loadings (N) applied to the asphalt sample as the abscissa, as shown in Figure 2, take the peak value of W ^R _s As the critical point of asphalt fatigue failure, the fatigue life (N _f ) of the asphalt sample can be determined at this specific temperature, loading frequency and loading rate.

(3) Mark the determined fatigue life (N _f ) in the relationship diagram between the shear stress (τ) collected by the dynamic shear rheometer and the number of cyclic loadings (N), as shown in Fig. 3 .

references

[1]Standard Method of Test for Estimating Damage Tolerance of Asphalt Binders Using the Linear Amplitude Sweep[S].American Association of State Highway andTransportation Officials(AASHTO)TP 101-14.

Description of drawings

Figure 1 is the analysis of asphalt accelerated fatigue test data in virtual strain coordinates and the characterization of stored virtual strain energy

Figure 2 is the evolution analysis of stored virtual strain energy during the asphalt accelerated fatigue test

Figure 3 is a typical identification result of asphalt fatigue failure critical point during accelerated fatigue test

Figure 4 is a comparison of fatigue failure identification of matrix asphalt and SBS modified asphalt when the scanning time is 5 minutes

Figure 5 is a comparison of fatigue failure identification of matrix asphalt and SBS modified asphalt when the scanning time is 10 minutes

Figure 6 is a comparison of fatigue failure identification of matrix asphalt and SBS modified asphalt when the scanning time is 15 minutes

Figure 7 is a comparison between the fatigue life determined by the accelerated fatigue test of asphalt and the actual fatigue life of asphalt

Detailed ways

Specific implementation mode 1: In this implementation mode, the accelerated fatigue test of controlled strain is carried out by using matrix asphalt and SBS modified asphalt (referred to as SBS asphalt), the test temperature is 19°C, the test frequency is 10Hz, and the linear strain scanning range is 0.1% to 30%. , The scanning time is designed to be completed in 5 minutes. After the test, the fatigue life of the two kinds of asphalt under this working condition was identified according to the above data analysis process, and the identification results are shown in Figure 4.

Embodiment 2: The difference between this embodiment and Embodiment 1 is that the scanning time of the linear strain scan is designed to be 10 minutes, and the others are the same as Embodiment 1. The recognition results are shown in Figure 5.

Embodiment 3: The difference between this embodiment and Embodiment 1 is that the scanning time of the linear strain scan is designed to be 15 minutes, and the others are the same as Embodiment 1. The recognition results are shown in Figure 6.

Embodiment 4: The difference between this embodiment and Embodiment 1 to Embodiment 3 is that the asphalt materials used are TP polymer modified asphalt (abbreviated as TP asphalt) and rubber powder modified asphalt (abbreviated as rubber asphalt), test temperature, The strain scanning range and loading frequency are the same as those in Embodiments 1 to 3, and accelerated fatigue tests with scanning times of 5 minutes, 10 minutes and 15 minutes were carried out respectively.

Comparing the identification results of the accelerated fatigue tests of the four kinds of asphalt in the above embodiment at different loading rates with the actual fatigue life of the asphalt (the fatigue strain level is 5% and 7%) in the accompanying drawing 7, it can be seen that different loading There is a good correlation between the fatigue life identified by the asphalt accelerated fatigue test and the actual fatigue life (5% fatigue strain and 7% fatigue strain). The invention aims at the scientific validity of the asphalt fatigue failure identification method proposed by the accelerated fatigue test.

Claims (4)

1. the recognition methods of pitch generation fatigue failure under dynamic shearing load action, it is characterized in that application dynamic shear rheometer to parallel-plate bitumen samples at 5 DEG C ~ 30 DEG C arbitrary temperature, complete the linear amplitude scan test of controlled strain, the sweep limit of dynamic strain amplitude linearly increases to 30% from 0.1%, dynamic load frequency is 10Hz, and sweep time is designed to 5-15 minute; Then according to the shear stress τ collected in test and shear strain γ data, calculate empty shear strain γ ^rthe virtual strain energy index W that in index and process of the test, material stores ^r _s; Finally, virtual strain energy W will be stored in process of the test ^r _speak point as the critical point of pitch fatigue failure, the CYCLIC LOADING times N corresponding to this unique point is the fatigue lifetime N of pitch under this temperature, loading frequency and loading speed _f.

2. pitch fatigue failure recognition methods according to claim 1, it is characterized in that the sweep time by changing linear strain scan test produces different loading speeds, under same strain sweep limit, test temperature and loading frequency condition, the pitch fatigue lifetime identified under different loading speed is also by difference.

3. pitch fatigue failure recognition methods according to claim 1, is characterized in that being designed to 5 minutes sweep time.

4. pitch fatigue failure recognition methods according to claim 1, is characterized in that being designed to 10 minutes or 15 minutes sweep time.