CN104316418A - Evaluation index of high-temperature stability performance of asphalt mixture in cold region - Google Patents

Abstract

The invention discloses an evaluation index of high-temperature stability performance of an asphalt mixture in a cold region, that is, when a wheel tracking test is performed at a temperature of 45 DEG C, the high-temperature stability of the asphalt mixture is evaluated by using a comprehensive damage variable d. The comprehensive damage variable d is a ratio of a loss delta E of an elasticity modulus E of a raw material after damage and an elasticity modulus E0 of the raw material before damage, namely, d=1-(E/E0); the elasticity modulus E of the damaged material is a ratio of a contact pressure intensity sigma of a wheel tracking test wheel and an asphalt mixture test piece and a vertical resilience strain epsilon generated by the damaged material; a relation equation N60min/Ns=k(E/E0) among a 60min traffic load action times N60min, service life Ns and elasticity modulus is established so that a continuous damage coefficient K is obtained, and thus the comprehensive damage variable d is obtained; the larger the comprehensive damage variable d is, and the poorer the high-temperature stability of the asphalt mixture in the cold region is. According to the index, factors such as driving speed, accumulated deformation amount and maximal permanent deformation amount are comprehensively considered, and the unreasonable problems that the high-temperature performance difference is remarkable and the dynamic stability is basically consistent are effectively prevented.

Description

The evaluation index of cold district stability at high temperature of asphalt mixture energy

Technical field

The present invention relates to road engineering technical field, is exactly the evaluation index setting up a kind of cold district stability at high temperature of asphalt mixture energy.

Background technology

China existing " highway engineering pitch and Asphalt Mixture Experiment code " (JTG E20-2011) adopts the dynamic stability index of asphalt mixture in track test to carry out stability at high temperature of asphalt mixture and can evaluate, and finds: High temperature stability index of hot mixed asphalt dynamic stability can not reflect the permanent deformation resistance of compound in whole use procedure in the High Temperature Stability of Asphalt Mixture of application wheel tracking test to gradation types of the same race is studied.Have problems as follows:

1. analyze the dynamic stability test process of compound, before discovery rut plate is rolled, 45min has produced darker rut, pass through this compacting process again and again, the residue voidage of rut plate is very little, packing tends towards stability substantially, and in 15min roller compaction process subsequently, the set deformation volume of compound has changed not quite, it is very large to there is total rutting depth in the dynamic stability calculated thus, then the unreasonable situation that dynamic stability is also very large.

2. the dynamic stability computing method of current design criteria only consider the permanent set of 15min after compacting asphalt, lacking the cumulative deformation of overall process and the consideration of maximal permanent deformation, making dynamic stability index there is larger limitation when evaluating the high-temperature behavior of asphalt.

Summary of the invention

The object of this invention is to provide the evaluation index of a kind of cold district stability at high temperature of asphalt mixture energy.The high temperature stability performance of cold district asphalt is evaluated with complex damage variable index.Concrete scheme is as follows: the evaluation index of cold district stability at high temperature of asphalt mixture energy, is characterized in that: when (1) carries out wheel tracking test under 45 DEG C of conditions, with the high-temperature stability of complex damage variable d metrics evaluation asphalt; (2) complex damage variable d is the loss amount △ E of elasticity modulus of materials E after damage and the ratio of the front raw-material elastic modulus E 0 of damage, namely (3) elastic modulus E of attacking material is under 45 DEG C of conditions, wheel tracking test wheel and the ratio of the footprint pressure σ of bitumen mixture specimen with the vertical resilience strain stress of its generation; (4) 60min Driving Loading times N is set up _60min, service life N _sand the relation equation between elastic modulus obtain continuous damage COEFFICIENT K, and then obtain complex damage variable d; (5) complex damage variable d is larger, and cold district stability at high temperature of asphalt mixture is poorer.

Advantage of the present invention is:

1. complex damage variable index has considered the factors such as driving speed, cumulative deformation and maximal permanent deformation, makes this high-temperature behavior evaluation index consistent with rut Formation rule in engineering reality, property more rational compared with dynamic stability index.

2. the proposition of complex damage variable index effectively prevent the unreasonable situation that cold district High Temperature Stability of Asphalt Mixture difference is obvious and dynamic stability is basically identical, makes it to have better differentiation rate to the evaluation of High Temperature Stability of Asphalt Mixture.

3. the complex damage variable index proposed can reflect the Rut resistance deformability of wheel tracking test Asphalt Mixture comprehensively.

Embodiment

1. set up Driving Loading number of times, service life, relation equation (1) between modulus of shearing and elastic modulus

$\frac{N_{60\min }}{N_s}=K^{\′}\frac{G}{G_0}=K\frac{E}{E_0}---\left(1\right)$

In formula:

N _s---the service life (secondary) of asphalt, obtains (see 4) by estimating;

N _60min---the number of times of 60min experimental wheel effect when carrying out wheel tracking test, experimental wheel effect per minute 42 times/min;

G ₀---raw-material modulus of shearing (MPa);

The modulus of shearing (MPa) of G---attacking material;

E ₀---raw-material elastic modulus (MPa), can obtain by current design criteria actual measurement;

The elastic modulus (MPa) of E---attacking material;

K---continuous damage coefficient, K value is calculated by equation (1).

2. determine raw-material elastic modulus E ₀

Measure by China existing " highway engineering pitch and Asphalt Mixture Experiment code " (JTG E20-2011) T0713 method.

3. determine the elastic modulus E of attacking material

$E\frac{\mathrm{\σ}}{\mathrm{\ϵ}}---\left(2\right)$

In formula:

σ---the footprint pressure of wheel tracking test wheel and test specimen; Be 0.7MPa 45 DEG C time, the total load (TL) of applying is about 780N, can adjust footprint pressure size as required;

ε---when experimental wheel unloads, the vertical resilience strain that bitumen mixture specimen produces.

In formula:

△ h---when experimental wheel unloads, the vertical resilience amount (mm) that bitumen mixture specimen produces;

D _60min---when experimental wheel effect 60min, (mm) vertical deformation that surface of test piece produces;

D _60min( _{actual measurement after unloading})---the vertical deformation (mm) that actual measurement surface of test piece produces after experimental wheel effect 60min unloads

The thickness (mm) of H---bitumen mixture specimen.

4. estimate the service life N of asphalt _s

N _s＝DS×R _d (5)

$\mathrm{DS}=\frac{(t_2-t_1)\×N}{d_2-d_1}\×C_1\×C_2---\left(6\right)$

In formula:

The dynamic stability (secondary/mm) of DS---asphalt;

D ₁---corresponding to time t ₁deflection (mm);

D ₂---corresponding to time t ₂deflection (mm);

C ₁---testing machine genre modulus, it is 1.0 that crank connecting link drive load wheel comes and goes the method for operation;

C ₂---test specimen coefficient, the test specimen that wide 300mm prepares in testing laboratory is 1.0;

N---experimental wheel comes and goes rolling speed, is generally 42 times/min;

R _d---asphalt allows vertical deformation value within the normal service phase.Advise that permanent strain degree of depth value is 15mm according to expert survey.

5. calculate continuous damage COEFFICIENT K

K value is calculated by equation (1)

6. set up the elastic modulus E of attacking material and raw-material elastic modulus E ₀relation equation

" elastic modulus method " from defect theory: E=(1-d) E ₀(7)

In formula:

D---complex damage variable (dimensionless);

7. determine complex damage variable d

Equation (7) is substituted into equation (1) and obtains equation (8):

$\frac{N_{60\min }}{N_s}=K(1-d)---\left(8\right)$

Complex damage variable d is tried to achieve by formula (9):

$d=1-\frac{N_{60\min }}{N_{s}K}---\left(9\right)$

D is larger for complex damage variable, and cold district stability at high temperature of asphalt mixture can be poorer.

Claims (1)

1. the evaluation index of cold district stability at high temperature of asphalt mixture energy, is characterized in that: when (1) carries out wheel tracking test under 45 DEG C of conditions, with the high-temperature stability of complex damage variable d metrics evaluation asphalt; (2) complex damage variable d is the loss amount △ E raw-material elastic modulus E front with damage of elasticity modulus of materials E after damage ₀ratio, namely (3) elastic modulus E of attacking material is under 45 DEG C of conditions, wheel tracking test wheel and the ratio of the footprint pressure σ of bitumen mixture specimen with the vertical resilience strain stress of its generation; (4) 60min Driving Loading times N is set up _60min, service life N _sand the relation equation between elastic modulus obtain continuous damage COEFFICIENT K, and then obtain complex damage variable d; (5) complex damage variable d is larger, and cold district stability at high temperature of asphalt mixture is poorer.