CN105486845A - Asphalt mixture multi-stage loaded high-temperature creep curve analysis method based on axle load spectrum - Google Patents

Abstract

The invention discloses a method for analyzing the high-temperature creep curve of asphalt mixture under multi-stage loading based on the shaft-loading spectrum. The accumulated micro-strain is obtained by linear fitting of the creep curve in the second stage of creep during the loading process of different stages. The growth slope is calculated according to the formula to calculate the corresponding high temperature creep characteristic indicators LSI, CDA and MFN. Among the parameters of the present invention, a larger MFN represents that the mixture has a stronger ability to resist permanent deformation under the action of multi-stage loads, and a smaller LSI indicates that the mixture is relatively insensitive to changes in axle load, and may be less effective in resisting heavy loads. A stronger and smaller CDA indicates that the rate of creep damage of the asphalt mixture is more uniform and insensitive to one-cycle spectral loading.

Description

Analysis method of high temperature creep curve of asphalt mixture based on shaft load spectrum

technical field

The invention belongs to the field of road maintenance, and in particular relates to an analysis method of asphalt mixture multi-stage loading high temperature creep curve based on axle load spectrum.

Background technique

Permanent deformation damage such as rutting has always been one of the most typical and harmful disease forms of high-grade asphalt pavement in my country. Scholars at home and abroad have done a lot of research on the high-temperature creep behavior of asphalt pavement, especially in terms of test methods. The NCHRP research project in the United States has carried out research on simple performance test methods for asphalt mixtures, and finally found that the dynamic modulus test and dynamic creep The test can well evaluate and predict the high temperature rutting resistance of asphalt mixture.

However, the dynamic creep test is based on the half-sine wave loading method of a single load, which is very different from the axle load on the actual road surface.

Therefore, the result of the existing calculation method is very different from the actual situation, and the effect of pavement maintenance cannot be realized in practical application.

Contents of the invention

The technical problem to be solved by the present invention is that the existing dynamic creep test is based on the half-sine wave loading method of a single load. This loading method is very different from the axle load on the actual road surface, and the effect of road surface maintenance cannot be realized in practical applications. .

In order to solve the above-mentioned technical problems, the technical solution adopted in the present invention is: a method for analyzing the high-temperature creep curve of asphalt mixture multi-stage loading based on shaft-loaded spectrum, comprising the following steps: 1) Asphalt mixture multi-stage loading high-temperature creep curve The curve is divided into three stages: the first stage: that is, the first loading sequence time period after the multi-stage loading of asphalt mixture starts; the second stage: after the end of the first loading sequence time period, each level of stress level is loaded The generated micro-strains all show a linear growth stage of the cumulative micro-strain linear growth stage; the third stage: the rapid growth stage of the cumulative micro-strain in which the asphalt mixture is in a state of high-temperature instability; 2) Calculate the three major indices based on the segmented data, The three indexes include load sensitivity index LSI, creep damage angle CDA and composite rheological number MFN; load sensitivity index LSI: select the cumulative microstrain and load under 3-5 different stress levels in the second stage The relationship between the number of actions is linearly fitted to obtain the slope of the creep curve under different stress levels. The slope is the growth rate of the micro-strain. The power function, Δε=a·σ ^LSI is used to fit the load sensitivity Exponential LSI, where σ is the stress level; Δε is the micro-strain growth rate; a is the regression coefficient; creep damage angle CDA: extract and analyze the first two major cycles in the second stage, and the loading sequence is two, three, four 1. The starting point of the second loading sequence is A, the end point of the second first loading sequence is B, and the end point of the third first loading sequence is C; connecting AB and BC, the acute angle between AB and BC is creep Variable damage angle CDA, through the formula Obtain CDA; among them, ε _A , ε _B , ε _C are the cumulative microstrains of A, B, C respectively; n _A , n _B , n _C are the cumulative action times of A, B, C respectively; Composite rheological number MFN: the number value at the boundary between the second stage and the third stage, that is, the end point where the cumulative microstrain increases linearly with the number of actions.

Further, the number of different stress levels selected in the second stage in step 2) is four. The reason for setting the number of stress levels to four is that too few selections will affect the accuracy of the experimental results, and too many selections will lead to a large amount of calculation. The selection of four can meet the accuracy requirements without causing the calculation The load is too large.

The advantages of the present invention are: the evaluation method is simple and easy, and the creep characteristics of the asphalt mixture under different stress levels are evaluated by the load sensitivity index LSI and the creep damage angle CDA, and its sensitivity to the load is analyzed, and according to The composite rheological number MFN evaluates the permanent deformation resistance of materials under the action of the actual axial load spectrum, and provides accurate and intuitive digital basis for guiding road engineering practice, especially for the decision-making of highway maintenance projects in my country.

Description of drawings

Fig. 1 is the linear fitting diagram of the second stage of the creep curve;

Figure 2 is a schematic diagram of the calculation of the creep damage angle CDA of the creep curve;

Fig. 3 is a schematic diagram of the method for determining the compound rheological number MFN of the creep curve.

detailed description

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

The inventive method comprises the following steps:

1) The high-temperature creep curve of asphalt mixture under multi-stage loading is divided into three stages:

The first stage is the initial compaction stage, and the control is completed within the first loading sequence; after the end of the first stage, it is the second stage, and the second stage is the linear growth stage of cumulative micro-strain, in which each level of stress level loading produces The microstrains of the microstrains all show a linear growth, but with the change of the stress level, the growth rate of the microstrains also changes greatly; Stage asphalt mixture is already in a state of high temperature instability.

2) Three major indexes are calculated according to the segmented data, and the three major indexes include load sensitivity index LSI, creep damage angle CDA and compound rheological number MFN.

As shown in Figure 1, it is the calculation method of the load sensitivity index LSI. The relationship between the cumulative micro-strain and the number of load actions under the four different stress levels in the second stage is linearly fitted, and the growth of the micro-strain under different stress levels is extracted. The rate value is fitted using a power function, as shown in formula 1, and the load sensitivity index LSI is the index value of the fitting result. The greater the LSI, the greater the difference in the stress level and the greater the difference in the growth rate of the micro-strain, that is, the asphalt mixture is more sensitive to the change of the load.

Δε＝a·σ ^LSI (1)

in:

σ: stress level;

Δε: micro-strain growth rate;

a: Regression coefficient.

As shown in Figure 2, for the calculation method of the creep damage angle CDA, the first loading sequence belonging to the first stage (compacting stage) of the creep curve is removed, and the first two large cycles belonging to the second stage ( The loading sequence is two, three, four, one) extracted for analysis. Point A is the starting point of the second loading sequence, point B is the end point of the second first loading sequence, and point C is the end point of the third first loading sequence. Connect AB and BC, and the acute angle between AB and BC is the creep damage angle CDA, which is calculated by formula 2. The smaller the CDA, the more balanced the rate of creep damage of the asphalt mixture. Since the cumulative action times of cycle 1 and cycle 2 are the same, it shows that the cumulative micro-strain produced by cycle 1 and cycle 2 is not much different. Therefore, the asphalt mixture Insensitive to the effects of cyclic axle load stresses.

$\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; D.</span>}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; arctan</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}}{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; arctan</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}}{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

in:

ε _A , ε _B , ε _C : Cumulative micro-strain at three points A, B, and C;

n _A , n _B , n _C : the cumulative action times of points A, B, and C.

Compared with the standard dynamic creep test, the multi-stage loading high-temperature creep test method of asphalt mixture based on the axle load spectrum takes into account the influence of different axle loads on the actual pavement. The high-temperature creep test curve found that in the second stage of creep, although the stress level is changing, the development of the cumulative micro-strain of the asphalt mixture still shows a linear growth trend, but the growth rate changes. Therefore, any definition In a loading sequence, as long as the cumulative microstrain of asphalt mixture shows a linear growth trend with the number of actions, it means that this stage still belongs to the second stage and has not reached the third stage of rapid growth.

As shown in Figure 3, the value of the number at the boundary between the second stage and the third stage is the value of the uncompounded rheological number MFN, and the composite rheological number MFN is defined as the termination point where the cumulative micro-strain increases linearly with the number of actions . The larger the MFN, the stronger the ability of the asphalt mixture material to resist permanent deformation under the action of the axial load spectrum.

The present invention divides the traditional multi-stage loading high temperature creep curve of asphalt mixture into three stages, calculates the load sensitivity index LSI and the creep damage angle CDA to evaluate the creep characteristics of asphalt mixture under different stress levels, Analyze its sensitivity to the load, and evaluate the anti-permanent deformation ability of the material under the action of the actual axle load spectrum according to the composite rheological number MFN, and provide accurate information for guiding the practice of road engineering, especially for the decision-making of highway maintenance and repair projects in my country. , intuitive digital basis.

Claims (2)

1. An asphalt mixture multi-stage loading high-temperature creep curve analysis method based on an axle load spectrum is characterized by comprising the following steps:

1) the multi-stage loading high-temperature creep curve of the asphalt mixture is divided into three stages:

the first stage is as follows: namely the first loading sequence time period after the start of the multi-stage loading of the asphalt mixture;

and a second stage: after the first loading sequence time period is finished, the micro strain generated by each level of stress horizontal loading shows a linear increasing stage of accumulated micro strain;

and a third stage: namely a rapid growth stage of accumulated micro-strain of the asphalt mixture in a high-temperature instability state;

2) calculating three indexes according to segmented data, wherein the three indexes comprise a load sensitivity index LSI, a creep damage included angle CDA and a composite rheological frequency MFN;

load sensitivity index LSI: selecting the relationship between the accumulated micro strain and the load action times under 3-5 different stress levels in the second stage for linear fitting, obtaining the slope of the creep curve under corresponding different stress levels, wherein the slope is the growth rate of the micro strain, and the power function is utilized, and delta is a.sigma.^LSIFitting to obtain a load sensitivity index LSI, wherein sigma is a stress level; Δ is the rate of microstrain growth; a is a regression coefficient;

creep damage included angle CDA: extracting and analyzing the first two major cycles of the second stage, wherein the loading sequence is two, three, four and one; the starting point of the second loading order is A, the end point of the second first loading order is B, and the end point of the third first loading order is C; the acute angle between AB and BC is the creep damage angle CDA, and the formula is shownObtaining the CDA; wherein,_A、_B、_Cthe accumulated micro strain of the three points A, B and C respectively; n is_A、n_B、n_CThe cumulative action times of the three points A, B and C are respectively;

composite rheological number MFN: the number of times at the boundary between the second stage and the third stage, i.e., the termination point at which the accumulated microstrain linearly increases with the number of times of application, is shown.

2. The method for analyzing the multi-stage loading high-temperature creep curve of the asphalt mixture based on the axle load spectrum according to claim 1, wherein the number of different stress levels selected in the second stage in the step 2) is four.