CN105486845A

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

Info

Publication number: CN105486845A
Application number: CN201610034622.5A
Authority: CN
Inventors: 倪富健; 蒋继望; 高磊; 娄深鑫
Original assignee: Southeast University
Current assignee: Southeast University
Priority date: 2016-01-19
Filing date: 2016-01-19
Publication date: 2016-04-13
Anticipated expiration: 2036-01-19
Also published as: CN105486845B

Abstract

The invention discloses an asphalt mixture multi-stage loaded high-temperature creep curve analysis method based on an axle load spectrum. Creep curves at the second creep stage in different-stage loading process are subjected to linear fitting to acquire a cumulative microstrain growth slope, the responsive high-temperature creep characteristic indexes LSI, CDA and MFN are calculated according to the formula. In the parameters, the relatively big MFN represents relatively strong permanent deformation resisting capability of the mixture under the multi-stage loading action, the relatively small LSI shows that the mixture is relatively insensitive to variation of axle load and probably is relatively strong in heavy duty resistance, and the relatively small CDA shows that the creep damage generation rate of the asphalt mixture is relatively balanced and the asphalt mixture is insensitive to loading of a circular spectral pattern.

Description

Asphalt mixture multi-stage loading high-temperature creep curve analysis method based on axle load spectrum

Technical Field

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

Background

Permanent deformation damage such as rutting and the like is one of the most typical and most harmful disease forms of high-grade asphalt pavements in China. The scholars at home and abroad carry out a great deal of research on the high-temperature creep behavior of the asphalt pavement, particularly on the aspect of test methods, the American NCHRP research project carries out the research on a simple performance test method of the asphalt mixture, and finally, the research shows that the dynamic modulus test and the dynamic creep test can well evaluate and predict the high-temperature rutting resistance of the asphalt mixture.

However, the dynamic creep test is based on a single load half sine wave loading mode, and the loading mode is greatly different from the actual axle load applied to the road surface.

Therefore, the results of the conventional calculation method are greatly different from the actual conditions, and the effect of road surface maintenance cannot be realized in the actual application.

Disclosure of Invention

The invention aims to solve the technical problem that the existing dynamic creep test is based on a single-load half sine wave loading mode, the difference between the loading mode and the actual axle load of a road surface is huge, and the road surface maintenance effect cannot be realized in the actual application.

In order to solve the technical problems, the invention adopts the technical scheme that: an asphalt mixture multi-stage loading high-temperature creep curve analysis method based on an axle load spectrum comprises the following steps: 1) mixing asphaltThe multistage loading high-temperature creep curve of the 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.

Further, the number of different stress levels selected in the second stage in step 2) is four. The reason why the number of stress levels is four is that too few selection numbers affect the accuracy of the experimental results, too many selection numbers result in too large calculation amount, and the selection number of four can meet the accuracy requirement and cannot cause too large calculation load amount.

The invention has the advantages that: the evaluation method is simple and easy to implement, the creep characteristics of the asphalt mixture under different stress levels are evaluated through a load sensitivity index LSI and a creep damage included angle CDA, the sensitivity degree of the asphalt mixture to the load is analyzed, the permanent deformation resistance of the material under the action of an actual axle load spectrum is evaluated according to the composite rheological frequency MFN, and an accurate and visual digital basis is provided for guiding the road engineering practice, especially the scheme decision of the highway maintenance engineering in China.

Drawings

FIG. 1 is a second stage linear fit of a creep curve;

FIG. 2 is a schematic diagram of a creep curve creep damage angle CDA calculation;

FIG. 3 is a schematic diagram of a method for determining a creep curve complex rheology number MFN.

Detailed Description

The invention is further described with reference to the following figures and detailed description.

The method comprises 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 an initial compaction stage, and control is finished in a first loading sequence; after the first stage is finished, the second stage is a linear growth stage of accumulated micro-strain, the micro-strain generated by loading each stage of stress level in the stage is linearly increased, but the rate of the micro-strain increase is greatly changed along with the change of the stress level; and after the second stage is finished, entering a third stage, wherein the third stage is a rapid increase stage of accumulated micro-strain, and the asphalt mixture is in a high-temperature instability state.

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

As shown in fig. 1, in order to calculate the load sensitivity index LSI, linear fitting is performed on the relationship between the accumulated micro-strain and the number of times of load action at four different stress levels in the second stage, the growth rate values of the micro-strain at the different stress levels are extracted, and fitting is performed using a power function as shown in formula 1, where the load sensitivity index LSI is an index value of the fitting result. The larger the LSI, the larger the difference in stress level, the larger the difference in the rate of increase of micro strain, i.e., the more sensitive the asphalt mixture is to the change of load.

Δ＝a·σ^LSI(1)

Wherein:

σ: a stress level;

Δ: rate of growth of microstrain;

a: and (4) regression coefficients.

As shown in fig. 2, in order to calculate the creep damage included angle CDA, the first loading sequence belonging to the first stage (compaction stage) of the creep curve is removed, and the first two large cycles (the loading sequence is two, three, four, and one) belonging to the second stage are extracted and analyzed. Point A is the start of the second load order, point B is the end of the second first load order, and point C is the end of the third first load order. The acute angle between AB and BC, which is the creep damage angle CDA, is calculated using equation 2. The smaller the CDA, the more balanced the creep damage rate of the asphalt mixture, and the same accumulative action times of the cycle 1 and the cycle 2 indicate that the accumulative microstrain generated by the cycle 1 and the cycle 2 is not greatly different, so the asphalt mixture is insensitive to the action of the cyclic axial load stress.

C D A = | \arctan (\frac{ϵ_{B} - ϵ_{A}}{n_{B} - n_{A}}) - \arctan (\frac{ϵ_{C} - ϵ_{B}}{n_{C} - n_{B}}) | - - - (2)

Wherein:

_A、_B、_C: accumulated microstrain of three points A, B and C;

n_A、n_B、n_C: cumulative action times of three points A, B and C.

Compared with a standard dynamic creep test, the asphalt mixture multi-stage loading high-temperature creep test method based on the axle load spectrum considers the influence of loads of different axle weights of an actual road surface, and the influence of the loads of different axle weights of the actual road surface is found by analyzing the asphalt mixture multi-stage loading high-temperature creep test curve based on the axle load spectrum, and although the stress level is changed, the development of the accumulated micro-strain of the asphalt mixture still presents a linear growth trend and only the growth rate is changed, so that in any one loading sequence is defined, as long as the accumulated micro-strain of the asphalt mixture presents a linear growth trend along with the action times, the stage still belongs to the second stage and does not reach the third stage of rapid growth.

As shown in fig. 3, the number of times at the boundary between the second stage and the third stage is the value of the uncompounded rheological number MFN, which is defined as the termination point at which the accumulated microstrain linearly increases with the number of times of action. The larger the MFN, the greater the resistance of the asphalt mixture material to permanent deformation under the action of the axle load spectrum.

The method comprises the steps of dividing a traditional asphalt mixture multistage loading high-temperature creep curve into three stages, sequentially calculating a load sensitivity index LSI, evaluating the creep characteristics of the asphalt mixture under different stress levels by a creep damage included angle CDA, analyzing the sensitivity degree of the asphalt mixture to the load, evaluating the permanent deformation resistance of the material under the action of an actual axle load spectrum according to the composite rheological frequency MFN, and providing an accurate and visual digital basis for guiding the road engineering practice, particularly the scheme decision of the expressway maintenance engineering in China.

Claims

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:

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.