CN105571933A - Asphalt mixture multi-stage loading high-temperature creep test method based on axle load spectrum - Google Patents

Abstract

The invention discloses an asphalt mixture multi-stage loading high-temperature creep test method based on an axle load spectrum. The test method includes the following steps that 1, the axle load spectrum of a road to be researched is analyzed, and a road axle load spectrum converted into a single-axle double-wheel set is obtained through a road maintenance management decision system (PMS); 2, the axle load stress level and weights of different axle loads are determined according to the road axle load spectrum; 3, a preloading test is conducted according to stress level data of a first loading sequence in the axle load stress level obtained in the step 2; 4, the number of action times of the first loading sequence in the test and the overall cycle length of multi-stage load actions are calculated according to weight data of the different axle loads obtained in the step 2; 5, a multi-stage loading high-temperature creep test is conducted according to the data obtained in the step 4; 6, a test result is obtained. High-temperature creep performance evaluation and prediction, which are more practical, for a material are provided for expressways with different traffic volumes and different axle load spectrums.

Description

Based on the asphalt multi-stage loading high-temerature creep test method of axle load spectrum

Technical field

The present invention is specifically related to a kind of asphalt multi-stage loading high-temerature creep test method based on axle load spectrum, belongs to road engineering technical field.

Background technology

In recent years, the permanent strain such as rut is destroyed becomes one of disease form of China Higher level bituminous pavement the most typical also most harmfulness day by day.For the high temperature rut problem of bituminous pavement, Chinese scholars has done large quantifier elimination in test condition, test method, material composition, load characteristic, environmental factor etc.U.S.'s NCHRP project has carried out the research of the simple performance experiment method of asphalt, through a large amount of screenings and shop experiment research, recommend 3 kinds of simple performance experiment (simpleperformancetest, be called for short SPT) be used for evaluating the ability of resistance to permanent deformation of asphalt, comprising: dynamic modulus test, static creep test and dynamic creep test.Wherein dynamic creep test can the ability of the comparatively resistance to permanent deformation of effectively evaluating asphalt.But the half-sine wave that the loading mode of this test method is single load loads, and the axle situation of carrying of this and the complexity suffered by actual road surface is not inconsistent.

Summary of the invention

The technical problem to be solved in the present invention is that the result that existing test method draws cannot react road conditions really, and provides accurately real-time Data support for road maintenance.

For solving the problems of the technologies described above, the technical solution used in the present invention is: a kind of asphalt multi-stage loading high-temerature creep test method based on axle load spectrum, comprise the following steps: step one: the axle load spectrum of studied road is analyzed, utilize road maintenance management decision system (PMS) to obtain the road axle load spectrum being scaled single shaft two-wheel group; Step 2: carry the weight that stress level and disalignment carry according to road axle load spectrum determination axle; Step 3: the stress level data of carrying the first loading sequence in stress level according to the axle obtained in step 2 carry out prestrain test; Step 4: the weighted data carried according to the disalignment obtained in step 2 calculates the loading sequence effect number of times and total Cycle Length of multistage load action of first time in test; Step 5: the data obtained according to step 4 carry out the high-temerature creep test of multi-stage loading; Step 6: obtain experimental result.

In the method, the high-temerature creep test of axle load spectrum, prestrain test and multi-stage loading is existing mature technology, but, because the data of the high-temerature creep test of bringing prestrain test and multi-stage loading in prior art into depart from true, cause the result tested cannot react road conditions really, for road maintenance provides accurately real-time Data support.Axle load spectrum type suffered by actual road surface is applied in shop experiment by the inventive method, utilize the volume of traffic to the highway be open to traffic in road maintenance management decision system (PMS), the accurately detailed statistics that axle load spectrum is made, take into full account the loading characteristic of asphalt in the middle of actual road surface, actual road surface axle load spectrum data are utilized to simulate the High-Temperature Creep Performance of asphalt under multiple axle carries multiple computation model exactly, it is high that the conclusion that the data that this method is drawn draw after bringing the high-temerature creep test of prestrain test and multi-stage loading into has authenticity, the effect that real-time is good, test findings is reliable and stable.

Further, described step 2 comprises the following steps: 1) select the heavy corresponding axle of each axle in road axle load spectrum to carry data, described axle is great in six tons, and described axle carries the heavy corresponding axle effect of carrying of data i.e. this axle time logarithmic data; Carry data according to axle and determine the heavy scope W of main axle _a~ W _baxle in the heavy scope of this axle is heavily serial number, the axle of the heavy correspondence of any one axle carries that data account for that the axle being greater than 6 tons carries the ratio of effect total degree in scope more than 1%, and in scope, the axle of the heavy correspondence of each axle carries data sum and accounts for the ratio more than 95% that the axle being greater than 6 tons carries effect total degree; 2) by W _a~ W _bevenly be divided into 4 and represent the heavy interval W of axle _a~ W ₂, W ₂~ W ₃, W ₃~ W ₄, W ₄~ W _b, wherein the intermediate value in each interval is for representing axle heavy q1, q2, q3, q4 (q1<q2<q3<q4); Four are represented axle and be heavily scaled corresponding tire ground connection pressure, σ ₁, σ ₂, σ ₃, σ ₄(σ ₁< σ ₂< σ ₃< σ ₄), reduction formula is: wherein σ ₁and q ₁be respectively tire ground connection pressure (unit: KPa) and axle heavy (unit: KN); σ _sand q _sbe respectively standard tire ground connection pressure 700KPa and standard axle load 100KN, namely four represent stress level, add up according to axle load spectrum the effect number of times weight A that four effect number of times ratio-dependents four representing the heavy interval of axle represent stress level ₁: A ₂: A ₃: A ₄.In actual use procedure, it is small that axle is heavily less than the damage that 6 tons of road pavement produce, and is consider more unfavorable load, and therefore, the axle being less than 6 tons is heavily ignored not to be added up.For needing in the data of statistics, general in axle load spectrum, axle is heavily larger, effect number of times is fewer, and the proportion accounting for resultant action number of times is less, so, the present invention gets rid of the axle weight that proportion is less than total degree 1%, and heavy moderate, that number of times the is larger data of chosen axis are added up, the operability tested of being more convenient for, to obtain reliable and stable data; Again, heavily increase with axle, tyre contact pressure is corresponding increase also, and the contact area of tire also can increase simultaneously, and therefore tyre contact pressure is not with the heavy linear increase of axle, after testing, adopts formula: accurately can reflect tire pressure.

Further, described step 4 comprises the following steps: 1) determine loading sequence; Choose four stress levels are sorted from small to large, i.e. σ ₁< σ ₂< σ ₃< σ ₄, then in a large period, loading sequence is defined as: σ ₂→ σ ₄→ σ ₃→ σ ₁; Prestrain is utilized to test the effect number of times X determining each loading sequence ₁, X ₂, X ₃, X ₄; 2) utilize the standard dynamic creep under the stress level of the first order in loading sequence to test, obtain creep curve; The creep curve of acquisition is divided into three phases: the first stage: namely asphalt multi-stage loading start after first loading sequence time period; Subordinate phase: after namely first loading sequence time period terminate, every one-level stress level loads the accumulation microstrain linear increase stage that the microstrain produced all presents linear increase; Phase III: namely asphalt is in the accumulation microstrain Fast growth phase of high temperature instability status; By carrying out linear fit to subordinate phase, determine the starting point n of subordinate phase ₁; Defining method is: pass through calculate average microstrain be defined as and use frequency n ₁for initial stage densification reaches the location point of 100%; Pass through formula $\stackrel{\&OverBar;}{{\mathrm{\&epsiv;}}_{100\%}}=\frac{{\mathrm{\&epsiv;}}_{n_1}-{\mathrm{\&epsiv;}}_{14}}{n_1-14}$ With $\stackrel{\&OverBar;}{{\mathrm{\&epsiv;}}_{90\%}}=\stackrel{\&OverBar;}{{\mathrm{\&epsiv;}}_{15}}-0.9(\stackrel{\&OverBar;}{{\mathrm{\&epsiv;}}_{15}}-\stackrel{\&OverBar;}{{\mathrm{\&epsiv;}}_{100\%}})$ Calculate with corresponding effect number of times is n ₂; Wherein: ε _i: the accumulation microstrain of i-th loading specimen; the average microstrain of i-th loading specimen; initial stage densification reaches the average microstrain of 100%; initial stage densification reaches the average microstrain of 90%; A ₁, A ₂, A ₃, A ₄: four represent effect number of times weight corresponding to stress level; X ₂for n ₂and n ₁between arbitrary value; Pass through X ₁=X ₂a ₁/ A ₂, try to achieve X ₁; Pass through X ₃=X ₂a ₃/ A ₂, try to achieve X ₃; Pass through X ₄=X ₂a ₄/ A ₂, try to achieve X ₄; 3) prestrain is utilized to test the total Cycle Length L determining multistage load action;

L＝X ₁+X ₂+X ₃+X ₄

Wherein: X ₁, X ₂, X ₃, X ₄: stress level 1,2, the effect number of times of 3,4, total Cycle Length of L: four loading sequences.

Preferably, n is worked as ₁and n ₂when difference is less than 200 times, X ₂for n ₁and n ₂between arbitrary value, work as n ₁and n ₂when differing by more than 200 times, X ₂for n ₁and n ₂intermediate value.。The advantage of such value ensures that multistage stress acts predominantly on creep curve subordinate phase and the length of creep curve subordinate phase enough carries out the superposition of four different stress levels.

Advantage of the present invention is: compared with prior art, the test method of the present invention's design has taken into full account the loading characteristic of asphalt in the middle of actual road surface, utilizes actual road surface axle load spectrum data can simulate the High-Temperature Creep Performance of asphalt under multiple axle carries multiple computation model exactly.Test method is simple, and test condition controls rationally, and test findings is reliable and stable.This test method is conducive to the research to asphalt high-temerature creep mechanism, thus instructs the design of asphalt concrete pavement structure and material, and especially the decision-making of road pavement maintenance plan has directive significance.

Accompanying drawing explanation

Fig. 1 is the first loading sequence effect number of times defining method schematic diagram of the present invention;

Fig. 2 is multi-stage loading stress level of the present invention change schematic diagram;

Fig. 3 is the Shanghai-Nanjing freeway average axle load spectrum of nearly 5 years (being scaled single shaft two-wheel group);

Fig. 4 is multi-stage loading high-temerature creep test method process flow diagram of the present invention;

Fig. 5 is the load mode schematic diagram of prestrain of the present invention test;

Fig. 6 is prestrain test findings subordinate phase linear fit instance graph of the present invention;

Fig. 7 is the first loading sequence effect number of times defining method instance graph of the present invention;

Fig. 8 is asphalt multi-stage loading creep curve instance graph.

Embodiment

As shown in figures 1-8, the high-temerature creep test method of a kind of asphalt multi-stage loading of the present invention, step is as follows:

Determine that axle carries stress level: utilize road maintenance management decision system (PMS) to obtain the axle load spectrum data of road to be studied, and be scaled the axle load spectrum of single shaft two-wheel set type.The damage that axle is heavily less than 6 tons of road pavement generations is small, is consider more unfavorable load, is ignored.Consider that the great axle in 6 tons of axle carries data, select representative and that effect number of times accounting is large axle heavily to convert.According to axle load spectrum feature, determine the heavy scope W of main axle _a~ W _b, the axle in the heavy scope of this axle carry effect number of times account for the axle being greater than 6 tons carry effect total degree ratio need to be greater than 95%.By W _a~ W _bbe divided into 4 and represent the heavy interval W of axle _a~ W ₂, W ₂~ W ₃, W ₃~ W ₄, W ₄~ W _b, interval division as far as possible evenly.Wherein the intermediate value in each interval is for representing the heavy q of axle ₁, q ₂, q ₃, q ₄(q ₁<q ₂<q ₃<q ₄).Represent axle by question blank 1 by four and be heavily scaled corresponding tire pressure, namely four represent stress level σ ₁, σ ₂, σ ₃, σ ₄(σ ₁< σ ₂< σ ₃< σ ₄).Four stress levels represent four respectively and represent the heavy interval of axle.Adding up four effect number of times ratios representing effect number of times ratio-dependent four kinds of stress levels in the heavy interval of axle according to axle load spectrum is: A ₁: A ₂: A ₃: A ₄.

Table 1 axle weighs and stress level conversion table

Stress level (KPa)	320	386	446	502	555	605	654	700
									Axle heavy (KN)	30	40	50	60	70	80	90	100
Stress level (KPa)	745	788	830	871	911	950	988	1026
									Axle heavy (KN)	110	120	130	140	150	160	170	180

Specimen molding: it is mainly according to the needs of this test, utilize the cylinder specimen of rotary compactor forming diameter 150mm height 180mm, again by overall test specimen by turning the operation such as core, cutting, be made as diameter 100mm, the right cylinder test specimen of height 150mm, ensure that test specimen upper and lower surface is parallel to each other, thus the making completing the right cylinder bitumen mixture specimen of the multi-stage loading high-temerature creep test needs based on axle load spectrum is shaping.

Prestrain is tested: choose three parallel test specimens, and test specimen needs at 60 DEG C of constant temperature oven insulation more than 4h, and employing class of loading is σ ₂standard dynamic creep is tested, and loading cycle is 1s, and wherein 0.1s loads, and 0.9s unloads, and load waveform is half-sine wave, and peak value is σ ₂.Be connected with load and displacement transducer by registering instrument, start testing machine, the vertical strain of process of the test record asphalt is with the curve loading number of times change.Test end condition reaches 100000 μ ε for vertical strain or loads number of times and reaches 10000 times.

Determine the first loading sequence effect number of times X ₂: for ensureing that multi-stage loading acts predominantly on the subordinate phase (i.e. linear increase stage) of compound creep curve, need to determine that class of loading is σ ₂standard dynamic creep test creep curve first stage (i.e. densification stage) final position.The creep curve of standard dynamic creep test is divided into three phases, and wherein the first stage is distortion Fast growth phase, and subordinate phase is stabilization build phase, as shown in block curve in Fig. 1.By carrying out linear fit to subordinate phase, determine the starting point n of subordinate phase ₁.Fig. 1 dotted line is average microstrain with the relation curve loading number of times. calculated by formula 1.And in the first stage, the average microstrain of compound starts to be quick reduction, densification in the early stage reaches more than 90%, and the speed of reduction is slow.Be defined as and use frequency n ₁for initial stage densification reaches the location point of 100%. with by formula 2,3 calculate, and corresponding effect number of times is n ₂.X ₂need to control at n ₂and n ₁between.

$\stackrel{\&OverBar;}{{\mathrm{\&epsiv;}}_i}=\frac{{\mathrm{\&epsiv;}}_i-{\mathrm{\&epsiv;}}_{14}}{n-14}---\left(1\right)$

$\stackrel{\&OverBar;}{{\mathrm{\&epsiv;}}_{100\%}}=\frac{{\mathrm{\&epsiv;}}_{n_1}-{\mathrm{\&epsiv;}}_{14}}{n_1-14}---\left(2\right)$

$\stackrel{\&OverBar;}{{\mathrm{\&epsiv;}}_{90\%}}=\stackrel{\&OverBar;}{{\mathrm{\&epsiv;}}_{15}}-0.9(\stackrel{\&OverBar;}{{\mathrm{\&epsiv;}}_{15}}-\stackrel{\&OverBar;}{{\mathrm{\&epsiv;}}_{100\%}})---\left(3\right)$

Wherein:

ε _i: the accumulation microstrain of i-th loading specimen;

the average microstrain of i-th loading specimen;

initial stage densification reaches the average microstrain of 100%;

initial stage densification reaches the average microstrain of 90%.

The loading sequence determining total Cycle Length L: four stress levels of multistage load action is σ ₂→ σ ₄→ σ ₃→ σ ₁, for guaranteeing the first loading sequence (i.e. σ ₂load) afterwards compound creep curve enter subordinate phase, determine the effect number of times X of total Cycle Length L and four loading sequence ₂, X ₄, X ₃, X ₁, as shown in formula 4 ~ 7.

X ₁＝X ₂A ₁/A ₂(4)

X ₃＝X ₂A ₃/A ₂(5)

X ₄＝X ₂A ₄/A ₂(6)

L＝X ₁+X ₂+X ₃+X ₄(7)

Wherein:

X ₁, X ₂, X ₃, X ₄: stress level 1,2, the effect number of times of 3,4

A ₁, A ₂, A ₃, A ₄: stress level 1,2, the effect number of times ratio of 3,4

Total Cycle Length of L: four loading sequences

Multi-stage loading high-temerature creep is tested: choose three parallel test specimens, and test specimen needs at 60 DEG C of constant temperature oven insulation more than 4h, and using L as a large period, in the cycle, axle carries order is σ ₂→ σ ₄→ σ ₃→ σ ₁, the action time of each order is X ₂, X ₄, X ₃, X ₁, the cycle acted on each time is that 1s, 0.1s load, and 0.9s unloads, and load waveform is half-sine wave, and load peak value is σ ₂, σ ₄, σ ₃, σ ₁, as shown in Fig. 2 and table 2.The vertical strain of process of the test record asphalt is with the curve loading number of times change.Test end condition be accumulation microstrain reach 100000 or the creep curve of asphalt obviously enter the phase III (namely straining Fast growth phase).

The load mode table of table 2 multi-stage loading high-temerature creep test

Stress level (KPa)

σ 2

σ 4

σ 3

σ 1

σ 2

σ 4

σ 3

σ 1

……

Load number of times

X 2

X 4

X 3

X 1

X 2

X 4

X 3

X 1

……

Interpretation of result: based on the asphalt multi-stage loading high-temerature creep test method of axle load spectrum, the creep curve that the asphalt multi-stage loading high-temerature creep based on axle load spectrum is tested can be obtained, in-depth analysis can obtain the flow number of asphalt under axle load spectrum load mode, the strain variation rate under maximum microstrain and average strain rate and different stress level.

Asphalt multi-stage loading high-temerature creep test method based on axle load spectrum of the present invention is applicable to measure the mechanical property of asphalt when set point of temperature and loading speed under different stress level superposition, also can be used to select asphalt mechanical index parameter and evaluate asphalt to use when actual axle carries the High-Temperature Creep Performance under spectral pattern effect to building up when Maintenance Decision making is carried out on road surface.Test temperature and loading speed can be selected according to test objective by local climate condition, when High-Temperature Creep Performance under being used to evaluate asphalt actual axle and carrying spectral pattern effect, test temperature 60 DEG C ± 0.5 DEG C and loading speed should be adopted to be that 0.1s loads, and 0.9s unloads.

(1) test method principle

Asphalt multi-stage loading high-temerature creep test method based on axle load spectrum of the present invention combines the road axis that road maintenance management decision system (PMS) obtains to carry modal data and asphalt dynamic creep test unit, choose suitable test condition and test index, realize lab simulation asphalt being carried to the High-Temperature Creep Performance under spectral pattern effect in actual axle.Utilize the axle load spectrum data that road maintenance management decision system (PMS) is added up, disalignment is carried and carries out weight analysis, load mode and the stress level of creep test can be changed flexibly, and the combination of stress level, thus realize the evaluation and the prediction that the highway of the different volume of traffic, different axle load spectrum are provided to the high temperature creep property of more realistic material.

(2) test method prepares

(1) test condition is determined:

The test of this asphalt multi-stage loading high-temerature creep can complete in UTM universal testing machine, and testing machine needs to provide the test temperature of requirement and the compression load of fixed frequency, and records the accumulation microstrain-effect frequency curve in process of the test.Through repetition test, different types of asphalt multi-stage loading high-temerature creep test findings based on axle load spectrum relatively under three kinds of test temperatures (40 DEG C, 50 DEG C, 70 DEG C), finally determines that the test condition that this asphalt high-temerature creep is tested is: test temperature is 60 DEG C ± 0.5 DEG C; Test loading frequency is 1Hz, and namely 0.1s loads, and 0.9s unloads.Under this kind of test condition, the test of asphalt multi-stage loading high-temerature creep more can reflect the feature of high-temerature creep really, and the coefficient of variation of test findings is minimum.

(2) equipment needed thereby is tested:

The test of asphalt multi-stage loading high-temerature creep needs to use asphalt dynamic creep test fixture to carry out in UTM universal testing machine.UTM universal testing machine needs to provide the test temperature of requirement and the compression load of fixed frequency, and records the accumulation microstrain-effect frequency curve in process of the test.

(3) test method step

As shown in Figure 4, asphalt multi-stage loading high-temerature creep test method based on axle load spectrum mainly comprises: obtain road axle load spectrum, determine that main axle carries stress level, determines weight that disalignment carries, prestrain test, the high-temerature creep test determining the effect number of times of the first loading sequence, the total Cycle Length determining multistage load action, multi-stage loading and interpretation

The main experimental step of the compound cracking of asphalt is as follows:

Step one: obtain road axle load spectrum

Road maintenance management decision system (PMS) obtains the Shanghai-Nanjing freeway average axle load spectrum of nearly 5 years, is scaled single shaft two-wheel group data, as shown in Figure 3, with 2 tons of intervals, has added up the effect number of times that the disalignment of 2-30 ton is heavy.

Step 2: determine the weight that main axle carries stress level and disalignment and carries

As shown in Figure 3, although the axle of 2-6 ton heavy effect number of times is a lot, because weight is less, the damage for road surface is negligible, does not therefore consider.And heavy interval for the axle of 6-30 ton, the effect number of times that the axle of 6-16 ton is heavy occupies about 99% of the heavy total effect number of times of 6-30 ton axle, is greater than 95%.Therefore determine that the heavy scope of main axle is 6-16 ton, be divided into four axles heavy interval: 6-8 ton, 8-10 ton, 10-12 ton, 12-16 ton, wherein each interval intermediate value 7 tons, 9 tons, 11 tons, 14 tons for representing axle weight.The stress level σ of creep test loading can be converted into by question blank 1 ₁, σ ₂, σ ₃, σ ₄(σ ₁< σ ₂< σ ₃< σ ₄), be respectively 555KPa, 654KPa, 745KPa and 871KPa.Calculate the ratio that the heavy interval axle of four axles carries effect number of times can obtain, four effect number of times weight A representing stress level ₁: A ₂: A ₃: A ₄for: 26:30:15:8.

Step 3: shaping test piece

Utilize the right cylinder test specimen of rotary compactor forming diameter 150mm height 180mm, again by overall test specimen by turning the operation such as core, cutting, be made as diameter 100mm, height 150mm right cylinder test specimen, ensure that test specimen upper and lower surface is parallel to each other, make 6 parallel test specimens, wherein test specimen 1,2,3 are used for carrying out prestrain test, test specimen 4,5,6 are used for the multi-stage loading high-temerature creep carried out based on axle load spectrum tests.

Step 4: prestrain is tested:

Asphalt multi-stage loading high-temerature creep test based on axle load spectrum can be carried out in UTM universal testing machine.Before experiment starts, be incubated in the Tempeerature-constant air case of 60 DEG C by the asphalt 1,2,3 after cutting and be no less than 4h, till test specimen internal temperature reaches test temperature ± 0.5 DEG C, distance during insulation between test specimen is no less than 10mm.Arrange the parameters of testing machine, make the temperature of the environment insulation can of testing machine reach 60 DEG C ± 0.5 DEG C, the compression-loaded frequency of testing machine is 1Hz, and half-sine wave loads, and wherein 0.1s loads, and 0.9s unloads, and crest value is σ ₂, i.e. 654KPa, as shown in Figure 5.Be connected with load and displacement transducer by registering instrument, start testing machine, the vertical strain of process of the test record asphalt is with the curve loading number of times change.Test end condition reaches 100000 μ ε for vertical strain or loads number of times and reaches 10000 times.

Step 5: the effect number of times determining the first loading sequence

For ensureing that multi-stage loading acts predominantly on the subordinate phase (i.e. linear increase stage) of compound creep curve, need to determine that class of loading is σ ₂(654KPa) creep curve first stage (the i.e. densification stage) final position of standard dynamic creep test.The creep curve of standard dynamic creep test is divided into three phases, and wherein the first stage is distortion Fast growth phase, and subordinate phase is stabilization build phase.By carrying out linear fit to subordinate phase, as shown in Figure 6, the fitting result of the subordinate phase of test specimen 1 is: y=17.842x+18206, and R ²=0.9986, illustrate that fitting effect is fine, thus determine the starting point n of subordinate phase ₁it is the 200th time.In Fig. 7, dotted line is the average microstrain of test specimen 1 with the relation curve loading number of times.Fig. 7 shows in the first stage, and the average microstrain of compound starts to be quick reduction, and when densification reaches more than 90% in the early stage, the speed that average microstrain reduces is slow.Be defined as and use frequency n ₁(namely 200 times) reach the location point of 100% for initial stage densification. with calculated by formula 8 and 9, and the effect number of times of average microstrain 79.122 correspondence is 130 times, i.e. n ₂equal 130 times.X is determined according to test specimen 1 result ₂need to control between 130 times and 200, in like manner can obtain the n of test specimen 2 and 3 ₁, n ₂value, as shown in table 3, the n of three parallel test specimens ₁, n ₂value error need control within 20 times, otherwise cancels.Finally X is selected according to prestrain experimental result ₂size be 200 times.

The n of table 3 three parallel test specimens ₁, n ₂value

	Test specimen 1	Test specimen 2	Test specimen 3
				n 2	130	145	140
n 1	200	210	220

$\stackrel{\&OverBar;}{{\mathrm{\&epsiv;}}_{100\%}}=\frac{{\mathrm{\&epsiv;}}_{n_1}-{\mathrm{\&epsiv;}}_{14}}{n_1-14}=\frac{20580-8939}{200-14}=62.586---\left(8\right)$

$\stackrel{\&OverBar;}{{\mathrm{\&epsiv;}}_{90\%}}=\stackrel{\&OverBar;}{{\mathrm{\&epsiv;}}_{15}}-0.9(\stackrel{\&OverBar;}{{\mathrm{\&epsiv;}}_{15}}-\stackrel{\&OverBar;}{{\mathrm{\&epsiv;}}_{100\%}})=228-0.9(228-62.586)=79.122---\left(9\right)$

Wherein:

n-th ₁the accumulation microstrain of secondary loading specimen;

initial stage densification reaches the average microstrain of 100%;

initial stage densification reaches the average microstrain of 90%.

Step 6: the total Cycle Length determining multistage load action

The loading sequence of four stress levels is σ ₂→ σ ₄→ σ ₃→ σ ₁, for guaranteeing the first loading sequence (i.e. σ ₂load) afterwards compound creep curve enter subordinate phase, calculate the effect number of times X of total Cycle Length L and four loading sequence ₂, X ₄, X ₃, X ₁, as shown in formula 10 ~ 13.

X ₁＝X ₂A ₁/A ₂＝20026/30＝173(10)

X ₃＝X ₂A ₃/A ₂＝20015/30＝100(11)

X ₄＝X ₂A ₄/A ₂＝20030/8＝54(12)

L=X ₁+ X ₂+ X ₃+ X ₄=173+200+100+54=527 time (13)

Wherein:

X ₁, X ₂, X ₃, X ₄: stress level 1,2, the effect number of times of 3,4

A ₁, A ₂, A ₃, A ₄: stress level 1,2, the effect number of times ratio of 3,4

Total Cycle Length of L: four loading sequences

Step 7: the high-temerature creep test of multi-stage loading

By test specimen 4,5,6 in the Tempeerature-constant air case of 60 DEG C insulation be no less than 4h, till test specimen internal temperature reaches test temperature ± 0.5 DEG C, distance during insulation between test specimen is no less than 10mm.Arrange the parameters of testing machine, make the temperature of the environment insulation can of testing machine reach 60 DEG C ± 0.5 DEG C, the compression-loaded frequency of testing machine is 1Hz, and crest value is using L as a large period, and in the cycle, axle carries order is σ ₂→ σ ₄→ σ ₃→ σ ₁(that is: 654KPa → 871KPa → 745KPa → 555KPa), the action time of each order is X ₂, X ₄, X ₃, X ₁(that is: 200 times, 54 times, 100 times, 173 times), the cycle acted on each time is that 1s, 0.1s load, and 0.9s unloads, and load waveform is half-sine wave, as shown in table 4.The vertical strain of process of the test record asphalt is with the curve loading number of times change.Test end condition be accumulation microstrain reach 100000 or the creep curve of asphalt obviously enter the phase III (namely straining Fast growth phase).

The load mode example of table 4 multi-stage loading high-temerature creep test

Stress level (KPa)	654	871	745	555	654	871	745	555	……
										Load number of times	200	54	100	173	200	54	100	173	……

Step 8: interpretation of result

According to the test findings of registering instrument record, the creep curve that the asphalt multi-stage loading high-temerature creep based on axle load spectrum is tested can be obtained, Fig. 8 is the creep curve of test specimen 4 under 2 large periods, analyse in depth and obtain the flow number of asphalt under axle load spectrum load mode, the strain variation rate under maximum microstrain and average strain rate and different stress level.

This test method can be applied to the research to asphalt high-temerature creep mechanism, thus instructs the design of asphalt concrete pavement structure and material, and especially the decision-making of road pavement maintenance plan has directive significance.

Claims (4)

1., based on an asphalt multi-stage loading high-temerature creep test method for axle load spectrum, it is characterized in that, comprise the following steps:

Step one: analyze the axle load spectrum of studied road, utilizes road maintenance management decision system (PMS) to obtain the road axle load spectrum being scaled single shaft two-wheel group;

Step 2: carry the weight that stress level and disalignment carry according to road axle load spectrum determination axle;

Step 3: the stress level data of carrying the first loading sequence in stress level according to the axle obtained in step 2 carry out prestrain test;

Step 4: the weighted data carried according to the disalignment obtained in step 2 calculates the loading sequence effect number of times and total Cycle Length of multistage load action of first time in test;

Step 5: the data obtained according to step 4 carry out the high-temerature creep test of multi-stage loading;

Step 6: obtain experimental result.

2. a kind of asphalt multi-stage loading high-temerature creep test method based on axle load spectrum according to claim 1, is characterized in that: described step 2 comprises the following steps:

1) select the heavy corresponding axle of each axle in road axle load spectrum to carry data, described axle is great in six tons, and described axle carries the heavy corresponding axle effect of carrying of data i.e. this axle time logarithmic data; Carry data according to axle and determine the heavy scope W of main axle _a~ W _baxle in the heavy scope of this axle is heavily serial number, the axle of the heavy correspondence of any one axle carries that data account for that the axle being greater than 6 tons carries the ratio of effect total degree in scope more than 1%, and in scope, the axle of the heavy correspondence of each axle carries data sum and accounts for the ratio more than 95% that the axle being greater than 6 tons carries effect total degree;

2) by W _a~ W _bevenly be divided into 4 and represent the heavy interval W of axle _a~ W ₂, W ₂~ W ₃, W ₃~ W ₄, W ₄~ W _b, wherein the intermediate value in each interval is for representing the heavy q of axle ₁, q ₂, q ₃, q ₄(q ₁<q ₂<q ₃<q ₄); Four are represented axle and be heavily scaled corresponding tire ground connection pressure, σ ₁, σ ₂, σ ₃, σ ₄(σ ₁< σ ₂< σ ₃< σ ₄), reduction formula is: wherein σ ₁and q ₁be respectively tire ground connection pressure (unit: KPa) and axle heavy (unit: KN); σ _sand q _sbe respectively standard tire ground connection pressure 700KPa and standard axle load 100KN, namely four represent stress level, add up according to axle load spectrum the effect number of times weight A that four effect number of times ratio-dependents four representing the heavy interval of axle represent stress level ₁: A ₂: A ₃: A ₄.

3. a kind of asphalt multi-stage loading high-temerature creep test method based on axle load spectrum according to claim 2, is characterized in that: described step 4 comprises the following steps:

1) loading sequence is determined

Choose four stress levels are sorted from small to large, i.e. σ ₁< σ ₂< σ ₃< σ ₄, then in a large period, loading sequence is defined as: σ ₂→ σ ₄→ σ ₃→ σ ₁;

2) prestrain is utilized to test the effect number of times X determining each loading sequence ₁, X ₂, X ₃, X ₄;

Utilize the standard dynamic creep under the stress level of the first order in loading sequence to test, obtain creep curve;

The creep curve of acquisition is divided into three phases:

First stage: namely asphalt multi-stage loading start after first loading sequence time period;

Subordinate phase: after namely first loading sequence time period terminate, every one-level stress level loads the accumulation microstrain linear increase stage that the microstrain produced all presents linear increase;

Phase III: namely asphalt is in the accumulation microstrain Fast growth phase of high temperature instability status;

By carrying out linear fit to subordinate phase, determine the starting point n of subordinate phase ₁; Defining method is: pass through calculate average microstrain be defined as and use frequency n ₁for initial stage densification reaches the location point of 100%; Pass through formula $\stackrel{\&OverBar;}{{\mathrm{\&epsiv;}}_{100\%}}=\frac{{\mathrm{\&epsiv;}}_{n_1}-{\mathrm{\&epsiv;}}_{14}}{n_1-14}$ With $\stackrel{\&OverBar;}{{\mathrm{\&epsiv;}}_{90\%}}=\stackrel{\&OverBar;}{{\mathrm{\&epsiv;}}_{15}}-0.9(\stackrel{\&OverBar;}{{\mathrm{\&epsiv;}}_{15}}-\stackrel{\&OverBar;}{{\mathrm{\&epsiv;}}_{100\%}})$ Calculate with corresponding effect number of times is n ₂;

Wherein:

ε _i: the accumulation microstrain of i-th loading specimen;

the average microstrain of i-th loading specimen;

initial stage densification reaches the average microstrain of 100%;

initial stage densification reaches the average microstrain of 90%;

A ₁, A ₂, A ₃, A ₄: four represent effect number of times weight corresponding to stress level;

X ₂for n ₂and n ₁between arbitrary value; Pass through X ₁=X ₂a ₁/ A ₂, try to achieve X ₁; Pass through X ₃=X ₂a ₃/ A ₂, try to achieve X ₃; Pass through X ₄=X ₂a ₄/ A ₂, try to achieve X ₄;

3) prestrain is utilized to test the total Cycle Length L determining multistage load action

L＝X ₁+X ₂+X ₃+X ₄

Wherein:

X ₁, X ₂, X ₃, X ₄: stress level 1,2, the effect number of times of 3,4,

Total Cycle Length of L: four loading sequences.

4. a kind of asphalt multi-stage loading high-temerature creep test method based on axle load spectrum according to claim 3, is characterized in that: work as n ₁and n ₂when difference is less than 200 times, X ₂for n ₁and n ₂between arbitrary value, work as n ₁and n ₂when differing by more than 200 times, X ₂for n ₁and n ₂intermediate value.