Crack control method for top-down cracking of crc+ac composite pavement asphalt surface layer

Abstract

The application discloses a CRC+AC composite road surface asphalt surface layer Top-Down cracking control method, which comprises the following steps: step one, initial CRC+AC composite road surface asphalt surface layer design parameter value determination; step two, calculation of the pull-shear stress of Top-Down transverse cracking control; step three, calculation of the transverse tensile stress of Top-Down longitudinal cracking control; step four, Top-Down crack control criterion checking; and step five, when the checking in step four does not meet the requirement, returning to step one to redetermine the CRC+AC composite road surface asphalt surface layer design parameter value. The application can control the Top-Down cracking of the CRC+AC composite road surface asphalt surface layer.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of urban road composite pavement, and particularly relates to a CRC+AC composite pavement asphalt surface layer Top-Down cracking control method. BACKGROUND

[0002] The continuous reinforced concrete composite pavement (CRC+AC) is a new type of long-life composite pavement structure which fully utilizes the advantages of the continuous reinforced concrete layer (CRC) and the asphalt concrete layer (AC), improves the integrity and bearing capacity of the pavement, and has ideal driving comfort and durability, and is one of the most promising long-life pavement structure forms.

[0003] The asphalt pavement is prone to Top-Down cracking under the repeated action of wheel load or temperature stress, and most of the pavement function degradation and road life attenuation can be traced back to the expansion and propagation of the Top-Down cracking in the asphalt surface layer. In the design of the CRC+AC pavement structure, the thickness of the asphalt layer is generally thin, and the Top-Down cracking is more likely to form. However, the current CRC+AC pavement design is still mainly guided by the "Standard Specification for Design of Highway Asphalt Pavement" (JTGD50-2006), "Code for Asphalt Pavement of Urban Road" (CJJ-169) and the like, and the surface deflection value, the tensile strain of the flexible base asphalt layer bottom, the tensile stress of the semi-rigid base layer bottom and the shear stress of the asphalt layer are usually used as the design indexes of the asphalt pavement structure, and there is no new index requirement for the prevention of the Top-Down cracking of the asphalt surface layer, so the Top-Down cracking of the CRC+AC composite pavement asphalt surface layer cannot be controlled. SUMMARY

[0004] The present application aims to provide a CRC+AC composite pavement asphalt surface layer Top-Down cracking control method which can control the Top-Down cracking of the CRC+AC composite pavement asphalt surface layer.

[0005] The technical solution adopted by the present application is as follows:

[0006] A CRC+AC composite pavement asphalt surface layer Top-Down cracking control method comprises the following steps:

[0007] Step 1: preliminary determination of the design parameter values of the CRC+AC composite pavement asphalt surface layer;

[0008] Step 2: calculation of the tensile-shear stress for controlling the Top-Down transverse cracking;

[0009] Step 3: calculation of the transverse tensile stress for controlling the Top-Down longitudinal cracking;

[0010] Step four, Top-Down crack control criterion checking is carried out;

[0011] Step five, when the checking in step four does not meet the requirements, return to step one to re-determine the CRC+AC composite pavement asphalt surface layer design parameter value.

[0012] According to the above scheme, in step one, the CRC+AC composite pavement asphalt surface layer design parameters include load, asphalt layer modulus, asphalt layer thickness, and longitudinal horizontal force coefficient.

[0013] According to the above scheme, in step two, in the formation mechanism of Top-Down cracks, the asphalt pavement is prone to form transverse cracks under the combined action of longitudinal tensile stress and shear stress, so the longitudinal tensile stress and shear stress should be calculated respectively, and then the comprehensive tensile-shear stress is calculated; that is, the steps for calculating the tensile-shear stress of Top-Down transverse cracking control are:

[0014] 1) Calculate the longitudinal tensile stress:

[0015] 2) Calculate the shear stress:

[0016] 3) Calculate the tensile-shear stress.

[0017] According to the above scheme, in step 1), the calculation method of longitudinal tensile stress is:

[0018] The longitudinal tensile stress is calculated through the parameter value in step one:

[0019] δ L = 693.618f + 6.893h + 0.638P - 0.004E - 138.3 (1)

[0020] In the formula, δ L is the longitudinal tensile stress, unit: kPa; f is the longitudinal horizontal force coefficient; h is the thickness of the asphalt concrete layer, unit: cm; P is the vehicle load, unit: kN; E is the modulus of the asphalt concrete layer, unit: GPa.

[0021] According to the above scheme, in step 2), the calculation method of shear stress is:

[0022] The shear stress is calculated through the parameter value in step one:

[0023] τ = 489.197f + 1.501h + 0.826P - 0.471E - 6.793 (2)

[0024] In the formula, f is the longitudinal horizontal force coefficient; h is the thickness of the asphalt concrete layer, unit: cm; P is the vehicle load, unit: kN; E is the modulus of the asphalt concrete layer, unit: GPa; τ is the shear stress.

[0025] According to the above scheme, in step 3), the calculation method of the tensile-shear stress is:

[0026] The tensile-shear stress is calculated by the longitudinal tensile stress in step 1) and the shear stress in step 2):

[0027]

[0028] Formula, δ L is the longitudinal tensile stress, unit: kPa; τ is the shear stress; δ is the tensile-shear stress, unit: kPa.

[0029] According to the above scheme, in the formation mechanism of Top-Down crack, the asphalt pavement is easy to form longitudinal cracks under the action of transverse tensile stress; in step three, the method for calculating the transverse tensile stress of Top-Down longitudinal cracking control is:

[0030] The transverse tensile stress δ T is calculated by the parameter value in step one:

[0031] δ T = 39.057f + 9.876h + 1.089P - 5.075E-129.780 (4)

[0032] In the formula, δ T is the transverse tensile stress, unit: kPa; f is the longitudinal horizontal force coefficient; h is the thickness of asphalt concrete layer, unit: cm; P is the vehicle load, unit: kN; E is the modulus of asphalt concrete layer, unit: GPa.

[0033] According to the above scheme, in step four, the method for checking the Top-Down crack control criterion is:

[0034] The tensile strength of CRC+AC composite pavement surface layer asphalt concrete must meet the transverse cracking and longitudinal cracking control criteria at the same time, which is as follows:

[0035] The Top-Down transverse cracking control checking criterion is:

[0036]

[0037] The Top-Down longitudinal cracking control checking criterion is:

[0038] δ T ≤ [R m ] (6)

[0039] In the formula, [R m ] is the tensile strength of asphalt concrete, unit: kPa.

[0040] According to the above scheme, in step five, the design parameters of the CRC+AC composite pavement asphalt surface layer are re-determined as the asphalt layer modulus and the asphalt layer thickness.

[0041] The formulas (1) and (2) are regression fitting relation models based on finite element simulation analysis data, and the specific method is as follows:

[0042] Firstly, the finite element model is established by inputting the real CRC+AC composite pavement material constitutive and structure size; then, a large number of sample combinations of load, asphalt layer modulus, asphalt layer thickness and longitudinal horizontal force coefficient are obtained by using the hypercube Latin sampling method; secondly, a large number of simulation data samples are obtained by analyzing the finite element model with the sample combinations; thirdly, the regression equations of the longitudinal tensile stress and shear stress in the formulas (1) and (2) are obtained by using the support vector machine regression analysis method to fit the simulation data; finally, the regression fitting relation model is used to predict the longitudinal tensile stress and shear stress, and the mean square error of the predicted value and the actual value is calculated by comparing the difference between the predicted value and the actual value, and the square correlation coefficient is greater than 0.8, which verifies that the fitting model has high fitting precision and generalization ability.

[0043] The formula (4) is a relation model based on finite element simulation analysis data regression fitting, and the specific method for obtaining the formula (4) is the same as that for obtaining the formulas (1) and (2).

[0044] The beneficial effects of the present application are as follows:

[0045] The present application aims at the Top-Down crack prevention problem ignored in the design stage of the CRC+AC composite pavement, combines the formation mechanism of the Top-Down crack, proposes the control index and the relation model corresponding to the horizontal and longitudinal crack types, and establishes the Top-Down crack control checking criterion, so that the tensile strength of the CRC+AC pavement surface layer asphalt concrete can be checked in the design stage of the CRC+AC composite pavement according to the steps of the present application, whether the defects of too small tensile strength of the asphalt concrete or insufficient thickness of the asphalt layer exist in the current design can be judged, the quality guarantee of the CRC+AC composite pavement is improved, the premature appearance of the Top-Down crack is avoided or reduced, the blank of the early crack resistance prevention of the current design specification for the new long-life pavement structure is made up, and then the design level and service function of the CRC+AC composite pavement are effectively improved, the superiority of the new long-life pavement structure is fully displayed, and higher social and economic benefits are brought.

[0046] The present application supplements the relationship between the tensile strength of the asphalt layer material and the size of the surface layer structure parameter, improves the design points of the CRC+AC new long-life composite pavement on the basis of the traditional design specification, avoids the premature occurrence of Top-Down cracks of the asphalt surface layer, solves the problem of frequent occurrence of Top-Down cracks of the asphalt surface layer of the urban composite pavement (CRC+AC), and improves the design level of the CRC+AC composite pavement. BRIEF DESCRIPTION OF DRAWINGS

[0047] The present application will be further described below in combination with the drawings and examples, wherein:

[0048] Figure 1 is a flowchart of the Top-Down cracking control method of the CRC+AC composite pavement asphalt surface layer. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application will be further described in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application.

[0050] Example 1

[0051] In a certain CRC+AC composite pavement design, the asphalt surface layer uses 10cm thickness of AC-20 asphalt concrete, the tensile strength of the asphalt concrete is tested in the laboratory to be 180kPa, the longitudinal horizontal force coefficient is 0.3, the vehicle load is 120kN, the tensile-shear stress is calculated to be 239.6kPa by substituting the above data into formula (1)-(4), the transverse tensile stress is calculated to be 201.4kPa, both of which are greater than the tensile strength of the asphalt concrete (180kPa), and do not meet the Top-Down crack control criteria of formula (5) and (6).

[0052] Therefore, the tensile strength of the asphalt concrete in the present example is insufficient, and it is recommended to replace the asphalt layer type with TLA modified SMA-13 asphalt concrete which has stronger shear and tensile properties.

[0053] The present application can check the tensile strength of the surface layer asphalt concrete during the design stage of the CRC+AC composite pavement, supplement new indexes for the design of the CRC+AC new long-life composite pavement on the basis of the traditional design specification, assist in judging whether the tensile strength or thickness of the asphalt layer is reasonable, can judge whether there is a defect of too small tensile strength of the asphalt concrete or insufficient thickness of the asphalt layer in the current design, proposes improvement suggestions for the original design scheme, avoids or reduces the premature occurrence of Top-Down cracks, further guarantees the design level and service function (guarantees the reliability and service life of the composite pavement) of the CRC+AC composite pavement, and brings higher social and economic benefits.

[0054] Example 2

[0055] Top-Down crack detection was carried out on a CRC+AC composite pavement of a certain ring line half section, and it was found that transverse cracks appeared in local sections, which needed to be reconstructed.

[0056] The core sample was obtained by drilling at the transverse crack, the asphalt layer thickness was tested to be 8.5 cm, the tensile strength of the asphalt concrete was tested to be 226 kPa, the longitudinal horizontal force coefficient was taken as 0.3, and the driving load was 140 kN, the above data were substituted into formulas (1)-(4) to calculate that the tensile-shear stress was 244.5 kPa, the transverse tensile stress was 140.1 kPa, which met the Top-Down longitudinal crack control criterion of formula (6), but did not meet the Top-Down transverse crack control criterion of formula (5).

[0057] Combined with the on-site coring, it was found that there was a phenomenon of too thin asphalt layer in local areas, so it was judged that the original asphalt layer thickness design value was too small, and the quality was difficult to control during construction, and it was suggested to increase the asphalt layer thickness in the reconstruction scheme.

[0058] The present application can be used for the quality upgrading and reconstruction of the existing CRC+AC composite pavement, and the quality of the reconstructed CRC+AC composite pavement is improved.

[0059] It should be understood that, for those skilled in the art, improvements or changes can be made according to the above description, and all these improvements and changes shall belong to the protection scope of the appended claims of the present application.

Claims

1. A method for controlling Top-Down cracking of CRC+AC composite asphalt pavement surface layer, characterized in that, Includes the following steps: Step 1: Initially determine the design parameters for the CRC+AC composite pavement asphalt surface layer; The design parameters for the CRC+AC composite pavement asphalt surface layer include load, asphalt layer modulus, asphalt layer thickness, and longitudinal horizontal force coefficient. Step 2: Calculate the tensile-shear stress controlling the transverse cracking in the top-down region: 1) Calculate the longitudinal tensile stress: Calculate the longitudinal tensile stress using the parameter values ​​from step one: δ L =693.618f+6.893h+0.638P-0.004E-138.3 (1) In the formula, δ L ρ is the longitudinal tensile stress, in kPa; f is the longitudinal horizontal force coefficient; h is the asphalt concrete layer thickness, in cm; P is the traffic load, in kN; E is the asphalt concrete layer modulus, in GPa. 2) Calculate shear stress: Calculate the shear stress using the parameter values ​​from step one: τ=489.197f+1.501h+0.826P-0.471E-6.793 (2) In the formula, f is the longitudinal horizontal force coefficient; h is the thickness of the asphalt concrete layer in cm; P is the traffic load in kN; E is the modulus of the asphalt concrete layer in GPa; and τ is the shear stress. 3) Calculate tensile-shear stress: Calculate the tensile-shear stress using the longitudinal tensile stress from step 1) and the shear stress from step 2): In the formula, δ L τ is the longitudinal tensile stress, in kPa; τ is the shear stress. Tensile-shear stress, unit: kPa; Step 3: Calculate the transverse tensile stress controlling the longitudinal cracking in the top-down region: Calculate the transverse tensile stress δ using the parameter values ​​from step one. T : δ T =39.057f+9.876h+1.089P-5.075E-129.780 (4) In the formula, δ T Δ is the transverse tensile stress, in kPa; f is the longitudinal horizontal force coefficient; h is the asphalt concrete layer thickness, in cm; P is the traffic load, in kN; E is the asphalt concrete layer modulus, in GPa. Step 4: Verify the Top-Down crack control criteria: The tensile strength of the asphalt concrete in the CRC+AC composite pavement surface layer must simultaneously meet the control criteria for transverse and longitudinal cracking, as follows: The verification criteria for top-down transverse cracking control are as follows: The verification criteria for top-down longitudinal crack control are as follows: d T ≤[R m ] (6) In the formula: [R] m [This represents the tensile strength of asphalt concrete, expressed in kPa.] Step 5: If the verification in Step 4 does not meet the requirements, return to Step 1 to redetermine the design parameters of the CRC+AC composite pavement asphalt surface layer.

2. The method for controlling Top-Down cracking of CRC+AC composite asphalt pavement surface layer according to claim 1, characterized in that: In step five, the design parameters for the CRC+AC composite pavement asphalt surface layer are redefined as asphalt layer modulus and asphalt layer thickness.

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