1、Standard Practice for Determination of Low- Temperature Performance Grade (PG) of Asphalt Binders AASHTO Designation: R 49-09 (2013)1American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-2b R 49-1 AASHTO Standard Practic
2、e for Determination of Low-Temperature Performance Grade (PG) of Asphalt Binders AASHTO Designation: R 49-09 (2013)11. SCOPE 1.1. This standard practice covers the determination of low-temperature properties of asphalt binders using data from the bending beam rheometer (T 313) and the direct tension
3、 tester (T 314). This standard practice can be used on data from unaged material or from material aged using T 240 (RTFOT), R 28 (PAV), or T 240 (RTFOT) and R 28 (PAV). This standard practice can be used on data generated within the temperature range from +6 to 36C. 1.2. This standard practice is on
4、ly valid for data on materials that fall within the scope of suitability for both test methods T 313 and T 314. 1.3. This standard practice can be used to determine the following: 1.3.1. PG Grade Determination of an Asphalt BinderThe determination of a low-temperature grade or grades that are satisf
5、ied by an asphalt binder. The determination of the temperature corresponds to the specification parameter, Tcr, the critical cracking temperature. 1.3.2. Prequalification of an Asphalt BinderThe procedure required to qualify an asphalt binder for supply. 1.3.3. Verification of an Asphalt Binder Grad
6、eThe testing required to certify that a binder complies with an existing prequalified binder. 1.4. While this standard practice determines the critical cracking temperature for typical hot mix asphalt (HMA), the intent of this standard practice is grading of asphalt binder according to M 320, not pe
7、rformance prediction for asphalt pavement. This standard practice should not be used in lieu of T 322. 1.5. This standard practice may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns associated with its use. It is the respo
8、nsibility of the user of this procedure to establish appropriate safety and health practices and to determine the applicability of regulatory limitations prior to use. Note 1The algorithms contained in this standard require implementation by a person trained in the subject of numerical methods and v
9、iscoelasticity. However, due to the complexity of the calculations they must, of necessity, be performed on a computer. Software to perform the calculations may be written or purchased as a spreadsheet or as a stand-alone program.2 2015 by the American Association of State Highway and Transportation
10、 Officials.All rights reserved. Duplication is a violation of applicable law.TS-2b R 49-2 AASHTO 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: M 320, Performance-Graded Asphalt Binder R 28, Accelerated Aging of Asphalt Binder Using a Pressurized Aging Vessel (PAV) T 240, Effect of Heat and Air on a
11、 Moving Film of Asphalt Binder (Rolling Thin-Film Oven Test) T 313, Determining the Flexural Creep Stiffness of Asphalt Binder Using the Bending Beam Rheometer (BBR) T 314, Determining the Fracture Properties of Asphalt Binder in Direct Tension (DT) T 322, Determining the Creep Compliance and Streng
12、th of Hot Mix Asphalt (HMA) Using the Indirect Tensile Test Device 3. TERMINOLOGY 3.1. Definitions of Terms Specific to This Standard: 3.1.1. Arrhenius parameter (a1)the constant coefficient in the Arrhenius model for shift factors, ln(aT) = a1(1/T 1/Tref). 3.1.2. asphalt binderan asphalt-based ceme
13、nt that is produced from petroleum residue either with or without the addition of non-particulate organic modifiers. 3.1.3. coefficient of linear thermal expansion ()the fractional change in size in one dimension associated with a temperature increase of 1C. 3.1.4. conventional unmodified asphalt bi
14、ndersasphalt binders for which the following two conditions are satisfied: (1) The difference between the temperature at which S(60) = 300 MPa and m-value (60) = 0.300 is less than or equal to 2.0C. The S(60) and the m-value are determined using the T 313 BBR test; (2) The failure strength determine
15、d using T 314 must be within 3.77 0.77 MPa. 3.1.5. creep compliance D(T,t)the reciprocal of the stiffness of a material, 1/S(T,t), at temperature, T, and time, t. Creep compliance may also be expressed using reduced time, , as D(Tref, ). 3.1.6. critical cracking temperature (Tcr)the temperature, est
16、imated using this standard practice, at which the induced thermal stress in a material exceeds its fracture stress. The critical cracking temperature is a “single event cracking” limit prediction that does not include the effect of low-temperature thermal fatigue. 3.1.7. failure stress (f)the tensil
17、e stress value at the point of failure obtained from T 314. 3.1.8. glassy modulusthe modulus at which the binder exhibits glass-like behavior, assumed to be 3 109 Pa for this procedure. 3.1.9. induced thermal stress (th)the stress induced in a material by cooling it while it is restrained so that it
18、 cannot contract. 3.1.10. master curvea composite curve at a single reference temperature, Tref, which can be constructed by shifting, along the log time or log frequency axis, a series of overlapping modulus data curves at various test temperatures. The modulus data curve at the reference temperatu
19、re is not shifted. The shifted smooth curve is called the master curve at the reference temperature. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2b R 49-3 AASHTO 3.1.11. pavement constant (C)an em
20、pirical, constant factor that serves as a damage transfer function to convert the thermal stresses calculated from laboratory data to the thermal stresses generated in the pavement. The damage transfer function is needed to account for the differences in the strain rates experienced by the distribut
21、ion of binder films in the pavement and the bulk strain rate used in the T 314 direct tension test (DDT). Critical cracking temperatures of conventional unmodified asphalt binders were used to determine the pavement constant, C. The value of the pavement constant, C, is the value that minimizes the
22、difference between the critical cracking temperature, Tcr, determined using the procedure described in this standard practice and the T 313 bending beam rheometer (BBR) test. The Tcrfrom the BBR test is determined as the higher value between the temperature where S(60) is 300 MPa and the temperature
23、 where the m-value at 60 s is 0.3. Using the above procedure, the value of the pavement constant was determined to be 18. The pavement constant of 18 is based on the most current pavement performance data available. The Federal Highway Administration (FHWA) and the Transportation Research Board (TRB
24、) Binder Expert Task Group (ETG) continue to collect and analyze field-performance data. 3.1.12. reduced time ()the computed loading time at the reference temperature, Tref, equivalent to actual loading at temperature T. The reduced time is determined by dividing actual loading time, t, at temperatu
25、re T, by the shift factor, aT, = t/aT. 3.1.13. reference temperature (Tref)the temperature at which the master curve is constructed in degrees Kelvin. 3.1.14. relaxation modulus E(T,t)the modulus of a material determined using a strain-controlled (relaxation) experiment at temperature, T, and time,
26、t. Relaxation modulus may also be expressed using reduced time as E(Tref, ). 3.1.15. shift factor (aT)the shift in the time or frequency domain associated with a shift from temperature, T, to the reference, Tref. 3.1.16. specification temperature (Tspec)the specified low-temperature grade of the bin
27、der being prequalified. 3.1.17. stiffness modulus S(T,t)the modulus (stress/strain) of a material at temperature, T, and time, t. Stiffness modulus may also be expressed using reduced time as S(Tref, ). 4. SUMMARY OF THE PRACTICE 4.1. This standard practice describes the procedure used to calculate
28、the relaxation modulus master curve and subsequently the thermally induced stress curve for an asphalt binder from data generated from the bending beam rheometer test. 4.2. The stiffness master curve is calculated from the stiffness versus time data measured in the BBR at two temperatures. The fitti
29、ng procedure follows the Christensen-Anderson-Marasteanu (CAM) rheological model for asphalt binder. The stiffness master curve is then converted to the creep compliance curve by taking its inverse. 4.3. The creep compliance is converted to relaxation modulus using the Hopkins and Hamming method, wh
30、ich is fitted to the CAM model. The Hopkins and Hamming method is a numerical solution of the convolution integral. 4.4. The thermally induced stress is calculated by numerically solving the convolution integral. The thermal stress calculations are based on Boltzmanns superposition principle for lin
31、ear viscoelastic materials. The calculated thermally induced stress is then multiplied by the pavement constant to 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2b R 49-4 AASHTO predict the thermal
32、stress produced in the hot mix asphalt pavement. A value of 18 is used for the pavement constant. 4.5. The calculated thermal stress is then compared to the failure stress from the direct tension test to determine the critical cracking temperature of the pavement. 5. SIGNIFICANCE AND USE 5.1. Estima
33、ted cracking temperature, as determined by this standard practice, is a criterion for specifying the low-temperature properties of asphalt binder in accordance with M 320. 5.2. This standard practice is designed to identify the temperature region where the induced thermal stress in a typical hot mix
34、 asphalt subjected to rapid cooling (1C/h) exceeds the fracture stress of the HMA. 5.3. For evaluating an asphalt binder for conformance to M 320, the test temperature for the bending beam rheometer (BBR) and direct tension test (DTT) data is selected from Table 2 of M 320 according to the grade of
35、asphalt binder. Note 2Other cooling rates and test temperatures may be used to test asphalt binders for experimental purposes. 6. METHODOLOGY AND REQUIRED DATA 6.1. This standard practice uses data from both bending beam rheometer and direct tension measurements on an asphalt binder. 6.1.1. The DTT
36、data required is the stress at failure obtained by testing at a strain rate of 3 percent per minute. For continuous grade and PG determination, DTT results are required at a minimum of two test temperatures. The DT tests shall be conducted at the test temperatures from M 320 at 6C increments corresp
37、onding to the low-temperature binder grade. For prequalification and verification, DTT results are required at a single temperature that is equal to the low-temperature grade plus 10C. 6.1.2. Two BBR data sets at two different temperatures are required with deflection measurements at 8, 15, 30, 60,
38、120, and 240 s. The BBR test temperatures, T and T 6C, are selected such that S(T,60) 300 MPa and S(T 6,60) 300 MPa. T shall be the appropriate test temperatures from M 320 at 6C increments corresponding to the low-temperature binder grade. Note 3It is helpful to begin testing at a temperature that
39、is 6C lower than the critical low cracking temperature for a given grade in Table 2 of M 320. Depending upon the result, perform the next test either at the critical low cracking temperature for a given grade in Table 2 of M 320 or 12C lower than that temperature. Additional tests may be necessary t
40、o bracket 300 MPa. Using a PG xx-22 as an example, test the first set of BBR beams at a test temperature of 18C. If S(18C,60) 300 MPa, test the next set of BBR beams at a test temperature of 12C. If S(8C,60) 300 MPa, test the next set of BBR beams at a test temperature of 24C. 7. CALCULATIONS 7.1. C
41、alculation of the Stiffness Master Curve: 7.1.1. Calculate the BBR compliance data in accordance with T 313 to obtain the following data: D(T,t) = compliance at temperature, T, and time, t. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplicatio
42、n is a violation of applicable law.TS-2b R 49-5 AASHTO D(T,8), D(T,15), D(T,30), D(T,60), D(T,120), D(T,240), D(T 6,8), D(T 6,15), D(T 6,30), D(T 6,60), D(T 6,120), D(T 6,240) 7.1.2. Calculate the BBR stiffness data in accordance with T 313 as: ( )( )1,STtDTt= 7.1.3. Determine aT6, the shift factor
43、for the data at temperature T 6C, numerically using the Gordon and Shaw method (Gordon and Shaw, 1994) to produce a master curve. The reference temperature shall be the higher of the two test temperatures. The linear coefficient of thermal expansion, above and below the glass transition temperature,
44、 shall be 0.00017 m/m/C. The glass transition temperature is taken as 20C. Note 4This procedure is described in Gordon and Shaw, Computer Programs for Rheologists, Hanser Gardner (1994). The SHIFTT routine, which can be found in Chapter 5 of Computer Programs for Rheologists, is to be used. The valu
45、e of 20C is used for glass transition but has no effect on the calculation since the linear expansion coefficient is assumed to be the same either side of this temperature. Experimental data have indicated that some binders may have a variation in their glass transition temperature and value. For re
46、search purposes, these values may be determined and the measured values used in the calculations. 7.1.4. From aT6, calculate the Arrhenius parameter as: ( )61ref ref11ln6TaaTT= (1) where: 61ref refln( )116TaaTT=(2) Note 5The Gordon/Shaw method uses a shift factor (aT) in the form of a base 10 log (l
47、og10). However, this specification is based on the natural log (ln or loge). 7.1.5. Reduced time, , for data at temperature, T, is determined by integrating the reciprocal of the shift factor with respect to time as: 0()Ttdtat=(3) When T is constant with time, this reduces to the equation, as follow
48、s: ( )Ttta= (4) 7.1.6. All 12 values for S(T,t) obtained, as described in Section 7.1.1, are converted to S(Tref,) with time being replaced by reduced time. 7.1.7. The values are fitted to the Christensen-Anderson-Marasteanu (CAM) model for asphalt master curves solving three parameters (, , and ):
49、ref glassy( ,) 1ST S= +(5) 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2b R 49-6 AASHTO where: Sglassyis the assumed glassy modulus of the binder: Sglassy= 3 109Pa. 7.1.8. Fit the resulting stiffness master curve data to this equation using a nonlinear least squares fitting method to achieve a root mean square error, rms(p
