AASHTO PP 42-07 pdf free download

AASHTO PP 42-07 pdf free download.Determination of Low-Temperature Performance Grade (PG) of Asphalt Binders.
3.1.11. pavement constant (C)- -an empirical, 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 distribution 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 difference between the critical cracking temperature, Ter, determined using the procedure described in this practice and the T 313 bending beam rheometer (BBR) test. The Ter from the BBR test is determined as the higher value between the temperature where S( 60) is 300 MPa and the temperature 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. Federal Highway Administration (FHW A) and the Transportation Research Board (TRB) Binder Expert Task Group (ETG) continue to collect and analyze field-performance data.
5. SIGNIFICANCE AND USE 5.1. Estimated cracking temperature, as determined by this practice, is a criterion for specifying the low-temperature properties of asphalt binder in accordance with M 320. 5.2. This practice is designed to identify the temperature region where the induced thermal stress in a typical hot-mix asphalt subjected to rapid cooling (1°C/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 asphalt binder. Note 2- Other cooling rates and test temperatures may be used to test asphalt binders for experimental purposes.
6. METHODOL .OGY AND REQUIRED DATA 6.1. This practice uses data from both bending beam rheometer and direct tension measurements on an asphalt binder. 6.1.1. The DTT data required is the stress at failure obtained by testing at a strain rate of three 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 6°C increments corresponding 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 10°C.
8. PERFORMANCE-GRADE LOW-TEMPERATURE GRADE DETERMINATION OF AN ASPHALT BINDER 8.1. Grading of an asphalt binder requires bending beam rheometer data at two test temperatures and direct tension test data at a minimum of two test temperatures. Note 10- -The temperatures to be selected for the DTT may not be consistent with the BBR test temperatures as defined in Section 6. 1.2 and additional tests may be required. The example given in Appendix X2 required that one of the DTT temperatures be lower than that used for the BBR tests. 8.2. Using a linear relationship between the DTT results, determine the intercept with the thermally induced stress curve using linear interpolation. The intercept, rounded to the nearest 0.1 degree, shall be reported as the estimated critical cracking temperature, Ter. 8.3. In the case of no intercept being determined, additional direct tension tests shall be performed until an intercept is determined as described in Section 8.2.AASHTO PP 42-07 pdf download.