Haleh Azari, & Alaeddin Mohseni, Pavement Systems LLC USA
PAPER
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Abstract
Superpave introduced a Performance Graded (PG) system for bitumen selection. The high and low temperature PG requirements for any location, based on climatic conditions, are specified by LTPPBind. The PG of the bitumen in any location should match the PG requirement from LTPPBind. The low-temperature PG of bitumen is determined using a device called Bending Beam Rheometer (BBR) and the procedure is outlined in AASHTO T 313 and ASTM D6648. However, the BBR test is very time consuming and laborious and involves several hazardous liquids as listed in Section 8 of D6648. The Incremental Creep for Cracking at Low Temperature (iCCL) test is a low-temperature binder test procedure for determining low-temperature properties equivalent to those of BBR; however, significantly faster, safer, more reliable and less costly. iCCL provides continuous low-temperature grade (Low PG), as well as m-value, S, and delta Tc equivalent to those of BBR using PAV or RTFO aged binder. The test takes 30 minutes and has 2-3 times better between-laboratory precision than BBR. The iCCL test is performed using a Dynamic Shear Rheometer (DSR), which is significantly more advanced, in terms of load and temperature control, than the BBR device. The test may be conducted using a portable DSR that does not require compressed air or a water bath. AASHTO has recognized iCCL as a surrogate test for the BBR by the new Standard Practice PP 112 (2021). This paper outlines comparison of over two thousand pairs of iCCL and BBR test results from testing 367 RTFO aged and 635 RTFO/PAV aged binders from 23 U.S. laboratories, 13 of which performed the tests in house. The results show that iCCL provides low-temperature properties within the allowable limits of the BBR test in AASHTO T 313.
About the Authors
Dr Azari is the president of Pavement Systems in the USA, specializing in research and development in field of pavement materials. She and her colleagues have developed UPTiM test methods, including iCCL and iRLPD, for unified characterization of asphalt binder, mixture, and mastic. Dr Azari has also managed the AASHTO Research Program for eight years, as the principal investigator of several NCHRP projects for improving AASHTO specifications. She earned her Ph.D. in Pavement Materials Testing from the University of Maryland at College Park.
Dr Mohseni has been involved in the SHRP project since 1992 and contributed to the development of current PG asphalt binder grading system for Superpave. Dr Mohseni founded Pavement Systems LLC in 1994. He introduced a new Low-Temperature model for Superpave in 1997 to replace the SHRP model and a new model for High Temperature PG in 2004 based on Degree-Day concept. Since 2005, Dr Mohseni has worked on several new test methods based on an incremental concept, namely UPTiM. Â Dr Mohseni earned his Ph.D. in Civil Engineering (Pavements) from the University of Illinois at Urbana-Champaign in 1990.
