Preliminary Study on Developing a Surrogate Performance-Related Test for Fatigue Cracking of Asphalt Pavements

Currently, no performance-related test exists for fatigue cracking for use in routine asphalt mix design to approve job mix formula (JMF) and quality control and quality assurance (QC/QA) in California. The existing four-point bending (4PB) test was developed to evaluate the fatigue performance of asphalt pavement, but it is not necessarily appropriate for use in routine JMF and it is too slow for QC/QA. The objective of this study is to evaluate potential surrogate fatigue performance-related testing methods and identify a test that is simple and easy to perform but also able to provide guidance for asphalt mix design on routine projects and QC/QA on all projects. This report compares potential performance-related tests with 4PB tests for simplicity, repeatability (variability), and their relationship to stiffness and fatigue life. Tests evaluated in this study included the semicircular bend (SCB) test, indirect tensile asphalt cracking test (IDEAL-CT), and fatigue testing on fine aggregate matrix (FAM) mixes with linear amplitude sweep (LAS) analysis. These tests were conducted on a variety of asphalt mixtures. Fracture parameters obtained from SCB and IDEAL-CT tests and fatigue parameters from FAM mixes were included as potential fatigue cracking indicators. Linear regression analysis was used to correlate these indicators with the stiffness and fatigue life from 4PB tests. The comparison analysis demonstrates that SCB and IDEAL-CT tests are providing the same fracture information. Fracture parameters from SCB and IDEAL-CT tests are well correlated with the initial flexural stiffness from 4PB tests, and the initial flexural stiffness has a moderate inverse nonlinear correlation with the fatigue life from the controlled-strain 4PB tests. As the IDEAL-CT test is faster and requires less specimen preparation, the recommendation is that attention focus on this test. All the fracture tests indicate that the Strength parameter has low variability and good correlation with 4PB flexural stiffness and a moderate correlation with flexural fatigue, and it is proposed as a surrogate indicator for flexural stiffness and an indication of fatigue life. The FAM test showed promise regarding matching 4PB fatigue life as well as stiffness. The relationships identified in this study between flexural stiffness and flexural fatigue life and between flexural stiffness and the Strength parameter from the IDEAL-CT tests were used to develop a preliminary approach to using the Strength parameter to place upper and lower boundary limits on the stiffness of mixes for use in routine mix design and QC/QA. Examples of this approach are presented in the appendices based on flexural fatigue testing and on setting of those limits without 4PB tests. The sensitivity of performance for both approaches is demonstrated by mechanistic-empirical simulation using CalME. Recommendations are made to further develop the IDEAL-CT Strength parameter for routine mix design and QC/QA, with limits set following the approach developed in this study. Review of pavement management system field cracking data and indirect tensile strength from the AASHTO T 283 test in Caltrans databases is recommended to help this development. Further development of FAM mixes LAS testing is also recommended.