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Many road agencies worldwide still use the empirical AASHTO 1993 pavement design method. Since the release of the AASHTO 1993 design guide, many aspects of pavement design have changed, including asphalt material properties, traffic, environmental factors, etc. However, many agencies use a single layer coefficient for asphalt mixtures and pavements are currently designed with inaccurate values, as proved by many. This paper presents a four-step procedure (called AASHTO 93 Plus method) to determine structural layer coefficients of asphalt mixtures. The AASHTO 93 Plus method considers viscoelasticity and temperature-dependency of asphalt mixtures to estimate the layer coefficient. Five-hundred-eighteen (518) flexible pavements from USA and Canada roads and 1599 HMAs from the Long-Term Pavement Performance (LTPP) database were analyzed. The results showed that the new material-specific layer coefficients were well above the typical value of 0.44. The total number of 3,726 IRI data records of these 518 pavements were converted to PSI and then compared to those obtained from the traditional AASHTO 93 and AASHTO 93 Plus methods for validation. Results confirmed that the conventional AASHTO 93 method predicts faster deterioration of pavement conditions over time, while the results of AASHTO 93 Plus method better aligned with the field data. [ABSTRACT FROM AUTHOR]

The current test methods for measuring the fatigue cracking resistance of asphalt mixtures involve many steps which are time-consuming and costly. On the other hand, asphalt binder testing is less time-consuming and more accessible than mixtures testing. Therefore, if the routinely measured properties of the asphalt binder and volumetric properties of the mixtures can be used to predict cracking resistance performance of mixtures, much effort to perform the mixtures testing of asphalt mixtures can be minimised. In this study, prediction models of mixture parameters calculated from the Semi-Circular Bending-Illinois Flexibility Index Test (SCB-IFIT) are developed using an experimental database including 42 mixtures that are short-term aged and 30 mixtures that are long-term aged mixtures. Based on the correlation results and the validation using a separate set of the mixture, the developed models of SCB parameters are found to provide reliable estimates of the flexibility index (FI), post-peak slope and fracture energy (Gf) of asphalt mixtures. The developed models are recommended for initial screening of mixture components (binder and mix variables) or estimating the cracking resistance of asphalt mixtures when testing is not feasible. They are not meant to totally replace the testing of the final selected mixtures. [ABSTRACT FROM AUTHOR]

The linear amplitude sweep (LAS) test is useful for evaluating the fatigue of asphalt binders. In this paper, the combined effects of strain and temperatures are investigated, and a method for estimating binder fatigue behaviour is introduced at different temperatures from limited measurements. LAS tests were conducted on several different PG-grade binders at four different temperatures. The results show that LAS parameters A and B at different temperatures maintain a linear relationship with the binder complex modulus (G*) measured at corresponding temperatures. Therefore, a fatigue life model, accounting for strain level and temperature, is proposed using a power function of the binder G*, which can account for temperature effects. To verify the model, its parameters are fitted using test data at two temperatures were used to predict the fatigue life at additional temperatures. This study findings offer a simpler and reliable method to predict the values of fatigue life at new temperatures using both 35% damage level and maximum stress failure criteria that are recommended in AASHTO TP101-12 and AASHTO TP101-14, respectively. The new prediction method will allow a wider use of the LAS procedure regarding the effects of temperature and strain level for which binders are subjected to the pavement. [ABSTRACT FROM AUTHOR]