سال انتشار: ۱۳۸۳

محل انتشار: دومین همایش قیر و آسفالت ایران

تعداد صفحات: ۱۳

نویسنده(ها):

C. Sinadinos – General Manager IPC GLOBAL, AUSTRALIA
H. Khansari – Civils Division Manager A.B.SANGAR1 & SONS LIMITED

چکیده:

Historically, asphalt mixes have been designed and nlanufactured by using volumetric methods, and a number of procedures have been developed (e.g. Marshal and Hveem) to enable the performance of mixes tested in the laboratory to be predicted, based on largely empirical links between design models and practical field experience.
These procedures are useful where known materials are available and practical experience of their performance under given conditions is known, but can be unreliable when it is necessary to interpolate from known conditions.
It is now far more important for industry and road authorities to be able to characterize available materials and to have in place design and test pr:~cedures which will enable long term performance to be predicted, and the manufacturing and construction process to be controlled and assured.
The USA spent US$150 million on the Strategic Highway Research Program (SHRP); US$50 million on the Superpave asphalt mix design process alone. Although some excellent work was done, in formulating models and software to aid materials characterization and performance prediction, it was never implemented effectively.
linfortunately, the SHRP process did not deliver the product of this work in a useable form. This is mainly due to a decision to use test procedures and equipment developed by Monismith et al, at the University of California, Berkeley to collect data required for input to the performance based models developed by Lytton et al, at Texas Transportation Institute. Test procedures developed by Monismith using the ‘simple shear’ machine were not compatible with the Lytton models. Conversion of the data into a form suitable for input to the Lytton models introduced massive inaccuracies. Uncertainty of the repeatability of the ‘simple shear" machine based test and measurement process introduced further errors. The cost of the equipment (US$250,000 at the time) and resources required to operate it also mitigated against their general acceptance by industry.
However, the work by Monismith et a1 on "Determining the fatigue life of compacted bituminous mixes subject to repeated flexural bending" (SHR Designation M009) was the basis for AASHTO standard (TP8) and is presently used in a number of countries, including Australia and Iran.
Whilst the Superpave mix design method was designed to replace the Hveem and Marshall methods, the current Superpave mix design process utilizing the gyratory compactor is based upon volumetric mix requirements, and is not grossly dissimilar to the empirical approaches that were used in the Hveem and Marshall design approaches.
With this limitation in the mix design process in mind, FHWA initiated a research study through the Superpave Models Project to develop a "Simple Performance Test" that would be used in complementary manner along with the present volumetric-based Superpave mix design process.
The implementation of this test protocol is one of the most pressing issues facing industry.