Determination of master curves for asphalt mixtures by means of IT-CY tests
The concept of ecologically conscious and energy saving roads must be expanded to the performance of the asphalt mixtures as well as to the test related to it. This paper investigates the tests focusing on a better description of the behaviour of asphalts as well as on a deeper revelation of the impact of different compositions. Based on the international experiences the recording of the asphalt´s complex module over the entire temperature range by the determination and evaluation of the mater-curves appeared as a possible solution for more precise description of the asphalt behaviour.
Asphalt Mix Master Curve Construction Using Sigmoidal Fitting Function with Non-Linear Least Squares Optimization
This paper presents a new simplified method of constructing a master curve of asphalt mix using test data covering a large range of temperatures from –18°C to 55°C. It utilizes sigmoidal fitting function and compressive cyclic (complex) modulus test data obtained at matrix combination of different frequencies and test temperatures. In the master curve construction, the time temperature superposition was modeled two different ways. First, using known time-temperature superposition equations, and second, shilling test data experimentally, i.e., not assuming any functional form for the time-temperature relationship. The master curve construction was done using an Excel spreadsheet with the solver function, which is a tool for performing optimization with non-linear least squares regression technique. The analysis of over sixty mixtures indicated that the experimental approach agreed the best with the Arrhenius shifting equation, correlation coefficient R 2 being 0.922. Also, the experimental shifting was most flexible, producing the best fit among the studied shifting equations due to the fact that it has the most degree of freedom.
THE BELGIAN ROAD RESEARCH CENTER'S OVERALL APPROACH TO ASPHALT PAVEMENT STRUCTURAL DESIGN
A structural design system for asphalt pavement, based upon the utilization of measured fundamental properties of materials, is presented. While the experimental methods for the determination of the fundamental properties of the materials are now well defined, they involve sophisticated tests which are not well adapted to everyday practical purposes (long time, high cost). For this reason predictive methods, based on numerous laboratory results obtained for the different kinds of materials, are made use of, mainly for bituminous mixes and granular materials. The different elements of design, namely, criteria for riding quality, loading conditions, stresses and strains in layered systems, fundamental properties of road materials and climatic factors are reviewed. Models for cracking and for rut depth are supplied. A field verification is reported. For the pavement design method itself, two approaches are presented. The first is a complete rational one, while the second is more approximative, but simpler than the first and, consequently, more practical. /Author/