Abstract
Rheology is the most widely used technique to evaluate the performance and aging of bituminous binders. Since there are many available rheological tests, there is also a wide range of aging indexes and it is not easy to choose the most appropriate one, because a single value may hardly be adequate for different properties or operating conditions. In order to generalize the usefulness of an index, a good starting point is deriving it from a set of data, such as the master curves of linear viscoelastic functions. Then, the problem is the quantification of aging in a single numerical value from continuous curves, covering a wide range of frequencies/temperatures. In this work, a summary of the aging indexes derived from the master curves is reported and discussed. The indexes are applied to a bituminous binder either with or without the addition of an organo-modified layered silicate. The apparent molecular weight distributions and relaxation spectra were also calculated from the master curves and used to characterize the effect of aging on the binder properties and structure. In this way, an interesting parallelism was observed between the SARA fractions and the populations derived from a deconvolution analysis of the apparent molecular weight distributions.
Highlights
Aging mainly consists of a hardening process, which comes from the physical– chemical transformations due to the loss of volatiles and partial oxidation of the bitumen component
It is common practice to construct master curves of the linear viscoelastic functions by applying the time–temperature superposition principle to frequency sweep data obtained in the isothermal tests
The first one is between |Gc| and H(τ) with the dispersion index calculated from the apparent molecular weight distributions (AMWD)
Summary
Aging mainly consists of a hardening process, which comes from the physical– chemical transformations due to the loss of volatiles and partial oxidation of the bitumen component. Morian et al, underlined that even if some rheological indexes have good correlation with specific properties, the preferable choice is the development and analysis of full master curves [4]. The analysis starts from the development of viscoelastic master curves, and continues with the application of the δ-method [5] to obtain the apparent molecular weight distributions (AMWD) and the derivation of the relaxation spectra H(τ) [6]. The use of these three different representations, derived from the same experimental data, allows evaluating aging under several points of view. This permits comparing aging indexes with different physical meaning and to qualitatively evaluate the changes in the colloidal structure of the binder
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