Evaluation for Low Temperature Performance of SBS Modified Asphalt by Dynamic Shear Rheometer Method

Finding an alternative or supplementary test method to evaluating the low temperature performance of asphalt is an area of considerable interest. This paper tries to explore the possibility of using the dynamic shear rheometer (DSR) method for assessing the low temperature properties of styrenebutadienestyrene (SBS) modified asphalt. In the study, 60/80 and 80/100 pen grade asphalt binders, named binder A-70, binder B-70 and binder C-90, are used to produce the SBS modified asphalt samples. After that, the low temperature performance of the asphalt binders is characterized by using bending beam rheometer (BBR) test. The results indicate that the low temperature performance of the different binders is related to the source of the binder. The low temperature performance of asphalt could be improved with the addition of the SBS. The DSR test is used to develop the complex modulus master curves for binders. Based on the principle of time–temperature conversion, the glass transition temperature of asphalt is calculated by the Williams–Landel–Ferry (WLF) equation. The glass transition temperatures (Tg) of base asphalt and the SBS modified asphalt are determined by the viscoelastic parameters of the master curve and the WLF equation coefficients based on the time–temperature superposition principle. By establishing the relationship between the critical temperature and the Tg of the asphalt binder, the effectiveness of the method established in this paper is verified. The advantage of this method is the ability to use the DSR test for the rapid evaluation of the low temperature performance of asphalt, which is able to reduce testing materials and save testing time as well. The glass transition temperature of the SBS modified asphalt is closely associated with aging degree, asphalt source and the SBS content.

Viscoelastic behavior and construction of master curve for graphene/polyimide nanocomposites

Dynamic mechanical spectroscopy is used to investigate the variation of the glass rubbery transition temperature ( Tg) of graphene/polyimide nanocomposites. The Tg was obtained as the temperature corresponding to the peak of the tan δ versus temperature curve for the alpha transition. Cole–Cole curve was constructed for the matrix and the composites composite at 1 Hz and a hemispherical curve was obtained suggesting that the constituents have similar relaxation behavior. The time–temperature superposition principle was used to model the behavior of the nanocomposites at lower frequencies and longer times. Frequency sweep was performed in the range of 0.05–100 Hz at different temperatures. The storage modulus curves obtained at different temperatures (isothermal), as a function of frequency, were shifted horizontally to construct a continuous master curve. Both the generalized reduced gradient method and the Williams–Landel–Ferry (WLF) equation were used to calculate the activation energy for glass–rubber transition. The universal constants C1 and C2 were determined using the WLF equation. The dependence of relaxation time on temperature was verified.

Thermo-Mechanical Investigation of Free Volume Theory for Polyamie-6

Polymers always show time-dependent mechanical properties. In order to use polymers in engineering applications, long-term mechanical propertes should be characterized. Free volume theroy is the mostly used theory to predict and model the mechanical properties of polymers. The effect of temperature is modelled thorugh William-Landel-Ferry (WLF) equation, whereas, the combined effect of temperature and pressure is modelled by Filler-Moonan-Tschoegl (FMT) equation. Both of the models are based on free volume theory. A set of expermentations were performed to investigate the validity of free volume concpet for one of the most important engineering polymer; i.e. Polyamide-6.