The Effects of Salt on Rheological Properties of Asphalt after Long-Term Aging
Limited studies in recent years have shown that asphalt pavement subject to seawater in coastal regions or deicing salt in cold regions may be seriously damaged after being soaked in saline water for a long time. However, there is limited research into the influence of salt on rheological properties of asphalt after long-term aging. In this study, rheological properties of unmodified and polymer-modified asphalt after long-term aging were tested after being soaked in different concentrations of salt (0.3%~5%) for different durations (1 day~30 days). Orthogonal array based on the Taguchi method was used for experimental design. The frequency sweep tests were performed on the specimens of aged asphalt after being soaked for complex modulus and phase angle master curves and ultimate fatigue temperature. BBR tests were performed for stiffness. The test results indicate that saline water appears to reduce low temperature properties and fatigue resistance properties and improved high temperature properties of aged asphalt, and it also affects the sensitivity of complex modulus and phase angles at low frequencies.
Atomic Force Microscopy Studies of Salt Effects on Polyelectrolyte Multilayer Film Morphology
The morphology of multilayer films formed from polydiallyldimethylammonium chloride and polystyrene sulfonic acid deposited under a range of salt concentrations (from 10-4 to 1.0 M) was investigated using atomic force microscopy (AFM). Ten-bilayer films that were deposited with less than 0.3 M added NaCl were flat and featureless, with similar characteristics to the underlying silica substrate. When formed at and above this salt concentration, a vermiculate morphology was observed. Thickness and roughness measurements were also carried out using the AFM and were found to increase with the concentration of added salt. The evolution of the vermiculate pattern was investigated by AFM studies of each layer that is deposited under high salt concentration (1.0 M NaCl). The first three bilayers were featureless and had a thickness of ∼6 nm/bilayer. A change in morphology was observed by the fourth bilayer, and the average thickness had increased to ∼46 nm/bilayer. These results may be explained in terms of a tra...
SAFETY FIRST: OPEN-GRADED FRICTION COURSES
Transportation officials realize that one of the most significant factors influencing traffic safety was pavement-friction characteristics, especially in wet weather. Seal coats commonly consisted of high percentages of asphalt cement and uniform-size chip-seal aggregate. Known by many names, the most common was open-graded friction course (OGFC). The reasons for using OFCG are twofold: 1. increased safety incorporating increased skid resistance, increased drainage capacity, and longer lasting skid resistance and 2. quieter than conventional pavements. However the drawbacks include higher material cost, mix deterioration and an increased difficulty with snow removal.