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.
Evaluation of road performance and adhesive characteristic of asphalt binder in salt erosion environment
Abstract The salt erosion environment formed by deicing salts in cold areas significantly shortens the service life of asphalt pavement. The treatment method was designed to simulate the adverse effect of salt erosion environment on asphalt binder. Four fractions test and Atomic Force Microscopy (AFM) test of asphalt binder treated by salt erosion environment were carried out. Then the conventional tests and Strategic Highway Research Program (SHRP) tests of asphalt binder were also conducted. The improved water boiling test was developed to evaluate the adhesion between asphalt and aggregate. The results show that the chemical composition of asphalt binder varies significantly in salt erosion environment. The micro-morphological characteristics such as surface roughness and area ratio of bee structure of asphalt binder also decline to various extents. The high temperature performance of asphalt binder in salt erosion environment improves to a certain degree, but the fatigue resistance, low temperature cracking resistance and adhesion decreases. The performance deterioration mechanism of asphalt binder in salt erosion environment is that the chemical composition of asphalt binder changes and the salt aging phenomenon appears. For dry-wet cycle and freeze-thaw cycle in NaCl solution, the critical number of simulation cycles corresponding to the performance variation of asphalt binder is twelve and nine respectively.
Open Graded Asphalt Friction Course: State of the Practice
Open Graded Friction Course (OGFC) has been used since 1950 in the United States to improve the frictional resistance of asphalt pavements. However, experience of states with this kind of mix has been widely varied. While many transportation agencies have reported good performance, many others have stopped using OGFC due to poor performance. This report presents the results of a survey of state transportation agencies in the USA carried out to determine where OGFCs have been used, why they are used in some places and not others, mix design and construction practices, OGFC's performance history, and problems encountered. The survey showed that significant improvements have been observed in the performance of OGFCs since their introduction in the 1950s. These improvements have been achieved with the help of good design and construction practices. Although experience of transportation agencies with OGFC has been widely varied, half of the agencies surveyed in this study indicated good experience with OGFC. More than 70% of the agencies which use OGFCs reported service life of eight or more years. About 80% of the agencies using OGFCs have standard specifications for design and construction. A vast majority of agencies reporting good experience use polymer modified asphalt binders. Also, gradations of aggregates used by these transportation agencies tend to be somewhat coarser compared to gradations used earlier and gradations used by the agencies which had bad experience with OGFC. It seems that good design and construction practice is the key to improved performance of OGFC mixes. An improved mix design procedure is needed to help the transportation agencies adopt these good practices.