Effect of Styrene Butadiene Styrene Modifier on Cracking Resistance of Asphalt Mixture

Abstract

A laboratory investigation was conducted to evaluate the effects of styrene butadiene styrene (SBS) modification on the cracking resistance and healing characteristics of coarse-graded Superpave® mixtures. Four types of asphalt mixtures with 6.1% and 7.2% design asphalt contents using unmodified and SBS-modified asphalt cement were produced in the laboratory. Tests performed with the Superpave indirect tensile (IDT) test included repeated-load fracture and healing test, strength tests at two loading rates, and longer-term creep tests to failure. The test results showed that the benefit of SBS modifiers to mixture cracking resistance appeared to be primarily derived from a reduced rate of micro-damage accumulation. The reduced rate of damage accumulation was reflected in a lower m value without a reduction in fracture limit or healing rates. It was shown that the benefits of the SBS modifier were clearly identified by using the hot-mix asphalt fracture model, which accounts for the combined effects of m value and fracture energy limit on cracking resistance. It was also determined that the residual dissipated energy as determined from Superpave IDT strength tests appears to be uniquely associated with the presence and benefit of SBS modification and may provide a quick way to make relative comparisons of cracking performance. Longer-term creep test showed that time to crack initiation appeared to provide another parameter uniquely related to the effects of SBS modification. The key to characterizing the effects of SBS modifier on the cracking resistance of asphalt mixture is in the evaluation of the combined effects of creep and failure limits.

Rheological Properties, Compatibility, and Storage Stability of SBS Latex-Modified Asphalt

“…Polymer-modified asphalts are multiphase systems and the difference in the solubility and density between polymer and asphalt can result in phase separation of the modified asphalt during high-temperature storage processes [45]. On the basis of this, a storage stability test was performed on SBS latex-modified asphalt according to the aforementioned testing method.…”

Effect of Thermal Stresses on Pavement Performance under Mild Climate Conditions

“…The equation predicts the crack initiation and crack propagation in an asphalt mixture subjected to specified loading histories. This threshold has been found to be independent of mode of loading or loading history (2). Therefore, it is reasonable that the effect of thermal stress at the top, DCSE T , and the stress at the bottom, DCSE B , on pavement is evaluated through the HMA fracture model.…”

“…The reason was thought to be that the current pavement design methodology has been focused on maximum tensile stress rather than tensile stresses occurring over the design life of pavements. For the time-and temperaturedependent materials, loading time and temperature are as important as stress level (1)(2)(3)(4)(5). For example, thermal stresses occurring under mild climate conditions in pavement might not be as high as those occurring at the bottom of an asphalt layer, but the thermal stresses last over a long period of time; therefore, the total amount of thermal stress occurring, especially in winter, might not be negligible as opposed to that of tensile stress at the bottom of an asphalt layer.…”

“…The approach above is a conservative way of evaluating the safety of the structural design. The research studies performed on asphalt mixtures (1)(2)(3)(4)(5) indicate that a fatigue life of asphalt mixtures depends not only on the level of stress or strain but also on the loading time and temperature because of their time-and temperature-dependent nature. In this point of view, the maximum tensile stress that occurs during a short period of time at the bottom of an asphalt layer does not appear to be a good reference stress in terms of evaluating the time-and temperature-dependent damage evolution in the asphalt layer.…”

Effects of alternative polymer modifications on cracking performance of asphalt binders and resultant mixtures

“…However, there is still a lack of experience and documented performance data showing these potential substitutes can result in equivalent or better mixture cracking performance compared to a gold standard SBS PMA binder. A previous work found that the benefit of SBS polymer to mixture cracking resistance appeared to be primarily derived by a reduced rate of micro-damage accumulation [8]. Before relaxing the strict requirement for exclusive usage of SBS polymer, there is a strong need to evaluate the effects of alternative polymers on key mixture fracture properties known to control cracking performance.…”