| Are all asphalt rubber binders created alike? |
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| Written by Szabolcs Biro |
 The correct answer is definitely NO!At ECOPATH we know the importance of both raw ingredients and the processes behind the development of a successful asphalt rubber binder. Due to our experience in the field we have come across a number of state specifications requiring various additives, crumb rubber types, reaction times, crumb rubber gradations and reaction procedures. This experience allows us to better design the appropriate modified binder for our clients as we are aware of the specific requirements of each individual market, as well as the state binder specifications, and the need to balance these with the appropriate engineering properties. For this reason, we do not advocate a "one solution fits all" model. Instead, we perform an analysis of the pavement site to determine what properties that pavement will require for the best performance. Simlilarly, we balance the economic considerations to develop the best binder design for that particular location. By following different state requirements, our research team investigated and showed the differences behind the different practices. While all of the following asphalt rubber binders showed in this study performed better than conventional binder, it is apparent that performance properties differ depending on the modification method. The material performs better when the elasticity indicator shows minimum changes with respect to temperature. From this point of view the Arizona and California method produced asphalt rubbers performed the best followed by the Texas method manufactured asphalt rubber (Fig.1.a). Investigation of rutting potential from temperature sensitivity showed again the advantageous effect of 20 % rubber used by the Arizona and California blends, which was followed by the Texas method produced sample (Fig.1.b).  Figure 1. Elasticity (a) and rutting sensitivity (b) of various crumb rubber modified asphalts as a function of temperature (AZ: Arizona, CA: California, FL: Florida, SC: South Carolina, TX : Texas). The following information presnted here provides an indication of the peformance of various asphalt rubber binders as speed is varied. The testing was done using a Dynamic Shear Rheoemeter, during testing the frequencies were varied to simulate the effects of various speeds. Low frequencies represent high speeds, while high frequencies represent low vehicle speeds. The less steep the curve is, the less sensitive the binder is with respect to rutting. Also the higher the value of the rutting potential indicator the higher the resistance of the binder. Based on these findings, the Arizona method was found to be the most resistant against rutting, followed by the California and Texas (Fig.2.). The principal reason for these differences lies in the various rubber concentrations used. When comparing all the rubber modified binders to the neat, virgin asphalt at high vehicle speed around one decade differences were observed. Specifically, significant differences were found at low vehicle speeds. These findgs indicate that even at low speeds the type of binder used in the asphalt pavement plays an important role in the pavement properties.  Figure 3. Rutting sensitivity of various blended crumb rubber modified asphalts as a function of vehicle speed (AZ: Arizona, CA: California, FL: Florida, SC: South Carolina, TX Texas). |
| Last Updated ( Tuesday, 07 July 2009 18:07 ) |
