Design considerations of high RAP-content asphalt produced at reduced temperatures

In many countries recycling of reclaimed asphalt pavement (RAP) for road surface layers is limited to a maximum of 10–30%. This is due to technical limitation of common asphalt plant but also to specifications that are still restrictive when it comes to increasing RAP in surface courses. The mistrust in this practice is mainly related to uncertainty in performance of these mixes as well as to existing fundamental issues with the mix design, especially when production temperatures are lowered. This paper analyses some of the factors affecting the design of warm asphalt mixtures for surface course layers containing 50% RAP, and suggests a framework to justify the common assumption of full blending by optimising production conditions. A control hot mix asphalt which was manufactured with 49 dmm penetration binder and asphalt mixtures containing 50% RAP produced at temperatures between 95 and 135 °C and at different mixing times were investigated in terms of volumetric properties, indirect tensile stiffness modulus, and indirect tensile strength. The high-content RAP mixtures were produced within the warm mix region by using only a very soft binder as a rejuvenator, which reduces production costs. Statistical analysis was deployed, and different models were developed to estimate degree of blending between RAP binder and rejuvenator binder, and to predict the equivalent penetration of the blend without binder extraction and recovery. The analysis results showed that the selected performance indicators correlate significantly with mixing time and temperature, and provide evidence that only in certain circumstances and if the production conditions are accurately controlled, the practical full blending approach is acceptable

Hot Mix Asphalt with High RAP Content

AbstractDue to increasing cost of asphalt binder, significant economic savings can be realized using high content of reclaimed asphalt pavement (RAP) in the production of new hot mix asphalt (HMA). Moreover, this is an environmentally friendly alternative as it reduces the need for virgin materials. It has to be noted that in Latvia RAP is rarely used in production of HMA and this valuable material is mostly degraded for use in lower value applications. Three mixtures were designed, which were the combination of two different RAP sources and local dolomite aggregates. The RAP binder had significantly aged having penetration of around 38mm, softening point of 56°C and Fraass temperature of -10°C. RAP was added at rates 30% and 50% for each RAP source. A softer binder grade (70/100 versus traditional 50/70) was added to compensate for the aged RAP binder. Hamburg wheel tracking test results demonstrated that all mixtures have high rutting resistance and fatigue test results using four-point bending beam were similar to those of virgin mixture. This demonstrated that mixtures with high RAP content can be successfully designed to meet the local volumetric and performance-specification requirements