Impact of Silo Storage on the Performance of Plant-Produced Mixes Containing High Content of Reclaimed Asphalt Pavement or Reclaimed Asphalt Shingles

Use of recycled materials, such as reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles (RAS), is gaining widespread interest. Currently the California Department of Transportation standard specifications do not allow the use of RAS and limit the use of RAP contents to a maximum of 25% by dry weight of aggregate, though there is a non-standard special provision that allows use of up to 3% RAS by mass of aggregate and 40% RAP content by binder replacement. Nevertheless, mixes with high RAP and RAS are being produced across California for local agencies and commercial use. This study investigated the performance of four plant-produced high RAP or RAS mixes collected from different regions in California. The mixes were not designed and produced following Caltrans specifications. However, they provide insight into the effects of silo storage time on blending of virgin and RAP binder, the performancerelated properties of these mixes, and the measurement of properties by accepted performance-related tests. The mixes were collected before silo storage and after hours in the silo. Testing of the mixes included the following tests: four-point flexural beam stiffness and fatigue, Hamburg Wheel-Track (HWT), confined and unconfined repeated load triaxial (RLT), semicircular bending (SCB), and indirect tensile asphalt cracking test (IDEAL-CT). Additional testing was also conducted on the fine aggregate matrix (FAM) mixes to characterize fatigue and stiffness. This report presents preliminary findings from this study, including results related to the effects of silo storage time on stiffness, cracking resistance, and rutting resistance using performance-related tests as well as an initial comparison of the results from alternative cracking test types for these mixes. The results showed that silo storage time can increase stiffness on the order of 50% to 60%, with corresponding negative effects on fracture resistance and controlled-strain flexural fatigue life. The fatigue performance of the mixes reduced with increased silo storage, particularly at high strain levels, as measured by the flexural beam test. Use of a high rejuvenator dose could also potentially lead to rutting problems and poor fatigue performance. The FAM mix testing showed promising results in terms of characterizing fatigue. However, in its current form, it is not yet practical for use as a quality control/quality assurance test. The recommendation is that the effect of aging and blending of high RAP or RAS mixes be further investigated to understand the full impact of silo storage on these types of mixes. Performance-related specifications should consider the variation in mix properties due to silo storage.