Effect of RAP and virgin binder source on low-temperature PG reliability

MassDOT is evaluating the potential of increasing the RAP content in their asphalt surface layers from 15% RAP to 20-25% RAP while keeping the virgin binder PG fixed at PG64-28. However, each RAP can have different properties such as binder PG and binder content and can include highly aged binders. Thus, using some RAPs without changing the virgin binder PG could lead to blended binders with unacceptable low-temperature PGs even at low RAP contents. In this study, RAP binders and virgin binders were sampled from around Massachusetts. The low-temperature continuous PGs of both binders were measured. An AASHTO blending equation was used to determine the low-temperature continuous PGs of blended binders based on using 15% and 25% RAP binder contents. An LTPPbind equation was then used to calculate the standard normal distribution Z, which provides the reliability that a blended binder will meet the low temperature PG required at a specific geographic location. The results showed the high impact of RAP source, RAP binder content, virgin binder source, and geographic location on low-temperature PG reliability, and that keeping the virgin binder PG fixed at PG64-28 may not always provide binders suitable for western and northern Massachusetts.