Development of blending chart for different degrees of blending of RAP binder and virgin binder

Recent studies have consistently shown that RAP mixed with virgin binder and aggregates results in partial blending; that is, a phase between 100% blending and the “black rock” effect occurs. The impact of partial blending on new virgin binder content is apparent and may cause under-asphalting of mixture, resulting in poor pavement performance. Influence of partial blending on critical grade of RAP mixes and allowable percentages of RAP have not been evaluated. The purpose of this paper is to develop the blending chart for different degrees of blending to study the impacts of partial blending on the critical grade of blended binder. To achieve the objective, blending charts for 100%, 70% and 50% degree of blending have been developed for PG 70-28 and PG 58-28 binder by mixing virgin and RAP binders in differing proportions. The higher critical grade of blended binder does not change for different degrees of blending (70% and 50%) for low percentages of RAP binder (25% and 35%) with PG 70-28 binder. However, for high percentages of RAP binder (50%) and low degree of blending (50%), higher critical grade of blended binder can cause grade change.

► Examined impact of degree of blending (DOB) on properties of blended binder.
► Examined shape of blending chart for different degree of blending conditions.
► Decreasing DOB and increasing RAP binder will increase true high grade of blended binder.