Optimizing the Gradation of Fine Processed Reclaimed Asphalt Pavement and Aggregate Blends for Unbound Base Courses

Abstract

The purpose of this research was to investigate the effect of changes in grain size distribution to the permanent deformation of two different fine processed reclaimed asphalt pavement (RAP) blended with base course virgin aggregate (VA). Grain size distribution of the RAP-VA blends were created following two different approaches. The first approach was based on mixing RAP and VA to have one grain size distribution, regardless of how much RAP was added to VA (here referred to as the engineered mixture design). The second approach was based on mixing RAP and VA with as-is gradation from the plants to proportions determined by weight and not controlling the outcome of the specific grain size of the mixture. This approach resulted in various grain size distributions (here referred as the as-is mixture design). The engineered mixture design was useful to quantify the effect of adding RAP to the blends, but was not a realistic approach to create blends that may be achieved in the field. The as-is mixture design could not only be achieved in the field, as demonstrated in this study, but also resulted in better performance in terms of permanent deformation. This manuscript describes the comparison of these two approaches and a methodology to optimize the gradation and develop thresholds for RAP-VA blends that may result in similar or better performance than the 100% as-is VA that is used to construct base course in pavement systems.

Construction Quality Control of Unbound Base Course using Light Weight Deflectometer where Reclaimed Asphalt Pavement Aggregate is Used as an Example

“…The VA used in this study was classified as a typical base course material (21 aggregate gradation) by Virginia Department of Transportation (VDOT) as defined by their Road and Bridge Standards ( 32 ). This was the same material used in the previous study conducted by the authors when the performance of the RAP blended with VA was evaluated in the laboratory ( 8 ). The aggregate was created from the crushing of diabase rock and consisted of a maximum particle size of 25.4 mm and 11% fines.…”

“…The RAP used in this study was obtained from two different asphalt plants in Virginia. These were also the same materials that were previously used by the authors as part of the laboratory performance evaluation study ( 8 ). Both of these RAP materials classified as fine processed RAP with maximum particles being less than 12.7 mm sieve size.…”

“…Previous research has indicated that, in the case of creating a base course aggregate, it is best to blend RAP with virgin aggregate (VA) rather than using 100% RAP ( 5–7 ). Also, detailed guidelines on how to properly blend RAP with VA to create blends that are suited for road construction exist in the literature ( 8, 9 ). Additionally, twelve Department of Transportation (DOT) agencies in the U.S. and abroad including France, Germany, Netherlands, and United Kingdom have specified target blends to mix RAP with VA to create a base course for road construction ( 2 ).…”

“…Additionally, twelve Department of Transportation (DOT) agencies in the U.S. and abroad including France, Germany, Netherlands, and United Kingdom have specified target blends to mix RAP with VA to create a base course for road construction ( 2 ). Using RAP to create base course aggregate for road construction not only reduces the stockpile volumes but also provides an opportunity for sustainable development ( 8, 10, 11 ).…”

A Sustainability Perspective for Unbound Reclaimed Asphalt Pavement (RAP) as a Pavement Base Material

“…Hoppe et al [17] looked into the feasibility of utilizing RAP for road base applications, his review indicated a current direction to incorporate RAP to levels reaching 50% in unbound base layer blends; however, there is a lack of uniformity and limited specifications. Recent research by Ullah et al [18] investigated the impact of alterations in gradation in regards to the permanent deformation effects by looking into a variety of prepared RAP's that was combined together with virgin aggregate for the base course. The research aimed to improve gradation curves and to establish limits for mixtures containing RAP that may result in similar or better performance than the 100% VA that is used to construct base courses.…”