Dr. Yu Yan, Mr. George Lopp and Dr. Reynaldo Roque, from the University of Florida (UF) Department of Civil & Coastal Engineering, conducted a study to examine the possibility of increasing the percentage of reclaimed asphalt pavement (RAP) used for roadway surfaces without reducing pavement cracking performance. RAP is a valuable alternative to virgin pavement materials and importantly, excessive stockpiles of RAP are available for road construction (Image 1).
The Florida Department of Transportation (FDOT) currently allows only up to 20% RAP in asphalt mixes used for roadway surfaces, where expensive polymer-modified asphalt (PMA) binders are required to achieve high performance. Although increasing use of RAP is desirable, there is a primary concern that too much RAP may diminish the benefits of using PMA binder, resulting in unacceptable pavement cracking performance.
To address the concern, the researchers designed a comprehensive experimental plan, which includes two RAP sources representing typical and extreme RAP encountered in Florida, combined with two commonly used virgin modified binders, at four RAP content levels of 0, 20, 30 and 40%. The effects of RAP type and content on mixture cracking performance were evaluated by using several advanced laboratory tools previously developed at UF. Results showed that blends of virgin and RAP binders met FDOT specification for virgin modified binder, even when up to 40% RAP binder was used. Meanwhile, mixtures containing up to 40% RAP exhibited equivalent or superior cracking performance than a virgin mixture. Moreover, the researchers found that RAP gradation had a dominant effect on mixture cracking performance, which was not previously well known in the asphalt community (Image 2).
Therefore, it was recommended that consideration of RAP gradation to be included in future design guidelines. Improved guidelines will allow for greater amount of RAP to be used in roadway surfaces, so that cost savings and environmental benefits can be realized by reducing the need for virgin pavement materials and landfill space.