The primary objective of this study was to investigate the feasibility of implementation of the crumb rubber technology in Kentucky. The impetus for this study was provided by the Intermodal Surface Transportation Efficiency Act of 1991 (lSTEA).

This study included an overview of existing literature on the subject from an implementation point of view for Kentucky's conditions. Upon completion of this phase of the study, guidelines were developed by the KTC research team and were submitted to the Transportation Cabinet for field implementation of the crumb rubber modifier (CRM) technology in Kentucky. From the ease of implementation point of view, the Cabinet opted to construct a field trial section using the "wet process' which utilized a fine ground rubber (80 mesh} material. The rationale for this decision was based upon the fact that the fine ground CRM mix closely resembles the polymer modified HMA, and that both the Cabinet and Kentucky contractors have an extensive amount of experience with polymer modified asphalt.

In July 1993, a field trial project was constructed on a portion of the US 421, Franklin County, Kentucky. The project involved milling of nominally one inch of the wearing surface followed up by a nominally one-inch overlay. The four-lane trial project (two lanes in each direction) was divided into two approximately half-mile sections. This allowed for a comparison of performance between the CRM hot mix asphalt (HMA) and the conventional HMA.

In summary, the trial implementation of the CRM technology in Kentucky proved to be a success. The 177-micron (80-mesh) fine ground rubber at 7.5% by weight of asphalt cement provided a material similar to polymer modified asphalt. Construction of the field project was possible with existing specifications and practices in Kentucky. The non-intrusive nature of the fine ground technology was most desirable from the ease of implementation point of view.

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The contents of this report reflect the views of the authors who are responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Kentucky Transportation Cabinet, the Federal Highway Administration, nor of the University of Kentucky. This report does not constitute a standard, specification, or regulation. The inclusion of manufacturer names or trade names are not to be considered as endorsements.