VTRC Report Published - Evaluation of Hybrid Rubber Modified Asphalt Mixtures and Pavements: A Case

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Several state departments of transportation have recognized the benefits of modified asphalt mixtures in resisting multiple modes of climate- and load-induced distresses in flexible pavements.  Throughout the past 50 years, asphalt binders have been modified with various components such as styrene-butadiene-styrene (SBS) polymers, ground tire rubber, chemicals (e.g., acid), recycled engine oils, etc., to achieve the desired properties.  Hybrid rubber modified asphalt (HRMA) is an innovative engineered additive derived from ground tire rubber, elastomeric SBS polymers, and additive technologies.  HRMA is specifically formulated to improve the high temperature stiffness and elastic properties of performance graded binders and the storage stability of modified binders. 
The purpose of this study was to document and assess HRMA field trials constructed in Virginia.  This study documented and evaluated the constructability and laboratory performance of two plant-produced HRMA mixtures compared with the Virginia Department of Transportation (VDOT) typical SBS-modified surface mixtures as reference mixtures.  No changes from routine established practices in terms of surface preparation, production at the plant, or paving operations were reported. 
The four mixtures were evaluated in terms of durability, dynamic modulus, resistance to rutting, and resistance to cracking using multi-level performance tests (basic, intermediate, advanced).  All the derived observations indicated that HRMA modification could be as beneficial as regular SBS modification and could provide similar or better performance properties and characteristics for the resultant mixtures.   
The study recommends that VDOT consider the use of HRMA surface mixtures as an alternative to the current use of regular SBS-modified surface mixtures on higher-volume facilities.  Since the sections evaluated in this study were placed in 2021, the 2-year performance data and corresponding observations are still considered preliminary.  Continued monitoring of field performance will be needed to quantify any benefit of HRMA mixtures in comparison with regular SBS-modified surface mixtures.  The study also recommends additional field trials with HRMA mixtures for further performance evaluation. 
The full report can be found here.