Evaluation of Virginia Department of Transportation Chip Seal Practices: Materials and Design

About the report:

It is crucial for highway agencies, including the Virginia Department of Transportation (VDOT), to maintain the structural and functional conditions of existing pavements in a state of good repair.  Pavement preservation treatments can help achieve this objective by extending the service life of existing (flexible) pavements through delaying deterioration and improving the functional performance characteristics of these pavements.  Chip seals are among the most commonly used pavement preservation treatments, and their performance highly depends on the characteristics of the materials used and their application (design) rates.  In recent years, extensive research has been undertaken at the local and national levels to evaluate the effects of material characteristics and design techniques on the performance of chip seals.  Further, new materials and additives have been introduced into the construction market with the aim of enhancing the performance of chip seals.  Despite these advances and the long history of chip seal use on its roadway network, VDOT has not conducted a thorough review of its chip seal practices in more than 25 years. 

This study assessed VDOT’s single-layer chip seal practices, both conventional and modified, from the perspectives of materials characterization and design.  In this effort, aggregates and emulsions from eight chip seal projects across Virginia were acquired for laboratory characterization.  The materials were benchmarked using state-of-the-art methods and practices to determine how and if the current VDOT practice aligns with the nationally standardized practices.  In addition, the field performance of these projects was monitored for up to 1.2 years using macrotexture as a performance metric.  This was done to assess how the current design practice affects performance in the field. 

The study concluded that based on rheological characteristics, the emulsion used in chip seals may not be suitable for the conditions (traffic and climate) in which they were used.  Conversely, the physical characteristics of the chip seal aggregates were suitable for the conditions (traffic) in which the chip seals were used.  In addition, VDOT’s chip seal design practices for the single-layer chip seals may not be suitable.  Further, the study concluded that more vigorous quality measurement practices are essential for improved or optimal performance of chip seals. 

The study recommends that (1) AASHTO MP 37, used for performance grading of emulsions (residues), be adopted for optimized chip seal performance; (2) the traffic-based requirements for abrasion loss and flakiness index as specified in AASHTO M 340 be adopted to specify performance requirements for chip seal aggregates; (3) AASHTO R 102 be adopted as the standard used for chip seal design; and (4) more vigorous quality control measurement practices be explored by VDOT to further improve the performance of chip seals in the field.  It is anticipated that implementing these recommendations will help achieve the desired outcome of chip seals: longer service life, larger cost savings, reduced user delays, and safer roads.

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