Pavement Preservation Demonstration Projects for Chip Seal and Microsurfacing Treatments

About the report:

In 2021, the Virginia Department of Transportation (VDOT) collaborated with the National Cooperative Highway Research Program (NCHRP 20-44(26)) project research team to develop three specifications for chip seals, microsurfacing, and fog seals, incorporating recommendations from guidelines developed under the NCHRP 14-37 project and American Association of State Highway and Transportation Officials specifications. Subsequently, during the 2022 construction season, VDOT initiated two demonstration projects constructed under these new specifications. One project involved a chip seal application in the Richmond district, and the other project involved a microsurfacing application with a fog seal treatment on the shoulders in the Hampton Roads district. Each demonstration project included additional sections treated according to VDOT’s current specifications, serving as reference sections for the corresponding demonstration sections.

The study assessed the effectiveness and performance outcomes of the demonstration sections constructed using the new specifications by comparing them with the reference sections constructed using the existing specifications. The effort included comprehensive documentation of preconstruction surface conditions and construction processes across project sections, incorporating qualitative visual inspections, quantitative measurements, and evaluations of material selection, application methods, and quality control measures. Furthermore, researchers assessed the short‑term field performance of each section, monitored for up to 13 months, with performance metrics, such as texture, friction, rut depth, and ride quality.

The results indicated that the new chip seal specification did not lead to improved performance outcomes for the chip seal (demonstration) section compared with the chip seal (reference) section constructed using VDOT’s current chip seal specification. Various factors affected the field performance of the chip seal treatment under the new specification, including challenges in achieving the target aggregate application rate and non-uniform spreading of aggregates during construction. In addition, differences in structural application, with one section featuring a modified single-layer chip seal application and the other a single-layer chip seal application, contributed to performance disparities. Further assessment through additional field trials is necessary to comprehensively evaluate the effectiveness of the new specification. Similarly, the new microsurfacing specification did not yield short-term performance differences for the microsurfacing (demonstration) section compared with the microsurfacing (reference) section constructed using VDOT’s current microsurfacing specification.

The study recommends conducting additional field trials that include modified single-layer chip seal applications designed according to the new specification developed in this study to assess its effect on chip seal performance. In addition, the study recommends that VDOT should maintain the use of its current special provision for microsurfacing projects.

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