Analysis of New Zealand Chip Seal Design and Construction Practices

Abstract

Chip seal is the most frequently used preventive maintenance treatment on flexible pavements. Many public highway agencies use chip seals with limited knowledge of effective practices employed abroad. Information is available on good practice for materials, design, construction techniques, and effectiveness of chip seals both in the literature and through survey. This paper reports on a comparison of practices for the design of maintenance chip seals that springs from a survey of 40 U.S. states with those used in New Zealand. The study was confined to maintenance chip seals that were placed on top of an existing surface. The paper compares and contrasts the design methods used in North America and New Zealand and offers information regarding best practices in chip seal design including material selection criteria (physical, chemical, and gradation); design methodology for application rates; specifications; warranties and performance-based specifications. Additionally, it finds that the area that seems to have the greatest potential for enhancement of North American chip seal practice is the area of chip seal design. The major issue in chip seal design lies in accurately characterizing the surface on which the chip seal will be applied using engineering measurements of macrotexture and hardness. This knowledge allows engineers to select both binder types and aggregate gradations that are compatible with the surface on which they will be applied. Additionally, New Zealand pavement preservation practices such as the use of the ultra high pressure (UHP) watercutter machine to retexturize bleeding surfaces are also detailed and their potential for use in the United States is discussed. The paper finds that U.S. public agencies can benefit from an exchange of technical information between public and private organizations in each country. Additionally, it found that practices in the United States are quite similar across the nation but significantly less technical when compared to those used in New Zealand. The paper's major finding points to the need to evaluate chip seal construction practices from New Zealand for potential implementation in the United States.