Development of Specification for Chip Seal Construction Quality Assurance Based on Laser Texture Scanner

Abstract

Chip seal (or seal coat) is widely used by state and local governments for pavement preservation and maintenance. Currently, chip seal construction acceptance largely relies on the experience and visual observations of contractors and inspectors; this causes significant variations in chip seal performance, with some projects experiencing premature failure. Some agencies specify quality assurance of chip seal construction, based on the percent embedment of chips estimated by pulling chips or by a macrotexture that correlates with percent embedment. In either case, the specifications do not account for different traffic levels, climatic conditions, or existing pavement conditions between different projects, which can affect chip seal performance. The aim of this study is to develop a specification that addresses different project conditions, based on extensive field data collection. Nine chip seal projects were monitored during construction in 2022 and after construction, covering different traffic levels, materials, existing pavement conditions, and site conditions. Macrotextures were measured on the basis of mean profile depth (MPD). It was found that rut depths in existing pavement greatly affect MPD and thus bleeding potential. When the chip seal is placed on new hot mix asphalt (HMA), the emulsion can leak into HMA, decreasing chip embedment (or higher MPD) and increasing raveling potential. A regression model was developed, relating MPD after 1 year in service to such factors as truck volume, rut depth, pavement substrate condition, and initial MPD after construction. Accordingly, MPD during construction can be determined as a function of project conditions and can serve as a construction quality assurance threshold.