Long-Term Field Performance Evaluation of Chip Seals

Abstract

Chip seals are widely used to preserve asphalt pavements by reducing moisture intrusion, limiting environmental exposure, and slowing surface deterioration. However, the long-term effect of application timing remains difficult to isolate because pavement condition, materials, traffic, construction, and maintenance history also influence treatment performance. This study evaluated associations between chip seal application timing, long-term field condition, and recovered binder properties at test sites maintained by agencies in Cass County, Crow Wing County, and the City of St. Cloud, Minnesota, USA. At each site, five pavement sections were chip sealed in successive years from 2015 through 2019, while one section remained untreated as a control. Field performance was evaluated using directional International Roughness Index measurements, transverse crack counts, and surface ratings. Binders recovered from upper and underlying portions of pavement cores were characterized using Fourier transform infrared spectroscopy, rotational viscosity, continuous performance grading, bending beam rheometer testing, ∆Tc, multiple stress creep recovery, linear amplitude sweep, Glover-Rowe analysis, and binder bond strength testing. Treatment effects were interpreted primarily by comparing the underlying binder from each treated section with the corresponding bottom-layer control within the same agency. Field and laboratory results were compared descriptively at the section level. Field-performance measures did not produce a uniform treatment-year sequence. Roughness and cracking varied by agency and travel direction, while St. Cloud surface ratings remained within a narrow range. The strongest evidence of an early-treatment benefit occurred at Cass County, where Section 1 exhibited more favorable bottom-layer low-temperature grade, ∆Tc, Glover-Rowe, and combined LAS responses than the control. Crow Wing County and St. Cloud showed broader treated-versus control differences in selected binder properties, but these differences were not consistently ordered by application year. The findings indicate that timely chip sealing can preserve the underlying asphalt binder. The magnitude and timing of this benefit were site specific, and the study did not establish a universal application year or condition threshold. Agencies should select chip seal timing using an early, condition-based preservation window supported by multiple field indicators, material characteristics, and documented maintenance history.