Performance-Based Percent Embedment Limits for Chip Seals

Abstract

Chip seal treatments are used by many state departments of transportation and counties to cover minor fatigue and low-temperature cracks, retard raveling by reducing the moisture infiltration, and improve friction. Long-term performance of a chip seal treatment is affected by several factors including the type and morphology of the aggregates, emulsion/binder type, and most importantly, the microstructural characteristics such as the percent embedment of aggregates. This paper documents the efforts towards establishing performance-based threshold values of the percent embedment to minimize the common chip seal distresses (i.e. aggregate loss and bleeding). The laboratory performance tests were performed to evaluate aggregate loss and bleeding using a retrofitted Hamburg wheel tracking device. Two emulsion types (CRS-2M and CSEA) and two aggregate sources (slag and natural aggregates) were included in the testing program. Digital image analysis techniques were utilized to quantify and analyze the laboratory test results with respect to the percent embedment as well as chip seal macrotexture. Based on the test results, the minimum and maximum percent embedment thresholds for chip seals are established as 58% and 70%, respectively.