Effects of emulsion types, application rates, and crumb rubber on the laboratory performance of chip seal

Abstract

Chip sealing is a commonly used pavement maintenance method that aims to delay pavement deterioration by reducing water infiltration and restoring skid resistance. Loss of aggregate and bleeding are considered the major failure mechanisms in chip seal, and therefore, are the main design criteria for this treatment method. The objective of this study was to evaluate the laboratory performance of chip seals prepared with different types of asphalt emulsions, application rates, and aggregate blends. A newly introduced crumb rubber modified asphalt emulsion was evaluated that allows chip seal installation at the same temperature of a standard emulsion. Types of emulsion included a crumb-rubber modified asphalt emulsion (CRS-2TR), an asphalt rubber (AC20-TR), a polymer-modified emulsion (CRS-2P), and a conventional unmodified emulsion (CRS-2). Application rates were selected based on the Louisiana Department of Transportation and Development (LaDOTD) and the Texas Department of Transportation (TxDOT) specifications as well as from the chip seal design method recommended in NCHRP Report 680. A 90-10 aggregate blend of lightweight aggregate (LWA) and rubber aggregate (RA) was also investigated.The loss of aggregate was measured using two laboratory performance tests: the sweep test (ASTM D 7000) and the Pennsylvania Aggregate Retention Test (PART). The strength of adhesion of the four emulsions was also evaluated using the Bitumen Bond Strength (BBS) test. While asphalt rubber was the best performer in terms of aggregate loss, CRS-2P and CRS-2TR performed similarly followed by the conventional emulsion. Results of the BBS test showed a similar rank for the bond strength of the emulsions. It was also observed that the loss of aggregates in chip seal decreased with the increase in application rate. However, incorporation of rubber as aggregate in chip sealing increased the loss of aggregate in the specimens indicating poor adhesion between the emulsions and the rubber aggregate.