Laboratory And Short-Term Field Performance Of Crumb Rubber Modified Asphalt Emulsion In Chip Seal Applications

Abstract

Chip sealing is a commonly used pavement maintenance treatment 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 and short-term field 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 aggregate 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 chip seal specimens indicating poor adhesion between the emulsions and the rubber aggregate. Field application of chip seals was also conducted to assess the short-term field performance of chip seal sections. Manual distress survey was conducted on the chip seal sections after three months of construction, after six months of construction, and after 12 months of construction. Field distresses associated with chip seals such as, bleeding, rutting, longitudinal cracking, and transverse cracking were measured and the PCI for each chip seal section was calculated. Results indicated that chip seal sections constructed with CRS-2P and CRS-2TR had performed well whereas the chip seal sections constructed with CRS-2 had the worst performance. Furthermore,