COMPARISON OF CONVENTIONAL VERSUS MODIFIED SURFACE SEALS WITH THREE AGGREGATE TYPES

A 3-year field study was conducted of various materials used for surface seal treatments applied to a low-volume, bituminous pavement. The materials evaluated included two asphalt binder types (an asphalt emulsion and a polymer-modified asphalt emulsion) and three aggregates (wet-bottom boiler slag, mechanically crushed gravel, and crushed limestone). The materials were used in all combinations. Performance was evaluated visually, friction numbers were measured routinely, and accident data were collected to compare the different seals. A statistical analysis of the friction data indicated that the seals could be differentiated based on aggregate type but not on binder type. Visual evaluations of the performance confirmed this finding. Although all of the seals provided about the same initial improvement in friction number, the best long-term frictional performance was obtained with the mechanically crushed gravel. The slag aggregate was of a fine gradation and did not provide the great increase in macrotexture provided by the coarser gravel and limestone. In addition, the fine slag wore away fairly rapidly under turning traffic, resulting in a shorter service life, which is expected from this type of seal.