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Bituminous pavement surfaces constructed with aggregates of different rock types, or of the same rock type but from different sources, often exhibit different friction characteristics under comparable traffic conditions. Rock type, abrasive size, number of wheel passes, and contact pressure between surface and tire have been generally recognized as primary factors that control the polishing process. To investigate the relation of these factors to rock properties, but without bias caused by shape and size of the aggregate or by mix design, flat surfaces of six rock types varying in texture and mineral composition were polished in a laboratory procedure. Silica in eight grades ranging from 5 to 105 μm was employed as the abrasive in polishing the surfaces with a reciprocating rubber pad apparatus, and different abrasive sizes were used in succession. Contact pressure was normally 15 psi (103 kPa), but was varied in some cases. The polish attained was measured as friction with a pendulum tester after each cyle of 6000 passes of the polishing pad. The results indicate that the susceptibility to polishing increases with the softness and homogeneity of the rocks, the fineness of the abrasive, the number of polishing cycles, and increased contact pressure.
Associate professor of civil engineeringMember of ASTM, The Pennsylvania State University, Capitol Campus, Middletown, Pa.
Professor emeritus of mechanical engineeringMember of ASTM, The Pennsylvania State University, University Park, Pa.
Stock #: JTE10919J