Traction or frictional resistance of tires on clean, dry pavements tends to be fairly high (coefficient of friction of 0.6 to 0.8) and to be independent of the texture of the pavement surface. In contrast, the loss of traction on a wet pavement is due entirely to lubrication effects; and, while wet friction seems to be fairly independent of the identity of the aggregate, it is extremely dependent upon the texture and porosity of the surface. Likewise, the mineralogical and lithological characteristics of the aggregates largely determine the natural texture, i.e., type of wear (coarse or fine) which the aggregate will undergo in roadway service (1).

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Report Number

No. 178

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