Some Low-Temperature Characteristics of Bituminous Paving Compositions

Stability at temperatures approximating hot-weather temperatures in the pavement has become thoroughly established as a basic requirement of bituminous compositions. Means of measuring and rating this important property have been perfected as a result of laboratory experiments and have been proved sound through several years of practical application. Two contemporary tests have evolved with resistance to shear the basic principle of both: In one (the extrusion test) the shear is measured indirectly and in the other (the direct test), simple shear is measured directly, and values are expressed in pounds per square inch. The latter method is distinctly convenient in comparing a variety of compositions which may have been tested in cylinders of from 1 in to 6 in., or more, in diameter, since values by the extrusion test are not reducible to unit loads.

Although much work has been done in connection with summer temperature characteristics, with the result that the elements of mixture design involved have become thoroughly understood, little, if any, study has been made concerning low-temperature performance in paving compositions. With the thought that such an investigation should throw much light upon several questions that have long been unanswered and have given engineers much concern, the results of a systematic course of study, begun in 1931, are reported in this paper.