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This laboratory investigation was conducted with the purposeof determining the applicability of the Hveem Stabilometer to the testing of open-graded bituminous mixtures.

The study was divided into two major sections. The first of these investigated the validity of the Stabilometer displacement measurement when applied to open-graded specimens having large surface air voids. The second portion of the study had two specific purposes: (l) to investigate the stress-strain characteristics of open-graded mixturestested in the Hveem Stabilometer and (2) to determine whether surface voids on the ends of Stabilometer test specimens influenced Hveem stability values.

To check the validity of the displacement measurement, Stabilometertests were, conducted over a wide range of displacement values forduplicate specimens molded from three different mixtures. Displacement readings were varied by altering the surfaces of test specimens andby adjusting the quantity of air inside the Stabilometer oil chamber.

In studying the stress-strain characteristics of open-graded mixes, Stabilometer values and specimen deformation readings were obtained for two mixtures. The first of these open-type mixes was well-graded, but the second was essentially "one-sized" in gradation.

Results of this investigation showed that the final displacement value, when substituted into the Hveem stability equation, did notcompensate for the variations in lateral pressure caused by large changes(one or more turns) in the final displacement measurement.

Stress-strain relationships for the well-graded, open-type mixture indicated that the quantity of strain permitted a Stabilometer test specimen conformed closely with the amount of strain developed at the maximum shearing strength of a rational triaxial test specimen subjected to confining pressures similar to those present in a Stabilometer test.

Strain measurements recorded for Stabilometer specimens of the one-sized mixture used in this study were much lower than those obtained at the peak value of shearing resistance for triaxial test specimens ofthe same mixture and for similar confining pressures.

Surface air voids on the ends of Stabilometer test specimens hada small effect on test results. When these voids were filled, Hveem stability values were not significantly higher, but the reproducibility of test results was greatly improved by coating test specimens.

To improve the consistency of Stabilometer test results obtainedfrom open-graded mixtures, certain modifications in the testing technique were suggested. These changes involved the filling of air voids on thesurface of test specimens and the admittance of an increased amount of air in the Stabilometer oil chamber during the calibration of the testing apparatus

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Performing Organization

Joint Highway Research Project

Publisher Place

Lafayette, IN

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