Evaluation of VMA and other volumetric properties as criteria for the design and acceptance of superpave mixtures
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The effects of different volumetric properties, e.g., VMA, film thickness, asphalt content, and aggregate surface area on the durability (age-hardening rate), fracture resistance, and rutting resistance of Superpave mixtures were evaluated. Mixture shear resistance was measured with the Servopac Superpave Gyratory compactor. The rate of binder hardening in mixtures was not related to either the VMA or the film thickness of mixtures. Binder hardening was almost entirely controlled by the percentage of fine aggregate in the mixtures, where the Superpave restricted zone provided a proper definition between fine-and coarse-graded mixtures as related to binder hardening. Although low VMA and film thickness did not appear to result in durability or cracking problems in fine-graded mixtures, the low VMA identified potential shear instability for the fine-graded mixture at low air void contents. For the coarse-graded mixtures, VMA was not related to age-hardening, fracture resistance, or rutting resistance. Other factors, e.g., void structure, and perhaps film thickness, had a stronger effect on these characteristics.