Browsing by Subject "Moisture sensitivity"

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    Moisture Sensitivity in Asphalt Concrete Mixtures
    (Minnesota Department of Transportation, 1995-11) Stroup-Gardiner, Mary; Newcomb, David E.; Crow, Benita; Kussman, William; Wegman, Dan
    The research performed for this report was intended to recommend alternative mix design procedures and parameters for evaluation of asphalt mixture sensitivity, with more of an emphasis on volumetric relationships. Three Mn/DOT projects were selected to represent the following durability issues: 1) debonding of asphalt from aggregate, 2) cohesion problems, and 3) mix design problems. Materials were obtained from these construction projects and evaluated in the laboratory. Gradations were varied from the project specifications so that mixtures with more and less asphalt were evaluated along with the project mixture. Testing included the temperature susceptibility and moisture sensitivity of the mixtures, in addition to the net adsorption test on the aggregates. The results suggested means for identifying moisture sensitivity mechanisms in mixtures during the mixture design phase, although these need to be confirmed through more extensive investigation. Aggregate mineralogy, gradation, and mixture proportioning can all play a role in improving the durability characteristics of asphalt mixtures. Recommendations are made for continued research and implementation of an improved approach to asphalt mixture design.
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    Physio-chemical evaluation of asphalt-aggregate interactions
    (1994-06) Stroup-Gardiner, Mary; Newcomb, David
    The durability of selected asphalt concrete components and mixtures from six projects were evaluated with the newly recommended net adsorption test and the more common ASTM D4867 (a modified Lottman), respectively. The net adsorption test was used to assess the durability of the adhesion of the asphalt to the aggregate surface in the presence of water. The ASTM D4867 method evaluated the retained strengths of compacted mixture resistance after freeze/thaw conditioning. The net adsorption results indicated at least two of the six projects could be susceptible to moisture related adhesion problems. The test method was adjusted to use the full aggregate gradation rather than only the fine fraction. A comparison of these results to those originally reported by Strategic Highway Research Program (SHRP) researchers showed good agreement in both trends of results and withinlaboratory test method variability (about 0.14 mg/g). The mixture testing indicated that three of the six projects had tensile strength ratios of less than 70 percent and could be expected to show some evidence of moisture related damage. An evaluation of these results suggested that any moisture sensitivity could be due to mix design parameters such as lower film thicknesses, and lower initial strengths rather than a chemical loss of adhesion at the asphalt-aggregate interface. The influence of conventional mix design parameters on the moisture sensitivity of asphalt concrete mixtures should be more thoroughly investigated prior to any consideration of the use of additives.