United States Department of Transportation
i
Understanding The Performance of Modified Asphalt Binders in Mixtures: Evaluation of Moisture Sensitivity
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2002-10-01
[PDF-952.61 KB]
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Abstract:The effect of 11 asphalt binders on the moisture sensitivity of a mixture were measured using the Hamburg Wheel- Tracking Device (Hamburg WTD). The Hamburg WTD tests a slab of hot- mix asphalt submerged in hot water by rolling a steel wheel across its surface. The binders consisted of two unmodified asphalt binders, an air- blown asphalt binder, and eight polymer- modified asphalt binders. The continuous high- temperature performance grades (PG's) ranged from 67 to 77. Two aggregates were used: diabase and limestone. The mixture results using the limestone aggegate could not be used to evaluate the asphalt binders because the Hamburg WTD crushed the limestone aggregate. A test temperature of 58 degrees Celcius was chosen for the diabase mixtures based on trial tests using the air- blown and unmodified PG 70- 22 asphalt binders. It was expected that most of the mixtures with polymer- modified asphalt binders would have greater resistance to moisture damage than the mixture with the unmodified PG 70- 22 asphalt binder because they would provide increased adhesion to the aggregate or create a network within the asphalt that was more resistant to water penetration. However, only one polymer- modified asphalt binder provided a greater resistance at a 5- percent level of significance. Some of the asphalt binders provided significantly different resistances to moisture damage that were not related to differences in cohesive strength as measured by the asphalt binder parameter G*/sin(delta) at 58 degrees Celcius. It was concluded that polymer- modified asphalt binders having the same G*/sin(delta) can provide different adhesive strengths and/or different resistances to water penetration. Reasons for these differences need to be determined.
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