Modeling the Stripping Potential of Asphalt Concrete: Fid-Bau Portal

Modeling the Stripping Potential of Asphalt Concrete

Sarsam, S. I. / Al-Azawi, E. T.

The exposure of asphalt pavement to water is often considered one of the major factors affecting the durability of asphalt concrete. The water-induced damage in HMA layers may be associated with two mechanisms: loss of adhesion and loss of cohesion. In the first mechanism, the water gets between the asphalt and aggregate and strips the asphalt film away, leaving aggregate without asphalt film coverage. This is because the aggregates have a greater affinity for water than asphalt binder. The second mechanism includes the interaction of water with the asphalt cement that reduces the cohesion within the asphalt cement. This will lead to a severe reduction in the asphalt mixture strength. In this work, two penetration grades of asphalt cement, 40-50 and 60-70, have been implemented in the construction of asphalt-concrete specimens in the laboratory using the standard Marshall Compaction procedure. Three different asphalt percentages including the optimum have been implemented for each asphalt grade. A total of (50) specimens (loose or compacted) were prepared. For both of the asphalt grades specimens, visual rating of stripping has been conducted on loose asphalt concrete samples using both the static immersion test and the boiling water test. The visual rating was variable among both testing procedures and depends on eye judgment rather than a solid strength result. The values of percent stripping ranged between (65 - 90) percent. It was felt that the modeling of stripping potential should be related to a strength criterion only, then using the Marshall Immersion method, the index of retained strength (I.R.S %) for compacted asphalt concrete specimens was adopted to determine the stripping potential. Test results were analyzed for correlation of the tested Marshall properties including stability, flow, and stiffness with stripping phenomena. Finally, a mathematical model was obtained that correlates the stripping potential of asphalt concrete to the Marshall properties. It was concluded that the stripping potential as indicated by the index of retained strength is highly dependent on the stiffness of asphalt concrete; the developed model may be utilized in prediction of stripping potential of asphalt concrete using simple tests usually adopted for quality control.