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WISCONSIN STRUCTURES & MATERIALS TESTING LABORATORY (WSMTL)

Diagram A:  PATTI  device

a) PATTI device

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Evaluation of the Roles of Adhesion & Cohesion Properties of Asphalt Binders in Moisture Damage of Hot Mix Asphalt
Research by
Kunnawee Kanitpong/Prof. Hussain Bahia
Dept of Civil & Environmental Engineering

Resistance of asphalt mixtures to moisture damage is commonly known as a function of interaction between asphalt and aggregate as they are exposed to water. For many years, a number of research focused on moisture damage have listed a number of important factors. The mineralogical composition of aggregate and asphalt chemistry is well known as an important factor in the susceptibility of asphalt mixtures to moisture damage. However, the significance of asphalt binder properties in affecting moisture damage has not yet been widely investigated. In this study, the role of binders in moisture damage is separated into adhesion and cohesion properties. To measure the cohesion of asphalt, a method known as tackiness test of asphalt using the Dynamic Shear Rheometer (DSR) was employed. To measure the adhesion of asphalt to aggregate surface, a modified pull-off test using the Pneumatic Adhesion Tensile Tester (PATTI) was introduced.

b) Specimen preparation for adhesion or pull-off tensile strength test.

Diagram b: Specimen preparation for adhesion or pull-off tensile strength test.

This study was conducted to evaluate the relationship of the cohesion of asphalt binder, the resistance of asphalt binder to strip from aggregate surface (adhesion), and the resistance of asphalt mixtures to moisture damage in the laboratory. The resistance of mixtures was measured using the Indirect Tensile Test, the Uniaxial Compression Permanent Deformation Test, and the Hamburg Wheel-Tracking Test. Different types of asphalt binders including original, polymer modified, and anti-stripping modified binder were used. Two types of aggregate mineralogy, limestone and granite, were selected to produce the asphalt mixtures. All other mix design variables were controlled to minimize their effect on the performance of asphalt mixtures.

The results of this study indicated that the cohesion and adhesion of asphalt binder could be used as a good indicator to predict the performance of asphalt mixtures in resisting moisture damage. It is clear that asphalt modification with polymer can substantially improve cohesion and adhesion. In addition, the anti-stripping additive provides significant improvement of adhesion but neutral effect on cohesion. Finally, the aggregate mineralogy was also found to be an important factor in such a way that the granite mixture exhibits more susceptibility to the moisture damage than the limestone mixture for most of binder combinations.


 

 

 

 

 

 

 

c: Schematic of Cohesion or tack test

Figure 1: Schematic diagram of the devices for adhesion and cohesion testing of asphalt binder.

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