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Minnesota Department of Transportation
This study characterizes asphalt emulsions that are typically used in cold in-place recycling applications. A simple approach was presented that treated the cured residue as asphalt binder and applied the standard Superpave specifications to the material. A literature review examined methods that have historically been used to produce, characterize, and apply asphalt emulsions. Four emulsions were tested in this project. The emulsions were cured two ways, the first being allowed to sit overnight in a pan at room temperature, and the second being a modified rolling thin-film oven approach. Air cured samples were also aged in the pressurized aging vessel. These residues were then tested with the bending beam rheometer and direct tension tester (DTT) at low temperatures and with the dynamic shear rheometer (DSR) at high and intermediate temperatures. AASHTO MP1 specifications were applied in order to characterize the emulsions by performance grade. Following this, AASHTO MP1a specifications were followed in order to find the critical cracking temperature of the emulsions. Master curves were constructed from the DSR tests of complex shear modulus vs. frequency. Finally, a sample mix design was presented using these emulsions and an empirical equation to predict the dynamic modulus of the mixture. Results showed that the air-curing method of recovering asphalt emulsion residue produced more conservative results and is the recommended curing method. MP1 specifications provided a straightforward approach to characterizing the emulsion residues, but showed that the critical cracking temperature obtained by the intersection of thermal stress and strength curves was substantially higher than the limiting temperature obtained in MP1 specification. More research is needed to determine the reasons for the low DTT strength values for these emulsions.
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