Mix Design
A number of different HIR mix design methods have been used by various owner agencies; however, there is no nationally accepted method for undertaking an HIR mix design. In general, the philosophy has been to restore the properties of the existing aged asphalt pavement to those of, or close to, a new asphalt mixture. Mixture verification testing has shown that equivalent performance to a new asphalt mixture can be achieved with HIR mixtures even though they typically have reduced air voids due to the addition of rejuvenating agents. HIR mix designs, regardless of process, address all or a portion of the following steps shown below:
1. Obtain samples/cores of pavement
2. Determine existing mixture properties
3. Select type and grade of rejuvenating agent
4. Perform simplified HIR mix design
5. Perform additional tests necessary for comprehensive mix design, if desired, such as rut testing, moisture sensitivity and cracking tests
6. Establish job mix formula
7. Make field adjustments as required
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