Also, the addition of additives may cause equipment modification by the asphalt producer which in turn increase initial costs. Another component of the research that requires attention is the determination of what stage of the mix process should the modifier by added. Trials should bemade at different stages in the laboratory mixing process. When focusing on increased performance of bituminous materials, the binder portion of the mix seems to have the most opportunity for improvement. Past research has shown that modifiers to asphalt pavements serve two purposes.
Modifiers usually extend the life of pavement due to a decrease in distresses.
Some modifiers that are in fact waste products can be disposed of into the roadways. With the above two criteria, most polymers only satisfy the first condition. Some modifiers, such as pyrolized carbon black and recycled low density polyethylene, can fulfill both criteria. Some of the past research has showed encouraging results in pavement performance for a number of modifiers. Although many times the binder testing showed that the modifier was superior, sometimes field results showed no significant difference between modified and unmodified designs.