A five-year study was performed to investigate the behavior of asphalt mixtures containing plastic and latex modifiers. The plastics were functionalized polyolefins; high meltflow index acrylic acid copolymers that were used in a pelletized form. The styrene-butadiene rubber latex was supplied as an emulsion. These materials were used separately and in combinations with each other to change the characteristics of asphalt mixtures. The research included laboratory experiments to characterize the materials and field projects in five locations to ascertain their performance. Field projects of flexible pavement overlays were constructed in Alabama, Maine, Michigan, Idaho, and Texas. This paper presents some of the significant findings made during the course of the five-year effort.
Mixture variables which were examined in the laboratory included asphalt grade, modifier type, and modifier concentration. Mixture preparation was investigated with respect to the order of addition of the components and compaction temperature. Laboratory results showed that the effectiveness of these modifiers was very dependent upon the source of the asphalt used in the mixtures. The order of addition of ingredients was found to be important for latex modified mixtures, and was not as significant in mixtures containing latex and polyolefins. The concentration of modifier changed the mixture behavior only up to levels of about 10 percent by weight of total binder. Compaction temperature had a profound effect on the resilient modulus of the mixtures.
The field projects were built in climates ranging from hot and wet in Alabama to cold and dry in Idaho. Control sections of conventional mixtures were placed along with sections of modified mixtures. The mixtures containing latex only as a modifier showed problems during construction. These problems were confined to the mixtures sticking in the dump trucks and the workability through the paver. There were considerable differences noted between the results from behind-the-paver construction samples and test results from the inplace materials. The modifiers seemed to provide more mixture stiffness at higher temperatures which possibly indicated a greater resistance to permanent deformation, while maintaining about the same characteristics as conventional mixtures at low temperatures.