This research program was based on laboratory and field studies. All work was limited to the use of a 10-mesh crumb rubber in the dry process. An evaluation of the asphalt-rubber interactions indicated that there should be a reasonable level of interaction between the crumb rubber and the asphalt cement selected for the project. A suggested criterion for defining an acceptable level of interaction would be to establish a minimum viscosity of 15 Poise (Brookfield viscosity) for a neat asphalt cement modified with 20% crumb rubber. When designing a crumb rubber modified mixture, the aggregate gradation should be substantially gapped. The target gradation used in the construction of the Babbit, Minnesota test sections should be adjusted for crumb rubber gradations volumetrically; generally, 1 gram of crumb rubber occupies the same volume as 3 grams of aggregate for a given sieve size. The optimum asphalt content for crumb rubber mixtures should be based on air voids from 1.5 to 3%.

Focusing on asphalt paving technology, this work emphasizes quality control and quality assurance programmes in producing high-quality pavements. It combines theory and practice of asphalt paving including developments and information from the recently completed Strategic Highway Research Program which was designed to improve asphalt specifications, mix design and analysis systems.