Summary: The solution to the mounting problem of solid waste disposal in the United States has generated a profusion of innovative ideas regarding the constructive use of waste material. Products manufactured from waste for use in highway construction seem to have an unusual appeal for many. In light of the well-recognized infrastructure decay and given the loss of funding base for highway construction in the U.S., the country call ill afford to place this added burden on the Highway Program unless it pays its own way. As attractive as such uses might be they must be expected to do one of three things:
1. Impart some beneficial material property. 2. Provide some type of cost reduction. 3. At the very least, provide a beneficial cost/benefit ratio.
A truly effective program of recycling refuse into highway construction will only be realized when economic conditions are met and a method developed that utilizes and effective quantity of waste material. At the present time, these dual conditions have not been met with regard to asphaltic concrete that incorporates used tire rubber. Florida reports they have used rubber in asphalt mixes as required by State lay but only in minor quantities of 3-5%. Wisconsin, on the other hand, has used rubberized asphalt, but ceased when they developed problems with cold weather cracking in pavements. In both of these instances a common factor has been additional cost with little of no commensurate benefit. FHWA projects an overall increase in cost of about 30% nationwide. From a review of the results obtained by others and our own research efforts, it is clearly demonstrated that rubberized asphaltic concrete utilizing waste tires is a technology for which the time has not yet come. Whether it will or not is presently a matter of conjecture. There are, however, asphalt/tire-rubber mixtures that have found beneficial and successful use in this state; and it is in this area that attention should be focused until such time as there is a technological breakthrough in other uses.