| In rubber-modified asphalt pavements ground recycled tire particles are added to a gap-graded aggregate and then mixed with hot asphalt cement. The benefits of adding rubber to the mix include increased skid resistance under icy conditions, improved flexibility and crack resistance, elimination of solid waste, and reduced traffic noise. The major disadvantage is high cost in relation to conventional asphaltic concrete pavements.; This research project consisted of a laboratory study of mix properties as a function of variables such as rubber gradation and content, void content, aggregate gradation, mix process, temperature, and asphalt content. Twenty different mix combinations were evaluated for diametral modulus and fatigue at two different temperatures ({dollar}-{dollar}6{dollar}spcirc{dollar}C, +10{dollar}spcirc{dollar}C). Also, five different mix combinations were evaluated for static creep and permanent deformation. Layered theory was used to evaluate the effects of mixture variations on pavement life. The resulting information was used to develop guidelines for use of rubber asphalt mixes in United States road systems.; A field survey indicates that the rubber-modified asphalt mixture is more susceptible than conventional mixtures to preparation and compaction problems when adverse weather or equipment problems occur. However, with adequate equipment and favorable weather conditions, the rubber-modified asphalt mixture placement is similar to conventional mixture placement. The field study also indicates that stopping distances can be reduced 20 percent for the rubber-modified pavements in icy conditions. In view of the significant reductions in wintertime stopping distances under icy or frosty road surface conditions, the use of coarse rubber in asphalt pavements should be seriously considered. This is particularly true for areas such as bridge decks, on and off freeway ramps or insulated roadway sections.; The findings of the laboratory study indicate that the rubber gradation and content, aggregate gradation, and use of surcharge during sample preparation have considerable effect on modulus and fatigue life of the mix. The results of static creep and permanent deformation tests indicate that the rubber asphalt mixes had low stability and high elasticity. Also, due to greater allowable tensile strain in rubber-modified mixtures, the thickness of the modified mixture can be reduced, using a layer equivalency of 1.4 to 1.0. (Abstract shortened with permission of author.)... |
