Showing papers on "Rubberized asphalt published in 1992"

Advances in technology of asphalt paving materials containing used tire rubber

Abstract: The blending of crumb rubber with asphalt cement has been in practice for years and a number of manufacturing processes have been developed in Europe as well as in the United States. However, all these processes have a major drawback: the asphalt rubber binder must be used within a few hours after being manufactured. In 1987, Beugnet, a road contractor in France, designed a new rubberized asphalt formula. This new formula improved rheological properties of the asphalt rubber binder, including increasing the shelf life of the binder for up to 8 days. Therefore, this new asphalt rubber binder could be used just like conventional asphalts or polymer-modified asphalts. The dry system of rubber-modified asphalt concrete has historically been limited to only a patented process. Major drawbacks of this system include the addition of crumb rubber to a unique "gap-graded" aggregate gradation, and nonconventional design criteria. These factors contribute to the high cost of using the material when compared with conventional asphalt concrete. The dry system of rubber-modified asphalt concrete has also experienced a major advance. A rubber-modified asphalt concrete system has been developed by H. Barry Takallou. This system relates to a process for producing an asphalt concrete composition made up of coarse crumb rubber and fine crumb rubber incorporated into a standard dense-graded aggregate mixture. This process is characterized by the various constituents of the asphaltic binder and fine crumb rubber, mixed intimately by a physical reaction. This will result in a higher viscosity binder in which the optimum reaction is achieved when the fine crumb rubber particles reach optimum swelling. A pre-reaction or pre-treatment of crumb rubber with a catalyst may be needed to achieve the optimum crumb rubber particle swelling. This system can be designed using conventional testing procedures and complies with conventional design criteria. The use of this system is in the public domain.

Permanent deformation characteristics of recycled tire rubber-modified and unmodified asphalt concrete mixtures

Abstract: In recent years, modified asphalt mixtures have become increasingly popular in the construction of flexible pavements. These products have gained popularity because of their ability to increase resistance to rutting at warm temperatures while reducing the occurrence of thermal cracking at cold temperatures. This, coupled with the growing problem of waste rubber tires, has led to the reprocessing (grounding) of tire rubber for use in asphalt concrete mixtures. In order to investigate the warm temperature rutting hypothesis, a laboratory research program using both static and repeated load permanent deformation tests, carried out at two temperatures (77 deg F and 104 deg F), was designed to assess the potential benefits of rubberized asphalt concrete mixtures. Conclusions from this research indicated that the addition of ground tire rubber to asphalt concrete mixtures results in mixtures that exhibit less permanent deformation at high temperatures compared with unmodified mixtures. The research also indicated that permanent deformation testing should be carried out at high temperatures under repeated loading. The relative ranking of strain changes from 77 deg F to 104 deg F for both methods of testing and static testing indicates the presence of rubber; however, it does not indicate anything about the base asphalt. The repeated load testing indicates, in a reliable way, the differences that exist between binders.

Evaluation of western shale-oil residue as an additive to petroleum asphalt for use as a pavement crack and joint sealant material.

Abstract: The objective of this study was to perform a preliminary evaluation of using a distillation residue from Green River Formation (western) shale oil as an additive to a petroleum asphalt for use as a crack and joint filler material in portland cement concrete and asphaltic pavements. A commercially available rubberized asphalt crack and joint filler material was also tested for comparison. ASTM specification tests for sealant materials used in concrete and asphalt pavements were performed on the sealant materials. Portland cement concrete briquets prepared with an asphalt material sandwiched between two concrete wafers were tested in a stress-relaxation experiment to evaluate the relaxation and recovery properties of the sealant materials. The results show that the shale-oil modified petroleum asphalts and the neat petroleum asphalt do not pass the extension portion of the ASTM test; however, there is indication of improvement in the adhesive properties of the shale-oil modified asphalts. There is also evidence that the addition of shale-oil residue to the petroleum asphalt, especially at the 20% level, improves the relaxation and recovery properties compared with the petroleum asphalt.