Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-07-27
2002-02-12
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C521S040500, C521S041000, C521S043000, C521S043500, C521S044000, C524S064000, C524S066000, C524S068000, C524S071000, C524S270000, C524S274000, C524S313000, C524S322000
Reexamination Certificate
active
06346561
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the utilization of a post vulcanized rubber crumb combined with asphaltites to modify the physical performance of asphalt. More particularly, the invention relates to additives to the rubber crumb and asphaltite combination.
2. Description of the Prior Art
The utilization of post vulcanized rubber crumb, derived from the processing of scrap automobile and truck tires, to modify asphalt pavements has been common for a number of years. The general terminology used by the Federal Highway Administration, “FHWA”, for crumb rubber modifiers is “CRM.” Crumb rubber differs from other elastomers or polymers, used to modify asphalt, in that crumb rubber is vulcanized or crosslinked (the process forms irreversible chemical bonds) prior to use. “CRM” is incorporated into asphalt pavements by either a wet or dry process.
The “wet” process combines the rubber crumb with the asphalt binder under heat and agitation until reacted or digested and dispersed, prior to the addition of aggregates. The “dry” process typically specifies a high Natural Rubber, “NR,” content in the crumb rubber which often eliminates scrap automobile tires from use. Of the two processes the “wet” method is in wider use.
The “dry” process has produced pavements that tend to ravel and seems to have lost favor with highway engineers. The “wet” process is dependent on a heat induced reaction (digestion) of the crumb rubber into the asphalt. The crumb rubber particle surface area, grade of asphalt, temperature, and even rubber particle dispersion effect the distinct characteristics of resultant “CRM” pavement.
The “wet” process can be divided into two prevalent methods. The “Arizona Design” using a 10-mesh and smaller rubber particle normally of high “NR” content, which has been ambiently processed. The “Arizona Design” batch blends the crumb rubber with asphalt, at 375-425° F., until a gel of required viscosity is formed (typically one hour). The gel has a pot life determined by a lessening of viscosity as the rubber particles decompose.
The newer “wet” method is the “UltraFine Florida” process which uses 80 mesh and smaller rubber particles of high “NR” content, typically processed by wet grinding. The “UltraFine” process tends to use lesser content of crumb rubber and may be blended at the asphalt terminal.
The purpose of adding crumb rubber to asphalt in pavement applications is to enhance the asphalt binder's elastomeric properties thereby improving resistance to stress cracking, thermal cracking, reflective cracking, rutting and general pavement durability. In general “CRM” pavements have performed poorly in pavement stability and have required a higher asphalt binder content. Even though use is motivated by political mandates, “ISTEA” public law (102-240) Dec. 18, 1991, “CRM” pavements have had limited industry success. This lack of success relates directly to cost, performance and difficulty of use.
Gilsonite (unintaite), Glance Pitch and Grahamite are natural occurring hydrocarbon substances characterized by a high softening point (above 110° C.) in the class known as asphaltites. They are mined much like other minerals and sold essentially in their native state. They are fully compatible with asphalt and have long been known as asphalt hardeners and reinforcing agents. Gilsonite is currently sold all over the world as an asphalt modifier in the form of a dry bulk solid granular powder.
Gilsonite's benefits to asphalt pavements include increased stability, resistance to deformations problems such as rutting and shoving, resistance to water striping and increased load bearing ability. Gilsonite functions by making the pavements harder, stronger and increases asphalt's adhesion to aggregates. It is generally regarded that Gilsonite reduces pavements' low temperature properties making them susceptible to thermal cracking.
Gilsonite melted into hot asphalt will reduce penetration and increase viscosity of the asphalt binder. Gilsonite may also be mixed with aggregate prior to combining with the asphalt binder. Gilsonite modified asphalt pavements have been particularly successfully in highly stressed traffic areas. Gilsonite, as the majority constituent, has been combined with virgin polymers such as styrene-butadiene-styrene (SBS) and Ethyl Vinyl Acetate (EVA). Gilsonite modified asphalt binders generally do not increase asphalt binder content requirement in pavement mixtures.
Performance grading of asphalt binders and pavement mixtures became a reality with the conclusion of the, “FHWA” 50 million dollar, Strategic Highway Research Program, “SHRP”, in March of 1993. “SHRP” developed new asphalt binder specifications and test criteria based on the engineering properties related to pavement performance. The new emphasis is on low temperature performance of aged binder materials. Low temperature flexibility of aged asphalt binders became significant. Performance Grade “PG,” asphalt is based on the predicted temperature performance both high and low of asphalt binders. Neither Gilsonite nor post vulcanized crumb rubber have performed well under “SHRP” evaluations. “SHRP” specifications will cause increased demand for modified asphalt as state departments of transportation adopt the “PG” specifications.
It is well-known in the art to use tall oil with ground rubber waste for reuse as rubber. See “Ground Rubber Waste—A Supplementary Raw Material for the Rubber Industry” issued by Kahl & Co.; U.S. Pat. No. 4,481,335, issued Nov. 6, 1984 to Stark, Jr. entitled “Rubber Composition and Method”; U.S. Pat. No. 3,873,482, issued Mar. 25, 1975 to Severson et al, entitled “Pyrolyzed Tall Oil Products as Synthetic Rubber Tackifiers”; U.S. Pat. No. 4,895,911, issued Jan. 23, 1990 to Mowdood et al, entitled “Tall Oil Fatty Acid Mixture in Rubber”; U.S. Pat. No. 4,792,589, issued Dec. 20, 1988 to Colvin et al, entitled “Rubber Vulcanization Agents of Sulfur and Olefin”; and U.S. Pat. No. 4,244,841, issued Jan. 13, 1981 to Frankland, entitled “Method for Recycling Rubber and Recycled Rubber Product”. Generally for the area of ground polymer elastomer operation, see U.S. Pat. No. 4,771,110, issued Sep. 13, 1988 to Bouman et al, entitled “Polymeric Materials Having Controlled Physical Properties and Purposes for Obtaining These”; and for rubber discussions see U.S. Pat. No. 3,544,492, issued Dec. 1, 1970, to Taylor et al, entitled “Sulfur Containing Curing Agents”; and “Organic Chemistry” by Fieser and Fieser printed 1944 by D.C. Heath & Co. Boston, pages 346 and 347. See also U.S. Pat. No. 2,082,607, issued Sep. 1, 1936 to Cowdery, entitled “Rubber Compounding Material and Method of Using” and U.S. Pat. No. 2,133,690, issued Oct. 13, 1938 to Epstein, entitled “Rubber and Method of Making the Same”.
SUMMARY OF THE INVENTION
The present invention is a recipe and method for combining Gilsonite or other asphaltites with post vulcanized (cured) elastomers which have been further processed by ambient or cryogenic or wet grinding into powder or granules. The resulting mixture is designed to modify the physical performance characteristics of asphalt or bitumen (technically “bitumen” is used to denominate raw material heavy portions of crude oil, but in the Gilsonite industry “asphalt” and “bitumen” are used interchangeably) used in industrial, consumer and road pavement applications. The invention further discloses the recipe and method to create a Dry Liquid Concentrate, “DLC” comprised of post vulcanized (cured) elastomers processed by ambient or cryogenic grinding into powder or granules and tall oil, tall oil heads, tall oil pitches, residues of tall oil production and other fatty acids which enhances the post vulcanized rubber powder or granules effectiveness in the invention.
The preferred asphaltites are characterized by their high softening points above 110° C. and include Gilsonite (uintaite), Glance Pitch and Grahamite.
Post vulcanized crosslinked elastomer(s) which have been further processed by ambient or cryogenic or wet grind
Ostfeld David M.
Szekely Peter
Texas Encore Materials, Inc.
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