1. Field of the Invention
This invention relates to a process for absorbing refinery fractions for modified asphalt.
2. Description of the Related Art
Reclaimed asphalt pavement, “RAP”, has been used as an aggregate in hot recycling of asphalt paving mixtures. A common method is to combine RAP with virgin asphalt and aggregate in either a continuous plant (Drum) or batch (Pug Mill) central mixing plant(s) producing new pavement mixtures. In the United States these combined mixtures are generally restricted to a maximum content of about 50%, more commonly from 10% to about 25% of “RAP” due to a decrease in pavement performance as the RAP content is increased. Specifications for asphalt vary state to state, but the most common area of use is the base course of paving construction. General restrictions in this method relate to the milled size of the “RAP” and the ability to generate appropriate heat into the mixtures. Batch (“Pug Mill”) mixing systems tend to be better able to introduce heat and to control this factor than the continuous (Drum) mixing systems. Because of the high temperatures required to recycle high percentages of RAP materials into pavements, gaseous hydrocarbon emissions are also a limiting factor.
Hot in-place recycling “HIPR”, only used on a limited basis as set out below, involves the removal, rejuvenation, and replacement of the top 1-inch (25 mm) of the pavement. Remixing involves the use of some new aggregate as well as additional virgin asphalt binder combined in a Pug Mill, allowing for the placement of up to two inches of surface pavement. Three basic processes are recognized by the Asphalt Recycling and Reclaiming Association, “ARRA”: 1. heater-scarification (multiple pass), 2. repaving (single pass), and 3. remixing. The primary advantage of in-place recycling is cost savings. Stockpiling RAP is not necessary so there is no need to transport large quantities of milled old pavement. The quantity of new materials is also substantially reduced. The general description of rejuvenation agents, or new material, is described as follows: 1. Paraffinic fractions 2. Napthenic fractions (aromatic). 3. “Super Soft” asphalts. These rejuvenation products consist of organic compounds produced as extracts during the crude oil refining process.
Several technical difficulties are posed when attempting to recycle “RAP” into performance pavements and high percentage road base mixtures. These issues include a high energy required to heat the “RAP” into a useful temperature, “VOC” emissions due to high temperatures, the loss of binder properties in the asphalt due to high levels of oxidation, chemical compatibility with virgin asphalt binders, and improper aggregate size with the newly-specified mix designs. The most significant problem is establishing high percentage “RAP” mixtures which exhibit excellent properties of adhesion, cohesion and compaction.
Today's high price of crude oil has created very aggressive refining practices. This has led to the asphalt, the last fraction of the refining process, being reduced in quality. Oil companies replenish these asphalts to meet current specifications by adding percentages of aromatic, paraffinic and napthenic fractions as well as various polymers. These additions allow the virgin asphalt binder to meet the temperature failure points required by various states' current pavement construction performance grade, “PG”, specifications. Another problem faced in the prior art is the common polymer employed for asphalt modification is Styrene-Butadiene-Styrene, “SBS”. Aggressive refining practices, diverting butadiene streams into gasoline production as one example, has led to first-time worldwide shortage of “SBS”. See “SBS Polymer Supply Outlook” by Romugasa, et al, a publication of The Association of Modified Asphalt Products, describing a wet process (highlight 3, last page of article) as the response to the shortage, unlike the method of the present invention (while this article is not prior art, it does show the thinking of those skilled in the art as of August 2008.) This is providing difficulties both for the roofing and paving industries in producing quality electrometrically-modified products.
Beside the polymer discussed above, which is old in the arts, another method of modifying virgin asphalt binder is to blend ground scrap tire rubber (Crumb Rubber) with the asphalt. The Federal Highway Administration, “FHWA”, uses the terminology “CRM”, crumb rubber modifier for this application. The most common method is to blend rubber from 15%-22%, by weight of the asphalt, with the asphalt binder. These formulations are generally done as a recipe rather than as the more common performance specifications used by most states. The process is commonly referred to as the “Arizona Wet Process” and involves blending the crumb rubber at temperatures from 375° F. to 425° F. with the virgin asphalt binder until a stable viscosity is achieved. Variations of this process have been in use since the late 1960s. Vestamer® thermoplastic binder has been used in “Dry Blend” applications with CRM where the crumb rubber and Vestamer® are combined and added to the pavement mixture after the aggregate and asphalt binder have been mixed. U.S. Pat. No. 6,346,561 discloses a combination of tall oil fractions, crumb rubber and gilsonite to produce a mixture suitable to modify the temperature performance of asphalt binder in either “wet” or “dry” applications. None of the above-mentioned CRM-derived modifiers demonstrate or anticipate any ability to aid in the recycling of asphalt pavement. CRM modifiers typically consist of approximately 30% rubber hydrocarbon and approximately 70% filler agents such as, but not limited to, various clays, carbon black, and processing aides used in the tire manufacturing process. As a result of these filler agents. CRM-modified dense grade pavement mixes tend to avoid fatigue cracking by compensating with increased asphalt binder in these mixes.
It is well-known in the art to use tall oil with ground rubber waste for re-use 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 at, 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”.