Compositions: coating or plastic – Coating or plastic compositions – Bituminous material or tarry residue
Reexamination Certificate
2002-08-09
2002-12-03
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Bituminous material or tarry residue
C106S272000, C404S072000, C428S367000
Reexamination Certificate
active
06488755
ABSTRACT:
The present invention generally relates to asphalt compositions are improved by the inclusion of carbon fibers, particularly short length carbon fibers produced from mesophase pitches.
BACKGROUND OF THE INVENTION
Asphalt cement, is a well known material which finds use in a number of applications, including in road surfaces, such as paved roadways as well as in the production of roofing products, particularly roofing shingles. Primary advantages of asphalt cements encouraging their use are its relatively low cost, and its waterproof characteristics. Asphalt cements are often derived obtained from the residue or bottoms from the petroleum refining industry and are primarily hydrocarbon based compositions. Typically, these residue and bottoms must be further refined or processed before they may be readily used. A common preparation process is oxidation of these residue or bottoms which advantageously raise the softening point and increase the stiffness of the asphalt cement. Modified asphalt compositions are also known, and include materials to which further additives have been added. Examples of such additives include natural or synthetic rubbers. Due to asphalt cements's poor tensile strength, inorganic or organic fibers are also know to be useful in improving the tensile strength characteristics of asphalt. For example, in roofing products mats of inorganic fibers (usually glass fibers) are used which mats are impregnated with asphalt. Other fillers, both of inorganic and organic materials are also known to be used in asphalt products. Exemplary fillers include carbon black, various fines, finely comminuted mine chatt, mine tailings, clinkers, cinders, ash, finely ground tires, clay, ground glass and beads of various inorganic or organic materials.
Asphalt cements are widely used in the formulation of paving compositions which typically contain asphalt cement, or modified asphalt cement which contains one or more performance improving additives, and an aggregate. Such are referred to as asphalt paving compositions, and are used around the globe. Notwithstanding the successful use of asphalt paving compositions in the production of roadways, certain inherent limitations in asphalt paving compositions lead to various forms of degradation which are undesired. One form of degradation, known as “rutting” relates to permanent defamation of asphalt paving compositions typically due to the passage of heavy traffic and/or frequent traffic over a stretch of roadway. Rutting is clearly visible as depressions formed at these forms at these point of contact, i.e., where tires or wheels contact the roadway. These are evident as valleys or grooves in the roadway, and the presence of such defects lead to various hazards due to the uneven payment. A second common defect in such paved roadways is thermal cracking. This type of defect is readily visible in form of horizontal cracks which extend perpendicular to the normal direction of vehicular traffic on the roadway. Such thermal cracking most commonly occurs which the roadway is subjected to very cold temperatures, i.e., typically during winter. These cracks are formed due to the thermal contraction of the paving compositions in a roadway. Such contraction imparts tensile stress within the roadway and within the paving compositions itself, and when such tensile stress exceeds the strength of the paved roadway, a crack or cracks will develop at the point of failure. A further common defect known to occur in paved roadways, typically manifests itself over a longer period of time. This defect, attributable to the age or fatiguing of the roadway, is generally visible as a serious of cracking in both horizontal and vertical directions. These cracks are typically are the result of fatigue suffered by the roadway, and particularly in the asphalt composition used to make the paved roadway. These cracks typically developed as the paving compositions ages, and the failure attributable to the many cycle of loading and unloading of the roadway which the roadway experiences during the course of normal vehicular traffic. In an attempt to counteract one or more of these technical problems known to the relevant art, various modifications to the paving compositions have been suggested. For example, the addition of organic polymers are known to the art, as well as the addition of certain fibrous materials. However, these have not always met with uniform success. Additionally, the use of these additives frequently is required in a relatively high loading before any benefits of their inclusion are realized in the asphalt paving compositions.
In the use of asphalt paving compositions, particularly reinforced asphalt paving compositions for use in the production of or repair of roadway surfaces, various paving compositions as well as the use of asphalt paving compositions in conjunction with reinforcing webs are known. Such well known reinforcement layers include glass fibers in mat form, other woven or nonwoven fibers, asphalt impregnated mats, mats of organic materials, such as polyester fibers, mats in the form of an open weave or grid, as well as plural layers of glass fibers or other reinforcement fibers. Typically, these reinforcement layers are applied to the roadway beneath or between subsequently applied asphalt paving composition layers and in such a configuration the reinforcement layer(s) operate to reinforce the asphalt paving compositions. Such reinforcement layers are often advantageously used in locations where the underlying pavement has cracked, and repairs to the roadway become have become necessary. Reinforcement layers are also know to be used over a complete roadway, such as during the original construction of a roadway, or during later repaving of a roadway.
Notwithstanding these uses and configurations of reinforcing materials with asphalt paving compositions, the process of assembling various layers making up a roadway remains a time consuming and costly process. Thus, there remains a real and continuing need in the art for improved asphalt paving compositions which can be used in the original construction of, or repaving of, or in the localized repair of a roadway, as well as methods for the manufacture of such improved asphalt paving compositions as well as their use in such construction, repaving or repair operations.
The present invention is directed to addressing these needs in the art.
In one aspect the present invention provides an improved asphalt paving compositions which can be used in the original construction of, or repaving of, or in the localized repair of a roadway.
In another aspect of the present invention there is provided a method for the manufacture of improved asphalt paving compositions which can be used in the original construction of, or repaving of, or in the localized repair of a roadway.
In a further aspect, the present invention provides a methods for the original construction of, or repaving of, or in the localized repair of a roadway utilizing an improved asphalt composition.
DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
The present invention provides an improved asphalt paving compositions which can be used in the original construction of, or repaving of, or in the localized repair of a roadway.
According to the present invention, the present inventors have found that the inclusion of relatively short lengths of coated mesophase carbon fibers when included in an asphalt cement composition, and particularly when included in an asphalt paving compositions which includes an asphalt cement composition and which further includes an aggregate, provides a surprising improvement in many of the physical properties of the resultant asphalt paving compositions. These benefits and improvements have been observed even where the amount of the coated mesophase carbon fiber have been included in what would be considered generally minor amounts.
The asphalt paving compositions which are substantially improved by the inclusion of the mesophase carbon fibers are typically those which find present use the
Harris Stephen D.
Meyers Jeff D.
Seyler Paul E.
Sudbury John Byron
Brunsman David
Conoco Inc.
Fish & Richardson
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