Compositions: coating or plastic – Coating or plastic compositions – Bituminous material or tarry residue
Reexamination Certificate
2001-11-14
2004-02-24
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Bituminous material or tarry residue
C106S405000, C106S464000, C106S465000, C106S472000, C106SDIG001
Reexamination Certificate
active
06695902
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to fillers for asphalt composites such as roofing shingles, and more particularly relates to fly ash filler and filler blends for use in asphalt compositions and to methods for selecting or modifying a fly ash filler or filler blend for use in asphalt composites.
BACKGROUND OF THE INVENTION
Asphalt shingle manufacturing plants typically utilize a mineral filler, or extender, both to impart desired mechanical properties to the shingles and to reduce raw material costs. The mineral filler typically used for this purpose is a fine particulate inorganic material, commonly produced from ground limestone or calcium carbonate, and is typically used at filler loadings of 60-65% by weight of the asphalt composite. The principal role of the filler in this application is to extend the more costly asphalt to improve the economics of the process, while at the same time stabilizing and stiffening the asphalt matrix to improve its resistance to extreme heat and weathering.
As an alternative to calcium carbonate, U.S. Pat. No. 5,565,239 to Pike entitled “Method of Making Asphaltic Roofing Material Containing Class F Fly Ash Filler” describes the use of Class F fly ash as a filler for asphalt roofing materials. The patent discusses a number of disadvantages associated with using calcium carbonate and a number of advantages associated with using fly ash as a filler in asphalt shingles. Although some Class F fly ashes could be used as fillers for asphalt shingles, many fly ashes that meet Class F specifications cannot be used with asphalt at loadings of 60-65% by weight to produce a composite that meets industry standards. Therefore, there is a need in the art to better determine what fly ashes can indeed be used as fillers with asphalt shingles. Furthermore, there is a need in the art to increase the filler loadings for asphalt shingles to increase the mechanical properties of the shingles such as the pliability, tensile strength and tear strength and to decrease cost.
SUMMARY OF THE INVENTION
The present invention provides a method for determining what fly ashes can be used as fillers for asphalt composites such as roofing shingles. In addition, the invention provides a fly ash filler or filler blend that can used in amounts of greater than 45% by volume and 70% by weight to increase mechanical properties of the asphalt composites such as pliability, tensile strength and tear strength while reducing the cost to produce the asphalt composites.
In accordance with the invention, the inventors have discovered that the granulometry of the fly ash used as a filler or in filler blends for asphalt composites such as roofing shingles is important to the rheological performance of the filled asphalt in the production of the asphalt composites and to the mechanical properties of the resulting asphalt composites. In one embodiment, the asphalt composite includes asphalt and a filler, the filler comprising a blend of fly ash and at least one other filler wherein the filler blend has a particle size distribution having at least three modes and typically having three modes. Preferably, the particle size distribution includes a first mode having a median particle diameter from 0.3 to 1.0 microns, a second mode having a median particle diameter from 10 to 25 microns, and a third mode having a median particle diameter from 40 to 80 microns. The particle size distribution also preferably includes 11-17% of the particles by volume in the first mode, 56-74% of the particles by volume in the second mode, and 12-31% of the particles by volume in the third mode. Moreover, the ratio of the volume of particles in the second and third modes to the volume of particles in the first mode is preferably from about 4.5 to about 7.5. The fly ash can, for example, be a lignite coal fly ash or a subbituminous coal fly ash. The fly ash can also have a carbon content of from 1% to 5% by weight. In one preferred embodiment, the at least one additional filler in the filler blend is a second fly ash. For this embodiment, the filler blend preferably comprises a high fine particle content fly ash filler (e.g. having a median particle size of 10 microns or less) and a low fine particle content fly ash filler (e.g. having a median particle size of 20 microns or greater). Alternatively, the at least one additional filler in the filler blend can be a calcium carbonate filler. In this particular embodiment, the fly ash is preferably a high fine content fly ash. The filler blend can include from about 10% to about 90% by weight of the fly ash filler and from about 90% to about 10% by weight of the calcium carbonate filler. The filler blend preferably has a packing factor of at least 65% and can be loaded in the asphalt composite at a filler loading of greater than 45% by volume or at a filler loading of greater than 70% by weight. The present invention further includes a filler for asphalt composites comprising fly ash and at least one additional filler and having the properties discussed above.
The present invention also includes a method for producing an asphalt composite, comprising combining asphalt with a fly ash and at least one additional filler such that the fly ash and the at least one additional filler together produce a filler blend having a particle size distribution with at least three modes and producing an asphalt composite with the resulting filled asphalt. Preferably, the method includes the step of blending the fly ash and the at least one additional filler together to produce a filler blend prior to the combining step. Alternatively, a fly ash blend formed by burning two or more types of coal selected from the group consisting of lignite coal, subbituminous coal and bituminous coal can be used to form the asphalt composite. The filler blends can include the fillers and the filler properties described in the previous paragraph. Preferably, the fly ash and the at least one additional filler can be combined with the asphalt to produce a viscosity of 6000 centipoise (cps) or less at 400° F. when the fly ash filler is present in an amount of at least 45% by volume, at least 65% by weight, or even at least 70% by weight. The asphalt, fly ash and the at least one additional filler can also be combined with carbon to produce the asphalt composite. The fly ash used in the filler blend can be air classified to produce the fly ash filler for use in the filler blend. For example, a high fine particle content fly ash or a high coarse particle content fly ash can be air classified for use in the filler blend.
In another embodiment of the invention, the present invention comprises an asphalt composite comprising asphalt and a subbituminous coal fly ash filler, wherein the subbituminous coal fly ash filler has a particle size distribution having at least three modes and typically includes three modes. Preferably, the particle size distribution includes a first mode having a median particle diameter from 0.3 to 1.0 microns, a second mode having a median particle diameter from 10 to 25 microns, and a third mode having a median particle diameter from 40 to 80 microns. The particle size distribution also preferably includes 11-17% of the particles by volume in the first mode, 56-74% of the particles by volume in the second mode, and 12-31% of the particles by volume in the third mode. Moreover, the ratio of the volume of particles in the second and third modes to the volume of particles in the first mode is preferably from about 4.5 to about 7.5. The fly ash filler preferably has a packing factor of at least 65% and can be loaded in the asphalt composite at a filler loading of greater than 45% by volume or at a filler loading of greater than 70% by weight. Moreover, the subbituminous coal fly ash is typically a Class C fly ash. The present invention further includes a subbituminous coal fly ash filler for asphalt composites having the properties discussed above.
The present invention also includes a method for producing an asphalt composite, comprising the steps of combining asph
Cornelius Bruce J.
Hemmings Raymond T.
Hill Russell L.
McBay Aron
Boral Material Technologies Inc.
Brunsman David
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