Compositions: coating or plastic – Coating or plastic compositions – Natural resin or derivative containing
Reexamination Certificate
2002-05-16
2004-08-03
Klemanski, Helene (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Natural resin or derivative containing
C106S316000, C106S273100
Reexamination Certificate
active
06770127
ABSTRACT:
TECHNICAL FIELD
The present invention relates to asphalt cement compositions for use in paving and roofing products and more particularly to powder additive compositions that can be added to asphalt cements to impart multigrade properties thereto.
BACKGROUND ART
Asphalt compositions are used in over 90 percent of the pavement surface applications in the United States. Natural asphalts obtained from lakebeds were utilized as early as 1874. Years later, rock asphalt deposits found in several southern and western states were pulverized, placed and rolled to form pavement surfaces. Since the early 1900's, asphalts produced during the process of refining petroleum have dominated both paving and roofing applications.
Asphalt is a dark brown to black, highly viscous material containing bitumens as the principle constituent and is found in varying proportions in most crude petroleums. The asphaltic residuum from petroleum refining, substantially freed of lighter overhead fractions, is commonly called “asphalt.” Paving asphalts are classified as asphalt cement, cutback asphalt and asphalt emulsions.
Asphalt cement is an asphalt having properties that are particularly suitable for pavement surface and roofing applications and specialty products. For road construction, asphalt is heated to a free flowing consistency and mixed with an aggregate heated to approximately the same temperature (usually 135° C. to 160° C.). The resulting mixture is placed on a prepared surface, compacted and cured to produce hot mix asphalt (HMA). In the long history of asphalt paving, the hot mix process of mixing asphalt cement and aggregate has remained the process of choice as offering the most favorable balance of cost and quality.
Asphalt cements used in paving applications today are graded according to stiffness at different temperatures before and after aging. The most common grading system in the United States is based on specifications from the Association of American Highway and Transportation Officials (AASHTO).
Superpave (superior performing pavements) refers to pavements that are made by a method of construction developed in the United States through research funded by AASHTO. Grading is based on high and low temperature stiffness of the asphalt binder under Superpave performance graded (PG) binder specification. A PG graded binder PG 64-22 would have a stiffness modulus of at least 1 Kilo Pascal (kPa) at 64° C. This asphalt after short term and long term aging would also have a limiting stiffness of less than 300,000 kPa at −22° C. over a 2 hour time period. The low temperature stiffness gives equivalent values at −12° C. (10° C. warmer) over 2 minutes and is the method used by AASHTO. Adding the two temperatures together for a given PG grade gives the temperature range over which the asphalt performs. For PG 64-22 the temperature spread would be 86° C. This temperature spread is typical of a high quality unmodified paving asphalt cement. The PG grading system from AASHTO increases and decreases in grade in 6° C. increments. To produce a PG 70-22 grade which would be the next high temperature grade in the specification without reducing the low temperature to −16° C. is difficult with unmodified asphalt. Only a few asphalts can achieve the 92° C. spread without modification. In order to increase spread most asphalt cement manufacturers have resorted to adding modifiers. Modification can be done by a number of methods including addition of polymers or chemicals.
Outside of the United States asphalts are generally graded by other methods such as penetration or viscosity. Penetration involves dropping a needle with 100 grams of mass into the asphalt cement at 25° C. A soft asphalt will allow the needle to penetrate more deeply into the asphalt cement. Asphalts used in colder climates use softer grades and in warmer climates harder asphalts are used to avoid rutting of the pavement. Another grading system that is used is grading by viscosity. Asphalts cements are graded at 60° C. using viscosity and at 25° C. using penetration to characterize the asphalt at two temperatures. Roofing asphalts used in Build Up Roofs (BUR's) for flat or sloped roofs are graded by penetration and softening point under the ASTM Method D312 international specification. Softening point is the temperature at which the asphalt first begins to soften and is an indication of flow temperature in roofs and some paving specifications. Generally asphalts with softer penetration and higher softening points would be considered as having a broader temperature range analogous to PG grades with broader temperature ranges of 92° C. or greater, and again would contain modifiers to improve the temperature range for the asphalt to perform within.
Asphalt cements for paving applications must be selected with care based on the traffic loading, speed, and climate to which the pavement will be exposed. High traffic loading, low traffic speed and wide climate ranges require asphalts that have broad temperature requirements. The asphalt must have sufficient stiffness to resist flowing during excessive hot weather with slow moving trucks. It also must not crack on the coldest days of the year especially after many years of service. Pavements in more moderate climates with little traffic require much less of a temperature range and unmodified asphalts have shown historic performance in such applications.
In roofing asphalt, the roof location (climate) and slope of the roof are important considerations. Again, the asphalt must not soften too much on the hottest day of the year and cause the roof to slide or flow due to the slope of the roof. Minimum softening points have been found to be a good measure to assure against this happening. This is analogous to high temperature stiffness measurements in paving asphalts.
To avoid low temperature cracking in penetration graded asphalt cements, the material is evaluated for penetration at 25° C. and 4° C. with minimum values to insure that the asphalt does not reach its limiting stiffness of 300,000 kPa used in performance graded paving asphalt testing.
U.S. Pat. No. 4,874,432, assigned to Asphalt Materials, Inc. was developed to produce a “multigrade” or gelled asphalt cement having improved properties over conventional asphalt cements, including reduced temperature susceptibility and a lower age hardening rate. These improved properties were achieved using conventional hot-mix asphalt processes in existing hot-mix equipment, standard roofing application equipment and specialty asphalt application equipment.
The term multigrade asphalt was adopted by the assignee of U.S. Pat. No. 4,874,432 to describe a novel gelled asphalt cement having reduced temperature susceptibility and improved age hardening properties as compared to conventional asphalt cement. These improvements were accomplished by saponifying in the liquid asphalt, substantially free of water, at least one saponifiable organic acid and at least one resin acid with an alkali metal base, or by adding the already saponified product to the liquefied asphalt. The resulting gelled asphalt can be utilized in conventional processes in road, roofing and specialty applications.
Conventional asphalt cements have the Theological properties of viscous liquids when used at elevated temperatures in hot-mix processes. The asphalt remains a flowable liquid in accordance with its particular viscosity-temperature relationship, throughout its incorporation with aggregate and its laydown as an asphaltic concrete. In this physical state the asphalt is susceptible to flowing off the aggregate, depending on factors such as temperature, nature and surface area of the aggregate and the size and configuration of voids.
The inventors of U.S. Pat. No. 4,874,432 discovered that asphalt could be gelled by a direct saponification reaction requiring only a trace amount of an ionizing liquid to form an ionizing zone within the liquified asphalt where the saponification reaction can begin. Water produced as the reaction proceeds is sufficient to sustai
Kriech Anthony J.
Liu Xuefeng
Wissel Herbert L.
Xu Feng
Zhou Haifang
Baker & Daniels
Klemanski Helene
Shandong Heritage Highway Materials Technologies
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