Compositions: coating or plastic – Coating or plastic compositions – Bituminous material or tarry residue
Reexamination Certificate
1999-04-16
2001-04-10
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Bituminous material or tarry residue
C106S280000
Reexamination Certificate
active
06214103
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an asphalt paving mix suitable for use at ambient temperatures and, more specifically, to an asphalt paving mix formed of new aggregate, new asphalt, recycled asphalt concrete, and practically nonvolatile additive oil.
BACKGROUND OF THE INVENTION
Some asphalt mixes have been proposed in the past, which include new aggregate and new asphalt, and are suitable for paving at ambient temperatures. Typically, the new aggregate is heated, and heated new asphalt is added to produce a heated asphalt composition. Alternatively, a mixture of new aggregate and recycled aggregate, which is obtained from crushing recycled asphalt concrete, has been used, and heated asphalt is added to produce a heated asphalt composition. To these heated asphalt compositions, a suitable amount of volatile oil, such as heavy oil, light oil, or kerosene, is added to soften the asphalt, so that the resulting asphalt mix will not congeal and solidify immediately after returning to an ambient temperature.
These asphalt mixes are environmentally disadvantageous in that the volatile oil included in these mixes starts to evaporate and is emitted to ambient air immediately after the mixes are applied to form a pavement. Further, these mixes cannot harden immediately after their application at a paving site and, rather, take a considerable amount of time before achieving a desired hardness. The amount of volatile oil to be added may be reduced so as to achieve a sufficiently hard pavement surface immediately after paving. This, however, will make it impossible to store the asphalt mix for a long period since a reduced amount of volatile oil will almost entirely evaporate while in storage, thereby causing the asphalt mix to solidify.
Some other asphalt mixes have been proposed in the past, which include a special additive (chemical substance) to cause a polycondensation reaction, so as to increase the hardness of the resulting asphalt pavement after it is solidified. Production of such special additives, however, is extremely cumbersome and expensive, and the strength of the resulting asphalt pavement cannot be expected to improve substantially.
To overcome these disadvantages described above, some asphalt mixes using only recycled aggregate obtained from crushing recycled asphalt concrete have been proposed, which are also suited for application at ambient temperatures. These mixes include practically nonvolatile additive oil, such as petroleum hydrocarbons. Though this type of asphalt mix overcomes some disadvantages associated with other mixes described above, it still suffers some disadvantages.
Specifically, since recycled asphalt concrete used in this type of mix is obtained by peeling off a roadbed surface, the quality of recycled asphalt concrete tends to vary and, often, is poor. When poor quality recycled asphalt concrete is used to form an asphalt mix, the mix may not be suited to form a sufficiently strong and stable pavement. Further, recycled asphalt concrete is often excessively oxidized and becomes as stiff as a cement pavement material and, thus, may lack elasticity required to form a suitable asphalt pavement material.
A need exists for an improved asphalt mix suitable for forming and repairing a pavement at an ambient temperature, which can be stored for a long time, and is capable of achieving sufficient strength and stability immediately after its application at a paving site. Such asphalt mix preferably should also be environmentally friendly. Further, the quality of such asphalt mix preferably should not depend solely on the quality of recycled asphalt concrete, which often tends to be poor.
SUMMARY OF THE INVENTION
The present invention provides an improved asphalt mix and a process of making the same, which overcome many if not all of the disadvantages associated with the prior art asphalt mixes as described above. The asphalt mix includes new aggregate and new asphalt, which are mixed together at a high temperature so that the asphalt covers the surfaces of the new aggregate. The mix further includes recycled aggregate obtained from crushing recycled asphalt concrete at an ambient temperature to such an extent that each aggregate grain of the recycled asphalt concrete will retain some asphalt on its surface. The recycled aggregate is mixed with the new aggregate covered with the new asphalt to form an asphalt composition, lowering the overall asphalt composition temperature to, at the maximum, approximately 100° C. To the asphalt composition thus formed, additive oil is mixed to complete the asphalt mix. The additive oil has a low vapor pressure so as to be practically nonvolatile. The oil has mutual solubility with asphalt. Thus, when the asphalt composition is mixed with the additive oil, the asphalt on the surfaces of both new and recycled aggregate swells by absorbing the oil
Even after the asphalt mix is cooled to ambient temperatures, because the asphalt or the aggregate remains swollen at these temperatures, the asphalt mix does not congeal together and, thus, may be stored intact for a long time. However, when the mix is firmly compacted at ambient temperatures, the swollen asphalt on the aggregate surfaces amalgamates together to form a solid block or a pavement instantly after the compaction. As noted above, because the additive oil is practically nonvolatile, very little oil is emitted to ambient air and, thus, the asphalt mix of the present invention is environmentally friendly.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention provides an improved asphalt mix. The mi includes new aggregate including, for example, sand and crushed stones, and new asphalt. The mix also includes recycled aggregate obtained from crushing recycled asphalt concrete to such an extent that each aggregate grain of recycled asphalt concrete will retain recycled asphalt on its surface. The new aggregate and the new asphalt are heated (for example, 150°-160° C.) so that when the two are mixed together, the heated asphalt will cover the surfaces of the new aggregate.
To the new aggregate covered with the new asphalt, the recycled aggregate at an ambient temperature is mixed to form an asphalt composition, and to lower the overall asphalt composition temperature to, at the maximum, approximately 100° C. Into the asphalt composition thus formed, additive oil is mixed to complete the mix. The additive oil has a low vapor pressure, and preferably has a flashpoint higher than approximately 200° C. so as to be practically nonvolatile. The oil has mutual solubility with asphalt. Thus, when the additive oil and the asphalt composition are mixed together, the asphalt (both new and recycled) on the surfaces of the new and recycled aggregate swells by absorbing the oil. When the asphalt mix thus formed is cooled and later firmly compacted at ambient temperatures, the swollen asphalt on the aggregate surfaces amalgamates together to instantly form a stable paving surface.
Recycled aggregate is obtained from crushing recycled asphalt concrete at ambient temperatures, wherein each aggregate grain is sized sufficiently so as to retain some asphalt on its surface. Because the asphalt on these recycled aggregate is typically aged by weathering, it is typically stiffer than virgin asphalt. When a prescribed amount of the oil is added, the stiffened asphalt on recycled aggregate tends to swell easily without becoming softened excessively. It has been found that recycled aggregate grains sized to pass through a 13 mm sieve, which is a standard grain size as prescribed by the Japanese Ministry of Construction, work well in the present invention. It should be noted, though, that those skilled in the art may readily determine other recycled grain sizes that may be suitably used in accordance with the present invention. For example, to form a base asphalt concrete, recycled aggregate grains that pass through a 20 mm sieve may be preferable.
New aggregate is preheated so that, when the new aggregate and heated new asphalt (both typically at a temperature be
Brunsman David
Christensen O'Connor Johnson & Kindness PLLC
Hikarigiken Co., Ltd.
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