Road structure – process – or apparatus – Apparatus – With means for heating a road base – surface – or material
Reexamination Certificate
1998-09-03
2001-05-08
Lillis, Eileen D. (Department: 3673)
Road structure, process, or apparatus
Apparatus
With means for heating a road base, surface, or material
C404S079000, C404S077000
Reexamination Certificate
active
06227762
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of asphalt paving and, in particular, to an apparatus and method for increasing the durability of asphalt paving joints.
BACKGROUND OF THE INVENTION
Over the past thirty years, asphalt has replaced concrete as the material of choice for paving roadways. Asphalt provides a smooth road surface that is easier to apply and easier to resurface than concrete. However, asphalt pavers generally cannot pave an entire road surface in a single pass and therefore joints must be formed between the previously placed asphalt and the newly placed asphalt being placed by the paver. It is at these joints that asphalt is most susceptible to failure as the “cold”, previously placed, asphalt is not sufficiently heated by the hot asphalt from the paver to form a homogenous bond at the joint. These non-homogenous “cold joints” often will separate and create cracks, most usually in the center of two lane roads, which allows water to enter the pavement, migrate to the road base and, over a period of time, contribute substantially to base failure of the road.
To overcome this problem, the previously placed pavement joint, must be heated to approximately the same temperature as the new material that is being placed to provide the proper environment for thermal bonding. However, the chemical properties of asphalt make this a difficult task. First, asphalt is a petroleum based product and has a tendency to burn if overheated. Second, the mass and thermal conductivity of asphalt necessitate heating the asphalt for a significant period of time to raise the temperature of the entire asphalt layer to the desired bonding temperature. The combination of these properties makes traditional heating by propane torch, either hand-held or paver-mounted, an ineffective and dangerous exercise.
When paver-mounted heaters are used to preheat the asphalt, the temperature of the burning propane raises the temperature of the top layer of asphalt to its burning temperature well before the remainder of the asphalt layer has reached its desired bonding temperature. Thus, to avoid igniting the top of the asphalt layer, the paver must move before the entire layer is sufficiently heated, bonding the new hot asphalt to “warm” asphalt. This increases the adhesion somewhat, but does not provide the durability of a true “hot joint”. When hand held heaters are used, the heat to the pavement may be cycled to allow proper heating of the entire layer. However, the risk of fire increases with this approach as the exposure of the heater to the pavement is controlled by the operator. In addition, the use of hand held heaters requires additional manpower and slows the paving process.
A method or apparatus for joining a newly paced layer of asphalt to a previously placed layer of asphalt that creates a durable and substantially homogenous “hot joint”, that does not create a risk of fire, that does not require additional manpower, and that allows asphalt to be placed in a substantially continuous process, is not known in the art.
SUMMARY OF THE INVENTION
The present invention is method of preparing an asphalt edge for joining and a two part joint heating system for use in carrying out the method. In it most basic form, the method of the present invention includes the steps of placing a first layer of asphalt in a roadway and allowing the first layer of asphalt to cool to a temperature below a predetermined minimum bonding temperature. The surface of the joining area of the first layer is then preheated to a temperature above the minimum bonding temperature but below the ignition temperature of the asphalt. The remainder of the joining area of the first layer is then allowed to absorb the heat from the surface. After a predetermined period of time is allowed for absorption of heat, the surface of the joining area of the first layer of asphalt is again heated to a temperature below the ignition temperature of the asphalt and the second layer of asphalt is placed adjacent to the first layer such that a joint is formed between the first layer and the second layer. In the preferred method, the first layer of asphalt is maintained between a minimum bonding temperature of 275° Fahrenheit and below a danger temperature of 325° Fahrenheit. The preferred method also includes the step of scarifying a portion of the first layer after the heating step and before the second layer of asphalt is placed adjacent to the first layer.
The preferred heating system includes one twelve foot infrared heater attached to the side of the paver and a mobile pre-heater “train” composed of several twelve foot infrared joint heating units pulled by a motorized vehicle equipped with hydrostatic transmission to precede the paver and to travel at the same rate of speed as the paver. By assembling the proper number of pre-heater units to accommodate the speed of the paver, ambient temperature, and weather conditions, the proper heat penetration can be assured; with two to three preheat units being sufficient for most paving conditions. It is also preferred that both the mobile pre-heater and the paver-mounted heater include sensors for controlling the burners to eliminate the possibility of damage to the pavement if the paver stops or slows down.
In some embodiments of the system, a small rake is attached to the rear of the paver mounted heater, but still located beneath the infrared heater and is adjusted to scarify the joint to a depth of one half inch. This provides a clean joint free of foreign matter and acts to disperse any surface glaze that may develop when heating the joint. In these embodiments, it is important that the rake is maintained at a temperature equal to or greater than the asphalt to prevent the asphalt from sticking to the rake.
Therefore, it is an aspect of the invention to provide a system by which asphalt pavement can be placed in such a way that cold joints can be avoided.
It is a further aspect of the invention to provide a system to heat pavement joints at the time of placing adjacent and abutting sections of pavement.
It is a further aspect of the invention to provide a heating system that will penetrate to a depth sufficient to achieve proper and permanent bonding to an adjacent course of asphalt pavement.
It is a further aspect of the invention to provide a heating system for heating cold joints that will not burn or damage the asphalt pavement.
It is a further aspect of the invention to provide a means of cleaning (scarifying) the edge of previously placed pavement to assure better bonding.
It is a further aspect of the invention to provide a heating system which will supply adequate heat penetration to increase compaction at joint.
It is a further aspect of the invention to provide a system that will heat properly at any paving speed.
It is a further aspect of the invention to provide a joint heater that will be automatically controlled to eliminate human error and not be a burden to the paver operator.
It is a further aspect of the invention to provide a system that is fuel efficient.
It is a further aspect of the invention to provide a system that is easy to work on with little maintenance involved.
It is a still further aspect of the invention to provide pre-heater units that are easy to transport from job to job.
These aspects of the invention are not meant to be exclusive and other features, aspects, and advantages of the present invention will be readily apparent to those of ordinary skill in the art when read in conjunction with the following description, appended claims and accompanying drawings.
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Addie Raymond W
Lawson, Philpot & Persson
Lillis Eileen D.
Persson Michael J.
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