The prior art describes various processes for heating asphalt surfaces. A process for continuously heating an asphalt surface is described in Wiley et al., U.S. Pat. No. 5,653,552. The process involves moving at least two independent heaters arranged in a series back and forth along the asphalt surface until the asphalt is heated to the desired temperature. In addition, the process may involve rupturing the heated asphalt to establish a ruptured upper surface. After moisture is eliminated through mixing of the ruptured upper surface, the surface is pressed to provide a recycled asphalt surface.
U.S. Pat. No. 5,218,952 to Neufeldt describes a radiant heating apparatus used to heat a large surface area of asphalt to a desired temperature. The heating apparatus uses a pressurized gaseous fuel, such as propane, to generate heat and has an open bottom, covered with a layer of ceramic fiber between two layers of mesh and an upper chamber.
O'Brien, U.S. Pat. No. 5,188,481, discloses an asphalt heating unit which heats already existing asphalt surfaces. The heating unit rests on a movable frame which allows rotation of the heating unit to several positions. One embodiment of the invention substitutes a trailer for the movable frame. In addition, the heating unit may use various forms of heating sources in its heating chamber, such as an infrared heater.
U.S. Pat. No. 5,114,284 to Keizer et al. is a continuation of U.S. Pat. No. 4,749,303 to Keizer et al. The applications disclose a hinged asphalt heater. The heater has two heating sections with a hinge in the middle. Both sections contain wheels to allow the sections to be moved along the surface to be heated. The outer casing of the first section contains a removable fuel tank and the outer casing of the second section contains a set a trailer tires and a trailer tongue. The hinge allows the sections to be folded together so that the wheels of the second section are touching the ground and the trailer tongue can be attached to a vehicle for the easy movement of the heater. Each section has a mixing channel which receives a combustible fuel mixture for heating the section.
A gas pilot igniter for igniting combustible gases and burning fuel/air mixtures is described in London, U.S. Pat. No. 4,946,384. One advantage of the igniter is its ability to allow the use of fuels with variable combustion points. Here, the igniter includes a fuel gas inlet means, a primary mixing chamber, a main combustion chamber, a pre-combustion chamber and a baffle plate.
U.S. Pat. No. 3,852,025 to Placek discloses an infra-red heater. The heater is gas-fired and has a cup shaped body, an open front end and a mixing area for the combustible air mixture. A combustion screen is used to prevent flashbacks which are common in gas-fired radiant heat generators. In addition, the heater is particularly useful in the removal of paint, the softening of adhesives and the softening of flooring surfaces.
A particular difficulty is encountered when fabricating highways and other public thoroughfares. A standard two-lane highway is generally twice as wide as the width of a conventional, large-scale asphalt paving machine. Thus, asphalt roadways are conventionally made in lengthwise sections. One lane is fabricated first, and then the second lane (and any subsequent lanes) are fabricated afterward. To fabricate the second and subsequent lanes, a seam is formed between the cooled first lane of asphalt, and the hot asphalt of the second lane that is being disposed onto the road bed. This yields a finished roadway having one or more longitudinal seams that extend the length of the roadway.
This type of asphalt road construction yields one distinct advantage and one distinct disadvantage. The advantage is that the seam is normally (and purposefully) situated in the middle of the roadway, and is thus covered by the painted yellow line that separates the on-coming lanes of traffic. In multi-lane roadways, the seams are purposefully disposed between two lanes of traffic moving in the same direction, and are thus covered by the painted white lines that define the various lanes of traffic. In both instances, cars traveling on the roadway cross a seam only when changing lanes or turning. Each finished lane of the roadway is very smooth, essentially seamless, and yields a quiet, comfortable automobile ride.
The disadvantage is that the seam is a weak point in the road construction. Because the first-formed lane of asphalt is cold, and the second lane being formed is piping hot, the hot asphalt does not interpenetrate the cold asphalt. In essence, then, the two lanes of asphalt simply abut one another. In the trade, this type of seam is often referred to as a “cold joint.” When the asphalt is newly set, the lanes abut one another quite tightly. But over time, the seam begins to spread. This allows water to enter the seam. Through freeze-thaw cycling of the water trapped in the seam, the asphalt then begins to crumble at the seams. The problem is especially pronounced at far northern and far southern latitudes, where the summer temperatures soar, and the winter temperatures plummet.
The conventional treatment is to pour hot rubber into the parted seam to exclude the entry of still more water into the seam. This treatment, however, is a temporary expedient. Because the rubber does not expand and contract at the same rate as the asphalt, the treatment must be repeated essentially every spring in order to be effective. The need for continuous repair of the seams snarls traffic and increases the work of already over-extended municipal road crews. Thus, while the overall construction approach yields a quiet roadway, degradation of the roadway begins at the seams (which are located in the center of the roadway) and works its way out.
There is thus a long-felt and unmet need for an apparatus that yields strong and permanent seams in asphalt roadways.
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