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Section 8: Heater and Storage Unit

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Sometimes the contractor will set up a heater and storage unit for large projects. The asphalt is hauled from the source by truck and pumped into the heater and storage unit. When it is used, it is pumped either into another transporter or directly into the asphalt distributor.

There is no standard configuration for a storage and heater unit. It may be a tank with heating and circulating equipment combined, or it may be an insulated tank with a separate heater unit with interconnected piping. Storage capacity and size vary according to the needs of the project.

The heater and storage unit, usually called a heater unit, is inspected at the beginning of a project along with the other equipment. Sometimes the contractor has manufactured the heater unit, so there may not be any identifying data. The only numbers on the equipment may be an engine serial number on the pump unit.

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Asphalt must be stored at specific temperatures, which are usually somewhat higher than the temperatures at which the asphalt is applied. The asphalts used in seal coat work are stored at the following approximate temperatures:

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Asphalt cement

325°F to 400°F

Cutback asphalt

150°F to 200°F


150°F to 170°F

The higher temperatures are the maximum allowable storage and heating temperatures.

In order for these asphalts to be sprayed properly, with the desired results, the temperature must be closely controlled in order to maintain the correct viscosity for spraying. The heater unit operator must clearly understand the importance of the viscosity-temperature relationship.

The heating and storage unit must be equipped with a continuous recording thermometer so that the temperature of the asphalt may be closely monitored.

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The operator must be aware of the flash point (temperature at which ignition could occur) of whatever type of asphalt binder is being used. It is his responsibility to ensure that all necessary safety precautions are taken, but this can never be assumed. The flash point is especially critical with cutback asphalts. As an example, RC-250 has a flash point of 80°F. Standard Specifications Item 300.3 recommend that RC-250 be applied at temperatures between 125°F and 180°F. The maximum allowable temperature for application and storage is 200°F. With this type of asphalt, you are well into the dangerous range any time that you work with it.

There is also danger around the heater and storage unit, especially if using asphalt cement. Storage tanks, pipes, and valves are extremely hot. Adequate safety precautions should be taken to ensure that any part that might be touched is insulated.

Extreme care must be taken when obtaining a sample of asphalt cement. Very hot asphalt cement (350°F) can easily splatter. Proper safety equipment and clothing should be worn.

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Storage Tank

The storage tank must be inspected for cleanliness and the presence of any condition that would permit contamination of the asphalt. There should be a continuous-recording thermometer on the tank, which records any fluctuations in asphalt temperature.

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In some cases, the heater unit is a part of the storage tank. In others, it is a separate unit, consisting of a smaller tank with pump and heater. Regardless of the system used, the heater unit must be inspected.

It should have a burner that can be regulated to alter the intensity of heat. The burner should direct the flame into the flues, similar to the arrangement in an asphalt distributor. The pump should circulate the asphalt through the heater unit sufficiently to prevent the asphalt from burning next to the flues and from sticking (from cooling) near the outside of the tank.

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Pump Unit

The pump unit should be checked for proper operation, but the primary concern is to ensure that the pump and associated piping protects the asphalt from contamination. It should be assembled so that no dirt or fuel can enter the piping or pump unit.

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Heater Unit Location

Although the location of the heater unit is the contractor’s responsibility, the inspector should consider the location of the unit from the standpoint of safety for the motorists.

The heater unit will have transporters moving to and from it, as well as asphalt distributors or boosters pulling onto and off the highway in the vicinity of the heater. This traffic must be clearly visible to motorists driving through the construction area. Therefore, it should not be situated on or near blind curves and probably well clear of intersections.

If the heater unit is situated in the vicinity of the aggregate stockpile, it should be separated far enough away to ensure that no contamination of the aggregate occurs. Asphalt is often spilled around heater units, so it is best that the heater be situated well away from aggregate stockpiles, if practical.

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Recording Thermometer

When the project begins, the inspector must pick up the record card from the continuous reading thermometer each day. A new card is installed when the old one is removed.

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Transporter and Booster

Transporters sometimes belong to the contractor, sometimes to the petroleum company that supplies the asphalt to the contractor, and sometimes to independent truckers. Booster tanks are not used on all jobs but are frequently used on projects that cover 6 to 10 miles or more. This cuts down on the amount of time the distributor is tied up while being refilled.

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Identifying Data

If the transporter and boosters belong to the contractor, record the standard vehicle identification information and include it in the project file. This would also apply if the contractor has leased the equipment.

If the transporter belongs to the petroleum company or to an independent trucker, record the company name and the truck license or other unique number. Although this may not be required, it is a good practice, in case there is a problem with the asphalt.

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Check the transporter’s manifest before it is unloaded to make certain the asphalt in the truck is the right type for the project. Unfortunately, some inspectors have found out too late that the wrong asphalt was pumped into the heater unit. Once again, this is the contractor’s responsibility, but it will delay the project and can easily be prevented. A copy of the manifest of each load of asphalt delivered on the job must be retained in the project folder.

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If the transporter belongs to or is leased by the contractor, it should be cleaned if a different type of asphalt was transported on a previous project. It is not usually possible for the inspector to determine exactly what type of asphalt had been hauled previously, so a good rule of thumb is to be certain it is clean before it hauls asphalt to the current project.

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Besides guarding against contamination from previous asphalts, the inspector should ensure that the transporter tank and piping protect the asphalt from contamination during off-loading to the heater unit.

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Booster Tanks

On some jobs, booster tanks are used to refill the distributors close to where asphalt application occurs. These vehicles should be inspected for cleanliness; to guard against contamination; and have the identifying data recorded. Their piping and shut-off valves should be checked for leaks to guard against puddles of asphalt being left behind after they have refilled an asphalt distributor. This is especially important if the distributors are to be filled while parked on the pavement that is to be seal coated.

Sometimes a transporter is used as a booster tank on the job, transporting asphalt from the heater unit to where the distributors are filled directly from the transporter. If asphalt cement (AC) is being shot on the project, it must be shot near 300°F. This would necessitate having an insulated transporter, in order to keep the asphalt hot between the heater unit and the distributor.

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Like the transporter, it may be necessary to ensure that booster tanks, if used to carry AC at high temperatures, are adequately insulated. Without proper insulation, the asphalt may cool enough to raise the viscosity above the limits for being pumped into the distributor, especially if there are any unexpected delays.

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