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Heavy Industrial Facilities
"Heavy industrial facilities" encompasses any facility for use with heavily
loaded vehicles such as industrial drives, truck parking, bus terminals,
warehouse loading areas, log storage areas and container lots. HMA is a
durable, high-strength pavement material that is entirely appropriate for
industrial facilities.
One of the chief advantages of HMA in industrial facility paving is its short
construction time. During paving operations, industrial facilities often
cannot be used and thus the owner incurs a financial loss for the duration of
the paving project. Unlike rigid pavements, which may take from several
days to several weeks to construct, a flexible pavement can usually be
constructed in one working day or less thus minimizing the facility down-time.
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| Figure 1: Port of Tacoma |
Figure 2: Port of Seattle |
Assumed Traffic
Traffic for these types of facilities cannot be assumed. A methodical and
reasonably accurate estimation of the type and number of loads is essential in
determining the proper pavement
structural design,
mix type and
mix design. Sometimes,
intended industrial traffic is well beyond legal load limits for Washington
State highways, such as in a logging facility.
Design Considerations
The types and number of loads can vary widely requiring widely varying designs.
Industrial applications often require heavy duty mixes to ensure resistance to
loading such as tracked vehicles, stacked containers, stationary turning
operations and abrasive forces. A heavy duty mix is a
dense-graded mix
containing large nominal
maximum aggregate sizes, usually between 0.75 and 1.5 inches (NAPA, 2002).
0.75 inch or
larger Superpave,
Class E or large stone crushed aggregate
ATB can be used as a heavy duty
mix. Heavy duty mixes provide for superior load carrying characteristics
due to the improved aggregate interlock of the paving mixture matrix.
Because of the reduced surface area of the mix, the percentage of liquid asphalt
cement is lower in these mixes, providing a very good value and very “tough”
mixes. The final few lifts of a heavy load paving design should still
utilize Class A hot
mix for proper sealing and a tight surface texture for the final product.
Polymer modified asphalt
binders can also be incorporated in heavy load applications to further
increase the pavement structure’s load carrying capacity.
Construction Considerations
There are three principal challenges that arise when using heavy duty mixes
(Texas Transportation Institute, 1997):
-
Segregation. The single most common problem with large-stone
mixes (NAPA, 2002). These mixes are more prone to segregation than finer
mixes because the larger aggregate sizes vary greatly in the mix (TTI, 1997).
- Aggregate fracture. Larger aggregate particles may break down
in the manufacturing or compaction processes if they are not sufficiently
hard. This can affect gradation and other mixture characteristics.
- Equipment wear. Larger aggregate particles may create
additional wear on the manufacturing plant as well as the laydown and
compaction equipment.
Recommended Reference
- National Asphalt Pavement Association (NAPA). (2002).
Design, Construction, and Performance of Heavy Duty Mixes, Quality
Improvement Series 123. National
Asphalt Pavement Association. Landham, MD.
(www.hotmix.org)
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The Asphalt Institute. (1986).
Thickness Design - Asphalt Pavements for Heavy Wheel Loads, Manual Series No.
23. The Asphalt
Institute. Lexington, KY.
(www.asphaltinstitute.org)
Recommended Minimum Pavement Thickness and Design
(inches)
To be determined using an approved procedure.
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