Heavy 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.

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 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 a dense graded Superpave 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):

1. 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).
2. 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.
3. 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)
• The Asphalt Institute.  (2006).  Thickness Design – Asphalt Pavements for Heavy Wheel Loads, Manual Series No. 23 Second Edition.  The Asphalt Institute.  Lexington, KY. (www.asphaltinstitute.org)