By Dwight Walker and John Davis
Asphalt binder is one of the most commonly used engineering materials, with more than 100 million tons used annually worldwide. In the United States, annual usage averaged nearly 29 million tons for the years 2003 through 2007. Modern asphalt binders are carefully manufactured and it is important that they be transported appropriately. Barges, rail and trucks comprise the primary means of transporting asphalt.
Transporting by Barge
Shipping asphalt by barge offers the advantage of relatively low costs. Mike Caliendo, vice-president for transportation for Andrie, Inc., says that barges provide the cleanest and cheapest means of transporting asphalt. The stricter emission standards in place today result in barge shipments which move asphalt with fewer emissions.
According to Caliendo, keeping the asphalt binder at the correct temperature is a major consideration — particularly from a handling point of view. The mass of material involved on a loaded asphalt barge demands that it be held at the right temperature. He says that their barges are typically loaded at 300°F and the temperature is held at that range while in transit. Some barge contracts include a minimum temperature limit.
Andrie operates a fleet of four large, off-shore barges. Their barges load on the Great Lakes and deliver to refiners’ sales terminals, as well as directly to large asphalt-buying customers. Andrie’s barges typically have five compartments and commonly ship two or three grades of binder. PG 64-22 and PG 52-28 are the binders they transport most often. Their barges carry 43,000 barrels or 8,000 tons of asphalt — enough for 160,000 tons of hot (or warm) mix.
The disadvantages of shipping by barge are the limited availability of locations where waterways are available and the susceptibility to delays due to weather conditions (fog, high or low water conditions, etc.) and lock turn-around time.
Transporting by Rail
Another common means of transporting asphalt is by rail. John Janes, vice-president of supply and marketing for Associated Asphalt, says that much of their asphalt is delivered by rail in 90-ton cars. Associated operates 10 asphalt terminals, located from Martinsburg, West Virginia to Tampa, Florida.
Janes explained that the delivery temperature of the asphalt directly affects unloading time and their heating costs. The rail cars are not heated while underway and depending upon length of travel time and ambient temperature the railcars may require reheating. Some railcars may spend as much as three weeks in transit. If the asphalt has cooled to ambient temperature, it typically takes 24 hours of reheating before the material can be unloaded.
Transporting by Truck
The most familiar means of transporting asphalt is by truck. Trucking offers the advantage of having the most control over delivery time. Some facilities may be limited to truck transport only. Trucking is generally the most costly means of transporting asphalt.
According to Chip Ray, manager of supply and transportation for Asphalt Materials, contamination is a concern in transporting asphalt. Because of the relatively small quantity of material involved, it is a particular concern with trucks. Material left in the haul vehicle from the previous load can readily change the characteristics of the asphalt. To guard against this happening, many asphalt suppliers maintain a dedicated fleet of transport vessels. Ray says that they check the bills of lading to assure compatibility before loading. They recognize the value of retaining good drivers and make an effort to keep their drivers busy year round.
Asphalt suppliers are well aware of the need to deliver a product meeting their customer’s expectations. These expectations include heating and temperature control and specification compliance, as well as information about product usage.
At the mixing plant, the asphalt is expected to be delivered at the desired mixing temperature. Heating the asphalt results in delays and adds to production costs. Asphalt suppliers have to know how much heat will be lost in transit and make appropriate adjustments.
Scott Williams, health, safety, security and environmental advisor for BP Asphalt, says that a truck will only lose about 5°F per hour depending on the weather and haul distance. But in cool weather paving, a cold trailer can lose 10°F immediately. The loading temperature has to be adjusted to accommodate the customers’ needs.
The various state highway agencies have their own testing and certification requirements. With the adoption of Superpave procedures, the agencies have more consistent standards. The frequency of testing may vary somewhat state-to-state and they may apply some additional (PG-plus) tests.
Many asphalt suppliers require documentation of the product’s characteristics as a part of the transportation process. Most asphalt shipped by barges has a supplier’s certification. Similarly, most rail shipments include a certificate of analysis. Truck shipments are more often sampled and tested — the relatively small quantities are more subject to prior load contamination. New sources of supply are tested frequently until a history of compliance is established. Many of the testing labs are AMRL certified.
In addition to testing for specification compliance, some suppliers test the asphalt to determine how to best formulate modified asphalts or specific grades of asphalt emulsions.
Safety is a principle consideration for everyone involved with transporting asphalt. The basic source of information about fire and explosion potential is the Material Safety Data Sheet (MSDS). The MSDS includes specific information on the components present in the asphalt.
It should list all pertinent information including flashpoint, boiling point, acute and chronic effects of all chemical ingredients, recommended personal protective equipment (PPE), and fire and emergency clean-up information. Every employee should have access to the MSDS for the products being transported.
In addition to OSHA standards, Janes of Associated Asphalt says that his company has additional in-house safety standards. They have a safety manager who is responsible for not only their own operations but helps customers with best practices. Safety information is shared regularly by formal documentation and through informal discussions.
Hydrogen sulfide is a potential concern. According to the Asphalt Institute’s Safe Handling of Hot Asphalt DVD and workbook, hydrogen sulfide may be released from shipping containers or storage tanks whenever the hatch is opened for gauging or for visual inspection. Hydrogen sulfide, a highly toxic and flammable gas, can reach hazardous concentrations inside a storage vessel. At low concentrations, hydrogen sulfide emits an odor similar to rotten eggs. At high concentrations it is odorless because it quickly deadens the sense of smell.
Personal air monitors are available that will sound an alarm when hydrogen sulfide reaches dangerous levels. If it is necessary to open the hatch on an asphalt storage vessel, you should stand upwind of the hatch and at least two feet away from openings.
The Asphalt Institute has compiled a publication, IS-225, Management Practices for Asphalt Facility Control of Hydrogen Sulfide Exposure, which provides insight into the management practices to protect employees, contractors and visitors from the potential hazards of hydrogen sulfide exposures at a typical liquid asphalt industry facility. This publication is available from the Asphalt Institute’s website, www.asphaltinstitute.org.
For companies interested in developing and implementing a safety program, resources are available. The Asphalt Institute’s Guide to Safe Handling of Asphalt DVD and workbookprovides asphalt terminal workers and truck drivers with the basic steps for handling, transporting and storing asphalt. Industry programs such as BP’s TruckSafe and RailSafe are designed to reduce injuries and incidents related to the handling and transporting of hot liquid asphalt.
|Dwight Walker, P.E. and John Davis are contributing editors for Asphalt Magazine.|