By Richard S. Williammee, Jr., M.S., P.E.
Every producer and contractor that works around asphaltic concrete mixes (whether hot, warm, or cold) has experienced the need to clean up equipment on a daily if not semi-daily basis. For decades, this has been done with readily available diesel and solvents.
These products work well because they have been relatively cheap, easy to obtain and clean the equipment thoroughly. However, in performing this task, they are also causing the asphalt to “soften” and strip off of the aggregates. Without this “glue,” the mix quality is compromised.
People designing, constructing and maintaining roadway systems have recognized the need to preserve the integrity of the asphaltic concrete mixes and protect the environment.
Asphalt Release Agent (ARA) is now a general term used for products that have been developed to replace the stripping and environmentally hazardous diesel and solvents. From 1997 to 2004, the Texas Department of Transportation (TxDOT) created a new test procedure and specification for ARAs, compiled a list of approved products and then required it in their specifications.
In 2010, AASHTO’s National Transportation Product Evaluation Program (NTPEP) acknowledged the multiple testing programs used by the state DOTs and accepted the task of testing and reporting results of ARA products on a standardized national level.
NTPEP’s ARA program released an official work plan that has been accepted by all of the participating states. This work plan consists of three test procedures: a stripping test, a mixture slide test and an asphalt performance test.
The stripping test involves taking a vendor’s product, filling up a quart jar and placing actual hot mix into the solution. Based on the liquid discoloration, it is reported as “No Stripping.” “Slight Stripping,” “Moderate Stripping” or “Severe Stripping.” Additionally, a visual check of the hot mix is performed to see if the asphalt is stripping from the aggregate. The visual check is done for very dark to opaque products.
The mixture slide test involves the use of an actual plate cut out of a TxDOT truck bed. Hot mix is placed on the plate where the ARA product is sprayed. After a specified time, the plate is tilted to see how much of the mix slides off. This is repeated at least twice more without ARA product reapplication. This test simulates the effect of mix in truck beds.
The asphalt performance test involves the application of asphalt liquid poured onto the same truck bed plate. After a certain rest period, the asphalt “patty” is lifted from the plate. This test is repeated a minimum of twice more without reapplication of the ARA product. An accumulative weight is recorded until the specified percentage is achieved. Some ARAs will allow more than three lifts, which lowers the cost of the product. This test simulates asphalt sitting on items like the pavers, rollers, rakes, lutes, shovels and elevator slats at the hot mix plant.
NTPEP’s ARA program includes the previously discussed work plan, a user guide and a QCQA plan. Additional information about NTPEP and AASHTO are also available on their website at www.ntpep.org.
Many other states are now looking at their ARA program and quality products list. The concept is catching on with the DOTs and industry professionals to help create and place quality mixes, to provide a long lasting pavement to the traveling public and protect the environment.
Richard S. Williammee, Jr. is the TxDOT Fort Worth District Materials Manager and is the NTEP ARA Technical Chairman.