Release agents used to prevent bituminous materials from adhering to interior surfaces of truck bodies shall meet the requirements of applicable Iowa Department of Transportation Specifications.



Acceptance of release agents for use on Iowa Department of Transportation projects is based on manufacturer and brand name approval. Approved manufacturers and brand names are listed are listed in the Materials Approved Products Listing Enterprise (MAPLE).



Manufacturer shall provide product information and a copy of product evaluation report issued by the National Transportation Product Evaluation Program (NTPEP) to the Construction and Materials Bureau in Ames, Iowa. The NTPEP report includes the test result per AASHTO T383, Standard Practice for NEPEP Evaluation of Asphalt Release Agents.


Product approval is based on satisfactory evaluation of the NTPEP test report. To obtain approval, an asphalt release agent shall meet the following criteria:


        Does not strip at full and manufacturer recommended diluted strength per the Asphalt Stripping Test,

        Max. 10.0 grams retained of HMA after three repetitions per the Mixture Slide Test, and

        Does not fail after 3 pulls per the Asphalt Performance Test.


Approved products shall meet the safety and environmental requirements specified by NTPEP, and shall not contain flammable materials, solvents, or petroleum elements.



The Construction and Materials Bureau may sample and test release agents to verify compliance with specifications. Samples will be tested according to AASHTO T383, the Asphalt Stripping Test or the Iowa DOT Laboratory Method 632. For the Method 632, the release agent shall not alter the G*/sin (delta) results of the asphalt by more than 15%. Products failing the test will be removed from the approved list.



The manufacturer shall file a certification with the Construction and Materials Bureau at the beginning of each calendar year stating that the material supplied during that year is identical with the formulation previously tested and approved.


NOTE: Currently approved products that have not been submitted or resubmitted to NTPEP for testing by January 1, 2019 will be removed from the approved list.