NCHRP mix design practice for WMA - brief description

The NCHRP mix design for WMA refers to the AC type of mixtures that are produced at temperatures approximately 28 C (50°F) lower (or more) than temperatures typically used in the production of HMA. Is should be read in conjunction with AASHTO R 35 (2012). 

The proposed amendment to the specification AASHTO R 35 (2012) specifies additional laboratory equipment for mixing and for binder additive WMA processes. 

In selecting the WMA process, consideration should be given to the following factors (1) available performance data, (2) the cost of the warm mix additives, (3) plaimed production and compaction temperatures, (4) planned production rates, (5) plant capabilities and (6) modifications required to successfully use the WMA process with available field and laboratory equipment. 

A performance grade of binder should be selected in accordance with Section 5 of A ASHTO M 323 (2013) considering the environment and the traffic volume at the project site. 

RAP can be used in the WMA after selection is made in accordance with Section 6 of AASHTO M 323 (2013) and the recommendations stated. 

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