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Over 500 million tons of HMA are placed in the United States each year so it's important that the material be properly sampled and tested during construction to ensure satisfactory performance. When adequate testing is not conducted the performance of the HMA normally suffers.

There are several tests used during construction to help ensure adequate quality is produced. However, prior to beginning work in the field a mix design has to be developed and approved. The mix design provides a job mix formula that is used as the target for material and mixture properties during mix production. The tests discussed in this report include: aggregate gradation, asphalt content, volumetrics and in-place density.

Mix design
The mix design is developed before the project begins. The mix design evaluates the materials and determines the mixture proportions for optimum performance. As a result of the mix design, a job mix formula (JMF) is produced. The JMF tells how much of each aggregate source to use in the mixture and the optimum asphalt content. It also provides a target for the percent of the aggregate passing each size range. The mix design is really a starting point, and it is important to understand that during production the mix design will likely have to be adjusted.

It's also possible that performance testing will be done during the mix design stage but not during production. For example, some states conduct a rutting test on the mix during mix design but do not conduct additional tests during production. Also some states will conduct a moisture susceptibility test during mix design but not conduct these tests during production.

Most mix designs are now conducted in accordance with the Superpave procedures and criteria. The primary component of these tests is to compact the HMA using some specified compaction effort and determining the volumetric properties. These same tests are typically conducted during the construction process.