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Mix Design

To ensure the proper performance of the project, a mix design should be performed for the chip seal application to determine the following:

  • Application rate for aggregate
  • Application rate for binder
  • Appropriateness of the materials being used in a chip seal application.

It should be noted that the design rates are only a guide and should be adjusted for field variances such as pavement conditions and traffic.

Two of most notable chip seal design methods are the McLeod method and the Modified Kearby method.  To find out out more information on each method please click on the links below:


See also: the webinar developed by the Asphalt Institute and ISSA on chip seal mix design procedures

For the slurry seal/micro surfacing application:

To ensure proper performance of  a project, a mix design must be conducted to determine the compatibility of the aggregate, emulsified asphalt, water, mineral filler, and other additives.  The mix design must be performed with the same material components to be used on the project in order to properly predict the performance of the slurry seal/micro surfacing mixture applied in the field.  The mix design process results in a Job Mix Formula (JMF), which will specify the ratios of all materials to be used.

Mix designs must be completed according to ISSA A105/ASTM D3910 for slurry seal, and ISSA A143/ASTM D6372 for micro surfacing by a competent laboratory that is experienced with state of the art asphalt emulsion/aggregate mixing technology as it applies to slurry systems.  The laboratory must possess the necessary specialized equipment and knowledgeable staff to perform the required tests.  Knowing the specific system and the relationships of all the components is critical to the development of a good mix design.  Each of the material components - aggregate, asphalt emulsion, water, and additives, must meet all job specifications and test requirements.  Individual materials must be qualified through testing before the laboratory will perform further tests to determine the mix compatibility and performance under simulated wear conditions.

Although the contractor is responsible for providing the mix design, the owner’s representative should check the mix to verify that it meets the specification require­ment.  During mix design verification testing, an engineer conducts a series of tests on the basic materials.  The materials must be available to the engineer so that this verification can be completed prior to the project starting.  Mix design verification testing should be conducted at a laboratory designat­ed by the engineer.   Once the mix design is approved, all mixtures must follow the requirements stated in the resulting Job Mix Formula.

See the list of tests performed by the laboratory during the mix design process in the TESTING PROTOCOL section.