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Job Mix Formula

The end result of a successful mix design is a recommended mixture of aggregate and asphalt binder. This recommended mixture, which also includes aggregate gradation and asphalt binder type is often referred to as the job mix formula (JMF) or recipe.

For HMA manufacturing, target values of gradation and asphalt binder content are specified based on the JMF along with allowable specification bands to allow for inherent material and production variability (see Table 1 and Figure 1). It bears repeating that these target values and specification bands are based on the JMF and not any general HMA gradation requirements. Thus, the mix designer is allowed substantial freedom in choosing a particular gradation for the JMF and then the manufacturer is expected to adhere quite closely to this JMF gradation during production.

Table 1: Example Job Mix Formula (JMF) with Specification and Tolerance Bands
Sieve (metric) 19.0 mm 12.5 mm 9.5 mm 2.36 mm 0.075 mm
Sieve Size (U.S. units) 3/4 inch 1/2 inch 3/8 inch No. 8 No. 200
Gradation Control Points 100 min. 90 – 100 90 max. 28 – 58 2.0 – 7.0
Job Mix Formula (JMF) 100 96 75 29 4.5
Tolerance 99 – 100 +/- 6% +/- 6% +/- 4% +/- 2.0%
Tolerance Limits 99 – 100 90 – 100 69 – 81 25 – 33 2.5 – 6.5

Figure 1. Job mix formula (JMF) with specification bands example.

 

 

 

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Thanks for sharing Job Mix Formula.