2.2.1
Job Mix Formula (JMF)
The JMF for the bituminous mixture will be furnished to the Contractor by
the Contracting Officer. No payment will be made for mixtures produced
prior to receipt of the JMF by the Contractor. The estimated asphalt
content (percent by weight of aggregate) to be used in the JMF will be
determined by the equation 2.0 Kc + 4.0, where Kc, a surface area constant,
is determined by conducting CDT Test 303 tests on the proposed job
aggregates. A mixing temperature to provide an asphalt viscosity of 275
plus or minus 25 sq mm/sec centistokes will be determined in accordance
with ASTM D 2170. The formula will indicate the percentage of each
stockpile (as based on samples furnished) and mineral filler, the
percentage passing each sieve size, the percentage of bitumen, the amount
of anti-stripping agent, if needed, and the temperature of the completed
mixture when discharged from the mixer. Tolerances are given in TABLE II
for bitumen content, temperature, and aggregate grading for tests conducted
on the mix as discharged from the mixing plant; however, the final
evaluation of aggregate gradation and asphalt content will be based on
paragraph ACCEPTABILITY OF WORK. Bituminous mix that deviates more than 14
degrees C 25 degrees F from JMF shall be rejected. The JMF may be adjusted
during construction to improve paving mixtures, as directed by the
Contracting Officer, without adjustments in the contract unit prices.
Tolerances shown may permit the aggregate gradation to be outside the band
specified in TABLE I; this will be acceptable.
TABLE II.
JOB-MIX TOLERANCES
Tolerance,
Material
Plus or Minus
________
_____________
Aggregate passing 4.75 mm or larger sieves
4
percent
Aggregate passing 2.36 and 0.60 mm sieves
3
percent
Aggregate passing 0.075 mm sieve
1
percent
Bitumen
0.30
percent
Temperature of mixing
14
degrees C
TABLE II.
JOB-MIX TOLERANCES
Tolerance,
Material
Plus or Minus
________
_____________
Aggregate passing No. 4 sieve or larger sieves
4
percent
Aggregate passing Nos. 8 and 30 sieves
3
percent
Aggregate passing No. 200 sieve
1
percent
Bitumen
0.30
percent
Temperature of mixing
25
degrees F
2.2.2
Retained Coating
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NOTE: The antistripping agent, when added to the
mix, must provide a mixture which will have a
retained coating area of at least 95 percent.
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The aggregate passing the 10 mm 3/8 inch sieve and retained on the 6 mm 1/4
inch sieve shall have a retained coating area of at least 95 percent. When
SECTION 02747
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