15 May 2001
(3) Extraction tests. Extraction tests shall be made in accordance with ASTM D 2172 using
trichloroethylene as the extraction solvent. A nuclear gage can be used to determine the asphalt
content, when tested in accordance with ASTM D 4125, provided it is calibrated. The asphalt content
can also be determined by the ignition method in accordance with ASTM PS 090. Sieve analysis of
recovered aggregates shall follow procedures specified in ASTM D 5444.
(4) Mix proportions. Mix proportions shall be adjusted whenever tests indicate that specified
tolerances are not being met. In the case of batch plants, faulty scales, and failure of the operator to
accurately weight the required proportions of materials are common causes for mixture deficiencies.
Improper weighing or faulty scales may be detected readily and corrective measures taken by
maintaining a close check of load weights. Figure 2-9 presents other probable causes of mixture
deficiencies due to improper plant operations.
(5) Controlling plant production. The plant inspector should obtain a sample of the PFC mix
after the plant has been in production about 30 minutes. The sample should be tested as rapidly as
possible for compliance with gradation and asphalt content requirements.
(1) Pavement control. A PFC pavement has no density requirements. A characteristic of this
overlay is its rapid cooling. If minimum asphalt drainage is desired, the roller should closely follow the
paver to initially set the PFC so that asphalt drainage is minimized. If more drainage is desired, the roller
should wait longer before rolling the PFC. Rich spots will tend to drain if rolling is delayed. Two passes
with a 10-metric ton (10 ton) steel-wheel roller should be satisfactory to properly seat the PFC mix.
(2) Pavement sampling. Samples for determining thickness (ASTM D 979) may be taken
either with a coring machine or by cutting out a sample of pavement at least 100 millimeters (4 inches)
square with a concrete saw. The sample should include the entire thickness of the PFC.
(3) Storage silos. Storage of PFC mix should be avoided whenever possible; the maximum
allowable storage time under any circumstance should not exceed 15 minutes. Excessive storage time
will allow the asphalt to drain, causing segregation of the mixture. Proper coordination between the
plant and the laydown operations will eliminate the need for extended storage.
(4) Pavement operations under normal conditions. The Army and Air Force guide
specifications do not permit placement of PFC when the surface temperature of the existing pavement is
below 60EF. The most important consideration is whether the contractor can apply the necessary rolling
before the mixture becomes too cool to be properly seated. Generally, all rolling should be performed
before the PFC mixture cools to 80EC (175EF). A PFC will cool quickly because of the thin layer of
material and high void content in the thin PFC layer. Thus, judgment should be used in the application
of the temperature limitations in the guide specifications to avoid shutting down operations during
periods when satisfactory final pavement properties could be obtained.
STONE MATRIX ASPHALT.
a. GENERAL. Stone matrix asphalt (SMA) is a mixture of aggregate, mineral filler, asphalt cement,
and a stabilizer (cellulose or mineral fiber and/or modified asphalt). SMA is designed to prevent rutting
and abrasion even under high loads and/or high tire pressures. SMA mixtures depend on aggregate to
aggregate contact to support traffic loads thereby requiring a large percentage of coarse aggregate.
Excess fine aggregate or too much mastic can prevent the coarse aggregate particles from obtaining full
contact and therefore lower the mixture's resistance to rutting. The high void content of the mix is
occupied by fine aggregate, mineral filler, asphalt cement, and a stabilizer (polymer, cellulose, or mineral