15 May 2001
asphalt plant. Several items must be routinely controlled during the production and laydown operation to
provide an acceptable pavement. The mixture items include aggregate gradation, asphalt content,
voids, and voids filled. To a great extent these items are interdependent on each other and they should
be analyzed as a group. The laydown items include density, smoothness, and final grade. Departments
of the Army and Air Force require that five of these items be measured and analyzed statistically. These
items are air voids, asphalt content, density, smoothness, and final grade. A new guide specification,
CEGS-02749, that bases payment on air voids, density, grade, and smoothness is currently being
developed. If this specification is used, the results of the items tested should be employed in the same
manner as the current items. When these items do not meet the specified requirements, the contract
unit price is reduced or the mixture is rejected. Small projects of less than 1,000 metric tons of hot-mix
can be constructed without the pay reduction clause for economic reasons.
(6) In order to evaluate the quality of a job, the work is divided into lots. Each lot is considered
as a separate job and as such is evaluated solely on the test results for that lot. A lot should generally
not exceed 2,000 metric tons (2,000 tons) of production or one normal day's production. The lot should
be subdivided into four equal sublots, and a random sample should be taken from each sublot for
evaluation of air voids, asphalt content, and density. The random sublot sample for these properties will
include one sample of uncompacted asphalt mixture, one field core from a pavement joint area and one
field core from the compacted hot-mix asphalt at least 0.3 meter (1-foot) away from the joint.
(7) The asphalt content and aggregate gradation will be determined from samples of the
asphalt mix taken somewhere between the production and the laydown operation. The exact location of
the sample is not important, but the sample should be taken from the same location each time (for
example, truck at asphalt plant, truck, at laydown site, bituminous storage bin, or other locations). The
same sample of asphalt mixture should be used for determining asphalt content and aggregate
(8) If a lot size equal to 1,000 metric tons (1,000 tons) is selected, a sample of asphalt mix will
have to be taken for each 250 metric tons (250 tons) produced. Any approved method for locating
random samples can be used. As an example, suppose that a random number is selected between 1
and 250 and is determined to be 200. This selection means that the 200th ton batched will be sampled.
(9) After the four aggregate gradations and asphalt contents are determined for a lot, these
results are compared with the JMF and the absolute difference is determined. Suppose the design
asphalt content is 5.5 percent and the four extracted asphalt contents are determined to be 5.2, 5.4, 5.5,
and 5.8. The mean absolute deviation from the JMF is determined to be:
0.3 % 0.1 % 0.0 % 0.3
Mean absolute deviation '
The same procedure is used to determine the mean absolute deviation for each sieve size for the
aggregate gradation. After the mean absolute deviation is determined for the asphalt content and
aggregate gradation of a lot, the maximum percent payment for that lot can be determined from the
tables provided in the specification requirements.
(10) Density must be determined within the mat and at the joints between mats. One sample
should be obtained in the mat and one in the joint for each sublot. The total linear length of joint
constructed for a given lot will be divided into quarters and one random sample taken for each sublot.
These sample locations can be determined in a similar way as that for aggregate gradation and asphalt
content. All mat samples should be taken at least 0.3 meter (1 foot) from the edge of mat or joint. In
order to determine sample locations in the mat, each sublot must be divided into grids. The number of