15 May 2001
possible sampling locations will be approximately equal to the length in meters times 2 minus 1 times the
width in meters time 2 minus (length in feet - 1 foot) 1 (width in feet - 1 foot).
(11) As an example, suppose that 1,000 metric tons (one lot) of hot-mix asphalt were placed in
two adjacent lanes, one lane 2,000 meters long and the other 1,000 meters long. The joint length
between the two lanes would be 1,000 meters; thus, one sample would be taken at random for each
250 meters of joint length to evaluate joint density. The total length of the two lanes would be
3,000 meters; therefore, one random sample should be taken from the mat for each 750 meters of hot-
mix asphalt. The first 750 meters would have [750 x 2 - 1] x [3 x 2 - 1] possible sampling locations if a
3-meter-wide paver was used. (Possible sample locations are at 0.5 meter or 2 every meter intervals
longitudinally and transversely and no closer than 0.5 meter from the edge.) Hence, there are 7,495
(1,499 x 5) possible sampling locations for each of the 4 cores to be taken from the mat. Suppose that
the random number selected was 3,108. Divide 3,108 by 5 to get 621 with a remainder of 3 [0.6 x 5].
Hence, the sample should be taken 311 meters (621 2 + 0.5, possible horizontal sample locations
+ 0.5 meter) from the origin and 2.0 meters (3 2 + 0.5, possible transverse sample locations
+ 0.5 meter) from the edge (since the start point is 0.5 meter from the edge and 0.5 meter from the
beginning). The random samples do not have to be precisely located, but it is important that the surface
appearance does not affect the selection of sample locations.
(12) The average mat density and average joint density will each be expressed as a
percentage of the laboratory density. The laboratory density for each lot will be the average density
determined from at least two sets of samples representing the in-place material compacted in the
laboratory. Suppose that the average laboratory density is 2,404 kilograms per cubic meter (150 pounds
per cubic foot), the four mat samples have individual densities of 2.324 grams/centimeter3,
2.356 grams/centimeter3, 2.348 grams/centimeter3, and 2.373 grams/centimeter3, and the four joint
samples have individual densities of 2,311 grams/centimeter3, 2.324 grams/centimeter3,
2.343 grams/centimeter3, and 2.325 grams/centimeter3. Based on these results the average mat density
2.324 % 2.356 % 2.348 % 2.373
Mat density '
' 97.8 percent
and the average joint density would be
2.311 % 2.324 % 2.343 % 2.325
Joint density '
' 96.8 percent
The average density in the mat and the average density in the joint can be used along with the tables in
the specifications to determine the maximum percent payment for the lot of material being evaluated.
(13) The surface of the completed pavement will be evaluated on a systematic basis to
determine the acceptability of grade and smoothness. The results will be compared with the
specification requirements to determine percent payment for grade and smoothness.
(14) In order to properly evaluate quality control of a mixture and maintain up-to-date records
of test results, control charts should be maintained. It is recommended that the control charts be plotted
for each sieve size specified in the gradation requirements, asphalt content, laboratory density, stability,
flow, voids in total mixture, voids filled with asphalt, mat density, and joint density. A plot should be
made of individual values and for the running average of four samples.
(15) An example of the use of control charts follows. Assume the density results shown in
table 2-10 were obtained from the in-place mat.