UFC 3-260-03
15 Apr 01
c. Temperature Data, Bituminous Surface Layers. The modulus of bituminous concrete is
temperature-dependent. The mean pavement temperature at the time of testing can be obtained by
measuring the temperatures with thermometers installed 25 millimeters (1 inch) below the top, 25 milli-
meters (1 inch) above the bottom, and at middepth of the bituminous layer and averaging the values to
obtain the mean pavement temperature. If actual temperature measurements are not available, the
pavement temperature may be obtained by adding the measured pavement surface temperature at the
time of test to the average (mean) air temperature for the 5-day period prior to the day of testing and
obtaining the mean pavement temperature from figure 3-3. The latter is the more common practice and is
recommended. The design air temperature is required for estimating a design pavement temperature and
design modulus. The design air temperature for a particular locale is determined by averaging the
average daily maximum temperature and the average daily mean temperature for the design month.
Generally, the set of average temperatures will be necessary only for the hottest month indicated in the
reporting period. Values based on records for the previous 20 to 30 years should be chosen if available.
These data can be obtained from records of the National Oceanographic and Atmospheric Administration
for the particular locale or that nearest to it. With the design air temperature, the estimated design pave-
ment temperature can be determined from figure 3-4.
4.
DATA COLLECTION USING DIRECT SAMPLING.
a. General. The type of data needed and the scope of the testing program to obtain these data
depend on such factors as the amount and validity of existing data, the type of pavement being evaluated,
and the condition of the pavement, and thus will be based largely on the judgment of the evaluating engi-
neer. The condition survey is conducted, then test locations are selected, in-place tests made, samples
for laboratory tests secured, and test holes back-filled. The laboratory tests are the final phase in the pro-
curement of data. When NDT test data are obtained prior to direct sampling, the selection of the direct
sampling locations will be tailored to match the results of the NDT data. Areas exhibiting a high degree of
variation in the deflection measurements should be investigated as should areas exhibiting average
deflections.
b. Selection and Size of Test Areas. One of the first steps in the selection of sampling locations
should be the establishment of longitudinal profiles along the runways, taxiways, and aprons to develop a
general picture of subgrade, base, and pavement condition, so that test pits for collecting more detailed
data can be located to the best possible advantage. Data for these profiles can be obtained by coring
100- or 150-millimeter- (4- or 6-inch-) diameter holes in the pavement, through which thickness measure-
ments can be made and samples of the foundation materials obtained. These samples should be classi-
fied in accordance with the Unified Soil Classification System as presented in ASTM D 2487. Usually, a
spacing of 152 to 305 meters (500 to 1,000 feet) between these small holes will be sufficient, but occa-
sionally when nonuniformity of pavement or foundation conditions exists, closer spacings may be neces-
sary. From the information obtained, the pavements should be divided into features on the basis of pave-
ment type, construction history, known strength, thickness, and foundation types.
(1) The preliminary sampling locations should enable test pits to be placed in locations repre-
senting typical pavement and foundation conditions. In addition, the test pits should be placed in areas
that received intense traffic, that is, at or near the centers of runways, taxiways, or aprons instead of along
the edge of the pavement.
(2) If pavement and foundation conditions are uniform throughout the airfield area, a nominal
number of test pits (five or six) will generally be sufficient if they are located to provide representative
information for the entire system of airfield pavements. When the pavement or foundation conditions are
not uniform, test pits should be located to yield the necessary information for each type of pavement or
foundation material. When failed areas or areas of excessive pavement distress are encountered, a suffi-
cient number of test pits must be located in the failed or distressed areas to determine the cause of the
failure or distress.
3-4
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