ETL 1110-l-139
22 Jun 90
Chapter.1
SELECTING ASPHALT
General
Asphalt cements for use in pavement design and construction are graded or
classified in one of two ways. Grading can be done on the basis of pene-
tration depth of a standard test needle into asphalt cement at a standard test
temperature. The other method of grading is based on the use of a viscosity
test. Currently, in the continental United States
viscosity grades
of asphalt are common. However, outside the continental United States
(OCONUS), penetration grades of asphalt may be more easily obtained. Tables 1
and 2 give specifications for the two types of viscosity graded asphalts.
Table 3 gives specifications for penetration grades. All three tables are
from current standards of ASTM D 3381 for viscosity grades and ASTM D 946 for
penetration grades.
Selecting a grade of asphalt cement should be based on several items.
Among the most important are climate, traffic conditions, economics of asphalt
availability, and previous regional experiences. Traffic conditions and eco-
nomic considerations will vary from project to project, but environmental
conditions and regional experiences should have some similarity. For example,
warm and hot regions should have similar experiences in avoiding unstable
months, and cold regions should have
asphalt concrete mixes during the
similar experiences in avoiding crack-prone pavements during winter months.
Asphalt Cement Selection by Temperature Region
Table 4 gives guidance for selecting an asphalt cement by temperature
region. Climatological data are required to provide input into the selection
method. First, average monthly maximum temperature data are required to com-
When project locations have average
pute a pavement temperature index
monthly maximum temperatures above 75" F (23.9' C), the PTI is defined as the
F (23.9' C). Conversely, when no
sum of the monthly increments exceeding
monthly temperature exceeds 75" F (23.9' C), the PTI is defined as the differ-
ence between the highest average maximum temperature for the warmest month and
F (23.9' C). Enclosure 2 (Example 1) shows an example of PTI
When it is determined that a project will exist in a cold region, as
defined in Table 4, additional climate data are required. For the project
area under consideration , a design air freezing index (DFI) is also required
to further satisfy cold region requirements. (Reference TM
88-6,
Chap. 4 for determination of DFI.) Cold regions are areas where the penetra-
tion-viscosity number (PVN) method is used to aid in selecting an asphalt
cement.
1
Headquarters, Departments of the Army and the Air Force, Bituminous Pavements
Standard Practice, TM
88-6, Chap. 9.
Enclosure 1
1
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