E. M. PART XV
(1) For both flexible and rigid pavements a minimum of 4 inches of base between the subgrade soil and
overlying base-course material should be designed as a filter consisting of any non-frost-susceptible gravel, sand, or
crushed stone. The gradation of this filter material should be determined in accordance with criteria presented in
paragraph 2-11 of chapter 2, part XIII, of the Engineering Manual, with the added overriding limitation that the filter
material should in no case have more than 3 percent by weight finer than 0.02 mm. Non-frost-susceptible sand is
considered especially suitable for this filter course.
(2) For rigid pavements a filter should also be placed immediately beneath the pavement.
This filter should have a maximum of 85 percent by weight passing the 1/4-inch sieve.
(3) The purpose of the filter courses is to prevent the mixing of the frost-susceptible subgrade with the base
during the thaw period, and to prevent loss of support by pumping.
b. Recommendations for pavements. Either flexible or rigid types of pavements may be used in arctic and
subarctic regions. Type of pavement (rigid or flexible) constructed for USAF should be in accordance with current USAF
policy. Rigid pavements should be used only where favorable subgrade conditions exist, such as over non-frost-
susceptible subgrades and possibly uniform subgrade soils from groups F1 and F2. Even with the utmost care in soil
investigation, design, and construction, differential movements may occur. Repairs in flexible pavements are simpler
and more economical than those in rigid pavements. Hot plant-mix bituminous pavements are adapted for extremely
cold climates as they may be constructed under relatively adverse weather conditions. Soft grades of asphalt are
recommended for preparing hot-mix types of pavement subject to low temperatures. Asphalt cement grade AP 1 (pen.
120-150) conforming to Federal Specifications SS-A-706b is generally recommended. AP 2 (pen. 100-120) may be
used in areas where temperatures are relatively higher and weather may be warm part of the year. Paving operations
should be coordinated so that the temperature loss of the mixture during transporting and spreading is kept at a
minimum. There is a tendency to over-heat the bituminous material when preparing mixtures in cold weather; this should
be avoided as the resultant pavements are brittle and short-lived. The spread mixture should be compacted as rapidly as
possible to prevent further loss of temperature and to obtain a dense pavement.
In order to insure satisfactory results, concrete pavements must be protected from freezing during the placement and
curing period and must be permitted to gain substantial tensile strength before exposure to very low temperatures, to
minimize cracking. High early-strength cement with air entrainment is recommended. Joints should be at much smaller
spacing than usual because of exceptional expansion and contraction.
BASE COURSE DESIGN IN AREAS OF NON-FROST-SUSCEPTIBLE SOILS. In areas where the soils are
non-frost-susceptible, or where the soils are frost-susceptible but ground water conditions preclude significant ice
segregation, design principles are the same as in temperate zones. Airfield pavements and bases should be designed in
accordance with part XII, chapters 2 and 3, (1)* and (2)*; roads should be designed in accordance with part X, chapter 1
(3). If pockets of frost-susceptible-soil exist within the construction area, they should be removed and replaced with non-
frost-susceptible materials. The area of excavation of such a pocket should be large enough to allow feather-edging of
the backfill; the depth of excavation should be not less than the estimated depth of frost penetration in the backfill
BASE COURSE DESIGN IN AREAS OF FROST-SUSCEPTIBLIE SUBGRADES.
Two acceptable methods of design of base courses are available where frost-susceptible soils and frost-susceptible
ground water conditions exist. One method is to restrict the depth of seasonal thaw to the pavement and base course,
thereby preventing surface subsidence and subgrade weakening. The other method is to allow thawing to penetrate the
subgrade and to design on the basis of anticipated reduced strength of the subgrade during the thawing period.
*Refers to bibliographic references listed at end