TM 5-822-5/AFM 88-7, Chap. 1
RIGID PAVEMENT BASE COURSES
10-1. General Requirements.
If conditions indicate that a base course is desirable
Base courses may be required under rigid pave-
under a rigid pavement, a thorough investigation
ments for replacing soft, highly compressible or ex-
should be made to determine the source, quantity,
pansive soils and for providing the following.
and characteristics of the available materials. A
study should also be made to determine the most
a. Additional structural strength.
economical thickness of material for a base course
b. More uniform bearing surface for the pave-
that will meet the requirements. The base course
may consist of natural, processed, or stabilized
c. Protection for the subgrade against detrimen-
materials. The material selected should be the one
tal frost action.
that best accomplishes the intended purpose of the
base course. In general, the base- course material
should be a well-graded, high-stability material. In
e. Suitable surface for the operation of construc-
this connection all base courses to be placed
tion equipment, especially slipform pavers.
beneath concrete pavements for military roads and
streets should conform to the fol-lowing
Use of base courses under a rigid pavement to pro-
vide structural benefit should be based on econ.-my
a. Percent passing No.10 sieve; Not more than
of construction. The first cost is usually less for an
increase in thickness than for providing a thick base
b. Percent passing No.200 sieve: Not more than
course. However, thick base courses have often
resulted in lower maintenance costs since the thick
base course provides stronger foundation and
Where local experience indicates their desirability,
therefore less slab movement. A minimum base-
other control limitations such as limited abrasion
course thickness of 4 inches is required over
loss may be imposed to ensure a uniform high-
subgrades that are classified as OH, CH, CL, MH,
quality base course.
ML, and OL to provide protection against pumping.
In certain cases of adverse moisture conditions
(high water table or poor drainage), SM and SC
Where base courses are used under rigid pavements,
soils also may require base courses to prevent
the base-course material should be compacted to a
pumping. The designer is cautioned against the use
minimum of 95 percent of the maximum density.
The engineer is cautioned that it is difficult to
of fine-grained material for leveling courses or
compact thin base courses to high densities when
choking open-graded base courses since this may
they are placed on yielding subgrades.
create a pumping condition. Positive drainage
should be provided for all base courses to ensure
10-4. Frost Requirements.
water is not trapped directly beneath the pavement
In areas where subgrade soils are subjected to sea-
since saturation of these layers will cause the
sonal frost action detrimental to the performance of
pumping condition that the base course is intended
pavements, the requirements for base-course
to prevent. The base course material and drains
thickness and gradation will follow the criteria in
must meet the drainage criteria listed in TM 5-820-
chapter 18 of this manual.
2/AFM 88-5, Chap. 2.