stabilized base or subbase course, the thickness of

conditions are a factor. Where paving of shoulders

conventional base or subbase is divided by the

is deemed necessary, the shoulders will be designed

equivalency factor for the applicable stabilized soil.

as a class F road or street.

Examples for the application of the equivalency

factors are as follows--

Permanent bituminous sidewalks will consist of a 4-

pavement has been designed which requires a total

inch-thick base with a 1-inch-thick bituminous

thickness of 16 inches above the subgrade. The

surfacing. Material used locally in base construction

minimum thickness of AC and base is 2 and 4

for roads will normally be suitable as sidewalk base

inches, respectively, and the thickness of subbase is

material. Bases may also be constructed of soils

10 inches. It is desired to replace the base and

stabilized or modified in place with portland

subbase with a cement-stabilized gravelly soil

cement, lime, bituminous materials, or other

having an unconfined compressive strength of 890

acceptable stabilizers. In frost and permafrost areas,

psi. From figure 8-2 the equivalency factor for a

bases of sidewalks should be nonfrost-susceptible.

subbase having an unconfined compressive strength

The bituminous surfacing may consist of hot- or

of 890 is 2.0. Therefore, the thickness of stabilized

cold-mix bituminous concrete, sand-asphalt or sand-

subbase is 10 inches 2.0=5.0 inches. To calculate

tar mixes, or sheet asphalt; in locations where the

the thickness of stabilized base course, divide the

surface texture is not of prime importance,

subbase equivalency factor by 2 and then divide the

bituminous surface treatments may be used.

unbound base course thickness by the result.

Temporary walks or walks that are seldom used will

Therefore, 4 inches 1.0 = 4.0 inches of stabilized

be constructed of stable or stabilized soils or rock

base course. The final section would be 2 inches of

screenings containing granular and colloidal

AC and 9 inches of cement-stabilized gravelly soil.

materials combined in the proportions necessary to

The base course thickness of 4.0 inches would also

ensure maximum density and stability under varied

have been required due to the minimum thickness of

weather conditions, including frost action. Where

stabilized base.

necessary, the life of these walks may be prolonged

by the application of bituminous surface treatments

pavement has been designed which requires 2 inches

or by the addition of suitable stabilizing agents. The

of AC surface, 4 inches of crushed stone base, and

use of soil sterilants may be considered to prevent

6 inches of subbase. It is desired to construct an all-

vegetation growth through bituminous sidewalks.

bituminous pavement (ABC). The equivalency

factor from table 8-1 for a base course is 1.15 and

for a subbase is 2.30. The thickness of AC required

Base course materials in residence driveway areas

to replace the base is 4 inches 1.15=3.5 inches,

will be compacted to not less than 100 percent, and

and the thickness of AC required to replace the

the top 6 inches of the subgrade to not less than 90

subbase is 6 inches 2.30 = 2.6 inches. Therefore,

percent (95 percent for cohesionless sands and

the total thickness of the ABC pavement is

gravels) of the maximum density from ASTM D

2+3.5+2.6 or 8.1 inches, which would be rounded

1557. Minimum base course thicknesses for resi-

to 8.0 inches.

dence driveways are as follows:

These areas are provided only for the purpose of

minimizing damage to vehicles which use them ac-

cidentally or in emergencies; therefore, they are not

considered normal vehicular traffic areas. Normally,

only shoulders for class A roads will be paved.

Others will be surfaced with soils selected for their

stability in wet weather and will be compacted as

required. Dust and erosion control will be provided

The minimum paving requirements for residence

by means of vegetative cover, anchored mulch,

driveways are a multiple bituminous surface treat-

coarse-graded aggregate, or liquid palliatives (TM

ment for base course CBR values less than 80 and

5-830-3/AFM 88-17, Chap 3). Shoulders will not

a single-bituminous surface treatment for CBR

block base-course drainage, particularly where frost

values of 80 or above.

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