applied with a bituminous distributor in three equal
applications.
Each application is one-third of the
amount required.
Immediately following each application of the
bituminous material, the treated aggregate should be
mixed with spring-tooth or double-disk harrows,
graders, rotary tillers, or a combination of this
equipment until all the particles of the aggregate are
evenly coated. When a grader is used, the windrow is
moved from side-to-side by successive cuts with the
blade.
Several graders can operate, one behind the other,
to reduce the total time required for complete mixing.
In hilly terrain, blading should be from the bottom to the
top, as the mix tends to migrate down. After all the
aggregate has been mixed, the mix should be bladed into
a single windrow at or near the center of the road and
turned not less than four complete turns from one side
of the road to the other. Excess bitumen, a deficiency
of bitumen, or uneven mix should be corrected by the
addition of aggregate or bituminous material, followed
by remixing.
Mixing should continue until it is
complete and satisfactory; remember, mix will set up if
mixed too long.
Suppose that materials, weather conditions, and
equipment are well-suited to mixed-in-place paving, but
the road or airfield must carry traffic during
construction.
In such cases, the windrowing of
aggregate and the mixing and spreading of bitumen may
be done elsewhereon any area of smooth ground
which can be compacted for the purpose or on any
unused road or airfield surface. The road or airfield
surface, base, or subgrade to be paved is then primed or
tack-coated as required to complete construction and to
keep portions of the road or airfield open to traffic. As
soon as the prime or tack coat cures, the mix is picked
up, trucked to the jobsite, dumped, and then bladed into
windrows for spreading.
The bituminous mix should not be spread when the
surface is damp or when the mix itself contains an excess
of moisture. The mixed material should be spread to the
required width in thin, equal layers by a grader or
finisher. (When a finisher is used, additional support
equipment is required, and the material must be split into
two windrows for an 8- to 12-foot-wide pavement.)
When spreading the mix from a windrow, you should
take care to prevent cutting into the underlying subgrade
or base course. To prevent such cutting, you should
leave a layer of mix, approximately one-half inch thick,
at the bottom of the windrow.
16-16
The material being spread should be rolled once
and then leveled with a grader to remove irregularities.
The remaining material should be spread and rolled in
thin layers until the entire mix is evenly spread to the
depth and width specified. During the spreading and
compacting, the surface should be dragged or bladed, as
necessary, to fill any ruts and to remove corrugations,
waves, or other irregularities. Both pneumatic-tired and
steel-wheeled rollers may be used for rolling all surface
treatment jobs; however, the pneumatic-tired roller is
the preferred type.
After all layers have been satisfactorily spread, the
surface should be rolled with two-axle tandem rollers.
Rolling should begin at the outside edge of the surface
and proceed to the center, overlapping on successive
trips at least one half of the width of the wheel of the
roller. Alternate trips of the roller should be of different
lengths. The speed of the roller at all times should be
controlled to avoid displacement of the mix. Light
blading (or floating) of the surface with the grader
during rolling may be required. Rolling should be
continued until all roller marks are eliminated and
maximum density is obtained. To prevent adhesion of
the mix to the roller, you should keep the roller wheel
moist with water; use only enough water to avoid
picking up the material. At places not accessible to the
roller, the mix should be thoroughly compacted with
hand tampers. When the surface course becomes rough,
corrugated, uneven in texture, water soaked, or traffic
marked, unsatisfactory portions should be tom up and
reworked, relaid, or replaced. When forms are not used
and while the surface is being compacted and finished,
the outside edges should be trimmed neatly in line.
When the road-mix pavement surface course is
constructed from an open-graded aggregate, a surfs
treatment may be required to waterproof the surface. A
surface treatment is unnecessary on a dense-graded,
well-compacted, road-mix pavement.
When possible, traffic should be kept off freshly
sprayed asphalt or mixed materials.
When it is
necessary to route traffic over the new work speed must
be restricted to 25 mph or less until rolling is completed
and the asphalt mixture is firm enough to withstand
high-speed traffic.
DEFECTS IN FLEXIBLE PAVEMENTS
Defects inflexible pavements can be placed into one
of five classes. These classes are cracking, distortion,
disintegration, slippery surfaces, and surface treatment
problems.