pavement is a well-graded (dense or open) sandy gravel
or clean sand.
Maximum size of the aggregate, in
general, is limited to two thirds of the compacted
thickness of the layer. Loose thickness is approximately
1 1/4 times the desired compacted thickness.
Surface moisture is defined as the film of water
around each particle of stone or sand. The amount
present is determined by heating a weighed sample of
aggregate at 212°F in an open pan and stirring it with a
rod until the surface water disappears (3 to 10 minutes).
The difference between the original and final weights is
considered to be moisture lost during drying. The loss
in weight, expressed as a percent of the final or dry
weight, is the moisture content, allowed before the
aggregate is mixed with asphalt cutbacks or road tars.
When the aggregate is too wet, it should be worked with
mechanical mixers, graders, or improvised plows to
allow the excess moisture to evaporate. For cutbacks
and tars, moisture content of coarse-graded aggregate
should not exceed 3 percent, and of fine-graded
aggregate, 2 percent. For emulsions, moisture content
of coarse-graded aggregate should not exceed 5 percent,
and of fine-graded aggregate, 3 percent.
The quality of the road-mix pavement depends
largely upon the control of the mix. The percentage
of bitumen will vary in relation to the absorptive
quality of the aggregate, rate of evaporation of the
volatile substances, and other factors. Although an
exact formula is difficult to follow, proportioning
must be controlled within narrow limits to assure the
stability and life of the mix.
aggregates especially, too much bitumen should not
be used. All particles of the completed mix should be
coated and uniform in color. When the mix is too lean,
the aggregate in the windrow will stand almost
vertically and have a dull look; and when the mix is
too rich, it will ooze or slip out of shape. When the
mix is correctly proportioned, a handful, squeezed
into a ball, will retain its shape when the hand is
Road-mix pavements should be constructed only
on a dry base when the weather is not rainy.
Atmospheric temperature should be above 50°F.
Mixing should take place at the temperature of the
aggregate, but not below 50°F or above the
recommended temperature of the liquid asphalt being
used. The construction procedure depends upon
whether the base is a newly constructed base, a
scarified existing base, or an existing pavement.
When a newly constructed base is used, perform the
1. Inspect and condition the base.
2. Prime the base and allow the prime to cure.
3. Haul in and windrow the aggregate at the side of
the primed base. (Allow the aggregate to dry or aerate
with a blade when wet.)
4. Spread the aggregate on the cured prime base
one half of the roadbed width.
5. Spray the bitumen on the aggregate in incre-
ments of about one third of the total amount required.
6. Mix the bitumen with the aggregate; blade back
and forth until a uniform mix is obtained.
Repeat as directed in (5) and (6) until thoroughly
Spread the mix to the specified thickness.
Compact the surface.
Apply a seal coat when necessary.
For a scarified base, the aggregate is scarified when
it is not available from other sources. The construction
procedures are as follows:
1. Loosen the aggregate from the base.
2. Dry and breakup all lumps of material.
3. Blade into parallel windrows of uniform size at
one side or in the center.
4. Sweep the base, when needed
5. Prime the base and allow time to cure.
6. Continue as directed in (4) through (10) in
the above procedures for a newly constructed base.
When an existing pavement is to be used as a base,
the construction procedures are as follows:
1. Sweep the base.
2. Apply a tack coat and allow it to cure.
3. Bring in the aggregate and deposit in windrows
at the side of the cured, tacked base.
4. Aerate the aggregate.
5. Spread the aggregate on one half of the tacked
6. Spray bitumen on the aggregate in increments of
about one third of the total amount required
7. Mix the bitumen with the aggregate by blade.
8. Spread the mix to specified uncompacted