This specification is
intended to be used for pavement preventive maintenance, but may have other
applications as well. The specification
includes two mixture compositions: Type A and Type B. Both mixtures are required to use a polymer
binder.
Type A material is a very
fine graded mix composed primarily of natural sand and contains a very high
polymer binder content (8.5 percent).
This is a recipe mix. It is
designed to give a long life, but generally is not for high truck traffic
situations. A Type A mix is normally
specified as a 5/8-inch (16 mm) mat thickness.
Type B material is a fine
graded mix composed of more angular materials and contains less binder content
than the Type A mix (minimum of 6.4 percent).
This mix is designed by the Marshall Mix Design Method for light,
medium, or heavy traffic. The Type B mix
is designed to be more rut resistant than Type A. The Type B mix can be placed on medium and
high volume roads, including most interstate applications. A Type B mix is normally specified as a
3/4-inch to 1-inch (19 to 25 mm) mat thickness.
Figure 424.A – Item 424
(Type A and Type B) Mix Compositions
The equipment requirements of
401
apply to this work.
Both types of mixtures under
this specification use a polymer binder.
Either a PG 76-22M asphalt binder or a PG 64-22 asphalt binder modified
by the addition of 5.0 + 0.3 percent Styrene Butadiene Rubber (SBR) can
be used.
The use of reclaimed asphalt
pavement is not permitted in a Type A mix.
Fine aggregate for use in
this specification is required to have at least 50 percent silicon dioxide by
weight. This special requirement ensures
proper skid resistance for both mix types.
Coarse aggregate used in the
Type B mix is required to have 10 percent two-faced crushed aggregate by weight
for medium traffic applications and 100 percent two-faced crushed aggregate for
heavy traffic applications.
When these mixtures are
discharged from the plant, the mix temperature must be between 335 ºF and 370
ºF (168 ºC to 188 ºC).
Figure 424.B – Mix Texture
for Type A, Item 424
Figure 424.C – Mix Texture
for Type B, Item 424
The placement of either Type
A or B material cannot be placed if the exiting pavement temperature is less
than 60 °F or the ambient air temperature is less than 60 ºF (16 ºC).
Either mixture is to be placed
and compacted per the requirements of 401;
a three-wheel roller is required in the breakdown position behind the
paver. Do not use vibratory rollers when
the mat thickness is less than 1-1/2 inches.
Traffic is not allowed on the
compacted surface until it has cooled enough to prevent damage.
Surface tolerances are to be
checked and must be in conformance with 401.19
for transverse slope and surface smoothness.
The transverse slope cannot vary more than 3/8 inch in 10 feet. The surface smoothness cannot vary more than
1/4 inch in 10 feet. Ensure that the
finished surface is within these tolerances as the paving progresses.
Type A mixtures are to be
accepted using Item 301
procedures (see Item 403)
and Type II materials are to be accepted according to Item 448
procedures.
1. State condition of base (example: primed 304,
clean and dry concrete, etc.).
2. Write location on tickets where material is placed.
3. Mark on ticket time unloaded.
4. Obtain temperature of the mix at project site and
place this information on ticket of load checked. This should be done a minimum
of four times daily or any time temperature is in question.
5. State kind of rolling equipment and maximum tons per
hour they are allowed to cover. See example, “Roller Capacity and Placement
Rate.”
6. Calculate and document the required placement rate
(Tons/Station).
7. Document on form CA-FP-4.
8. Lift thickness if required.
9. Tickets should be totaled with initialed and dated
tape attached.