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.
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.