301 Asphalt Concrete Base

Description (301.01)

Composition (301.02)

Spreading and Finishing (301.04)

Hauling

Compaction

Spreading and Surface Tolerances (301.05)

Documentation Requirements 301 Asphalt Concrete Base

 

Description (301.01)

This work consists of constructing a base course of aggregate and asphalt binder, mixed in a central plant and spread and compacted on a prepared surface.

The requirements of Item 401 apply, except as modified by this specification.

 

Composition (301.02)

The Contractor shall furnish aggregate for the mix that conforms to the following gradation:

 

Sieve Size

Total Percent Passing

2 inch (50 mm)

100

1 inch (25.0 mm)

75 to 100

1/2 inch (12.5 mm)

50 to 85

No. 4 (4.75 mm)

25 to 60

No. 8 (2.36 mm)

15 to 45

No. 16 (1.18 mm)

10 to 35

No. 50 (300 m)

3 to 18

No. 200 (75 m)

1 to 7

 

The Contractor may use a maximum of 50 percent of reclaimed asphalt concrete pavement (RAP) as per 401.04. The Laboratory will establish the JMF according to 401.02.

Asphalt concrete is sampled and tested by the Contractor at the asphalt plant. Contractor tests are used for pay if they are verified by District testing. See 403.06 for sampling details.

 

Spreading and Finishing (301.04)

The Contractor must notify the Engineer at least 24 hours before starting paving. Spreading equipment must conform to 401.12 specifications. Ensure that the paver is approved by the Office of Materials Management. The maximum compacted thickness of any one lift is 6 inches. The uncompacted thickness will be greater than 6 inches.

The minimum air temperature required for paving 301 base is 40 F (5 C). The minimum mixture temperature when delivered to the paver is 250 F (120 C). When using warm mix asphalt the minimum temperature is 230 F (110 C). The mixture temperature should be checked at a minimum, 4 times per day and more if required. The temperature should be documented in the project records.

 

Hauling

Hauling must conform to specification 401.11.

The Contractor must use trucks for hauling asphalt concrete that have tight, clean, smooth metal beds from which the entire quantity of mixture is discharged smoothly into the spreading equipment.

If transporting hot asphalt concrete at prevailing air temperatures below 50 F (10 C) or if the length of haul exceeds 20 miles (32 km), ensure that all truck beds are insulated to maintain workable mix temperature, and that all covers are fastened to exclude the wind. Do not exceed a distance of 50 miles (80 km) from the asphalt concrete plant to the paving site except by specific permission of the Department.

 

Compaction

Compaction must conform to specification 401.16

Compact the mixture uniformly using a combination of both steel and Type I pneumatic tire rollers conforming to 401.13. Do not use a spreading rate that exceeds the total of the specified capacities of the rollers in use. A pneumatic tire roller is required for compaction of base mixes. The type and number of rollers must be documented in the project records.

Ensure that the maximum compacted depth of any one layer is 6 inches (150 mm) and the temperature of the mixture when delivered to the paver (not to the job site) is a minimum of 250 F (120 C).

 

Example: Roller Capacity and Placement Rate

A contractor is using 1 three-wheel roller, 1 vibratory roller with 66-inch drums (both vibrating) and 1 Type I pneumatic tire roller to compact a mat 5 inches thick using material with a Laboratory conversion factor of 2.0 tons per cubic yard.

From Table 401.13-1 the following is the capacity of the rollers the contractor will use:

         Three wheel = 700 sq yd/hr

         Vibratory roller = 2 drums x 66 in x (15 sq yd/in of width) = 1980 sq yd/ hr

         Type I Pneumatic Roller = 1000 sq yd/hr

         Maximum roller capacity = 700 + 1980 + 1000 = 3680 sq yd/hour

 

[(3360 sq yd/hr) X (9 ft2/sq yd) X (5 in) X (1 ft/12 in)] X (1 yd3/27 ft3) = 511.11 yd3/hr.

511.11 yd3 X 2.0 tons/Yd3 = 1022.22 tons per hour maximum placement rate.

 

Spreading and Surface Tolerances (301.05)

Spread the mixture at the rate calculated using the specified thickness, the compacted width of the pavement course being placed, and the weight-to-volume conversion factor established in 401.21. Maintain the actual rate of spreading the mixture within a tolerance of 5 percent.

Do not exceed 3/8 inch (10mm) in surface variation from the edge of a 10-foot (3 m) straightedge. Surface variations include bumps and depressions. If using Item 301 Asphalt Concrete Base as a subbase for a rigid pavement or base, do not exceed a variation of inch in 10 feet. (6 mm).

 

Example: Determining the Required Placing Rate per Station (RPRS)

A contractor is placing a 5 inch uniform mat of asphalt concrete pavement whose Laboratory conversion factor is 2.0 tons/cubic yard. The required placing rate (RPRS) in tons of material per station for a 12 ft wide mat is:

 

RPRS = [Volume of asphalt in cubic yards] x [Lab Conversion Factor]

= [{100 ft per station X 12 ft X (5 in 12 in/ft)} 27 ft3/ yd3] X 2.0 tons/yd3

= 37.04 tons/station

 

Documentation Requirements - 301 Asphalt Concrete Base

1.        Document condition of base material at the time of paving (example: primed 304, clean and dry concrete, etc.).

2.        Obtain JMF for the project.

3.        Determine and document if paver is on approved list.

4.        Document tack or prime used along with source and quantity used versus required.

5.        Document surface and air temperatures.

6.        Write location (station), date, and time on asphalt plant tickets. Tickets should be totaled daily, initialed, with the calculator tape attached.

7.        Document lift thickness, mat width, weather conditions, surface tolerance checks, equipment problems, mat problems (segregation, tearing, tenderness, etc), spreading rate, roller coverage, and any other issue or observations made during paving operations.

8.        Obtain and document 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.

9.        Document the kind of rolling equipment and maximum tons per hour allowed. See Example Roller Capacity and Placement Rate.

10.     Calculate and document the quantity of material placed for payment.

11.     Document on form CA-FP-4 or other approved forms as needed.