This work consists of constructing
a base course of aggregate and asphalt binder, which is mixed in a central
plant, and spread and compacted on a prepared surface. This item is similar to 301
and requires the same level of field inspection and documentation.
The requirements of Item 401
apply, except as modified by this specification.
The Contractor shall furnish
aggregate for the mix that conforms to the following gradation:
|
Sieve Size |
Total Percent Passing |
|
2 inch (50 mm) |
100 |
|
1-1/2 inch (37.5 mm) |
85 to 100 |
|
1 inch (25.0 mm)[1] |
68 to 88 |
|
3/4 inch (19.0 mm)[1] |
56 to 80 |
|
1/2 inch (12.5 mm)[1] |
44 to 68 |
|
3/8 inch (9.5 mm)[1] |
37 to 60 |
|
No. 4 (4.75 mm) |
22 to 45 |
|
No. 8 (2.36 mm) |
14 to 35 |
|
No. 16 (1.18 mm) |
8 to 25 |
|
No. 30 (600 µm) |
6 to 18 |
|
No. 50 (300 µm) |
4 to 13 |
|
No. 200 (75 µm) |
2 to 6 |
|
[1] Provide aggregate
to retain a minimum of 7 percent of the material on each of these
sieves. This requirement applies to
the gradation of the JMF and the mix production
according to Item 403. |
|
The Contractor may use
reclaimed asphalt concrete pavement (RAP) or reclaimed asphalt shingles (RAS)
as per 401.04. 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.
The Contractor must notify
the Engineer at least 24 hours before the start of paving. Spreading equipment must conform to 401.12
specifications. The Contractor must
submit, in writing, the model of asphalt spreader to be used, provide a
certification statement that all required modifications have been made, and
provide a signature. The compacted
thickness should be a minimum of 4 inches and a maximum of 7-3/4 inches.
The minimum air temperature
required for paving 302
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 a minimum of four times per day or more
if necessary. The temperature should be
documented in the project records.
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 a workable mix temperature and ensure 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, unless specified by the Department.
Compaction
must conform to specification 401.16.
Compact the mixture uniformly
using a combination of both steel and Type I pneumatic tire rollers which
conform to 401.13. Do not use a spreading rate that exceeds the
total of the specified capacities of the rollers in use.
Ensure that the compacted
depth of any one layer is between 4 and 7-3/4 inches 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 one
3-wheel roller, one vibratory roller with 66-inch drums (both vibrating), and
one Type I pneumatic tire roller to compact a 5-inch thick mat 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) = 1,980 sq
yd/hr
·
Type I Pneumatic
Roller = 1,000 sq yd/hr
·
Maximum roller
capacity = 700 + 1,980 + 1,000 = 3,680 sq yd/hr
[(3,360
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 = 1,022.22 tons per hour maximum placement rate.
Spread the mixture at a rate
calculated using the specified thickness and the compacted width of the
pavement course being placed, and the weight-to-volume conversion factors
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 302
Asphalt Concrete Base as a subbase for a rigid
pavement or base, do not exceed a variation of 1/4 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 Lab conversion factor is
2.0 tons/cubic yard. The required
placing rate (RPRS), in tons of material per station,
for a 12-foot 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
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. Obtain letter from Contractor stating paver to be used
and certifying that all modifications have been made as required.
4. Document tack or prime used along with source and
quantity used versus required.
5. Write location (station), date, and time on asphalt
plant tickets. Tickets should be totaled
daily, initialed, with the calculator tape attached.
6. 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 issues or observations made during paving operations.
7. 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.
8. Document the kind of rolling equipment and maximum
tons per hour allowed. See example,
“Roller Capacity and Placement Rate.”
9. Calculate and document the quantity of material placed
for payment.
10. Document on form CA-FP-4
or other approved form.