This item includes placing a surface
or intermediate course asphalt concrete that is accepted based on plant testing
and verification or plant testing and verification with field density
testing. The requirements of 401
and 441
apply to this item except as noted.
Supplement
1055 details the requirements for performing density testing using either a
nuclear gauge in the backscatter mode or an electronic density gauge, Pavement Quality
Indicator (PQI) Model 300, manufactured by TransTech Systems.
Each gauge requires a specific method of operation as detailed in
Appendices A and B of S1055.
Figure 448.A – PQI Electronic Density Gauge
The Contractor is required to
establish a “minimum density target” during the first production day or when
there are subsequent mix changes that require reestablishing the minimum
density target. The minimum density
target is determined by rolling the newly placed mat until there is no change
in the unit weight (pounds per cubic foot = PCF) as
recorded by the test gauge. At that
time, a core is cut and tested to correlate the gauge unit weight to
density. This is done in three separate
locations when using a nuclear gauge and in five separate locations when using
an electronic gauge. Readings and
calculations are recorded on Form TE – Min Density Target,
Nuclear, in
S1055
Appendix C or Form TE – Min Density Target Elec
Gauge, in S1055
Appendix D. The cores are sent to
the District Lab and tested for density.
Using the average of the gauge readings and the average of the
laboratory density results, a minimum target density unit weight (PCF) is calculated that corresponds to 93 percent
density. This means the gauge reading in
the field has to be at least that minimum unit weight (PCF)
in order to have 93 percent density of the asphalt mat.
Example:
The following information was
recorded on Form TE – Min Density Target, Nuclear.
Average
of nuclear gauge readings = 142.0 PCF
Average
of core density test results = 95.0%
Minimum
density target for 93 percent field density = [93 x (142.0/95.0)] = 139.0 PCF (unit weight)
Therefore,
in the field, the gauge has to read 139.0 PCF in
order to have a minimum 93 percent mat density.
Note: There is a time lag
between when the cores are cut and tested, and the project will not know what
unit weight (as recorded by the gauge) corresponds to 93 percent field
density. During this period, the
Contractor will calculate a required unit weight based on the JMF Maximum Theoretical Specific Gravity. The testing technician will use this unit
weight in the gauge until the lab unit weight is determined from the actual
cores.
During
paving, after startup, the Contractor uses the minimum target density unit
weight to maintain mat density above 93.0 percent, but less than 96.5 percent. Quality control (QC) tests are
required to be taken at 1,000 feet intervals, but the Contractor is expected to
perform more than the minimum required.
Alternate the transverse location of each 1,000 foot test; start at the
left side of the mat, move to the middle of the mat, then the right side of the
mat, and repeat. Tests at the edge of
the mat should be taken one foot from the edge.
The Contractor will mark the test location on the pavement.
The minimum
required QC tests must be recorded; interim tests do not have to be
recorded. Use Form TE – Mat Density QCQA to record
the required tests.
The
Contractor is expected to make changes to the rolling pattern to keep the
density above 93.0 percent.
The project
Inspector will randomly select two locations during each production day for
Quality Assurance Testing (QA). Each
test should represent one-half of the day’s production. The first location will be at a Contractor QC
test area where tests were performed that day.
The second location will be anywhere on the mat, but at least 500 feet
from the start of the day’s paving. QA
tests must be located inside the closed lane.
The project Inspector must witness and initial the QA tests.
QA tests are
completed using three gauge readings across the mat, left, center, and right,
and averaging the density results. The
results are recorded on Form TE – Mat Density QCQA.
When one of
the daily QA test density results is less than 91.0 percent, a deduction is
applied to the Contractor’s payment for that half day’s production as detailed
in Table 1055.04-1 in S1055. If both daily
QA test densities are below 92.0 percent, the payment deduction is based on Table
1055.04-2 in S1055 and is applied to each half day’s production.
Minimum Density
Target in PCF
Figure 448.B – Example of Completed QC/QA Report
Acceptance of
the asphalt mix is based the Contractor’s quality control testing at the
asphalt plant and the District Lab Monitoring Team’s verification of the
Contractor’s testing. Sampling is
typically not required at the project site, but in the event there are
workmanship problems during placement, or quality control problems at the
plant, the Monitoring Team may require a sample taken from the road in
accordance with Supplement 1035. If the
pavement mat is less than 1-1/4 inches, the sample would be taken from the
paver hopper. After a plate or hopper sample is obtained, it should be packaged
and identified in accordance with current District or Laboratory policy. The sample must be shipped to the District
Lab as soon as possible or as directed by the Engineer or DET. Samples obtained by plate sampling are tested
to determine the gradation and binder content of the asphalt concrete mix.
In addition
to plant sampling and verification for acceptance, the specifications require
density gauge testing according to Supplement 1055 when placing a uniform course 1 inch or thicker. When field density testing is required, the
roller selection is at the discretion of the Contractor and not governed by 401.13. The
requirements of 401.16 are waived except the last four paragraphs. These applicable paragraphs detail the
compaction operation and sequence.
Field density
testing is used to determine compaction and whether a deduction to the
Contractor’s pay will be made for inadequate compaction.
Refer to Supplement 1055 for the details of density testing requirements. The Inspector should understand and monitor
the testing for compliance.
In addition to the
Documentation Requirements listed in 401,
ensure forms for Minimum Target Density, Quality Control, and Quality Assurance
testing are completed and submitted to the project on a daily basis.