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.
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.
Target in PCF
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.