CC2 -Test Items: Material Testing
Material testing was conducted December 4, 2002 to April 11, 2005. The following summarizes the tests for material properties performed during construction, trafficking, and the post-traffic period and when testing was accomplished.
Tests and Timeframes
Moisture content of the subgrade material was used to establish the subgrade strength during construction. CBR and moisture content bear a direct relationship to each other for a given compaction method. The relationship was determined during CC-1 for compaction using the dual steel drum vibratory roller, and during CC-2 for compaction using the rubber tire roller. CBR test results on each subgrade lift formed the basis for the acceptance criteria. The remaining tests listed below were performed for material characterization purposes and subsequent analysis of the traffic test results.
· CBRs on subgrade lifts (acceptance tests for strength), December 4, 2002 to December 19, 2003.
· Moisture content of subgrade lifts (acceptance tests), December 4, 2002 to December 19, 2003.
· Shelby tubes in subgrade (moisture gradient tests, post-traffic) March 16 and 17, 2005.
· Plate load tests, base, subbase, subgrade (stiffness; construction and post-traffic), November 25, 2003 to March 14, 2005.
· Portable Seismic Pavement Analyzer (PSPA, stiffness of concrete slabs, MRS, construction) February 25 to March 30, 2004.
Field Tests Timeframe
Slump and air content of concrete, day of placement (acceptance tests), were conducted January 7 to March 2, 2004.
Laboratory Test Timeframes
Timeframes for the various test activities were:
· Beams and cylinders molded during concrete placement (flexural and compressive strengths, various time intervals), January 15 to June 2, 2004.
· Free-free resonance (stiffness), taken on molded beam and cylinder samples on the day of testing, January 15 to June 2, 2004.
· Sawed beams and cored cylinders (flexural, split tensile, and compressive strengths of concrete, post-traffic), following time of pavement failure, September 1, 2004 to April 11, 2005.
· Free-free resonance tests taken on cored cylinders one week prior to testing.
CBR Test Locations
Below is information about the test locations during construction on medium strength subgrade for cc-2 rigid pavements at the naptf
CBR tests will be performed on each lift during construction of the medium-strength subgrade sections. Three penetrations will be made at each test location and the mean value will be reported as the CBR value. The test locations will be selected randomly, however any test location on the north side will be mirrored on the south side or vice-versa. It is proposed that the CBR test locations preferably lie in the wheel tracks on both the sides (north side and south side). The test locations should lie between the offsets (from centerline) of –7-feet and –18-feet on the north side and 7-feet and 18-feet on the south side. At least one CBR test should be conducted in each test item for each lift. Figure 1 shows the area preferable for the CBR tests.
Figure 1. CBR Test Locations in Medium-Strength Subgrade
1. Target CBR to be defined.
2. Acceptance criteria to be defined.
SG Acceptance Criteria
TABLE 1. Allowable CBR Ranges
Click here to download (MSExcel) CC2 Test Item Materials Testing data spreadsheet
Item P‑152LM Subgrade
(FOR MEDIUM STRENGTH SUBGRADE)
152LM‑3.4 Acceptance Testing for CBR. Each layer of the subgrade will be accepted when the measured CBR meets the requirements defined in Section 152LM-3.4.
Acceptance measurements will be made on each lot of completed subgrade. Each lift of subgrade, including the bottom layer, for the required length of medium strength subgrade shown on the plans, shall be divided into two (2) lots, representing material placed on the north and south sides of the test pavement centerline. Each lot area will be divided into two (2) equal areas, or sublots (See figure 1). A random location will be located in one sublot within the vehicle wheel path in accordance with procedures described in ASTM D 3665.
A corresponding location shall be established in the adjacent lot at the same station and corresponding offset. The Engineer reserves the right to perform additional CBR tests at random locations outside the vehicle wheel path to verify material quality in those areas and include these additional tests in the lot samples for acceptance evaluation.
Three (3) CBR penetrations will be made within one foot of each other at each random location in each sublot. The average of the three penetrations will be considered as an individual CBR test for that sublot provided the range in the three penetrations is less than, or equal to, 1.5. Should the range exceed 1.5, an additional penetration(s) shall be performed adjacent to the first three to test for local variability. ASTM E-178 shall be consulted to establish whether any one or more of the set of penetrations is an outlier at a significance level of 5 percent, to determine if any value(s) should be discarded when performing the acceptance computations. The average of the penetrations (or those remaining after the E-178 test for outliers), shall be averaged to establish the individual CBR test for that sublot location.
The lot shall be considered acceptable when (See Table 1):
a. The range between the high and low CBR tests within a particular lot is less than or equal to 2.0 for the lot.
b. The range between the high and low CBR for two contiguous side by side (i.e., north and south) sublots is 1.0.
c. The difference in the average CBRs (i.e., the average CBR for the two sublots representing the particular lot) for contiguous north – south lots is equal to, or less than, 2.0.
d. The average of the two lots is equal to, or less than, 2.5. For a nominal target CBR of 7, the average of the two lots material is between 5.5 and 8.0 (1.5 below target to 1.0 above target).
Table 1 assumes sublot 1A is the starting point. “X” is the value obtained from the average of 3 CBR penetrations. “X” (as the starting point) should be as close to the Target CBR as possible.
Subgrade material not meeting the CBR acceptance criteria shall be reported to the engineer as soon as practicable to determine a corrective course of action. In most cases, the material will pulverized, reworked by wetting or drying, and recompacted until the CBR acceptance criteria is satisfied.
FIGURE 1. CBR Test Configuration For Each Lift
FIGURE 2. TORVANE
Figure 3. Relationship Between Shear Strength and CBR
Figure 4. Plate Load Test on Top of Subgrade
Lift Test Output
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