CC7 Trench Laboratory Testing

P-401 Asphalt Mix and ATDB Materials

Laboratory Testing Program

Laboratory testing program for P-401 and Asphalt Treated Drainable Base (ATDB) materials included asphalt pavement analyzer (APA), dynamic modulus, flow number, high temperature indirect tensile strength (IDTH), tensile strength ratio (TSR), and permeability test as shown in the table below. Number of test specimens test standards are also included.

Laboratory Testing Program for P-401 Asphalt Concrete and ATDB

Observations

• Pre-traffic specimens were prepared in the laboratory with a design air void (AV) of ~3.5% using Superpave Gyratory Compactor (SGC). However, post-traffic cores from the non-traffic areas had higher AV (6-10% range).
• APA rut depths for the north side specimens were slightly lower than the south side at both 100 and 250 psi pressures. Both north and south specimens performed well as per the recommended criteria for satisfactory APA rutting performance: less than 10-mm rut depth after 4,000 cycles.
• FN, IDTH, and tensile strength from TSR test were significantly higher for the north side specimens as compared to the south side due to the use of polymer modified binder (PG 76-22). TSR value was found to be satisfactory for both north and south specimens (TSR = 75%).
• ATDB coefficient of permeability for the non-trafficked area was 2.2 times higher than the trafficked area.

P-209 Crushed Aggregate Base and P-154 Subbase Materials

Laboratory Testing Program

The objective of post-traffic material characterization was to identify potential changes in the material properties due to traffic loads. Two tests were conducted on the P-154 and P-209 materials: 1) Grain Size Distribution (GSD) and 2) Resilient Modulus followed by a Quick Shear test at different levels of confining pressure. Determination of GSD was conducted by performing ASTM C117 Standard Test Method for Materials Finer than 75-µm (No. 200) Sieve in Mineral Aggregates by Washing, and ASTM C136 Standard Test Method for Sieve or Screen Analysis of Fine and Coarse Aggregates. The measurement of stiffness-strength was conducted in accordance with AASHTO T307 Determining the Resilient Modulus of Soils and Aggregate Materials. The number of tests per test procedure are summarized in the table below.

Laboratory Testing Program for P-209 and P-154 Materials

Observations

General

• Observations from GSD and triaxial test results were consistent for both P-154 and P-209 materials.
• Besides showing high correspondence to each other, GSD and triaxial test results on P-154 material also confirmed the field performance captured by surface rut depth measurements, and examination during CC7 post-traffic trenching. However, the same was not observed for P-209 material.
• Some discrepancy between friction angle values obtained from testing P-154 small (4 inch-diameter) and large specimens (6-inch diameter) was observed. Possible sources of such discrepancy were the specimen size and compaction method.

GSD and Triaxial Test Results of P-154 Subbase

• North Side: Observed differences in gradation corresponded to the degree of exposure to the damage imposed by a specific pavement structure, and to the specific traffic history in each particular test item. This indicated possible particle breakage in the form of attrition or abrasion.
• South Side: Observed differences in gradation corresponded to the changes in traffic conditions across test items imposed by the overloads. This indicated possible particle breakage in the form of abrasion.
• In both the north and south sides, these particle breakage mechanisms may promote increasing particle roundness which leads to the loss of particle interlock. This was found to be consistent with the triaxial test results that showed a decrease in friction angle with increasing level of exposure to compaction energy imparted by traffic.

GSD and Triaxial Test Results of P-209 Crushed Aggregate Base

• No differences were observed in gradation, modulus, and shear strength parameters that corresponded to the changes in traffic conditions across test items.

P-152 Dupont Subgrade

Laboratory Testing Program

For P-152 subgrade soil, only Resilient Modulus followed by unconfined Quick Shear test was conducted. The measurement of stiffness-strength was performed in accordance with AASHTO T307 Determining the Resilient Modulus of Soils and Aggregate Materials. A total of 14 undisturbed P-152 subgrade Shelby tube specimens of 2.8-inch diameter by 5.6-inch height were tested. Twelve of these specimens were sampled from trafficked areas and 2 from non-trafficked areas.

Observations

• Resilient modulus of subgrade on the north side was higher than the south side, which confirmed a stiffer subgrade on the north side. The target construction CBR values were 5.5 and 5.0 for the north and south side, respectively.
• Minimal difference between the north and south sides in terms of unconfined compressive strength was observed. The subgrade strength of the north side was uniformly distributed across test items, whereas on the south side a relatively high coefficient of variation was observed.
• Based on the triaxial test results, there was no observable effect of pavement structure and specific traffic history on the north side, and the changes in traffic conditions imposed by the overloads on the south side.

For detailed results, click here to download the CC7 Post-Traffic Report – Material Characterization.

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