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Update on CC6

Update on CC6. Review of CC6 Test Objectives. Investigate the relative effect of concrete strength on test item performance. Will concrete that is “too strong” perform poorly due to embrittlement? (Or is “embrittlement” really more a function of the cement content than of flexural strength?)

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Update on CC6

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  1. Update on CC6

  2. Review of CC6 Test Objectives • Investigate the relative effect of concrete strength on test item performance. • Will concrete that is “too strong” perform poorly due to embrittlement? (Or is “embrittlement” really more a function of the cement content than of flexural strength?) • Is the current flexural strength limitation in AC 150/5320-6E justified by objective full-scale test data? • Investigate the effect of subbase material (cement stabilized vs. asphalt stabilized) on performance. • Will test items on econocrete prove more susceptible to top-down cracks (e.g., corner breaks) than HMA stabilized base? • Is the stiffness of the subbase the key subbase parameter affecting life (as assumed in the FAARFIELD model)? • CC6 test items give 6 combinations of concrete strength and subbase type.

  3. Thickened Edge Isolation Joint (A) Reinforced Isolation Joint (A1) CC6 Test Item Structure Summary “Low Strength”Target 500 psi “Medium Strength”Target 750 psi “High Strength”Target 1000 psi

  4. CC6 Test Items – Concrete Strength

  5. CC6 Trafficking History * Preliminary traffic tests (zero wander) on MRS-1 North only

  6. SCI vs. Passes (All Test Items)

  7. SCI versus Traffic Analysis • All test items (except MRS-1 South) experienced traffic at a mixture of different load levels. • All 6 test items received 15,708 passes at the 45,000 lb. wheel load level. • MRS-2 and MRS-3 received additional traffic at higher loads (52,000 and 70,000 lbs.). • During the preliminary test phase, MRS-1 North received 6,790 passes (zero wander) at 45,000 lbs. Only 6 of 10 slabs were trafficked in this preliminary phase. • To compare performance of test items, need to compensate for different loads. • Use a variation of compensation procedure for CC5.

  8. Load Compensation Procedure • Assume the rigid failure model takes the form : (The FAARFIELD model can be reduced to this form.) • Hold B constant and find A that satisfies the condition:CDF = 1.0. • For a given reference wheel load, find the number of equivalent coverages at that load that gives CDF = 1.0. CF = coverages to failure (failure defined as some value of SCI) R = concrete flexural strength  = computed slab stress A, B = parameters

  9. Example – MRS-3 North Start trafficking at 70,000 lbs./wheel No. of passes to SCI 50 = 31,325(4,595 passes @ 70 K) For purposes of comparison between test items, assume SCI 50 is the failure condition.

  10. Example – MRS-3 North (Step 1) • Unadjusted coverages to SCI 50 condition: • Fit the above data to the failure model. At failure: • Substituting R = 1000 psi, B = 4.011 (from the FAARFIELD model), solve to get A = 1.199  10-3.

  11. Example – MRS-3 North (Step 2) • Obtain the equivalent number of passes normalized to the 70 kip reference wheel load: • Substitute A = 1.199  10-3 and  = 668.96 psi in each term of the CDF equation. • In a spreadsheet, adjust the number of coverages until the value of each term matches the previous step and CDF = 1.0. • Equivalent passes @ 70 kips = 1185.5 x 3.96 = 4695(accounts for damage due to traffic at lower loads).

  12. Equivalent Passes to Failure

  13. Use of Laser Imaging to Document CC6 Distresses Josh Davis to brief on distress mapping

  14. Isolation Joint Damage (April 13, 2012) Reinforced Isolation Joint Thickened Edge Isolation Joint

  15. CC6 Preliminary Conclusions • As expected, CC6 pavement life was strongly correlated to 28-day concrete strength. • This is apparent when test items are compared on the basis of equivalent passes at a reference load. • Test items ranked by life: MRS-3 > MRS-2 > MRS-1. • After 15,708 passes at 45 kips/wheel, only the low-strength (MRS-1) test items exhibited significant distress. Higher loads were required to fail MRS-2 and MRS-3. • No significant difference in SCI for HMA (north) and econocrete (south) base. However, some differences in crack patterns were observed. • Thickened edge joint performed better than reinforced isolation joint.

  16. CC6 Work Remaining • Obtain sawed concrete beam specimens from all test items for additional strength testing in lab. • Complete fatigue testing on lab-cured beams. • Posttraffic testing: • Characterize cracks (top-down, bottom-up) where possible. • Document condition of P-401 & P-306 base layers. • Posttraffic HWD, CBR, plate-load tests, elevations. • Obtain data on posttraffic density in lower layers. • Sensor data: • Populate CC6 database. • Analyze sensor data and correlate with condition survey data.

  17. Follow-On Work • What are implications of CC6 test data for: • Concrete design strength limitations as given in AC 150/5320-6E. • Use of C78 beam flexural strength as a predictor of as-built concrete fatigue strength (and by extension, rigid pavement life). • Reasonableness of table 3-4 subgrade compaction criteria as applied to rigid pavements. • Continue beam fatigue studies for different concrete strengths.

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