Case Studies Using Falling Weight Deflectometer Data with Mechanistic Empirical Design and Analysis International Symposium on Pavement Performance Trends, Advances, and Challenges December 5, 2011, Tampa, FL Presented by: Linda M. Pierce, PhD, PE
Outline Project purpose Use of deflection data in the MEPDG Case studies
Project Purpose FHWAstudy DTFH61 06 C 00046 00046 Release of MEPDG and heightened need for characterizing existing layers COTR Nadarajah Siva Sivaneswaran
Project Reports
Use of Deflection Data in MEPDG Backcalculated moduli only Level 1 materials characterization only No internal MEPDG forward or backcalculation procedures
Flexible Pavements Dynamic modulus of HMA layers Resilient modulus of chemically stabilized layers Resilient modulus of unbound layers Non linear considered, but not calibrated, and not recommended Elastic modulus of the bedrock layer
Rigid Pavements Elastic modulus of the concrete and base layers Subgrade k value Concrete flexural strength Determined from the backcalculated concrete elastic modulus
Characterization of HMA Layer 1. Conduct FWD testing 2. Determine mix properties from cores (air voids, AC%, gradation, dti viscosity it parameters) 3. Determine undamaged dynamic modulus 4. Estimate fatigue damage (using results from step 1 & 3) 5. Calculate α f (mix gradation parameters) 6. Determine field damaged dynamic modulus
Characterization of HMA Layer
Characterization of PCC Layer Effective k value Composite stiffness of all layers beneath the base Internal conversion from backcalculated layer moduli Backcalculated subgrade modulus not directly used in the MEPDG
Characterization of Stabilized Layer Backcalculated moduli Assumed to be at time of overlay application Reduced based on current condition of stabilized layer and surface f (alligator cracking, reflective cracking)
Characterization of Stabilized Layer
Characterization of Unbound Layers Backcalculated moduli Adjusted to laboratory values 0.67 for granular layers 0.40 for subgrade layers Other materials see Table 1
Case Studies LTPP sections Backcalculation methods Flexible: Evercalc, MODTAG, MICHBACK Rigid: AREA method MEPDG v 1.003 Nationally calibrated models only
Case Studies HMA LTPP Section 30 01000100 Great Falls, Montana Interstate 15 4 in HMA over 8 in aggregate g base Overall pavement condition: Fair condition Rutting Rehabilitation type evaluated: HMA overlay
Case Studies HMA Scenario Layer Moduli, MPa (lb/in 2 ) HMA Base Subgrade A. MEPDG Default Internal 262 100 calculation (38,000) (14,500) B. MODTAG (uncorrected 3 layer) 4,195 (608,500) 115 (16,700) 148 (21,500) C. MODTAG 4,195 72 52 (corrected 3 layer) (608,500) (10,400) (7,500) D. Evercalc/MICHBACK (corrected 3 layer) 4,116 (597,000) 52 (7,500) 62 (9,000) E. LTPP Laboratory Testing Results 2,413 (350,000) 91 (13,200) 27 (3,900) F. MODTAG 4,075 84 43 (corrected 4 layer) (591,000) (12,200) (6,300)
Case Studies HMA Predicted Distress Distress Quantity (Reliability) A B C D E F Terminal IRI (in/mi) 109 97 97 97 101 98 (98) (100) (100) (100) (99) (100) Long. Cracking (ft/mile) 5.2 62.7 69.5 165.0 49.4 50.4 (100) (92) (91) (86) (93) (93) Alligator Cracking (%) 0 0 0 0 0.3 0 (100) (100) (100) (100) (100) (100) Transverse Cracking (ft/mi) 1 1 1 1 1 1 (100) (100) (100) (100) (100) (100) HMA Rutting (in) 013 0.13 008 0.08 007 0.07 008 0.08 012 0.12 008 0.08 (99) (100) (100) (100) (100) (100) Total Rutting (in) 0.38 0.08 0.08 0.08 0.16 0.12 (100 (100) (100) (100) (100) (100) Overlay Thickness (in) 3 3 3.5 3 3 3
Case Studies HMA Findings Untilfurther study Use MEPDG provided field lab correction factors Use 30 Hz for equivalent frequency
Case Studies PCC LTPP Section 32 0200 Lander County, Nevada Interstate 80 11.6 in PCC over 25.7 in base/subbase over 12 in lime treated subgrade Overall pavement condition: Poor Transverse cracking, faulting Rehabilitation type evaluated: HMA overlay, bonded PCC overlay, and unbonded PCC overlay
Case Studies PCC Alternatives Laboratory determined material properties Backcalculated PCC dynamic elastic modulus & dynamic k value for supporting layers (all layers beneath the base) Backcalculated PCC dynamic elastic modulus & dynamic k value for supporting layers (all layers beneath the slab)
Case Studies PCC Alternative 1. Laboratory determined 1. Backcalculated PCC 1. Composite stiffness PCC Elastic Modulus, lb/in 2 (MPa) k value, lb/in 2 /in (kpa/mm) 2,783,000 NA (19,188) 3,100,000 000 310 (21,359) (84) 3,100,000 375 (21,359) (101)
Case Studies PCC Alternativeti 1. Laboratory determined 1. Backcalculated PCC 1. Composite stiffness HMA Overlay, Unbonded PCC Overlay, Bonded PCC Overlay, in (mm) in (mm) in (mm) 12 7 4 (305) (178) (100) 12 7 4 (305) (178) (100) 12 7 4 (305) (178) (100)
Case Studies PCC Findings HMA overlay Varying subbase stiffness had little influence on determined k value Stiffness of base may not be included in k value calculation (possible bug) MEPDG possibly ignores entered k value (possible bug)
Questions Linda Pierce 505.796.6101 lpierce@appliedpavement.com