Thomas Bennert Rutgers University CAIT RUTGERS. NEAUPG October 6-7th, 2010 Saratoga Springs, NY

Transcription

1 Thomas Bennert Rutgers University NEAUPG October 6-7th, 2010 Saratoga Springs, NY

2 Although moisture damage can, and does, occur in HMA, higher potential in WMA due to its method of production Potential for inadequate drying at lower temperatures Introduction of moisture due to technology used

3 Spontaneous Emulsification when water gets suspended within asphalt binder Detachment excessive moisture in aggregate not removed and migrates to agg/ asphalt interface Displacement moisture absorbed into aggregate from break or lack of coating on aggregate

4 Pore Pressure Mechanism densification of HMA traps moisture in voids with traffic creating pore pressure 5. Hydraulic Scour traffic applying compression-tension cycle of water pressure leads to displacement or spontaneous emulsification - Also ph Instability of aggregate and asphalt binder 4.

5 Although moisture damage can, and does, occur in HMA, higher potential in WMA due to its method of production Potential for inadequate drying at lower temperatures Introduction of moisture due to technology used Other issue: moisture damage may not occur immediately, and most likely requires combination of factors

6 Schmidt and Graf, 1972 (AAPT)

7 NJDOT conducted first WMA project in 2007 Rt 38 Sasobit at dosage rate of 0.8% by weight of asphalt binder 9.5mm, PG76-22, 15% RAP, 5.1% AC Mix Design TSR = 88% (80% min.)

8 TSR Test Results (cores) Normal = 71.1% W315 = 80.2% W270 = 55.9% TSR Test Results (reheated loose mix) Normal = 97.1% W315 = 87.3% W270 = 79.9% Trapped moisture in field cores? Additional drying/stiffening from reheating?

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10 Besides everything let s just talk aggregates Mix Design Dry aggregates completely Heat to mixing temperature No moisture remaining in aggregate or mix Plant Production Dry aggregates until mixing temperature achieved Are aggregates completely dry now?

11 Evaluate moisture damage potential of WMA mixtures Look at modified mixing procedure to better simulate plant production Evaluate other tests/conditioning methods for moisture damage potential Modified mixing procedure to better simulate plant production

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13 Initial WMA work conducted at NCAT looked at adding moisture In real life, moisture already there and absorbed in stone at the stockpile

14 Step 1 Dry aggregate blend and then add predetermined moisture content Place in air-tight container or bag Allow wetted aggregate to absorb water for minimum of 16 hours

15 Step 2 Dump contents in bucket mixer Mix and heat using propane rosebud torch Mix and heat until aggregates reach specified mixing temperature Once temperature reached, mix with binder

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18 Aggregate Sources Trap Rock aggregate blend absorption = 0.61% Crushed Gravel aggregate blend absorption = 1.47% PG76-22, 12.5mm Superpave Mix Mixing Temperatures 315 and 270oF Conditioned for 2 hours before compaction at 15oF lower than mixing temperatures Test Procedures TSR (AASHTO T283) and Hamburg

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21 Clear trend showing reduction in mixing temperature and increase in moisture content increases moisture damage potential Higher absorptive aggregate more prone to higher degree of moisture damage potential Large reduction in tensile strength from HMA, even when WMA TSR is passing

22 Evaluating moisture damage potential of various WMA additives Sasobit, Rediset WMX, Evotherm 3G, Advera, Cecabase, and SonneWarm Evaluating other test methods for sensitivity and conditioning methods TSR, Hamburg, E* Stress Ratio AASHTO T283 Freeze-Thaw and MiST Device AASHTO T329 Moisture Content of HMA

23 Induces pore pressure to compacted specimen Can varying water temp, pore pressure, and number of applied cycles Simulates Pore Pressure Mechanism and Hydraulic Scour

24 Approximately 4,000 cycles in MiST Equaled TSR Results

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26 Dynamic Modulus (E*) evaluated for moisture damage under NCHRP Project 9-34, as well as others Procedure used here: Test specimen at 20oC Condition specimen Repeat test at 20oC Ratio between unconditioned and conditioned = DMR

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28 Due to it method of production, WMA has higher potential for moisture damage Important to consider differences between laboratory and plant production processes Modified Moisture Damage Procedure Can simulate production temperature and aggregate moisture properties Results to date mimic those observed from plant produced mixtures MiST appears to include two major moisture damage mechanisms critical in evaluating stripping potential

29 Thomas Bennert Rutgers University