Impact of Healing Self healing in bituminous materials N 18.3 C E* f 3.291 0,845 t 0? Lab. Field log N
Healing Mechanism Step 1: Interfacial Wetting Step 2: Intrinsic healing d t, X dt a b = fn (healing zone, bonding stress, creep compliance properties, work of cohesion) R h t fn (work of cohesion, self diffusivity) The two processes are combined using the approach originally proposed by Wool and O Connor as follows: R t R h d, X t dt d
Healing Mechanism Step 1: Interfacial Wetting Bonding stress: Indirectly dependent on the surface energy Crack surface b a b Crack closing speed Healing process zone Work of cohesion: From surface energy d t, X dt a b 1 D k W 2 c D = fn (healing zone, bonding stress, 2 creep 1 mcompliance 4 1 properties, b work of cohesion) 0 1 m Viscoelastic property: Creep parameters from power law, (t)=d 0 +D 1 t m
Healing Mechanism Step 2: Intrinsic healing Strength gain of wetted surfaces over time is defined using an intrinsic healing function: t Strength gain is also a two step process: 1. Instantaneous adhesion due to surface energy 2. Time dependent self diffusion and randomization R h Collectively, the intrinsic healing function can be modeled as: Instantaneous healing proportional to work of cohesion R h qt t R p 1 e 0 r Time dependent healing proportional to self diffusivity
Healing Mechanism Instantaneous healing proportional to work of cohesion R h qt t R p 1 e 0 r Time dependent healing proportional to self diffusivity The approach used in polymers is based on the random walk approach requires detailed knowledge of the molecular structure of the material more applicable to materials with chain like molecules With Instead asphalt we used binders, a DSR we to do determine not have the the intrinsic luxury of healing either of the above function two. of different asphalt binders
Quantifying Intrinsic Healing Outline of the procedure ω = 10 rad/sec D 1 = 25 mm t 3.5 mm t 3.5 mm t 1 = 7 mm D = 18 mm Two piece specimen of asphalt binder was brought into contact to obtain a wetted interface G* was recorded intermittently at 0, 2, 4, 6, 8, 10, 15, 20, 25, 30, 40, 50 and 60 seconds after bringing the two specimens into contact with each other
Quantifying Intrinsic Healing Outline of the procedure The final results were normalized by repeating the test with a single specimen of the same asphalt binder and twice the thickness D 1 = 25 mm ω = 10 rad/sec t 7.0 mm t 1 = 7 mm D = 18 mm
Quantifying Intrinsic Healing Images of the test being performed with the two piece specimen before and after the test
Data analysis Quantifying Intrinsic Healing
Replicate data Quantifying Intrinsic Healing
Quantifying Intrinsic Healing Results for the SHRP binders
Results for the SHRP binders Quantifying Intrinsic Healing This data were fit to the functional form for intrinsic healing to obtain the relevant parameters R h qt t R p 1 e 0 r Recall that the term Ro, was due to the surface free energy or work of cohesion of the binder
Validation of Model R t R h t d, X dt d Force Data Acquisition & Properties related to intrinsic healing
Validation of Model R t R h t d, X dt d 0.450 0.400 0.350 Healing Index 0.300 0.250 0.200 0.150 0.100 0.050 S-20 F-20 -CH 2 /-CH 3 = 3.9 -CH 2 /-CH 3 = 3.3 5 minutes 10 minutes 20 minutes 40 minutes -CH 2 /-CH 3 = 2.1 W-40 0.000 2.05 2.1 2.15 2.2 2.25 2.3 2.35 MMHC Ratio
Validation of Model R t R h t d, X dt d
Intrinsic Healing Temperature and Age Dependency Total intrinsic healing at the end of 1 hour for RTFO and PAV aged binders at different temperatures
Quantifying Healing: DMA o Cyclic Rotation time Specimen Fabrication Test Setup Test Form
Quantifying Healing: DMA
Healing: Convolution of Wetting/Intrinsic Healing
Healing: Convolution of Wetting/Intrinsic Healing
Healing: Convolution of Wetting/Intrinsic Healing
Healing: Convolution of Wetting/Intrinsic Healing
Healing: Convolution of Wetting/Intrinsic Healing Damage evolution of the intact specimen Extension in fatigue cracking life due to each rest period
Healing: Convolution of Wetting/Intrinsic Healing
t h d dt X d t R R, Measured experimentally (FAM DMA fatigue) Measured experimentally (DSR binder) Elements of Micromechanical Model m b c m b D W D k a dt X t d 1 0 2 2 1 1 4 1, Wetting function obtained using overall healing curves with different materials will be used to validate relationship to surface free energy and viscoelastic properties
Micro-damage Healing Evolution fn 1 b 2 T 1 1 exp 1 cr T0 Abu Al-Rub, Darabi, h eff h h Little, and Masad (2010) b1 & b2 Model parameters related to history h Healing viscosity parameter (second -1 ) that controls how fast healing occurs, and increases as surface energy increases. The maximum healing rate: a h b h max h D0, D1, m, and km : Viscoelastic properties G : Surface energy : Size of the fracture process zone : Poisson s ratio h 1 2 G Dk 1 m 4(1 ) b 2 2 b D 0 1 m
Micro-damage Healing: Comparison with Experiments Axial strain (%) 9 8 7 6 5 4 3 Experimental data Model prediction without healing Model prediction including healing Axial strain (%) 10 9 8 7 6 5 4 3 Experimental data Model prediction without healing and damage Model prediction without healing Model prediction with healing 2 2 1 1 0 0 200 400 600 800 1000 Time (Sec) 0 0 500 1000 1500 2000 Time (Sec) =1500kPa LT=120 sec, Compression UT=100 sec =1500kPa LT=60 sec, UT=100 sec Compression LT : loading time UT : Rest period (unloading time)
Micro-damage Healing: Comparison with Experiments 14 5 12 10 Experimental data Model prediction without healing Model prediction including healing 4 Experimental data Model prediction without healing Model prediction including healing Axial strain (%) 8 6 Axial strain (%) 3 2 4 2 1 0 0 5000 10000 15000 20000 25000 30000 35000 Time (Sec) 0 0 200 400 600 800 1000 1200 Time (Sec) =1500kPa LT=60 sec, UT=1500 sec Compression =300kPa LT 120 sec, UT 100 sec Tension LT : loading time UT : Rest period (unloading time)
Micro-damage Healing: Comparison with Experiments Axial strain (%) 3.0 2.5 2.0 1.5 1.0 Experimental data Model prediction without healing Model prediction including healing Axial strain (%) 3.5 3.0 2.5 2.0 1.5 1.0 Experimental data Model prediction without healing Model prediction including healing 0.5 0.5 0.0 0 500 1000 1500 2000 Time (Sec) 0.0 0 5000 10000 15000 20000 25000 Time (Sec) =300kPa LT 60 sec, UT 100 sec Tension LT : loading time UT : Rest period (unloading time) =300kPa LT 60 sec, UT 1500 sec Tension
Mechanical Properties and Morphology Additional Work Techniques: AFM Nano-indentation Ref http://www.nanotech-now.com/art_gallery/antonio-siber.htm
Mechanical Properties and Morphology Techniques: AFM Nano-indentation Ref: Allan Grover, Master s Thesis
Mechanical Properties and Morphology Three dimensional depiction of phases (AAD unaged)
Mechanical Properties and Morphology Techniques: AFM Nano-indentation Ref: Allan Grover, Master s Thesis
Mechanical Properties and Morphology Three dimensional depiction of phases (AAD aged)
Mechanical Properties and Morphology Techniques: AFM Nano-indentation Creep measurements before and after aging Ref: Allan Grover, Master s Thesis