investigation of thermal cracking at a test site near rochester
TRANSCRIPT
Investigation of Thermal Cracking at a Test Site near Rochester, Minnesota
Mike Farrar & Changping SuiWestern Research Institute
July 17, 20092009 PAVEMENT PERFORMANCE PREDICTION SYMPOSIUMLaramie, Wyoming
Principal Researchers: Fred Turner, Mike Harnsberger, Shin-Che Huang, Troy Pauli, Eric Kalberer, Will Grimes, Ron Glaser, Ryan Boysen, Will Schuster, Fran Miknis, Bill Tuminello, technical staff.
www.westernresearch.org
Acknowledgements
Minnesota DOT
Abatech TSARTM and RHEATM software
This work is being performed in supportof FHWA Contract DTFH61-07D-00005
Evaluation of apparent thermal cracking
1. How does the observed transverse cracking compare to BBR results using laboratory aged binders?
2. How does the observed transverse cracking compare to DSR (4 mm diameter parallel plates) results using laboratory aged binders?
3. How well do the BBR and DSR results compare?
Four asphalts from different sources were used to construct 5 comparative test sections at the Rochester, MN site. The crude oil source used to produce the asphalt binders is the only significant variable from section to section, except one section includes 20%RAP. One of the test sections is showing significantly more thermal cracking than theother 4 test sections.
Rochester, MN Comparative test sites
Constructed August 2006
Asphalt binder source
Asphalt Code Description
MN1-2 Canadian blend, Elvaloy modified
MN1-3 Canadian blend (a different blend compared to MN1-2)
MN1-4 Blend of Arab heavy, Arab medium, and Kirkuk
MN1-5 Venezuelan blend
31P NMR of MN1-2 Evaloy Modified binder
FTIR
Apparent Thermal Cracking
BBR vs. transverse cracking
Modified Tcr
MN 1-3 RTFO
0
2
4
6
8
10
12
14
16
18
-46 -40 -34 -28 -22 -16 -10
Temp (°C)
Ther
mal
Str
ess
(Mpa
)
Tsar+ Two-Point Six-Point
Two-Point Tcr = -33.9°CSix-Point Tcr = -32.3°C
Modified Tcr based on: Shenoy, A., “Single –Event Cracking Temperature of Asphalt Pavements Directly from the Bending Beam Rheometer Data”, Journal of Transportation Engineering, Vol. 128, No. 5, September 2002.
Modified Tcr vs. transverse cracking
Modified Tcr based on: Shenoy, A., “Single –Event Cracking Temperature of Asphalt Pavements Directly from the Bending Beam Rheometer Data”, Journal of Transportation Engineering, Vol. 128, No. 5, September 2002.
T BBR vs. Tcr
Dynamic Shear Rheometer (DSR) with 4 mm diam. parallel plates
---- Problem: Error due to machine compliance at low temperature---- Solution: Correct compliance error using method developed by Schröter et al.1
1 K. Schröter, S. A. Hutcheson, X. Shi, A. Mandanici, and G. B. McKenna, J. Chem. Phys. 125, 2006, 214507.
Plate radius = 2 mmSample gap = 1.5 ~ 1.75 mmSample volume = 18.84 ~ 21.98 mm3
TA Instruments has adjusted the ARES rheometer software to correct for machine compliance
WRI’s ARES rheometer
K*mes is the measured complex torsional stiffness K*s is the actual complex torsional stiffness of the sample Kt is the machine torsional stiffness. G is the shear modulush is the gapR is the plate radius
Compliance correction cont.
Compliance Correction for Dynamic Data
tsmes KKK1
*1
*1
+=
hRGK
4
2π
= tsmes KRGh
RGh 1
*2
*2
44 +=ππ
From Schröter et al 2006
Assume the machineis a spring in series with the viscoelastic sample
BBR vs.. DSR (4-mm diam. parallel plates)
BBR DSR (PP4)
Materials required for one specimen
~ 10 g ~ 25 mg
Temperature for preparing specimen
Above 135 oC 50 – 70 oC
Pre-mold for specimen Yes No
Temperature conditioning Alcohol/glycol Nitrogen gas
Time needed to run one isotherm
~ 5 hrs ~ 1/2 hr (5.5 hrs for 10 isotherms)
Material, fabrication, time requirements
Comparison: BBR, and 4,8, and 25 mm diam. plates G* master curves
Time at T+10C & G(t) = (G(t) at T, 7200s)
Interconversion - dynamic to creep stiffness
1.E+07
1.E+08
1.E+09
1.E+10
1.E-07 1.E-05 1.E-03 1.E-01 1.E+01 1.E+03 1.E+05 1.E+07
Red. Time (s)
Cree
p St
iffne
ss S
(t) M
Pa
MN1-5 RTFO S(t) from dynamicdata (RHEA)MN1-5 RTFO BBR S(t)
MN1-5 RTFO S(t) from dynamicdata (RHEA Leaderman)
Reference temperature = -20˚C
BBR and DSR low temperature Performance Grade
Slope = relaxation rate mr
7200
Log reduced time, s
log
G(t),
Pa
60Log loading time, s
Log
S(t)
, Pa
Slope = mc-value
BBRCreep Stiffness S(t) and m-value
DSRRelaxation modulus G(t) and the
slope at 2 hours (4-mm diam. plates)
Similarity of two plots: (1) Both S(t) and G(t) represent the stiffness of material(2) Slopes of both plots are related to relaxation rate of
material
Temperature = Low PG + 10 ˚C Ref. temperature = Low PG
BBR S(t) vs. DSR G(t)
S (t) = 300 MPa at 60 S
G (t) = 156 MPa at 2 hr
Tem
pera
ture
= L
ow P
G +
10˚C
Temperature = Low PG
6 WRI/FHWA validation site asphalts
2.0x107 4.0x107 6.0x107 8.0x107 1.0x108 1.2x1084.0x107
8.0x107
1.2x108
1.6x108
2.0x108
2.4x108
Linear Regression: S(t) = A + B * G(t) A 1.74237E7 B 1.80759R2 0.9396
S( t
) at 6
0 s,
Pa
G( t ) at 2 hours, Pa
BBR m-value (mc) vs. the relaxationmodulus slope (mr)
mc = 0.3 at 60 S
mr = 0.258 at 2 hr
Temperature = Low PG
Tem
pera
ture
= L
ow P
G +
10˚C 6 WRI/FHWA
validation site asphalts
0.275 0.300 0.325 0.350 0.375
0.32
0.34
0.36
0.38
Linear Regression: mc = A + B * mrA 0.12529B 0.67632R2 0.8925
mc v
alue
S(t)
on
BBR
at 6
0 s
mr value from G(t) on DSR at 2 hours
T BBR vs. T 4mm DSR
T (4 mm DSR) vs. transverse cracking
MN1-4 Loss Tangent
Transverse cracking vs. loss tangent
Summary and Questions
• BBR and 4 mm diam. parallel plate DSR did not seem to explain the higher level of cracking in the MN1-4 section compared to the other sections.
• Will the current trend in transverse cracking continue?• BBR and 4 mm DSR appear to correlate well.• Consider fracture: DTT or ABC Device?• Consider ductility using G’/(η’/G’) at low temperatures (< 0 ˚C).• Consider converting the relaxation modulus from the 4 mm
DSR to thermal stress using Boltzmann’s hereditary integral.• Would it be useful to extract the asphalt from two or three year
old cores and evaluate using 4 mm DSR?• Do we need to consider physical hardening?