Transcript No Slide Title

ACBM
Fatigue Analysis of JPCP With Transverse Surface Crack
Ya Wei, Will Hansen, Elin A. Jensen, University of Michigan
Collaborating Faculty: Prof. S. P. Shah, Northwestern University
Industrial Advisor: Scott Johnson, MTS
Introduction
Unloading compliance vs. effective crack length
during fatigue test for 7days notched beam
Unloading compliance vs. Effective crack length for 3 & 7 days
Figure 2 Test Setup
3.5E-05
7 days
3.0E-05
3 days
6.00E-06
Unloading compliance
5.50E-06
A representative fatigue analysis method for JPCP with transverse surface crack is based on fracture
mechanics, in which fatigue life is controlled by the rate of crack propagation relating with fracture
properties and behavior of pavement concrete.
y = 9E-07e0.0191x
2
R = 0.9874
指数 (7 days)
2.5E-05
指数 (3 days)
2.0E-05
1.5E-05
1.0E-05
y = 6E-07e0.0199x
2
R = 0.9857
5.0E-06
5.00E-06
Unloading compliance
It has been known that surface edge crack of JPCP (Joint Plain Concrete Pavement) is due to the built-in
negative temperature gradient from hot weather construction, and being able to develop into partial-depth,
full-width transverse surface crack under repetitive joint truck loading (Figure 1). Hence the fatigue
failure position will shift from the bottom to the surface of the slab (W. Hansen).
4.50E-06
4.00E-06
3.50E-06
3.00E-06
2.50E-06
2.00E-06
1.50E-06
0.0E+00
1.00E-06
40
60
80
100
120
140
160
180
40
50
Effective crack length (mm)
From Quasi-static four-point bending test, 7-days notched concrete beam gives quite larger value of fracture
toughness than 3-days’ at close peak loading, which indicates that crack is much more inclined to initiate at
very early age (3-days). According to E A. Jensen & W. Hansen, the resistance to crack propagation does not
change significantly as the strength or curing time increases for the same course aggregate source. Hence
fracture toughness which relates to crack initiation becomes the most important fracture parameter to quantify
K
the fatigue life of concrete pavement with transverse surface crack.
Peak-load
stress (MPa)
Split tensile
stress (MPa)
3 days
25
1.8
3.0
2
120
1
110
tested crack growth rate
0
predicated crack growth rate
-1
-2
-3
-4
Scope
-5
7 days
41.4
2.1
40
60
•the fracture properties of typical concrete pavement materials were determined under quasi-static and
cyclic loading at various ages in the lab.
Notched concrete beams with dimension of 630mm (span), 100mm (width), 200mm (depth) were
tested using closed-loop MTS in this research to obtain load-CMOD curve under four-point bending,
Figure 2. Illustrates the four-point bending test setup.
Effective crack length (mm)
0.14
10000
0.12
0.10
0.08
0.06
0.04
0.02
Cyclic test determining effective crack length- compliance relationship, the compliance is defined as
the value of crack mouth opening displacement per unit load and determined by unloading the
specimen at different points in both pre-peak and post-peak parts of the quasi-static response;
High-cycle fatigue test of notched beams were conducted at 7days age. For highway concrete
pavement, the combined tensile stress on the mid-slab surface due to curling stress at negative
temperature difference –10 centigrade and federal standard trucking loading at joint is 1.2MPa
calculated form EverFE for 200mm slab thickness. Comparing with average peak load of Quasi-static
response of notched concrete beams, the stress ratio was obtained as 0.6.
120
tested crack growth
100
90
80
70
60
50
40
0.0E+00 2.0E+05 4.0E+05 6.0E+05 8.0E+05 1.0E+06 1.2E+06 1.4E+06
Number of cycles
0.01
0.02
0.03
0.04
CMOD (mm)
0.05
6000
90
80
70
60
4000
50
7 days
2000
40
0.0E+00
0.06
0.07
0
0.25
Therefore, fatigue life of concrete pavement with
transverse surface crack can be divided into three
stage: accelerated stage 1; steady stage 2; failure
stage 3. The first stage(early-age concrete
pavement) is the critical stage which determines at
what effective crack length the steady stage is
being able to start and thus how fast the pavement
will fail.
100
3 days
0.00
0
8000
2.0E+05
4.0E+05
6.0E+05
8.0E+05
1.0E+06
1.2E+06
Number of cycles (N)
0.3
0.35
0.4
0.45
0.5
0.55
CMOD (mm)
Three types of tests were conducted at different beam ages (3 days and 7 days):
Quasi-static test determining the failure envelop and fracture toughness K1c of notched beam
according to Shah’s Two-Parameter Model, fracture toughness is related with the crack initiation and
calculated from the peak load and geometric function representing the specimen size and load
configuration;
100
110
12000
0.16
Load (N)
Experimental Design
14000
0.18
Far-field stress (MPa)
•fatigue life of JPCP from designed experimental test was compared with the predicted fatigue life, and
the variation was considered.
80
120
• notched plain concrete beams were tested in a four-point bending test configuration under flexural
fatigue loading to investigate the relation between crack growth and number of flexural loading cycles.
120
Effective crack length vs. number of cycles
Load vs. CMOD for 7 days Notched Beam
0.20
110
Predicted crack growth
Effective crack length (mm)
Far-Field Stress vs. CMOD
100
3.2
-6
• fatigue prediction model by Kolluru et al was adopted to quantify the fatigue life of JPCP with premature crack subject to joint loading.
90
Effective crack length vs. Number of cycles
Effective crack length (mm)
Fracture toughness
1
( MPa.mm 2 )
80
Effective crack length (mm)
Crack growth rate vs. effective crack length
Log(da/dN)
Age
70
Comparing effective crack length-Number of cycles relation determined from experimental test and predicted
using Kolluru’s fatigue model, Kolluru’s model exaggerates the real fatigue life of this particular case. From
experimental fatigue curve, crack growths rapidly from initial notch length 40mm to 64mm at very first 25000
cycles, only 2.5% of total fatigue life, but with a crack increase of 30% of total amount of crack increase. Then
followed by a steady stage with almost no crack growth, which accounts for 80% of total fatigue life. After
steady stage, there is a significant crack growth up to a sudden failure. This fatigue trend also can be illustrated
by crack growth rate-effective crack length relation.
Results and Discussion
Figure 1.
JPCP along I-94 (East Bound) in Van Buren County, Michigan with premature mid-slab
cracking four years after construction.
60
Conclusions
Cyclic beam test determined unloading compliance-effective crack length relation at 3 &7 days, as
expected that 7-days’ beam gave larger effective crack length than 3-days’ for same unloading
compliance. This relation provides a critical approach to determine the effective crack length at certain
number of cycles during fatigue test since it is hard to measure the effective crack length through
experimental way. This approach is based on such a hypothesis that unloading compliance is uniquely
related with the effective crack length.
•For typical concrete pavement, 7days’ slab have a quite larger value of fracture toughness relating to crack
initiation than 3 days’ slab. It is necessary to take steps to avoid any factors that could prompt crack to initiate at
very early-age (3 days).
•Kolluru’s fatigue model gives a longer fatigue life than that determined from experimental test.
•According to Kolluru’s fatigue model, concrete pavement with different coarse aggregate can have same
fatigue behavior during decelerated stage, which is conflict with the finding made by E A. Jensen & W. Hansen,
that strong coarse aggregates improve concrete’s resistance to crack propagation in terms of increased fracture
energy.
•Fatigue behavior of concrete pavement with transverse surface crack can be divided into three stages. Stage 1
should be the critical stage, this needs more experimental test to verify.