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Microstructure Variability and Macroscopic Composite Properties of High Performance Fiber Reinforced Cementitious Composites. Victor C. Li and Shuxin Wang Advanced Civil Engineering Materials Research Laboratory The University of Michigan. - PowerPoint PPT Presentation
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Microstructure Variability and Macroscopic Composite Properties of High Performance Fiber Reinforced Cementitious Composites
Victor C. Li and Shuxin Wang
Advanced Civil Engineering Materials
Research Laboratory
The University of Michigan
2
High Performance Fiber Reinforced Cementitious Composites
High strength High durability Self-compacting High tensile failure resistance
3
HPFRCC Characteristics: Strain-Hardening
Concrete FRC
HPFRCC
4
Engineered Cementitious Composites
Composite response in uniaxial tension
20 m
m
Damage
Fiber volume fraction 2%
0
1
2
3
4
5
0 1 2 3 4 5 6Strain (%)
Ten
sile
Str
ess
(MP
a)
0
20
40
60
80
100
Cra
ck W
idth
(m
)
Concrete Strain 10 times expanded
ECC
5
Mihara Bridge in HokkaidoOpen to traffic: April, 2005Length: 1000 m, span: 340 mDeck area: 20,000 sq. m.; ECC layer thickness: 38 mm
Composite ECC-Steel DeckSuper light-weight 40% reductionExpected service life: 100 yrs
6
Bridge-deck Link Slab RetrofitMichigan, 2005
Conventional Bridge Joint
Durable ECC Link Slab
ECC Link Slab
Lspan Lspan
Llink slab = 0.1 x Lspan
7
Variation of Tensile Behavior
PVA fiber reinforced ECC, Vf = 2%
Extreme variability case
8
Microstructure Inhomogeneity
Matrix flaws
Fiber distribution10 mm
9
Scale Linking
Le
aP
z
Single fiber pullout behavior Crack initiation at flaw
Bridging stress vs. crack opening Multiple-cracking process
Composite stress vs. strain
Steady State Cracking Requirement Crack Saturation Requirement
10
Single Fiber Modeling
idfy dAGdWdWdW ++=
Le
a
€
=4τ 0a 1+ η( )
d f+
8GdE f 1+ η( )
d f
Le
€
=τ 0 1+ β δ −δc( ) / d f( ) Le −δ +δ c( ) / d f
€
c =2τ 0Le
2 1+ η( )
E f d f+
8Gd Le2 1+ η( )
E f d f
Debonding Pullout
Fiber parameters
Interface parameters
11
Modeling of Fiber Randomness
( ) ( ) ( ) φφφ dzdzpzPVA ff
,,1
∫=
( ) ( ) ( )φφ pzpzp =,
( )fl
zp1
=22ff l
zl
≤≤−
( ) ( )D
Dp
2
3
/2
sin
⎩⎨⎧
=π
φφ
20
πφ ≤≤
12
Conditions for Strain-hardening
ss
Jb’ complementary energy
Jtip crack tip fracture energy
ss
ss
€
J tip ≤ σ oδo − σ (δ )dδ ≡ Jb'
0
δ o
∫
Variability of Jtip, Jb’ ?Matrix parameter
13
Effect of Initial Flaw Size on Cracking Strength(Computed)
Matrix intrinsic tensile strength 5 MPa
14
Tailoring of Flaw Size Distribution for Saturated Multiple Cracking
flaw size ccmc
p(c)
flaw size c cmc
p(c)
artificial flaw distribution
natural flaw distribution
Superimpose artificial flaws with prescribed sizes Artificial flaws: plastic, bubbles, lightweight aggregates,
etc.
Activated flawsactivated flaws
15
Flaw Size Tailoring in PVA-ECC
lightweight aggregatessize: 3.5 mm
4mm plastic beads
16
Lightweight Aggregates as Artificial Flaws
s/c = 0.8, fa/c = 0.8, w/b = 0.24, PVA Vf = 2.0%
lightweight aggr.: 7 vol%w/o lightweight aggr.
17
Plastic Beads as Artificial Flaws
s/c = 0.8, fa/c = 1.2, w/b = 0.24, PVA Vf = 2.0%
w/ 7 vol% beadsw/o beads
18
Open Issues
Further understand linkages between randomness of microstructures and variability in composite behaviors
Capture and quantify randomness of critical microstructures
Incorporate probabilistic models in ECC theoretical framework
19
Multiple Cracking Process
20
Conclusions
Microstructure variability significantly influences ductility of ECC materials
Control of key microstructure variability is critical to achieve robust strain-hardening behavior Ensure enough margin between Jtip and Jb’
Implantation of artificial flaws with controlled size
Further work in characterization and modeling of microstructure randomness is needed