Post on 28-Mar-2015
Mechanics of Cracking in Fiber ReinforcedCementitious Composites
Eduardo B. Pereira
2011, October 24 - 27
Supervisors:
Joaquim A. O. Barros, Gregor Fischer
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
2|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
Outline of the Presentation
• Introduction to the material:• Definitions;• Some applications.
• Assessment of tensile performance:• Tensile stress-strain behavior: pseudo-strain hardening and multiple cracking;• Tensile stress-crack opening characterisation: PVA, PAN, PP.• Relevant features of the tensile stress-crack opening behavior in SHCC.
• Mechanics of cracking: initiation and propagation: • Investigation of crack initiation and propagation in cementitious composites: CT speciments;• Observation of cracking process using digital image analysis;• Analysis of the influence of aggregate size and fiber reinforcement;• Measurement of crack profiles and analysis of FPZ.
• Conclusions
3|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
• FRC: Fiber Reinforced Concretes;
• FRCC: Fiber Reinforced Cementitious Composites;
• SHCC: Strain Hardening Cementitious Composites;
• HPFRCC: High Performance Fiber Reinforced Cement Composites;
• UHPFRCC: Ultra HPFRCC;
Definitions
• Composite = Fibers + Matrix
• Matrix = cement + other fine additions + chemical admixtures + aggregates...
in Naaman and Reinhardt, 2005
4|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
• FRC: Fiber Reinforced Concretes;
• FRCC: Fiber Reinforced Cementitious Composites;
• SHCC: Strain Hardening Cementitious Composites;
• HPFRCC: High Performance Fiber Reinforced Cement Composites;
• UHPFRCC: Ultra HPFRCC;
Definitions
• Composite = Fibers + Matrix
• Matrix = cement + other fine additions + chemical admixtures + aggregates...
5|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
Some applications
In Rokugo et al. Materials and Structures 2009http://ace-mrl.engin.umich.edu/NewFiles/webapp_files/frame.htm
• Extruded elements• Continuum bridges• Retrofitting of dams, viaducts,
retaining walls and irrigation channels• Seismic aplications: coupling beams
in high-rise buildings;
ECC link slab
6|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
- s e .
From Li, V.C. 2005
Material characterization
Material design - s w
PART 1: Assessment of the tensile performance of SHCC
7|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
Single Crack Tension Test - SCTT
8|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
Single Crack Tension Test - SCTT
9|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
Analysis of crack formation and propagation: DIC
10|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
Analysis of crack formation and propagation: DIC
11|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
Analysis of crack formation and propagation: DIC
12|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
Analysis of crack formation and propagation: DIC
13|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
E = 20 GPa
n = 0.2
Analysis of crack formation and propagation: FEM
14|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
Analysis of crack formation and propagation: FEM
Load increment 10s = 2.34 MPa
w = 0.0029 mm
Load increment 37s = 4.57 MPa
w = 0.0075 mm
15|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
Tensile strength
Length Diam Fiber reinforcement (%vol) Fiber
MPa mm m C1 C2 C3 C4 C5 C6
PVA 15 1600 8 40.0 1 2 0 0 1 1
PP 900 12 40.0 0 0 2.5 0 1.25 0
PAN 1.5 826 6 12.7 0 0 0 2 0 1
Long plates
Casting formwork shape:600 mm
120 mm
(20 mm)
Materials:
16|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
0.0 0.5 1.0 1.5 2.00
1
2
3
4
5
6
7
Ten
sile
Str
ess
(MPa
)
CMOD (mm)
average curve
experimental results
0.0 0.5 1.0 1.5 2.00
1
2
3
4
5
6
7
average curve
Ten
sile
Str
ess
(MPa
)
CMOD (mm)
experimental results
0.0 0.5 1.0 1.5 2.00
1
2
3
4
5
6
7
Ten
sile
Str
ess
(MPa
)
CMOD (mm)
average curve
experimental results
0.0 0.5 1.0 1.5 2.00
1
2
3
4
5
6
7
Ten
sile
Str
ess
(MPa
)
CMOD (mm)
average curve
experimental results
0.0 0.5 1.0 1.5 2.00
1
2
3
4
5
6
7
Ten
sile
Str
ess
(MPa
)CMOD (mm)
average curve
experimental results
0.0 0.5 1.0 1.5 2.00
1
2
3
4
5
6
7
Ten
sile
Str
ess
(MPa
)
CMOD (mm)
average curve
experimental results
1% PVA
2% PVA
2% PAN
1% PVA + 1% PAN
2.5% PP
1% PVA + 1.25% PP
Results:
17|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
• Importance of the assessment of the s - w law:• Material design;• Structural analysis / modelling / design.
• Tailoring of the tensile properties of SHCC:• Distinction of characteristic behaviors of different types of fibers and/or matrices;• Explicit quantification of possible synergistic effects resulting of the combination of different
types of fibers. • Test results are very sensitive to the main composite parameters; slight differences are detected,
important to guiding efficiently the material design process.
Remarks:
18|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
PART 2: Mechanics of cracking - initiation and propagation• Investigation of cracking mechanisms near the crack tip of propagating cracks:
• Study the application of digital image analysis;• Composites with different aggregate sizes and matrices;• Effect of fiber reinforcement in the fracture process zone and crack profiles.
19|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
• Specimen geometry: CT specimen.
From Sanford, R. “ Principles of Fracture Mechanics”.
Mechanics of cracking in Cementitious Composites
20|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
Mechanics of cracking in Cementitious Composites
SPECIMEN GEOMETRY
21|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
Mechanics of cracking in Cementitious Composites
SPECIMEN GEOMETRY
22|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
Cement Fly ash Fine sand(0.170 mm)
Quartz Powder
Water
420 g 850 g 150 g 150 g 100 cm3
MORTAR and FRCC
Fiber Tensile strength Length Diameter
PVA 1600 MPa 8 mm 40 mm
Cement Water
1360 g 570 cm3
CEMENT PASTE (w/c =0.42)
Cement Aggregates (0-4 mm) Water
660 g 1341 g 275 cm3
CONCRETE (w/c = 0.42)
DISPLACEMENT RATE: 5 mm/s
Depth = 12 mm
Notch width = 0.5 mm
Materials and test procedure:
23|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
0
50
100
150
200
250
300
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6CMOD [mm]
Lo
ad [
N]
cement paste
mortar
concrete
FRCC - initial peak
FRCC - ultimate peak
CEMENT PASTE MORTAR
CONCRETE
FRCCMechanical results:
24|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
Example:concrete
Digital Image-based monitoring setup:
25|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
Entire loading sequence. Example:
concrete specimen
Digital Image-based monitoring results:
26|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
Real surface(B&W)
27|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
Facet overlay
28|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
0
50
100
150
200
250
300
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
Loa
d [N
]
cement paste
mortar
concrete
FRCC - initial peak
FRCC - ultimate peak
90% of peak load
(before peak) peak load 50% of peak load
(after peak)
Cement
paste
concrete
mortar
FRCC
Digital Image-based monitoring results:
29|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
Measurement of the crack profiles:
• Virtual clip gage length:2 mm• Longiturinal spacing: 1 mm• Total length covered: 30 mm
• Virtual clip gage length:10 mm
• Longiturinal spacing: 1 mm• Total length covered: 30 mm
Specimens analyzed: Mortar and FRCC
x
Morphology of FPZ
30|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
x
-0.005
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0 10 20 30
d(m
m)
x (mm)
measured resultspolinomial trendline
P-10%
P
P-20%
P-50%
P-10%
x
-0.005
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0 10 20 30
d(m
m)
x (mm)
measured resultspolinomial trendline
P-20%
P-50%
P-10%
P
P-50%
P-10%
2 mm
10 mm
2 mm
10 mm
2 mm 10 mm
P P - 20%
Morphology of FPZ - mortar
31|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
-0.005
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0 10 20 30
d(m
m)
x (mm)
measured resultspolinomial trendline
MORTAR FRCC
• Alteration of crack profiles;• Formation of a compression zone ahead of the crack tip;• Smaller crack lengths for the same CTOD;• Sharper transition from the intact bulk material to the open crack.
-0.005
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0 10 20 30
d(m
m)
x (mm)
measured resultspolinomial trendline
P-10%
P
P-20%
P-50%
P-10%
2 mmMorphology of FPZ – influence of fiber reinforcement
32|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
• The compression zone extends to the material surrounding the crack, including the open crack region.
-0.010
-0.005
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0 10 20 30d
(mm
)
x (mm)
measured resultspolinomial trendline
-0.005
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0 10 20 30
d(m
m)
x (mm)
measured resultspolinomial trendline
P-20%
P-50%
P-10%
P
P-50%
P-10%
MORTAR FRCC10 mm
Morphology of FPZ – influence of fiber reinforcement
33|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
Remarks:
• The initiation and propagation of cracks can be traced in cementicious composites with appreciable resolution using the digital image analysis;
• Different crack smearing or branching features were identified, deppending of aggregate size and matrix composition; secondary shrinkage cracks were also detected; the analysis of these features of the cracking processes helped to explain the mechanical results observed.
• The precise measurement of the crack profiles showed that the fibers in the FRCC alter the shape and the micromechanics of the fracture process zone. For the same crack opening, crack shape and crack length are modified, as well as the strains surrounding the fracture process zone. Therefore the fiber contribution is not confined to the fiber bridging region of the fracture process zone.
34|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
Conclusions:
• The complex interaction between phases in cementitious matrix composites requires a thorough knowledge of the underlying mechanics of cracking;
• The test-setup proposed during the first part of this presentation contributes to an effective assessment of the tensile performance of SHCC. It is sensitive to important parameters of the composite, therefore it is useful both to the optimal design of the material and to the accurate constitutive modeling with SHCC;
• The better understanding of cracking process, crack morphology and the mechanics of the fracture process zone contribute to the efficient design and the full exploration of SHCC special features; the use of digital image analysis to study the surface of specimens while undergoing cracking showed addequate resolution and potential in the present research context.
35|Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira
Escola de Engenharia
Semana da Escola de Engenharia October 24 - 27, 2011
Semana da Escola de EngenhariaOctober 24 – 27, 2011
Thank you!