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Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira 2011, October 24 - 27 Supervisors: Joaquim A. O. Barros, Gregor Fischer.

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Presentation on theme: "Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira 2011, October 24 - 27 Supervisors: Joaquim A. O. Barros, Gregor Fischer."— Presentation transcript:

1 Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira 2011, October Supervisors: Joaquim A. O. Barros, Gregor Fischer

2 2 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 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 3 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 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 4 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 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 5 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 Some applications In Rokugo et al. Materials and Structures 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 6 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, From Li, V.C Material characterization Material design w PART 1: Assessment of the tensile performance of SHCC

7 7 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 Single Crack Tension Test - SCTT

8 8 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 Single Crack Tension Test - SCTT

9 9 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 Analysis of crack formation and propagation: DIC

10 10 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 Analysis of crack formation and propagation: DIC

11 11 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 Analysis of crack formation and propagation: DIC

12 12 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 Analysis of crack formation and propagation: DIC

13 13 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 E = 20 GPa = 0.2 Analysis of crack formation and propagation: FEM

14 14 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 Analysis of crack formation and propagation: FEM Load increment 10 = 2.34 MPa w = mm Load increment 37 = 4.57 MPa w = mm

15 15 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 Long plates Casting formwork shape: 600 mm 120 mm (20 mm) Materials:

16 16 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, % PVA 2% PVA 2% PAN 1% PVA + 1% PAN 2.5% PP 1% PVA % PP Results:

17 17 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 Importance of the assessment of the - 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 18 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 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 19 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 Specimen geometry: CT specimen. From Sanford, R. Principles of Fracture Mechanics. Mechanics of cracking in Cementitious Composites

20 20 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 Mechanics of cracking in Cementitious Composites SPECIMEN GEOMETRY

21 21 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 Mechanics of cracking in Cementitious Composites SPECIMEN GEOMETRY

22 22 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 CementFly ashFine sand (0.170 mm) Quartz Powder Water 420 g850 g150 g 100 cm 3 MORTAR and FRCC FiberTensile strengthLengthDiameter PVA1600 MPa8 mm40 mm CementWater 1360 g570 cm 3 CEMENT PASTE (w/c =0.42) CementAggregates (0-4 mm)Water 660 g1341 g275 cm 3 CONCRETE (w/c = 0.42) DISPLACEMENT RATE: 5 m/s Depth = 12 mm Notch width = 0.5 mm Materials and test procedure:

23 23 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 CEMENT PASTE MORTAR CONCRETE FRCC Mechanical results:

24 24 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 Example:concrete Digital Image-based monitoring setup:

25 25 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 Entire loading sequence. Example: concrete specimen Digital Image-based monitoring results:

26 26 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 Real surface (B&W)

27 27 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 Facet overlay

28 28 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, % of peakload (before peak) peakload 50% of peakload (after peak) Cement paste concrete mortar FRCC Digital Image-based monitoring results:

29 29 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 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 30 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 x x 2 mm 10 mm 2 mm 10 mm 2 mm10 mm P P - 20% Morphology of FPZ - mortar

31 31 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 MORTARFRCC 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. 2 mm Morphology of FPZ – influence of fiber reinforcement

32 32 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 The compression zone extends to the material surrounding the crack, including the open crack region. MORTARFRCC 10 mm Morphology of FPZ – influence of fiber reinforcement

33 33 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 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 34 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 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 35 | Mechanics of Cracking in Fiber Reinforced Cementitious Composites Eduardo B. Pereira Semana da Escola de Engenharia October 24 – 27, 2011 Thank you!


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