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High-Performance Stress-Relaxing Cementitious Composites (SRCC)

High-Performance Stress-Relaxing Cementitious Composites (SRCC) . Federal Highway Administration, Exploratory Advanced Research. ARDAVAN YAZDANBAKSH, ZACHARY GRASLEY DEPARTMENT OF CIVIL ENGINEERING TEXAS A&M UNIVERSITY. Cracking and Durability of Concrete. 2. External Loading. Shrinkage.

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High-Performance Stress-Relaxing Cementitious Composites (SRCC)

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  1. High-Performance Stress-Relaxing Cementitious Composites (SRCC) Federal Highway Administration, Exploratory Advanced Research ARDAVAN YAZDANBAKSH, ZACHARY GRASLEY DEPARTMENT OF CIVIL ENGINEERING TEXAS A&M UNIVERSITY

  2. Cracking and Durability of Concrete 2 External Loading Shrinkage Tensile Stress and/or Tensile Stress Low Tensile Strength of Concrete Crack Corrosion Moisture Moves Freely in Concrete Poor ride quality Sulfate Attack Spalling alkali-silica reaction

  3. Methods of Reducing Cracking 3

  4. Objectives 4 To develop a methodology for the design and fabrication of concrete that exhibits remarkable stress-relaxing behavior For this purpose: • Different methods of distributing the nano/micro particles in cement paste and controlling particle-matrix bond will be examined • Cementitious composites will be produced, mechanically tested for stress relaxation. The results will be compared with the prediction of theoretical models

  5. Why choose CNF/Ts? • Advantageous properties of CNF/Ts: • Strength 100 times more than that of steel, specific gravity is one sixth of steel • Elastic strain capacity of 12%; 60 times higher than that of steel • Modulus of elasticity: approximately 103 GPa, 5 times more than steel • Excellent electrical properties • Importance of dispersion (3) (2) (1)

  6. Challenges 6 Effective inclusion of nano-particles in cement paste is difficult because: • The nanoparticles tend to strongly attract each other and form clumps or bundles • Non-hydrated cement particles are significantly larger than nano-particles, which prevents uniform distribution of nano-particles • The bond between cementitious matrix and inclusions like carbon nanoparticles is weak

  7. Current State of the Project Inclusion of CNF/Ts in Cement paste

  8. CNFs Dispersed in Water CNF Concentration 1.5% wt – Sonicated for 20 mins with surfactant (2.0% wt)

  9. Non-Uniform Dispersion of CNFs • Non-dispersed clumps of CNF • Reasons: • Short period of sonication • Using inadequate amount of surfactant • Longitudinal agglomeration of CNFs • Reasons: • Long storage period of dispersion • Drying of dispersion

  10. Dispersion in Water vs. Dispersion in Paste 10 Good dispersion in water Poor dispersion in paste

  11. Causes and Solutions for Poor Dispersion in Paste 11 Cause: Reagglomeration of CNFs in paste due to • Absorption of water by cement • Consumption of surfactant (superplastisizer) by cement Solution: Using more water and superplastisizer Drawback: Negative effect on durability, strength, and retardation of hydration Cause: Large size of cement particles and clumps Solution: Using fine-grain cement Drawback?

  12. SEM Images of Type I Portland Cement 12 Some particles as large as 10 μm Edge of a huge particle (>100 μm)

  13. Very Fine Cement Grains and Their Downside 13 Due to the very large surface area, production of a workable paste requires w/c>0.70 and a lot of superplastisizer Ball-milled cement. The average particle size is less than 1 μm. The average particle size is less than the length of a typical CNT. Drawback:

  14. Some Important Observations 14 In areas of matrix with CNFs, pullout, fracture, and also fibers parallel to crack surface were observed.

  15. The Next Step 15 • Functionalization of CNFs with acid • Producing fibrous cement paste using treated CNFs and SEM observation of hardened matrix • Mechanical testing of CNF-reinforced hardened paste beams for stress-relaxation

  16. Concluding Remarks 16 • Using nano-particles in cementitious composites may enhance stress relaxation properties • Challenges: poor dispersion of fibers and weak CNF/T-matrix bond • SEM images of fractured surface of CNF-reinforced hardened paste suggest that manipulation of interfacial bond is possible • Acid treatment of CNFs will be examined in order to improve dispersion and bond

  17. Jeff Foxworthy says: If you aren’t sure what will happen next… … your research might be exploratory. If people think your ideas are mildly crazy (Mark Sanford crazy, not Unabomber crazy)…. … your research might be exploratory. If you are not only “thinking outside the box” but have to squint a little to see the box… … your research might be exploratory.

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