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. Cracking and Durability of Concrete. . Tensile Stress. Low Tensile Strength of Concrete. . External Loading. Shrinkage. Tensile Stress. . Crack. Moisture Moves Freely in Concrete. . Corrosion. and/or. Sulfate Attack. alkali-silica reaction. Poor ride quality. Spalling. . 2. Methods of Reducing Cracking.
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1. ARDAVAN YAZDANBAKSH, ZACHARY GRASLEY
DEPARTMENT OF CIVIL ENGINEERING
TEXAS A&M UNIVERSITY High-Performance Stress-Relaxing Cementitious Composites (SRCC)
2. Cracking and Durability of Concrete
3. Methods of Reducing Cracking
4. Objectives 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 5
6. Challenges 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
8. CNFs Dispersed in Water 8
9. Non-Uniform Dispersion of CNFs 9
10. Dispersion in Water vs. Dispersion in Paste
11. Causes and Solutions for Poor Dispersion in Paste 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
13. Very Fine Cement Grains and Their Downside Due to the very large surface area, production of a workable paste requires w/c>0.70 and a lot of superplastisizer
14. Some Important Observations
15. The Next Step
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 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.