ARDAVAN YAZDANBAKSH, ZACHARY GRASLEY

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High-Performance Stress-Relaxing Cementitious
Composites (SRCC)
Federal Highway Administration, Exploratory
Advanced Research

• ARDAVAN YAZDANBAKSH, ZACHARY GRASLEY
• DEPARTMENT OF CIVIL ENGINEERING
• TEXAS AM UNIVERSITY

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Cracking and Durability of Concrete
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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
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Methods of Reducing Cracking
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Objectives
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• 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

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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)
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Challenges
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• 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

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Current State of the Project
Inclusion of CNF/Ts in Cement paste
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CNFs Dispersed in Water
CNF Concentration 1.5 wt Sonicated for 20 mins
with surfactant (2.0 wt)
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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

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Dispersion in Water vs. Dispersion in Paste
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Good dispersion in water
Poor dispersion in paste
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Causes and Solutions for Poor Dispersion in Paste
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• 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?

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SEM Images of Type I Portland Cement
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Some particles as large as 10 µm
Edge of a huge particle (gt100 µm)
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Very Fine Cement Grains and Their Downside
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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

• Due to the very large surface area, production of
  a workable paste requires w/cgt0.70 and a lot of
  superplastisizer

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

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Concluding Remarks
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• 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

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Jeff Foxworthy says

• If you arent 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.