Lithum Additives: The Cure of AlkaliSilica Reaction

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Lithum AdditivesThe Cure of Alkali-Silica
Reaction?
Courtney Collins . Jason Ideker . Gayle
Willis . Jessica Hurst
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Outline

• What is ASR?
• How does ASR gel expand?
• How could lithium prevent ASR gel expansion?

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What is ASR?
Alkali Silica Reaction (ASR)
Alkalis Reactive Silica Moisture
Concrete expansion and cracking
ASR Gel which expands
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Images of ASR damage
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Images of ASR damage
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Images of ASR damage
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Why does the gel expand?
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Why does the gel expand?

• Theories of expansion
• Double-layer theory
• (Prezzi, 1997)
• Osmotic pressure theory
• (Hansen, 1944)
• CSH-shell theory
• (Chatterji et al. 1986, 1988)
• CSH/alkali exchange theory
• (Rotter 1995)

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Why does the gel expand?
Double-Layer Theory (Prezzi, 1997)
Solid particles in the alkali-silica gel are
surrounded by a sea of cations and anions Two
layers form 1. rigid layer of cations near
surface of particle 2. diffuse layer of
cations and anions further from particle
surface Expansion occurs when 1. water is taken
in 2. water increases layer size and lowers
ionic strength 3. particle-distance increases 4.
electrostatic repulsive forces push particles
apart
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Why does the gel expand?
Double-Layer Theory (Prezzi, 1997)
Initial state
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Why does the gel expand?
Double-Layer Theory (Prezzi, 1997)
Water is taken in, increasing layer size around
particle
Electrostatic forces predominate, particles push
apart and gel increases
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Why does the gel expand?
Double-Layer Theory (Prezzi, 1997)
Water is taken in, increasing layer size around
particle
Electrostatic forces predominate, particles push
apart and gel increases
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Why does the gel expand?
Osmotic Pressure Theory (Hansen, 1944)

• Cement paste acts as semi-permeable membrane,
  allowing
• water and cations in, while keeping silica from
  escaping.
• Gel expands, exerting pressure on surrounding
  matrix until
• cracking results

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Why does the gel expand?
CSH-Shell Theory (Chatterji et al. 1986, 1988)

• Calcium reacts with grain to make calcium
  silicate hydrate
• (CSH), forming a shell around the grain.
• Silica reacts to form gel, grain size increases

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Why does the gel expand?
Calcium/Alkali Exchange Theory (Rotter 1995)

• Gel takes in Ca2 ions, releasing alkali ions
  to react and
• create more alkali-silica gel

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Why does the gel expand?
Why the theories may be inaccurate

• Role of short-range forces were not
  
• accounted for in any theory
• Role of calcium was not considered for the
• double-layer and osmotic pressure theories

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How does lithium help?
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How does lithium help?
Theory 1 Silica loves lithium Lithium (Li) is
believed to be preferentially bound to silica
over Na and K, making lithium silicates that
are non-expansive. (Stark, 1992) Theory 2 ASR
hates ions with large radii Rate of silica
dissolution decreases as cation radius near
silica surface increases. Therefore, as Li has
a larger hydrated radius than Na and K,
concentrations of lithium near the silica would
decrease alkali-silica gel creation. (Wijnen,
1989)
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How does lithium help?
Theory 3 Lithium and the double layer The
addition of lithium (Li) causes the
concentration of ions in the double layer to
increase. Higher ionic concentration results in
a smaller double layer because attractive Van der
Waals forces predominate and particles are held
closer together. (Prezzi)
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How does lithium help?

• Research shows a threshold concentration of
• lithium exists, below which gel continues to
• expand Li/NaK ? 0.74 (Blackwell, 1997)
• LiNO3 is preferred over other compounds
• because it has no pessimum effect (increased
• gel expansion at lithium doses below threshold
• concentration). (Stark, 1992 Diamond and
  Ong,
• 1992)

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Conclusion
What we know Lithium does help prevent ASR
damage. Here is one graph of expansion in mortar
bars, each with a different lithium additive.
(LiOH, LiNO3, or LiCl)
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Conclusion

• What we dont know
• How does ASR gel expand?
• How does lithium help?
• We at Georgia Tech, along with many other
  researchers in concrete science, are looking to
  answer those questions!

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Conclusion
Any questions?