Courtney Collins. Jason Ideker. Gayle Willis. Jessica Hurst Lithum Additives: The Cure of...
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![Page 1: Courtney Collins. Jason Ideker. Gayle Willis. Jessica Hurst Lithum Additives: The Cure of Alkali-Silica Reaction?](https://reader036.fdocuments.in/reader036/viewer/2022062409/56649e675503460f94b6280c/html5/thumbnails/1.jpg)
Courtney Collins . Jason Ideker . Gayle Willis . Jessica Hurst
Lithum Additives:The Cure of Alkali-Silica Reaction?
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• What is ASR?
• How does ASR gel expand?
• How could lithium prevent ASR gel expansion?
Outline
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Alkali Silica Reaction (ASR)
Alkalis+
Reactive Silica
+Moisture
ASR Gel which
expands
Concrete expansion
andcracking
What is ASR?
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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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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)
Why does the gel expand?
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Double-Layer Theory (Prezzi, 1997)
Why does the gel expand?
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 particle2. “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 increases4. electrostatic repulsive forces push particles apart
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Why does the gel expand?
Initial state
Double-Layer Theory (Prezzi, 1997)
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Why does the gel expand?
Water is taken in,increasing layer sizearound particle
Electrostatic forces predominate,particles push apart and gel increases
Double-Layer Theory (Prezzi, 1997)
![Page 12: Courtney Collins. Jason Ideker. Gayle Willis. Jessica Hurst Lithum Additives: The Cure of Alkali-Silica Reaction?](https://reader036.fdocuments.in/reader036/viewer/2022062409/56649e675503460f94b6280c/html5/thumbnails/12.jpg)
Why does the gel expand?
Water is taken in,increasing layer sizearound particle
Electrostatic forces predominate,particles push apart and gel increases
Double-Layer Theory (Prezzi, 1997)
![Page 13: Courtney Collins. Jason Ideker. Gayle Willis. Jessica Hurst Lithum Additives: The Cure of Alkali-Silica Reaction?](https://reader036.fdocuments.in/reader036/viewer/2022062409/56649e675503460f94b6280c/html5/thumbnails/13.jpg)
Osmotic Pressure Theory (Hansen, 1944)
Why does the gel expand?
• 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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CSH-Shell Theory (Chatterji et al. [1986, 1988])
Why does the gel expand?
• 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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Calcium/Alkali Exchange Theory (Rotter 1995)
Why does the gel expand?
• Gel takes in Ca+2 ions, releasing alkali ions to react and create more alkali-silica gel
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Why does the gel expand?
• 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
Why the theories may be inaccurate:
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How does lithium help?
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How does lithium help?
Theory 1: Silica loves lithiumLithium (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 radiiRate 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 layerThe 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]/[Na+K] 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 don’t 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?