ASR of Candidate Aggregates for OMP Concrete

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ASR of Candidate Aggregates for OMP Concrete

• Francis B. Nelson III, Jamila Beale,
• Jan Moritz, Leslie J. Struble
• July 20, 2006

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Scope

• ASR background
• Tests of materials to mitigate expansion
• Tests with potassium acetate deicer
• Expansion
• pH

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Alkali Silica Reaction

• Chemical reaction between alkali and hydroxide
  ions in pore solution and reactive silica in
  aggregate
• Reaction produces gel
• Gel adsorbs water and swells, causing expansion
  and cracking of aggregate

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To Mitigate ASR Expansion

• Recognize and avoid susceptible aggregate
• Use low alkali cement
• Use supplemental cementing material

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Background on Supplemental Cementing Materials

• Fly ash, slag, silica fume, metakaolin all
  mitigate expansion by lowering alkali
  concentration
• Effective replacement level must be determined
  for specific material

PCA
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Standard Tests for ASR

• ASTM C1260 to test aggregate
• Mortar test
• Immerse mortar bars in 1-M NaOH at 80C
• Measure expansion after 14 days
• ASTM C1567 to test supplemental cementing
  materials
• Modified C1260 for deicer
• Immerse mortar bars in potassium acetate deicer
  at 80C

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Supplemental Cementing Materials Tested

• Fly Ash
• Class F (1) 15 (2), 10, 5
• Class F (2) 15
• Class C 15
• Slag
• 35, 30, 25, 20
• Silica Fume
• 10
• Metakaolin
• 10

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Expansion Results with Fly Ash
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Expansion Results with Slag
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Expansion Results with Other Materials
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Discussion on Mitigation

• ASR expansion reduced to acceptable level by
  using one of the following
• 10 fly ash
• 30 slag
• 10 silica fume

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Background on Potassium Acetate Deicer

• Non-chloride based deicer used for airport
  runways
• Non-toxic, biodegradable, non corrosive
• Lowers freezing temperature (-76o F)
• Anti-icing agent (prevents freezing)
• May be corrosive to galvanized metals, electrical
  systems
• Rangaraju (Clemson University) showed that deicer
  causes ASR expansion

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Deicer Test - 1

• Tested all 5 sands from last year in clear deicer
  from Cryotech

• All sands showed little expansion

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Deicer Test - 2

• Retested all 5 sands in blue deicer

• Rangaraju suggested indicator dye might affect
  expansion
• Still little expansion

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Deicer Test - 3

• Tested fused silica
• Used by Rangaraju, known to show expansion
• Highly expansive

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Discussion

• Verified results of Rangaraju fused silica shows
  very high expansion in deicer solution
• Showed that candidate OMP sands do not expand
  much with deicer solution

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Why Does Deicer Cause ASR?

• Deicer provides very high level of K (about 5 M)
• Reaction requires a pH gt 13.6, deicer pH much
  lower than this

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pH of Deicer Solution - 1

• Tested ASR expansion using modified C1260
  procedure
• Measured pH of deicer solution after mortar bars
  tested

Rangaraju et al 2005
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pH of Deicer Solution - 2

• We found similar increase in pH in contact with
  mortar bars
• No clear relationship between pH and expansion

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Remaining Questions

• What drives up the pH?
• Something in the mortar must be reacting with the
  deicer to raise the pH
• Exploring effects of Ca(OH)2 and cement mortar
• Why did test sands show little expansion with
  deicer
• Exploring effect of chert amount (pessimum
  proportion)