asr of candidate aggregates for omp concrete francis b. nelson iii, jamila beale, jan moritz, &...
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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
Scope
• ASR background
• Tests of materials to mitigate expansion
• Tests with potassium acetate deicer – Expansion– pH
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
To Mitigate ASR Expansion
• Recognize and avoid susceptible aggregate
• Use low alkali cement
• Use supplemental cementing material
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
Standard Tests for ASR
• ASTM C1260 to test aggregate – Mortar test– Immerse mortar bars in 1-M NaOH at 80°C– Measure expansion after 14 days
• ASTM C1567 to test supplemental cementing materials
• Modified C1260 for deicer– Immerse mortar bars in potassium acetate
deicer at 80°C
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%
Expansion Results with Fly Ash
15% Class F (3)
15% Class C
15% Class F (1)15% Class F (2)
10% Class F
5% Class F
Sand 5
0.000%
0.050%
0.100%
0.150%
0.200%
0.250%
0.300%
0.350%
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Time (days)
Exp
an
sio
n (
%)
Slag Expansion (ASTM C 1567)
Sand 5
35%30%
25%20%
0.000%
0.050%
0.100%
0.150%
0.200%
0.250%
0.300%
0.350%
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Time (days)
Exp
ansi
on (
%)
Expansion Results with Slag
Other Materials Expansion (ASTM C 1567)
10% Silica Fume
10% Metakaolin
Sand 5
0.000%
0.050%
0.100%
0.150%
0.200%
0.250%
0.300%
0.350%
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Time (days)
Exp
ansi
on (
%)
Expansion Results with Other Materials
Discussion on Mitigation
• ASR expansion reduced to acceptable level by using one of the following: – 10% fly ash– 30% slag– 10% silica fume
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
Deicer Test - 1
• Tested all 5 sands from last year in clear deicer from Cryotech
Deicer Expansion (Modified ASTM C 1260)
Sand 1 Deicer
Sand 2 Deicer
Sand 3 Deicer
Sand 4 DeicerSand 5 Deicer
Sand 1
Sand 2
Sand 3
Sand 4
Sand 5
0.000%
0.050%
0.100%
0.150%
0.200%
0.250%
0.300%
0.350%
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Time (days)
Exp
ansi
on (
%)
– All sands showed little expansion
Deicer Test - 2
• Retested all 5 sands in blue deicer
– Rangaraju suggested indicator dye might affect expansion– Still little expansion
Blue Deicer Expansion (Modified ASTM C 1260)
Sand 1 Deicer
Sand 3 Deicer
Sand 5 Deicer
Sand 1
Sand 2
Sand 3
Sand 4
Sand 5
0.000%
0.050%
0.100%
0.150%
0.200%
0.250%
0.300%
0.350%
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Time (days)
Exp
ansi
on (
%)
Deicer Test - 3
• Tested fused silica– Used by Rangaraju,
known to show expansion
– Highly expansive
Day Beam 1 Beam 2 Beam 3 Average Day Beam 1 Beam 2 Beam 3 Average1 (cured) 1 (cured)2 (H20) 0.000 0.000 0.000 0.000 2 (H20) 0.000 0.000 0.000 0.000
4 0.001% 0.005% 0.003% 0.003% 4 13.250% 14.680% 12.563% 13.497%9 0.020% 0.019% 0.019% 0.019% 6 25.313% 26.209% 23.940% 25.154%14 0.042% 0.040% 0.041% 0.041%
16 0.048% 0.050% 0.050% 0.049% 25.154%
Sand 5 - Blue Deicer Fused Silica - Blue Deicer
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
Why Does Deicer Cause ASR?
• Deicer provides very high level of K (about 5 M)
• Reaction requires a pH > 13.6, deicer pH much lower than this
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
pH of Deicer Solution - 2
• We found similar increase in pH in contact with mortar bars
• No clear relationship between pH and expansion
ASTM 1260 Deicer Blue Deicer pHSand 1 0.142% 0.045% 0.064% naSand 2 0.111% 0.076% 13.8Sand 3 0.134% 0.051% 13.5Sand 4 0.163% 0.071% 13.4Sand 5 0.186% 0.061% 0.049% 12.9
Fused Silica 25.154% 13.6
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)
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