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)