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

Expansion Results with Slag

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 (-76 o 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 – 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

Deicer Test - 3 Tested fused silica –Used by Rangaraju, known to show expansion –Highly expansive

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

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)