Impact of Potassium Acetate Deicing Chemicals on ASR of Candidate OMP Concrete Materials Francis B. Nelson III Leslie J. Struble January 12, 2006

Overview Alkali Silica Reaction Previous Work Deicer Background Tasks Schedule Testing Programs

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

Affected Concretes Highway pavement and bridge abutment in Peoria, Illinois Concrete anchor for cable-stay bridge, Royal Gorge, Colorado

Effect of Supplemental Cementing Materials Fly ash, slag, silica fume, metakaolin all reduce expansion by replacing cement, lowering alkali concentration Effective replacement level must be determined for specific material PCA

To Prevent ASR Recognize and avoid susceptible aggregate Use low alkali cement Use supplemental cementing material

Previous Work Tech Notes IDOT work UIUC Testing Recommendations to OMP

Tech Notes #9 – Freeze Thaw Performance of Coarse Aggregates –Recommended Use of IDOT F/T list #10 – Summary of IDOT & ASTM Specifications for Coarse Aggregate Gradation –Described CA Gradations for Use at OMP #20 – FAA Concrete Materials Specification Evaluation –Recommended Material Guidelines for OMP

IDOT Working Group Meetings Working with Industry to develop ASR specification Slowly introduce a statewide specification (June 2006) –Special provision on job specific basis (Dan Ryan Project using GGBFS) Only District 4 (Peoria) showing evidence in pavements of ASR currently –Other districts have reactive aggregates however Developing List of Fine Aggregate Producers –Proposed Four Categories of Aggregate Reactivity –According to ASTM C 1260 Test Results Allowing mitigation according to ASTM C 1567

UIUC ASR Testing Aggregates selected from Chicago market –5 natural sands and 1 manufactured sand –Ottawa sand and Pyrex glass

UIUC ASR Recommendations Two categories of expansion rather than three ( 0.1%) No maximum alkali content for cements (due to potassium in deicer) Allow contractors to use ASTM C 1567 to make a combination of aggregate, cement, and mineral admixture that yields expansion less than 0.1%

Mitigating ASR Testing Test Mineral Admixtures –Test for potential combinations to mitigate against reactive aggregates, use ASTM C 1567 test method. –Use fine aggregates previously tested and combine with mitigating materials, such as fly ash and slag, to test for decreased expansion.

Mitigating Materials Test Program ASTM C 1567 –Class F Fly Ash 15%, 10%, 5%, +/- –Class C Fly Ash 15%, +/- –Ground Granulated Blast Furnace Slag 20%, 25%, 15%, +/- –Silica Fume* 10%, +/- –Metakaolin* 10%, +/-

Background on Potassium Acetate Deicer Non-chloride based deicer Non-toxic, Biodegradable and less corrosive Lowers freezing temperature (-76 o F) Also anti-icing agent (prevents freezing) Avoid use with non air entrained concrete, galvanized metals, and non-watertight electrical systems

Tasks 1.Conduct literature review 2.Select representative fine aggregates 3.Survey/test deicing chemical 4.Test selected samples for ASR using ASTM C 1260 modified to simulate potassium acetate solution 5.Test mitigating materials for effective level of replacement according to ASTM C Obtain concrete cores from pavement using deicer 7.Examine cores for possible alkali-silica reaction 8.Recommend materials for OMP pavements 9.Write final report at end of project and Technical Notes as necessary throughout the study.

Schedule Task Number 1 ( perform literature review) 2 (select aggregates) 3 (survey alkali concentration) 4-5 (test samples) 6 (obtain concrete cores) 7 (test cores) 8 (make recommendations) 9 (write final report) Month

Potassium Acetate Studies Modified ASTM C 1260 tests –Work done by Prasad Rangaraju, PhD pH and Chemical Composition Rangaraju et al 2005

Modified ASTM C 1260 Compare 14 day expansions between NaOH (left) and PA (right) Rangaraju et al 2005

Mortar Bars and Concentration Concentration of 6.46 M is what is applied to pavements Expansion accelerated so much tests ended due to severe cracking and warping of mortar bars Rangaraju et al 2005

Deicer Testing Program 5 natural sands tested previously –Test in deicer solution and compare expansions Test mitigating mixtures from ASTM C 1567 results –Test in deicer solution and compare expansions

Assistance from OMP Obtaining cores from pavements at Midway and/or O’Hare History and understanding of deicer use so far in Chicago Open for discussion