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ACRP Synthesis 11-03 Alkali-Silica Reactivity: Causes and Solutions

ACRP Synthesis 11-03 Alkali-Silica Reactivity: Causes and Solutions. Thomas Van Dam, Ph.D., P.E. Principal Wednesday, September 11, 2019 Association of California Airports Fall Conference. Concrete Making Materials. 9 - 15% Cement + SCM. Paste (cement + water). 15 - 16% Water.

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ACRP Synthesis 11-03 Alkali-Silica Reactivity: Causes and Solutions

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  1. ACRP Synthesis 11-03 Alkali-Silica Reactivity: Causes and Solutions Thomas Van Dam, Ph.D., P.E. Principal Wednesday, September 11, 2019 Association of California Airports Fall Conference

  2. Concrete Making Materials 9 - 15%Cement + SCM Paste(cement + water) 15 - 16%Water Mortar(paste + fine aggregate) 25 - 35%Fine aggregate Concrete(mortar + coarse aggregate) 30 - 45%Coarse aggregate

  3. Introduction • Concrete has a history of exceptional long-term performance in various applications • In some instances, the service life of a structure has been adversely affected by the concrete’s inability to maintain its integrity in the environment in which it serves • These type of failure are attributed to a lack of durability

  4. What Durability in Not? • Durability is not an intrinsic material property • “Durability” cannot be measured • Concrete that is durable in one application may rapidly deteriorate if placed in another application • It is not related to loading, although loading can exacerbate the distress

  5. Alkali–Silica Reactivity (ASR) • Reaction between alkalis in the concrete pore solution and reactive silica present in aggregate • Manifest as map cracking. Exudate is common, as is expansion of the structure Sequence of ASR Development (Thomas et al. 2011)

  6. ASTM C1778-16: Standard Guide for AAR • Field performance? • Has limitations • Laboratory testing • Petrographic analysis (ASTM C295) • Accelerated Mortar Bar Test (ASTM C1260) • Concrete Prism Test (ASTM C1293) • Verification of mechanism • ASR or ACR (ASTM C856)

  7. Prevention of Alkali-Silica Reaction • Use non-susceptible aggregates • Low-alkali cement (Na2Oeq less than 0.6%) • Use SCMs (low-calcium fly ash, silica fume, slag cement, and so on) • Consider lithium compounds • Combinations of the above

  8. Effect of Fly Ash on Alkali-Silica Reactivity

  9. Effect of Supplementary Cementing Materials on ASR

  10. FAA Mitigation of ASR • Aggregate reactivity assessed separately according to ASTM C1260 and combined according to ASTM C1567 • Only ASTM C1567 results use in acceptance • Greater than 0.10% expansion @ 28 days must be mitigated • Mitigation with SCMs assessed using ASTM C1567

  11. Recommended Ranges of SCM Contents (DOD 2015) *Silica fume must only be used for projects outside of the continental U.S. (OCONUS) where Class F fly ash and slag cement are not available, and when approved.

  12. ACRP Project No. 11-03: Practices to Mitigate ASR Affected Pavements at Airports • Project team consisted of APTech and NCE • Focused exclusively on treatment of ASR affected airport pavements • Based on literature search and survey results • Case examples prepared

  13. Results of Literature Review • ASR is a problem at a number of airports • Many feel that the FAA mitigation strategy, although somewhat onerous, are effective • Treatments that have been used by airports are varied, but no “silver bullet” was found • Topical application of lithium solution not effective • Treatments focused on repair

  14. Treatment Strategies • Joint and cracking sealing • Retrofitted subsurface drainage • Surface sealers and treatments • Silanes, siloxanes, high-molecular weight methacrylates • Lithium compounds • Corrective treatments including partial-depth repair (PDR), full-depth repair (FDR), and pressure relief joints (PRJ) • Overlays including asphalt and unbonded concrete overlays • Reconstruction

  15. Airport Surveys • Responses received from 19 airport • 25 facilities (R/W, T/W, and aprons) affected

  16. Age of ASR-affected Pavements Construction Decade of ASR-Affected Airfield Facilities Age of Airfield Facilities when ASR First Observed

  17. ASR Manifestations and Detection Indicators of ASR Cited by Survey Respondents Confirmation Method for ASR Identification

  18. Corrective Treatments

  19. Pavement Age When Treatments Applied

  20. Life Expectancy of Treatments

  21. Satisfaction With Treatments

  22. Four Case Examples • Distress appeared in 10 to 15 years • Pattern cracking at joints and map cracking, followed by spalling and pressure-related damage • PDR was the primary treatment utilized to control FOD • Proprietary materials that allow movement popular • Sawed and sealed HMA overlay provided good service at one airport • Surface application of lithium compounds found not to be effective • New FAA specifications appear to be effective

  23. Summary • ASR has affected many airport pavements around the country • There is no “silver bullet” treatment that has been found to stop or slow the progression of ASR once it has begun • Patching (PDR and FDR) are effective and treating FOD and extending life • New FAA specifications seem to be preventing occurrence in new pavements

  24. Questions? Thomas Van Dam, Ph.D., P.E., FACI Principal tvandam@ncenet.com 775-527-0690

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