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ConcreteOnline self-study

Reinforced Concrete Deterioration Mechanisms

1 PDH · about 60 minutes · Course no. BR-C01 · Instructor: Michael Craig, PE

About the instructor

Michael Craig, PE is Senior Vice President and Southeast Director at Strinteg Corporation, leading bridge inspection and structural engineering across eight states and Puerto Rico. In 27+ years he has inspected over 4,000 structures and completed 3,000+ load ratings and 160+ load tests. He has managed repair and preservation design for complex bridges, including cable-stayed bridges. He holds PE licenses in twelve states, DC and Puerto Rico, SPRAT Level 1, and FAA Part 107 credentials.

Most reinforced concrete bridge deterioration traces back to a short list of mechanisms: corrosion of reinforcing steel (driven mainly by chlorides from deicing salt and seawater, and less often by carbonation), alkali-silica and alkali-carbonate reaction, freeze-thaw damage to paste and aggregate, deicer scaling, and external and internal sulfate attack. Each needs particular materials and a particular exposure, and each leaves a recognizable pattern of cracking, staining and spalling. This course explains how each mechanism works, how concrete cover and permeability control the time to corrosion, and how to read field findings back to a probable cause and the tests that confirm it. Its main sources are FHWA's Corrosion Protection: Concrete Bridges (FHWA-RD-98-088, Virmani and Clemena, 1998), FHWA-HRT-12-067 on corrosion-resistant reinforcement (2012), FHWA's ASR diagnosis and prognosis report (FHWA-HIF-09-004, January 2010) and FHWA's guidelines on materials-related distress (FHWA-RD-01-163, March 2002). The ACI 345.1R and ACI 546 references in the catalog are paywalled and were not reviewed for this course, so no requirement is quoted from them. Worked numbers in the examples are illustrative and computed for this course, not from a real bridge.

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Learning objectives

  • Explain chloride-induced corrosion
  • Recognize ASR, freeze-thaw and sulfate attack
  • Relate cover and permeability to durability
  • Connect mechanisms to inspection findings

Outline

  1. Why concrete bridges deteriorate
  2. How steel corrodes in concrete
  3. The chloride threshold
  4. Cover, permeability and time to corrosion
  5. Protection systems and what they imply for inspection
  6. Alkali-silica reaction
  7. Freeze-thaw damage to the paste
  8. Deicer scaling and D-cracking
  9. Sulfate attack and delayed ettringite formation
  10. Reading field findings back to a mechanism
  11. Field and laboratory evaluation methods
  12. Illustrative case: diagnosing a 1970s deck
  13. Exposure zones on a typical bridge
  14. Prestressed concrete and other considerations
  15. Inspector's checklist for concrete deterioration
  16. Open the course (21 screens, 2 knowledge checks)
  17. Final quiz — 10 questions, 70% to pass

References

  1. ACI 345.1R-16, Guide for Maintenance of Concrete Bridge Members
  2. ACI 546R-14, Guide to Concrete Repair
  3. FHWA, Bridge Inspector's Reference Manual (BIRM), FHWA-NHI-12-049, 2012 (as revised)
  4. FHWA, Corrosion Protection: Concrete Bridges, FHWA-RD-98-088, Y. P. Virmani and G. G. Clemena, September 1998 (rosap.ntl.bts.gov/view/dot/35835)
  5. FHWA, Corrosion-Resistant Reinforcing Steels / alternative reinforcement study, FHWA-HRT-12-067, November 2012 (fhwa.dot.gov/publications/research/infrastructure/structures/bridge/12067/)
  6. FHWA, Report on the Diagnosis, Prognosis, and Mitigation of Alkali-Silica Reaction (ASR) in Transportation Structures, FHWA-HIF-09-004, B. Fournier, M.-A. Bérubé, K. J. Folliard and M. Thomas, January 2010
  7. FHWA, Guidelines for Detection, Analysis, and Treatment of Materials-Related Distress in Concrete Pavements, FHWA-RD-01-163, March 2002, Ch. 2
  8. FHWA, Tech Brief: Air Entrainment and Concrete Durability, FHWA-HIF-17-009