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Petrography A Tool for Concrete Investigations Lee Lawrence, P.E. and Derek Cong, Ph.D. Wiss, Janney, Elstner Associates, Inc . Austin, Texas (512) 835-0940. Petrography A Tool for Concrete Investigations. Outline. What is concrete petrography? What can it do for you? How it is done ?

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  1. Petrography A Tool for Concrete InvestigationsLee Lawrence, P.E.and Derek Cong, Ph.D.Wiss, Janney, Elstner Associates, Inc.Austin, Texas(512) 835-0940 WJE

  2. Petrography A Tool for Concrete Investigations Outline • What is concrete petrography? • What can it do for you? • How it is done? • Limitations • Case Studies WJE

  3. What is concrete petrography? Petrography is a branch of geology, a general term for systematic description of rocks, particularly under a polarizing microscope Concrete petrography is to apply petrographic techniques to study concrete, a man-made rock. WJE

  4. What can petrography do for you? It can be useful in identification of characteristics or problems at essentially any stage of concrete production and service: • Raw materials, aggregates, cementitious materials, etc. • Mix proportions, w/cm, cementitious materials content, air content, etc. • Problems during placement, consolidation, finishing, and curing • Problems that occur in service, durability issues, ASR, DEF, chemical attacks, F/T, etc. WJE

  5. How is it Performed? • ASTM C856, for concrete, mortar, grout, stucco, and other materials; • ASTM C457, point count; • ASTM C295, aggregates; • ASTM C1324, mortar WJE

  6. How is it Performed? • Observation • Comparison • Interpretation WJE

  7. How is it Performed? • Stereo microscopes • Petrographic microscopes • Supplementary techniques: • SEM/EDX • XRD • FTIR • other chemical and physical techniques WJE

  8. How is it Performed? WJE

  9. Limitations • Cannot estimate compressive strength • Cannot estimate slump of fresh concrete • Cannot estimate absolute age of concrete • Cannot estimate silica fume content • Cannot differentiate between Class C and Class F fly ash • Ineffective in admixture investigation WJE

  10. Case Studies – What’s in this Stuff? • Cementitious Materials - portlandcement WJE

  11. Cementitious Materials • Supplementary cementitious materials WJE

  12. WJE

  13. w/cm WJE

  14. WJE

  15. Retempering WJE

  16. Case Studies – Why is it Cracked? • Differential Shrinkage WJE

  17. Case Studies – Why is it Cracked? • Long-term Drying Shrinkage (Restraint to Shortening) WJE

  18. Case Studies – Why is it Cracked? • Short-term Drying Shrinkage (Plastic) WJE

  19. Case Studies – Why is it Cracked? • Thermal Cracking WJE

  20. Case Studies – Why is it Cracked? • Internal Expansion Mechanisms (ASR, D-CRACKING, DEF) D-CRACKING ASR DEF WJE

  21. Case Studies – Why is it Cracked? • Internal Expansion Mechanisms (ASR, D-CRACKING) WJE

  22. Case Studies – Why is it Cracked? • Internal Expansion Mechanisms (DEF) WJE

  23. Case Studies – Why is it Cracked? • Plastic Settlement (Subsidence) WJE

  24. Case Studies – Why is it Cracked? • Plastic Settlement (Subsidence) WJE

  25. Case Studies – Why is it Cracked? • Craze Cracking WJE

  26. Case Studies – Why is it Cracked? • Structural (Flexural, Shear) WJE

  27. Questions?

  28. Predictions?

  29. Hook'em Horns - 34 Mizzou - 10

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