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Distress, Evaluation, and Repair of Historic Concrete

Distress, Evaluation, and Repair of Historic Concrete. Jarkko Simonen, P.E. Wiss, Janney, Elstner Associates, Inc. Introduction. History Common Distress Mechanisms Corrosion Freeze Thaw Material problems Analysis or Evaluation Methods Repair. Introduction. Cement has a long history

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Distress, Evaluation, and Repair of Historic Concrete

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  1. Distress, Evaluation, and Repair of Historic Concrete Jarkko Simonen, P.E. Wiss, Janney, Elstner Associates, Inc.

  2. Introduction • History • Common Distress Mechanisms • Corrosion • Freeze Thaw • Material problems • Analysis or Evaluation Methods • Repair

  3. Introduction • Cement has a long history • Certain types of cement have been used by the Babylonians, Egyptians, and Romans • Portland cement 1824 • Reinforced concrete 1867 • In the northwest one of the early examples of concrete construction is Fort Casey - 1890 • Generally the use of concrete became common after about 1900

  4. Concrete Vintage Generalizations Modern Concrete (1945 to present) • Homogenous pour • Improved placement • Lower w/c (higher f ’c) • Modern reinforcing • Carbonation • Air entrainment? • Admixtures Older Concrete (1900 to 1945) • Multiple layers • Placement in lifts • Higher w/c (lower f ’c) • Early reinforcing systems • Carbonation • No air entrainment

  5. Introduction Environment • Wet • Cold • Coastal Deterioration due to the environment • Corrosion • Freeze thaw

  6. Corrosion • Common in environments that contain salt and moisture • Distress manifests as staining, cracking, and spalling of the concrete

  7. Concrete Concrete provides a great environment for steel against corrosion

  8. Problem with rust • Corrosion of the rebar causes rust to form • Rust is 6 to 10 time less dense than steel • Increased volume causes concrete to crack

  9. Effects of Chloride Contamination • Destroys natural passive oxide layer provided by portland cement paste • Complicated chemical interactions • Hygroscopic

  10. Chloride Contamination • Environment (soils, sea water) • Applied (deicing chemicals) • Integral (admixtures, aggregate, water)

  11. Carbonation Carbonation CO2 + H2O + Ca(OH)2 CaCO3 + H2O atmospheric rain cementpaste limestone water

  12. Carbonation • Advances about 1 mm per year in normal concrete • Once carbonation reaches steel, the steel is unprotected • Corrosion can affect large areas

  13. Freeze-thaw weathering regions (ASTM C33)

  14. Freeze-thaw • Damages the near surface region of concrete • Surface flakes off typically in horizontal layers • More aggressive if surface is exposed to chlorides

  15. Air entrainment can be effective in mitigating freeze-thaw

  16. ASR- Reaction between silica and hydroxyls (OH-) in the pore solution, forming silica gel. As the gel forms, it absorbs water and expands.

  17. Alkali Silica Reaction • ASR must have all three components present to cause a problem • Reactive aggregates • Abundance of alkalis • Water • In the northwest we have two out of three • Reactive Aggregates • Water • Generally cement has low alkalinity • ASR aggravates F/T and corrosion

  18. Assessment Methods Field • Visual survey • Mechanical sounding survey • Corrosion assessment • Half-cell potential measurements • Linear Polarization Resistance Method • Other non-destructive methods (rebound hammer, impact-echo, pulse velocity, etc.)

  19. Assessment Methods Laboratory • Chloride content • Depth of Carbonation (Phenolphthaleinindicator) • Petrographic examination

  20. Condition Assessments References • ACI 201.1R Guide to Making a Condition Survey of Concrete in Service • ACI 224.1R Causes, Evaluation and Repair of Cracks in Concrete Structures • ACI 364.1R Guide for Evaluation of Concrete Structures Prior to Rehabilitation • ACI 437.1R Strength Evaluation of Existing Concrete Buildings • ACI 546R Concrete Repair Guide • Technical Guidelines by International Concrete Repair Institute (ICRI) • Guide to Nondestructive Testing of Concrete • Others

  21. Visual Survey • Identify distress mechanisms • Repair quantities • Repair locations/types Mechanical Survey • Identify hidden distress • Dislodge dangerous fragments • Gives you a better feel about the concrete quality

  22. Corrosion Surveys Half cell surveys • Identify potential areas of corrosion • Repair quantities • Repair locations/types Linear Polarization • Corrosion rate/aggressiveness

  23. NDT Investigative Techniques • Impact echo • Pulse velocity • GPR • Magnetic rebar locators

  24. Laboratory Analysis • Initial opinion of deterioration and conditions • Type of concrete exposure • Discuss testing with petrographer/chemist • Repair type being considered • Type of testing and expected results

  25. Evaluation for Chlorides Two methods • Cores • Drill/powder samples Testing • ASTM C 1152:Acid-Soluble Chloride in Mortar and Concrete • ASTM C 1218:Water-Soluble Chloride in Mortar and Concrete

  26. Evaluation for Carbonation

  27. Petrography • ASTM C856: Standard Practice for Petrographic Examination of Hardened Concrete • Freeze thaw • ASR • Finishing Problems • Identify substrate materials • Etc.

  28. Repair Concrete repair • Protection/Mitigation • Patch repairs • Reconstruction

  29. Protection/Mitigation • Coatings • Prevent moisture • Electrochemical treatments • Cathodic protection • Chloride extraction • Re-alkalinization • Other • Sealers • Silanes • Siloxanes • Migratory corrosion inhibitors

  30. Patch Repairs Considerations • Compatibility • Strength • Wear • Thermal • Appearance • Color • Texture • Finish • Profile

  31. Repairs should blend in

  32. Blending Repairs • Lift lines • Form board lines • Color • Texture

  33. Surface Preparation • Saw cuts • Rectangular • Installation • Dry as possible • Finishing • Curing

  34. Samples and Mock-ups • Cleaning • Coating removal • Color • Finish • Texture • Surface preparation • Design mix • All installation and finishing procedures and • Techniques

  35. Repair Special Considerations with Historic/Architectural Concrete • Tasks are similar of work with other concrete • Options may be more limited • Rules of good concrete repair practice apply • Original design may need to be improved • Emphasis is needed on investigation, laboratory analysis, samples, mock-ups, and trial repairs

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