Distress, Evaluation, and Repair of Historic Concrete

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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