Initial Condition Assessment: Concrete Traffic

1. Initial Condition Assessment:Concrete Traffic John Lawler & Joshua Freedland

2. Intro to WJE • Interdisciplinary engineering, architecture, and materials science firm; Founded in 1956 • Specialized in the evaluation and repair of existing structures

3. Background: Construction of Concrete Traffic • 1967 Cadillac DeVille • Cage of rebar and welded wire fabric (mesh) • Plywood forms supported with steel angles • Ready-mix concrete • Cast in January 8, 1970 • Concrete likely needed accelerator - Typical in Chicago at that time: calcium chloride

4. Background: Distress Mechanisms in Concrete Structures • Corrosion • Carbonation • Chlorides • Cyclic Freezing and Thawing/Scaling • Structural Loading • Volumetric Changes • Drying Shrinkage • Thermal Contraction

5. Initial Assessment of Concrete Traffic • Visual Survey • GPR (Ground Penetrating Radar) • Concrete Sample • Electrical Continuity

6. Findings: Visual Survey • Overall concrete condition • Honeycomb • Previous repairs (Two types) – at least one is original

7. Findings: Visual Survey • Cracking – at bottomand at corners Rear Right Front Left

8. Findings: Visual Survey • Cracking – at corners Front Right

9. Findings: Visual Survey • Cracking - Vertical & Structural and Shrinkage Front Right

10. Findings: Visual Survey • Cracking - Vertical & Structural and Shrinkage

11. Findings: Visual Survey • Cracking - In repairs

12. Findings: Visual Survey • Corrosion of Angles

13. Findings: Visual Survey • Corrosion of Angles

14. Findings: Visual Survey • Concrete Distressed Caused by Corrosion of Angles

15. Findings: Visual Survey • Freeze-thaw/Scaling distress

16. Findings: Visual Survey • Organic Growth

17. Findings: Visual Survey • Iron Staining • Misc. sealant

18. Findings: Visual Survey • Underside condition Support of “X-frame”

19. Findings:GPR • Cracks do not line up with reinforcing cracks not corrosion

20. Findings:GPR Right Side Left Side

21. Findings:GPR • Deflection in roofline 5 in. Front of roof Middle of roof

22. Findings:GPR

23. Findings: Concrete Sample • Sample from over angle from front of car • Freeze-thaw damage – concrete not air entrained • Chloride content = 0.043% chloride by mass of sample– acid soluble • Threshold is approx. 0.03 ppm • Carbonation = ~1/8 in. • Cause of corrosion likely admixed chloride

24. Significance of Observed Distress for Durability of Concrete Traffic • Corrosion of angles • Cracking at corners • Corrosion of embedded steel (?) • Freeze-thaw/scaling • Vertical cracking at rear support • Cracking - in original repairs & vertical cracks • Organic growth (algae) • Isolated other stains

25. Repair Options: Corrosion of Angles • Cathodic Protection • Impressed Current (Active) • Galvanic (Passive) • Chloride Extraction • Remove Angle (?!)

26. Repair Options: Other Items • Overall concrete distress • Water-repellant sealer (silane) – keep dry • Cracking • Crack Injection • Crack Filling • Organic Growth • Cleaners

27. Next Steps for Investigation • Condition Survey • Crack widths • Petrographic Analysis • Chloride Testing • Half-cell potential survey • Steel Section Loss • Repair Development • Cleaning studies

28. Thank you

29. New Site on CAMPUS • The site must be prepared with a custom made structural support frame and waterproofed pad, designed in collaboration with structural engineers and under the conservators recommendations. • The site must also fulfill the following criteria: • It should also not be under or too close to a tree with falling leaves. • It should be in an area with reasonably dense pedestrian traffic and good lighting to protect it from vandalism. • It should be where a real car could be, but it should be protected from collision with moving cars and regular street maintenance such as salting, street cleaning and snow ploughing.

30. Landscape design for north resident hall and commons by studio gang Due for completion in 2016