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I-275, two sites, varying performance.

I-275, two sites, varying performance. Site 2, showing deterioration at joint. Site 4, not exhibiting deterioration at joint. Stereo-microscope work.

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I-275, two sites, varying performance.

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  1. I-275, two sites, varying performance. • Site 2, showing deterioration at joint. • Site 4, not exhibiting deterioration at joint.

  2. Stereo-microscope work • Site 2, poor air-void system, alkali-silica reaction with fine aggregate particles and related cracks extending into hardened paste, but only within the top inch. • Site 4, adequate air-void system, alkali-silica reaction with fine aggregate particles, but without cracks extending into hardened paste.

  3. Cross-section through entire pavement, pink boxes show locations of stereo-microscope images of ASR fine aggregate, tic marks every inch.

  4. Polished slabs from cores taken near joint after sodium cobaltinitrite treatment to show alkali-silica reaction.

  5. Site 2, stereo-microscope images of ASR susceptible fine aggregate and related cracking, both before and after sodium cobaltinitrite stain.

  6. Site 2, stereo-microscope images of ASR susceptible fine aggregate and related cracking, both before and after sodium cobaltinitrite stain.

  7. Site 2, stereo-microscope images of ASR susceptible fine aggregate and related cracking, both before and after sodium cobaltinitrite stain.

  8. Site 4, stereo-microscope images of ASR susceptible fine aggregate, both before and after sodium cobaltinitrite stain.

  9. Site 4, stereo-microscope images of ASR susceptible fine aggregate, both before and after sodium cobaltinitrite stain.

  10. Site 4, stereo-microscope images of ASR susceptible fine aggregate, both before and after sodium cobaltinitrite stain.

  11. Pink boxes show area of automated air void analyses. Air voids visibly more abundant in bottom halves of all cores.

  12. Phenolphthalein stain to show depth of carbonation. Pink boxes show area of stereo-microscope images.

  13. Site 2, (left) with carbonation depth of approx. 3 to 5 mm, and Site 4 (right) with carbonation depth of approx. 2 to 3 mm.

  14. Chloride-profiling work • Two billets were cut to represent cross-section of pavement at surface. • The billets were cut from cores taken at mid-panel. • RGB elemental maps collected where calcium assigned to red channel, chlorine assigned to green channel, and silicon assigned to blue channel. • Tic marks every ¼ inch.

  15. Chloride-profiling work • Bright green spots are from x-ray diffraction events, and not due to characteristic chlorine K-alpha radiation. These areas were avoided during collection of spot-analyses for construction of chloride profiles.

  16. Chloride profile from Site 2, and best fit according Fick’s 2nd Law, calculated as outlined in ASTM C1556.

  17. Chloride profile from Site 4, and best fit according Fick’s 2nd Law, calculated as outlined in ASTM C1556.

  18. Comparison of best fit lines to Fick’s 2nd Law – chloride penetration more pronounced at Site 2 as compared to Site 4.

  19. Predicted profile for 0.45 w/c concrete after continuous NaCl brine exposure (2N conc.) for 5 years (http://ciks.cbt.nist.gov/~bentz/clpencon.html)

  20. Shape of profile of NIST model better approximates shape of data set as compared to straight fit to Fick’s 2nd law.

  21. Shape of profile of NIST model better approximates shape of data set as compared to straight fit to Fick’s 2nd law.

  22. On-going work • Chloride penetration more pronounced at Site 2. Underlying reasons for increased permeability have not been determined. Production of thin sections to compare microstructure of both sites is underway.

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