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Update on Deicer Distress

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A presentation given at the 39th Annual NCPA Concrete Paving Workshop. By Larry Sutter, PhD., P.E., FACI, Michigan Technological University

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Update on Deicer Distress

  1. 1. Update on Deicer Distress Larry Sutter Ph. D., P.E., FACI Michigan Technological University Material Science& Engineering
  2. 2. Outline • Background • A little theory • Discuss the causes • Discuss some solutions
  3. 3. Wisconsin
  4. 4. Wisconsin
  5. 5. Wisconsin
  6. 6. Michigan
  7. 7. Michigan
  8. 8. Wisconsin
  9. 9. Michigan I-275
  10. 10. Michigan I-94
  11. 11. Michigan I-94
  12. 12. Material Science & Engineering
  13. 13. Material Science & Engineering Premature Joint Deterioration
  14. 14. Many Suspects • Air entraining agents • Early entry sawing • Curing • Deicing practices
  15. 15. What Do We Know? • We understand the causes –Physical Attack (factors: permeability) • Saturated paste localized at joints • Freeze-Thaw deterioration located at joints –Chemical Attack (factors: permeability, CaOH) • Oxychloride formation – paste deterioration
  16. 16. Physical Attack • Concrete is a porous material – water goes in, out and is absorbed • Durability is achieved through reduced permeability • Porosity (permeability) is a result of: – The cement hydration process – Other materials used (aggregates) Materials Science & Engineering
  17. 17. Cement Hydration Cement Grains Water
  18. 18. Cement Hydration Early Hydration Products
  19. 19. Later Hydration Products or “Outer Product” Cement Hydration Hydration products are porous (gel pores) causing permeability at a nano-scale
  20. 20. Inner Hydration Product Unhydrated Cement Hydrated Portland Cement Paste Capillary Pores (nano - microns) Outer Hydration Product Gel Pores (nano scale) Entrained Air Voids (microns - millimeters)
  21. 21. Capillary Pores CSH Framework Neville High Permeability (Capillary Pores Interconnected)
  22. 22. Capillary Pores CSH Framework Low-Permeability Capillary Pores Segmented and Only Partially Connected Neville
  23. 23. Mindess & Young Porosity & Permeability Connectivity 0.45 w/c 45% connected at 75% hydration 0.60 w/c 90% connected at 75% hydration
  24. 24. Mindess & Young Porosity & Permeability Permeability
  25. 25. w/c Effects on Permeability ASTM C1585 0.55 w/c OPC Sorptivity 0.45 w/c OPC Sorptivity Materials Science & Engineering
  26. 26. Inner Hydration Product Unhydrated Cement Hydrated Portland Cement Paste Capillary Pores (nano - microns) Outer Hydration Product Gel Pores (nano scale) Entrained Air Voids (microns - millimeters)
  27. 27. Air-Void System Materials Science & Engineering
  28. 28. Hydraulic Pressure Theory – Powers 1945 Attributed damage to excessive hydraulic pressures resulting from the expansion of ice Materials Science & Engineering
  29. 29. Hydraulic Pressure Theory – Powers 1945 • Water fills capillary pore space Materials Science & Engineering air voids capillary voids
  30. 30. Hydraulic Pressure Theory – Powers 1945 • Ice begins to form in a saturated capillary pore system Materials Science & Engineering
  31. 31. Hydraulic Pressure Theory – Powers 1945 • As ice forms - volume expansion causes the unfrozen water to be expelled away from the freezing sites Materials Science & Engineering
  32. 32. Hydraulic Pressure Theory – Powers 1945 • Depending on the nature of the pore system, excessive internal stresses result from resistance to this flow Materials Science & Engineering
  33. 33. Hydraulic Pressure Theory – Powers 1945 • The pressurized water moving away from the freezing sites finds relief at the air voids, where it freezes without causing damage Materials Science & Engineering
  34. 34. Hydraulic Pressure Theory – Powers 1945 • Powers recognized the spacing between voids, rather than total volume of air, was the better measure of resistance to F-T damage Materials Science & Engineering
  35. 35. Hydraulic Pressure Theory – Powers 1945 • If the total void system is saturated... Materials Science & Engineering
  36. 36. Hydraulic Pressure Theory – Powers 1945 • Volume expansion leads to tensile forces and cracking Materials Science & Engineering
  37. 37. • Water moves through concrete under pressure – Hydraulic Pressure; Osmotic Pressure • Resistance to flow and expansive forces cause tensile forces in concrete • Air voids relieve the pressure – need an adequate air void system • Big Two affecting permeability – w/c and curing • Dissolved salts affect the fluids (to be discussed more) Materials Science & Engineering Take Aways – Pore Structure
  38. 38. S Poor Durability Good Durability Degree of Saturation (%) 60 65 70 75 80 85 90 95 100 ResistancetoFrost(%) 100 80 60 40 20 0 After CEB 1957 Poor Durability Good Durability Degree of Saturation (%) 60 65 70 75 80 85 90 95 100 ResistancetoFrost(%) 100 80 60 40 20 0 After CEB 1957 There is a critical saturation that makes concrete susceptible to repeated F-T So what does this have to do with joint distress? • Mechanism – Results when the paste becomes “critically saturated” and concrete under goes F-T cycles – The expansion of ice causes tensile forces that crack concrete Figure from J. Weiss
  39. 39. Deicers and Sealers January 16th, 2012 Slide 45 of 1,348 Freeze-Thaw Damage and the Degree of Saturation • Rate to reach DOS • FT at different DOS
  40. 40. Take Aways - Paste F-T • Concrete porosity cannot be avoided • Concrete porosity (permeability) is directly linked to w/cm and curing (connectivity) • Air is entrained to protect the paste – but it is not a bullet-proof solution – Critically saturated paste will crack when frozen • Need proper air content and air-void system (spacing factor, specific surface)
  41. 41. Take Aways - Paste F-T • Do deicers play a role in physical attack? • YES
  42. 42. Take Aways - Paste F-T • Salts suck up water & hold it • Helps concrete reach saturation sooner Photos courtesy Peter Taylor, Iowa State University
  43. 43. • Residual salt in the pore structure imbibes and holds water • The concrete does not completely “dry” out in drying conditions • Retained moisture incrementally increases the concrete moisture content and reduces the time to reach critical saturation Take Aways - Paste F-T
  44. 44. What Do We Know? • We think we understand the causes –Physical Attack • Saturated paste localized at joints • Freeze-Thaw deterioration located at joints –Chemical Attack from deicers • Oxychloride formation – paste deterioration
  45. 45. Cylinders exposed to MgCl2 solution after 84 days of constant low temperature test. From left to right: 0.40, 0.50, and 0.60 w/c
  46. 46. Cylinders exposed to CaCl2 solution after 84 days of constant low temperature test. From left to right: 0.40, 0.50, and 0.60 w/c
  47. 47. Cylinders exposed to NaCl solution after 84 days of constant low temperature test. From left to right: 0.40, 0.50, and 0.60 w/c
  48. 48. Cylinders exposed to Ca(OH)2 solution after 84 days of constant low temperature test. From left to right: 0.40, 0.50, and 0.60 w/c
  49. 49. Hi conc. CaCl2 – 500 days – 40 ºF
  50. 50. Hi conc. MgCl2 – 500 days – 40 ºF
  51. 51. Chemical Mechanisms of Deicer Attack How Calcium Chloride (CaCl2) Attacks 3Ca(OH)2 + CaCl2 + 12H2O  3CaO·CaCl2·15H2O  How Sodium Chloride (NaCl) Attacks 2NaCl + Ca(OH)2  CaCl2 + 2NaOH  How Magnesium Chloride (MgCl2) Attacks Ca(OH)2 + MgCl2  CaCl2 + Mg(OH)2 C-S-H + MgCl2  CaCl2 + M-S-H Calcium Oxychloride
  52. 52. Chemical Mechanisms of Deicer Attack How Calcium Chloride (CaCl2) Attacks 3Ca(OH)2 + CaCl2 + 12H2O  3CaO·CaCl2·15H2O  How Sodium Chloride (NaCl) Attacks 2NaCl + Ca(OH)2  CaCl2 + 2NaOH  How Magnesium Chloride (MgCl2) Attacks Ca(OH)2 + MgCl2  CaCl2 + Mg(OH)2 C-S-H + MgCl2  CaCl2 + M-S-H Calcium Oxychloride
  53. 53. Chemical Mechanisms of Deicer Attack How Calcium Chloride (CaCl2) Attacks 3Ca(OH)2 + CaCl2 + 12H2O  3CaO·CaCl2·15H2O  How Sodium Chloride (NaCl) Attacks 2NaCl + Ca(OH)2  CaCl2 + 2NaOH  How Magnesium Chloride (MgCl2) Attacks Ca(OH)2 + MgCl2  CaCl2 + Mg(OH)2 C-S-H + MgCl2  CaCl2 + M-S-H Calcium Oxychloride
  54. 54. Chemical Mechanisms of Deicer Attack How Calcium Chloride (CaCl2) Attacks 3Ca(OH)2 + CaCl2 + 12H2O  3CaO·CaCl2·15H2O  How Sodium Chloride (NaCl) Attacks 2NaCl + Ca(OH)2  CaCl2 + 2NaOH  How Magnesium Chloride (MgCl2) Attacks Ca(OH)2 + MgCl2  CaCl2 + Mg(OH)2 C-S-H + MgCl2  CaCl2 + M-S-H Calcium Oxychloride Left of arrow – Reactants Right of arrow – Products Products occupy larger volume than reactants! EXPANSIVE!
  55. 55. Chemical Mechanisms of Deicer Attack How Calcium Chloride (CaCl2) Attacks 3Ca(OH)2 + CaCl2 + 12H2O  3CaO·CaCl2·15H2O  How Sodium Chloride (NaCl) Attacks 2NaCl + Ca(OH)2  CaCl2 + 2NaOH  How Magnesium Chloride (MgCl2) Attacks Ca(OH)2 + MgCl2  CaCl2 + Mg(OH)2 C-S-H + MgCl2  CaCl2 + M-S-H Calcium Oxychloride
  56. 56. Chemical Mechanisms of Deicer Attack How Calcium Chloride (CaCl2) Attacks 3Ca(OH)2 + CaCl2 + 12H2O  3CaO·CaCl2·15H2O  How Sodium Chloride (NaCl) Attacks 2NaCl + Ca(OH)2  CaCl2 + 2NaOH  How Magnesium Chloride (MgCl2) Attacks Ca(OH)2 + MgCl2  CaCl2 + Mg(OH)2 C-S-H + MgCl2  CaCl2 + M-S-H Calcium Oxychloride
  57. 57. New Work - Purdue • The solutions that freeze are not a mixture of salt and water (a) – there are alkalis and other species in the solution (b) Farnam Y., S Dick, A Wiese, J Davis, D Bentz, J Weiss. “The Influence of Calcium Chloride Deicing Salt on Phase Changes and Damage Development in Cementitious Materials.” Cement and Concrete Composites, Volume 64, November 2015, Pages 1-15.
  58. 58. Calcium Oxychloride Farnam Y., S Dick, A Wiese, J Davis, D Bentz, J Weiss. “The Influence of Calcium Chloride Deicing Salt on Phase Changes and Damage Development in Cementitious Materials.” Cement and Concrete Composites, Volume 64, November 2015, Pages 1-15. Calcium oxychloride and brine solution
  59. 59. Oxychloride Formation • Work at Michigan Tech and now confirmed at Purdue shows oxychloride forms at temperatures above freezing • Implications – residual salt in concrete pore structure will form oxychloride – chemical attack year round ???? • To what extent is this happening ????
  60. 60. Take Aways – Chemical Attack • Brines of magnesium and calcium chloride have been demonstrated to react deleteriously with hydrated cement paste – Expansive calcium oxychloride forms – Reaction is slower than physical attack mechanisms – Reaction may occur year round
  61. 61. What do we do? • Reduce permeability • Use SCMs • Drainage
  62. 62. Reduce Permeability • Keep the water out and reduce the salt brine ingress – Lower w/cm (0.40 or less) – Need functioning sealants – Penetrating sealers – Permeability reducing admixtures – Use SCMs
  63. 63. D1 0980-127 1992
  64. 64. D1 0980-127 1992 Silicone sealant completely de-bonded. Severe joint distress.
  65. 65. D1 3805-67 (TH61) Sealant Bonded 1997
  66. 66. D1 3805-67 (TH61) Sealant bonded both sides, pristine joint crack
  67. 67. D3 7380-199 1999 Well bonded
  68. 68. D3 7380-199 Silicone sealant well bonded both sides. LATE, pristine crack
  69. 69. A word on sealers... • Silane and siloxane are effective at reducing the ingress of fluid into concrete
  70. 70. A word on sealers... • Silane and siloxane are effective at reducing the ingress of fluid into concrete • Questions? – How long do they last? – F-T durability of the sealer? – Cost effectiveness compared to other options? – Can you get it where you need it (in the joint)?
  71. 71. Salt Ingress for OPC mixture
  72. 72. PCC Mixtures Tri-siloxane 12% (aliphatic hydrocarbon)
  73. 73. Permeability Reducing Admixtures • Different types – different mechanisms – Water repellents – Crystal formers – Colloidal silica/silicates • Need more research • Similar questions to sealers • MiDOT research – Phase I completed – Durability testing included
  74. 74. Deicer Resistance in 17% CaCl2
  75. 75. Primary and Secondary Sorptivity ASTM C1585
  76. 76. SCMs • Oxychloride requires calcium hydroxide (CH) to form • Reduce the CH – reduce oxychloride formation Portland Cement Reaction Cement + Water -> C-S-H + CH Pozzolanic Reaction (example: Class F Fly Ash) CH + Pozzolan + Water -> C-S-H • Forming C-S-H reduces permeability • Consuming CH reduces oxychloride formation
  77. 77. Sorptivity of 15% MgCl2 into Different 0.45 w/c Concrete Mixtures Materials Science & Engineering 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0 200 400 600 800 1000 Absorption[I](mm) Time (s1/2) OPC fly ash slag
  78. 78. Take Aways – Actions • SCMs, reduced w/cm, and proper curing are the best options • Sealants can be effective – we still do not have a good way to install • PRAs offer opportunity – more research is needed – Cost is a key factor
  79. 79. Take Aways – Actions • Use of SCMs reduces susceptibility of concrete for chemical attack – Reduces CH available to react – Permeability of concrete not compromised by CH leaching – Improves concrete strength (affects physical and chemical attack)
  80. 80. Summary • Keep fluids out of concrete and all materials- related distress is minimized • Materials selection is very important – Low w/c – Low paste content – Use SCMs • Curing is essential – Keep the mixture water in and allow the materials time to form dense, impermeable, hydration products
  81. 81. Summary • Deicing chemicals are a serious concern – Contribute to physical attack – Contribute to chemical attack • Sealers may be required to offset deicing fluids – Keep brines out – Slow ingress of salt solutions
  82. 82. Questions? Larry Sutter llsutter@mtu.edu

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