CON 124 Session 3 - Concrete Durability

924 views

Published on

CON 124 - Session 3
Sulfate Attack
O. Tavares

Published in: Business, Technology
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
924
On SlideShare
0
From Embeds
0
Number of Embeds
72
Actions
Shares
0
Downloads
34
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

CON 124 Session 3 - Concrete Durability

  1. 1. CON 124 Basic Concrete Mix Design Proportioning Session 3 Concrete Durability
  2. 2. CON 124 - Session 3  This session will discuss  Sulfate Attack  Corrosion of Steel  Mechanisms  Recommendations and solutions
  3. 3. Sulfate Attack Mechanism  Sulfate ions (SO4 -2) react with hydration products (calcium hydroxide and aluminate hydrates)  Reaction products result in swelling (mechanism is uncertain)  Swelling pressures destroy cement matrix  Affected by  Cement type  Sulfate ion concentration in water or soil  Permeability of concrete  Presence water
  4. 4. External Sulfate Attack External to internal progression of deterioration
  5. 5. Mitigation of Sulfate Attack  Use low w/c  Use sulfate resistant cement (Type V)  Use supplementary cementitious materials
  6. 6. Test method ASTM C1580 for determining water-soluble sulfates in soil
  7. 7. Table 4.2.1.b Exposure Category S – Sulfate Exposure Class Description Water-soluble sulfate (SO4) in soil, % by weight Sulfate (SO4) in water, ppm S0 NA < 0.10 < 150 S1 Moderate 0.10 to 0.20 150 to 1500 S2 Severe 0.20 to 2.00 1500 to 10,000 S3 Very Severe > 2.00 >10,000
  8. 8. Sulfate Class Maximum w/cm (Normal wt.), by mass Minimum f'c, MPa (psi) ASTM C150 ASTM C595 ASTM C1157 Other S0 — — — — — — S1 0.50 28 (4000) II IP(MS), IS(<70) (MS) MS — S2 0.45 31 (4500) V — HS No calcium chloride S3 0.45 31 (4500) V + pozz or slag — HS + pozz or slag No calcium chloride Table 4.3.1.b Exposure Category S – Sulfate Exposure Cement Types for Sulfate Resistance of various classes of sulfate attack, most severe sulfate resistance class is S3
  9. 9. Exposure Class Max. Expansion When Tested Using ASTM C1012 S1 0.10% at 6 months S2 0.05% at 6 months, or 0.10% at 12 months* S3 0.10% at 18 months * 12 month applies when 6 month is not met Table 4.5.1 Requirements for Establishing Suitability of Cementitious Materials Combinations When Exposed to Water-Soluble Sulfate Exposure Class and maximum expansion according to test method ASTM C1012
  10. 10. ASTM C1012 Standard Test Method ASTM C1012 for testing expansion due to sulfate solution.
  11. 11. ASTM C1012 • Evaluate sulfate resistance of different cementitious materials (cement, pozzolans, slag) • Use ASTM C109/C109M mortar mixture proportions to make 25 x 15 x 185 mm prisms • Immerse in sodium sulfate solution • Measure length change
  12. 12. Effect of Cement C3A on Sulfate Resistance 121110987654 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 C3A SulfateAttack4Month%Expansion R-Sq = 0.320 Y = 0.116075 - 3.71E -02X + 5.80E -03X **2
  13. 13. Long-term Sulfate Exposure Study Visual Rating Scale 1.1 2.5 5.0
  14. 14. Corrosion of Bridge Structures  Fulton Road Bridge, Cleveland, Ohio  Corrosion due to deicing salts used on roadway  Wooden platform was built underneath concrete arch to protect patrons to the zoo from falling concrete  Deck and columns need to be replaced because structurally deficient. Consulting Engineers trying to save arches and apply cathodic protection
  15. 15. Corrosion: How Big a Problem? “The average bridge deck located in a snow-belt State with black reinforcing steel and 40 mm (1.5 in.) of concrete cover has shown spalling in about 7 to 10 years after construction and has required construction and has required rehabilitation in about 20 years after construction.” Repair / Replacement Cost: ~ $ 20 billion & increasing
  16. 16. Marine Corrosion
  17. 17. Marine Corrosion – Replacement Bridge
  18. 18. Corrosion of Steel in Concrete High alkalinity of concrete promotes formation & stabilization of natural protective oxide layer at steel surface.
  19. 19. Corrosion of Steel in Concrete  Electrochemical process that requires:  Moisture & Oxygen  Breakdown of Protective Oxide Layer (the Passive Layer)
  20. 20. 1/2 O2 + H2O + 2e- 2OH- Water Oxygen Chlorides, CO2 iron OH- Cathode Anode “ionic path” Electronic Path Fe 2e- + Fe2+ e- Corrosion Reaction - Necessary Factors Corrosion Reaction due to movement of ions
  21. 21. Corrosion of Steel in Concrete: Net Effect  Corrosion by-product (rust) induces tensile stresses within matrix…..
  22. 22. Sources of Chloride  De-icing Salts for Snow & Ice Removal  Groundwater  Brackish Water  Seawater & Airborne  Mixture design
  23. 23. Sources of Chloride  De-icing Salts for Snow & Ice Removal  Groundwater  Brackish Water  Seawater & Airborne  Mixture design
  24. 24. Sources of Chloride  De-icing Salts for Snow & Ice Removal  Groundwater  Brackish Water  Seawater & Airborne  Mixture design
  25. 25. Sources of Chloride  De-icing Salts for Snow & Ice Removal  Groundwater  Brackish Water  Seawater & Airborne  Mixture design
  26. 26. Rule #1 for Corrosion Protection of Steel in Concrete Good Concreting Practices  Good quality concrete  Low water-cementitious materials ratio  High-range water-reducing admixture  Proper placement & consolidation  Good Curing !!!
  27. 27. ACI 318 Classes for Corrosion Exposure Category Category Severity Class Condition C Corrosion Protection of Reinforcement Not Applicable C0 Concrete dry or protected from moisture Moderate C1 Concrete exposed to moisture but not to external sources of chlorides Severe C2 Concrete exposed to moisture and an external source of chlorides from deicing chemicals, salt, brackish water, seawater, or spray from these sources
  28. 28. ACI 318 Requirements for Concrete for Corrosion Exposure Category Exposure Class Max.w /cm Min.f’ c (psi) Additional Minimum Requirements Max Water-Soluble Chloride Ion (Cl-) Content in Concrete (percent by weight of cement) Related Provisions Reinforced Concrete Prestressed Concrete C0 n/a 2,500 1.00 0.06 None C1 n/a 2,500 0.30 0.06 C2 0.40 5,000 0.15 0.06 7.7.6, 18.16
  29. 29. Please return to Blackboard and watch the following videos:  Video 1: Concrete Durability Freezing-Thawing Freethaw.mpg
  30. 30. Questions? Email cemtek@netzero.net

×