2. CON 124 - Session 3
ďŽ This session will discuss
ďŽ Sulfate Attack
ďŽ Corrosion of Steel
ďŽ Mechanisms
ďŽ Recommendations and solutions
3. Sulfate Attack Mechanism
ďŽ Sulfate ions (SO4
-2) react with hydration products
(calcium hydroxide and aluminate hydrates)
ďŽ Reaction products result in swelling (mechanism
is uncertain)
ďŽ Swelling pressures destroy cement matrix
ďŽ Affected by
ďŽ Cement type
ďŽ Sulfate ion concentration in water or soil
ďŽ Permeability of concrete
ďŽ Presence water
5. Mitigation of Sulfate Attack
ďŽ Use low w/c
ďŽ Use sulfate resistant cement (Type V)
ďŽ Use supplementary cementitious materials
6. Test method ASTM C1580 for determining
water-soluble sulfates in soil
7. Table 4.2.1.b Exposure Category S â
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. Sulfate
Class
Maximum
w/cm (Normal
wt.), by mass
Minimum f'c,
MPa (psi)
ASTM C150
ASTM
C595
ASTM
C1157
Other
S0 â â â â â â
S1 0.50 28 (4000) II
IP(MS),
IS(<70)
(MS)
MS â
S2 0.45 31 (4500) V â HS
No calcium
chloride
S3 0.45 31 (4500)
V + pozz
or slag
â
HS +
pozz or
slag
No calcium
chloride
Table 4.3.1.b Exposure Category S â
Sulfate Exposure
Cement Types for Sulfate Resistance of various classes of sulfate attack, most
severe sulfate resistance class is S3
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
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
14. Corrosion of Bridge Structures
ďŽ Fulton Road Bridge, Cleveland, Ohio
ďŽ Corrosion due to deicing salts used on roadway
ďŽ Wooden platform was built underneath concrete arch to protect patrons to
the zoo from falling concrete
ďŽ Deck and columns need to be replaced because structurally deficient.
Consulting Engineers trying to save arches and apply cathodic protection
15. Corrosion: How Big a Problem?
âThe 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.â
Repair / Replacement Cost: ~ $ 20 billion & increasing
18. Corrosion of Steel in Concrete
High alkalinity of concrete promotes
formation & stabilization of natural
protective oxide layer at steel surface.
19. Corrosion of Steel in Concrete
ďŽ Electrochemical process that requires:
ďŽ Moisture & Oxygen
ďŽ Breakdown of Protective Oxide Layer (the Passive
Layer)
20. 1/2 O2 + H2O + 2e- 2OH-
Water
Oxygen
Chlorides, CO2
iron
OH-
Cathode
Anode
âionic pathâ
Electronic Path
Fe 2e- + Fe2+
e-
Corrosion Reaction - Necessary Factors
Corrosion Reaction due to movement of ions
21. Corrosion of Steel in Concrete:
Net Effect
ďŽ Corrosion by-product (rust) induces tensile
stresses within matrixâŚ..
22. Sources of Chloride
ďŽ De-icing Salts for
Snow & Ice Removal
ďŽ Groundwater
ďŽ Brackish Water
ďŽ Seawater &
Airborne
ďŽ Mixture design
23. Sources of Chloride
ďŽ De-icing Salts for
Snow & Ice Removal
ďŽ Groundwater
ďŽ Brackish Water
ďŽ Seawater &
Airborne
ďŽ Mixture design
24. Sources of Chloride
ďŽ De-icing Salts for
Snow & Ice Removal
ďŽ Groundwater
ďŽ Brackish Water
ďŽ Seawater &
Airborne
ďŽ Mixture design
25. Sources of Chloride
ďŽ De-icing Salts for
Snow & Ice Removal
ďŽ Groundwater
ďŽ Brackish Water
ďŽ Seawater &
Airborne
ďŽ Mixture design
26. Rule #1 for Corrosion Protection of
Steel in Concrete
Good Concreting Practices
ďŽ Good quality concrete
ďŽ Low water-cementitious materials ratio
ďŽ High-range water-reducing admixture
ďŽ Proper placement & consolidation
ďŽ Good Curing !!!
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. ACI 318 Requirements for Concrete for
Corrosion Exposure Category
Exposure
Class
Max.w
/cm
Min.fâ
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. Please return to Blackboard and watch
the following videos:
ďŽ Video 1: Concrete Durability Freezing-Thawing
Freethaw.mpg