CON 124 Session 3 - Concrete Durability
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Transcript of CON 124 Session 3 - Concrete Durability
CON 124Basic Concrete Mix Design Proportioning
Session 3Concrete Durability
CON 124 - Session 3
This session will discuss Sulfate Attack Corrosion of Steel
Mechanisms Recommendations and solutions
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
External Sulfate Attack
External to internal progression of deterioration
Mitigation of Sulfate Attack
Use low w/c Use sulfate resistant cement (Type V) Use supplementary cementitious materials
Test method ASTM C1580 for determining water-soluble sulfates in soil
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
Sulfate Class
Maximum w/cm (Normal wt.), by mass
Minimum f'c, MPa (psi) ASTM C150 ASTM
C595ASTM C1157 Other
S0 — — — — — —
S1 0.50 28 (4000) IIIP(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
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*
S30.10% 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
ASTM C1012
Standard Test Method ASTM C1012 for testing expansion due to sulfate solution.
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
Effect of Cement C3A on Sulfate Resistance
121110 9 8 7 6 5 4
0.80.7
0.6
0.50.40.3
0.2
0.1
0.0
C3A
Su
lfate
Att
ack
4 M
onth
% E
xpan
sion
R-Sq = 0.320Y = 0.116075 - 3.71E-02X + 5.80E-03X**2
Long-term Sulfate Exposure Study
Visual Rating Scale
1.1 2.5 5.0
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
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
Marine Corrosion
Marine Corrosion – Replacement Bridge
Corrosion of Steel in Concrete
High alkalinity of concrete promotes formation & stabilization of natural
protective oxide layer at steel surface.
Corrosion of Steel in Concrete
Electrochemical process that requires: Moisture & Oxygen Breakdown of Protective Oxide Layer (the Passive
Layer)
1/2 O2 + H2O + 2e- 2OH-
WaterOxygen
Chlorides, CO2
ironOH-
CathodeAnode
“ionic path”
Electronic Path
Fe 2e- + Fe2+
e-
Corrosion Reaction - Necessary Factors
Corrosion Reaction due to movement of ions
Corrosion of Steel in Concrete: Net Effect
Corrosion by-product (rust) induces tensile stresses within matrix…..
Sources of Chloride
De-icing Salts for Snow & Ice Removal
Groundwater Brackish Water Seawater &
Airborne Mixture design
Sources of Chloride
De-icing Salts for Snow & Ice Removal
Groundwater Brackish Water Seawater &
Airborne Mixture design
Sources of Chloride
De-icing Salts for Snow & Ice Removal
Groundwater Brackish Water Seawater &
Airborne Mixture design
Sources of Chloride
De-icing Salts for Snow & Ice Removal
Groundwater Brackish Water Seawater &
Airborne Mixture design
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 !!!
ACI 318 Classes for Corrosion Exposure Category
Category Severity Class Condition
CCorrosion
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
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
Please return to Blackboard and watch the following videos: Video 1: Concrete Durability Freezing-Thawing
Freethaw.mpg
Questions?Email [email protected]