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 cemtek@netzero.net