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MAB 1033Structural Assessment and Repair
Professor Dr. Mohammad bin IsmailC09-313
3. CONCRETE BEHAVIOUR
DISINTEGRATION MECHANISMS
Learning Outcome
At the end of the course students should be
able to attack:able to attack:
• due to sulphate
• due to AAR
• cavitation
Exposure to Aggressive Chemicals
• Aggressive chemicals can be categorized as:
– Inorganic acids
– Organic acids
– Alkaline solutions
– Salt solutions
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– Salt solutions
• Acid attack on concrete is the reaction between the acid and the calcium hydroxide. The reaction produce water soluble calcium compounds, which are leached away.
• Limestone or dolomitic dissolve by acid
Alkali-Aggregate Reaction (AAR)
• AAR may create expansion and severe cracking
• Certain aggregates such as reactive form of silica, react with potassium, sodium and
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silica, react with potassium, sodium and calcium hydroxide from the cement and form a gel around the reacting aggregates
• When exposed to moisture, it expands creating forces that cause tension cracks
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Stage 1:
Gel
... .....
.. . .. .. Gel
Saturated
Paste
Stage 2:
Gel Filled
microcrack
Gel Filled
microcrack
surrounded by
Gel saturated
paste
MAB 10337
Stage 3:
Stage 4:
Reactive silica or
silicate in the
aggregate react with
alkali in the cement.
A gel forms on the
aggregate surface
when sufficient
moisture is present.
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moisture is present.
When gel is exposed
to moisture , Swelling
takes place. Swelling
of gel causes
surrounding concrete
to grow, causing
tension and
compressive stresses.
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Sulfate attack
• Soluble sulfate (Na,Ca&Mg) is common in mining operations, chemical and paper milling industries
• Sodium and calcium most common sulfate in soils, water and industrial processes
• All sulfates are potentially to concrete. They react
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• All sulfates are potentially to concrete. They react chemically with cement paste’s hydrated lime and hydrated calcium aluminate
• The formation of gypsum and ettringite expands, pressurizes and disrupts the paste result in surface scaling, disintegration and mass deterioration.
Sulfate Ions Cement Matrix Gypsum + Ettringite+ =
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Ettringite and gypsum expand, disintegrating the cement matrix.
Sulphate Attack
Department of Structures and Materials,
Faculty of Civil Engineering
UTM
12
40
60
80
100
120
Cement
Content
225 kg/m3
310 kg/m3
Ra
te o
f D
ete
rio
rati
on
(%
pe
r Y
ea
r)
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0 2 6 8 10 12 14 164
0
20
390 kg/m3
Ra
te o
f D
ete
rio
rati
on
(%
pe
r Y
ea
r)
Average C3A Content (%)
The effect of C3A Content of cement and Cement content of concrete on deterioration in a soil containing 10 per cent Na2SO4. (Verbeck, 1968).
ABRASION
Either of human action
wear and tear of factory or
warehouse floor;
movement of machinery, movement of machinery,
goods, etc.
gradual wear of concrete
roads by traffic
or
forces of nature
pounding of the ocean on
concrete sea defenses, jetties,
etc.
Erosion-Cavitation
• The formation of water bubbles and their
subsequent collapse is called “cavitation”. The
energy released upon their collapse causes
cavitation damage
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cavitation damage
• Cavitation damage results in the erosion of
the cement matrix, leaving harder aggregate
in place.
.
Dam
Water Flow
Cavitation Area
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Circulating Debris causes additional abrasion damage.
2. Vapor forms in low pressure area.
3. Collapsing air bubbles cause water to jet
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water to jet with extreme force at surface below vapor bubbles.
1. Curved surface causes localized high velocity .
Erosion-Abrasion
• Wearing away of the surface by rubbing and friction
• Factors affecting abrasion resistance include:
– Compressive strength
– Aggregate properties
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– Aggregate properties
– Finishing methods
– Use of toppings
– curing
Freeze-Thaw Disintegration
• Take place when the following conditions
present:
– Freezing and thawing temperature cycles-within
the concrete
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the concrete
– Porous concrete that absorbs water
• The freezing water contained in the pore
structure expands as it is converted into ice
Zone of Saturation
°
C
Tension Micro-Cracking
Small flakes break away from concrete
Water penetrates capillaries and upon freezing, swells, causing tension and small surface disintegration
Capillary Cavity
Swelling
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Pore and Capillary swelling causes Tension
Cracking
Ice
°C
Freezing water in pore structure expands
fracturing aggregate and spalling
surrounding concrete.
Water penetrates aggregates with high
absorption.
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Classification Of Cracks (1)
MAB 1033 Structural Assessment & Repair 23
Du Beton
Typical Crack Types
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a) Reinforcement corrosion
c) Sulphate attack
b) Plastic shrinkage
d) Alkali-aggregate reaction
Typical Crack Types
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a) Reinforcement corrosion
a) Corrosion of Reinforcement
b) Plastic shrinkage
c) Alkali-aggregate reaction
ASR Corrosion
Shrinkage
Crazing
Freeze
& Thaw
Thermal
Thank You
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