mab 1033 structural assessment and repair

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

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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)

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Du Beton

Typical Crack Types


a) Reinforcement corrosion

c) Sulphate attack

b) Plastic shrinkage

d) Alkali-aggregate reaction

Typical Crack Types


a) Reinforcement corrosion

a) Corrosion of Reinforcement

b) Plastic shrinkage

c) Alkali-aggregate reaction

ASR Corrosion

Shrinkage

Crazing

Freeze

& Thaw

Thermal

Thank You

mab 1033 structural assessment and repair

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