Concrete -Durability Flashcards
1
Q
What is durability?
A
Ability to exist for a long time without significant damage
2
Q
What are the categories of deterioration mechanisms?
A
- Physical attack
- Chemical attack
- Electrochemical attack
3
Q
What are water transport mechanisms for deterioration?
A
- Diffusion
- Absorption
- Permeation
4
Q
What is diffusion?
A
- Movement of liquid or gas driven by a concentration gradient
- High concentration -> low concentration
5
Q
What is permeation?
A
- Movement of liquid or gas driven by a pressure gradient
- High pressure -> low pressure
6
Q
What is absorption?
A
- Movement of water driven by surface tension
- Unsaturated -> saturated
7
Q
What are the types of physical attacks?
A
- Freeze-thaw
- Abrasion and wear
- Cavitation and erosion
- Temperature changes (heat and fire)
8
Q
What is freeze-thaw?
A
- Damage induced by repetitive cycles of freezing and thawing of water
- Water expands from freezing
- Large pores freeze first because large pores freeze at a high temperature
- Smaller pores freeze later at a lower temperature
- Hydraulic pressure is pushing water into smaller and smaller pores which cracks the concrete
9
Q
What is abrasion and wear?
A
Physical rubbing between surfaces
10
Q
What is cavitation and erosion?
A
- Tiny bubbles created when water lifts from surface
- Popping bubbles creates a shockwave and damages concrete
- Damage due to physical particles suspended in water rubbing against concrete
11
Q
What happens to temperature changes (heat and fire)?
A
- Concrete is a bad thermal conductor
- It is therefore resistant to fire damage
12
Q
What are the types of chemical attacks?
A
- Alkali-silica reaction (ASR)
- Sulphate attack
- Leaching/efflorescence
- Acid attack
- Carbonation
13
Q
What is ASR?
A
- Chemical reaction between alkali in paste and silica in aggregates
- Cracks form inside aggregates
- On a macro scale, map cracking
14
Q
What are factors that affect ASR?
A
- Nature of reactive silica
- Amount of reactive silica
- Particle size of reactive material
- Amount of alkalis available
- Amount of moisture available
15
Q
How do you prevent ASR?
A
- Avoid reactive aggregates!
- Limit amount of alkalis in cement paste
- Use SCMs in cement paste
- Lower concrete permeability