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Concrete > 1. Intro > Flashcards

1. Intro Flashcards

1
Q

Why use concrete? (5)

A

Resistant to moisture
Compatible with any shape/mould
Cheap
Less energy input
Recycled materials as cement/aggregate

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2
Q

What does fresh concrete need to?

A

Form into required shape
Transport over long distances without segregation
Compacted to remove air

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3
Q

Ignoring good fresh concrete practices leads to?

A

Void formation
Poor bond between reinforcement
Segregation

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4
Q

What does hardened concrete need to?

A

Achieve strength
Curability
Desired surface appearance

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5
Q

Why do voids need to be minimised?

A

To improve strength and durability

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6
Q

Why do bonds need to be maximised?

A

To improve strength and durability

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7
Q

What is the function of cement?

A

Fill voids between aggregates
Lubrication and water tightness
Strength of hardened concrete

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8
Q

What is the function of aggregate?

A

Low cost filler
Resistance to loads, abrasion & percolation
Reduce volume change

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9
Q

What is W/C ration determined by?

A

Pozzolanic materials
Admixtures
Temp
Optimal particle sizes

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10
Q

What is cement paste quality based on?

A

W/C ratio
Cement type
Degree of compaction

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11
Q

Three sources of weakness in concrete

A

Pores
Interfaces
Structural defects

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12
Q

What is the definition of durability?

A

The ability of concrete to withstand the damaging effects of the environment and of its service conditions until it reaches a minimum level of performance.

Minimum acceptable level of performance.

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13
Q

What is design life?

A

Period of use intended by the designer

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14
Q

What is service life?

A

Period of use intended by the user
(Intended working life)

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15
Q

What are the factors of durability in concrete (4)

A

Structural design
Materials used
Workmanship/Execution
Curing

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16
Q

Causes of variability due to workmanship (6)

A

Non uniform supply of materials
Inaccurate batching
Excessive mixing
Segregation when placing
Over compaction or too little compaction (honeycombing)
Bad curing

17
Q

Causes of variability due to materials

A

Aggregates - yield strength & durability
Cement and admixtures

18
Q

Causes of variability due to properties (5)

A

Bleeding - loss of internal water for hydration
Heat of hydration - formation of thermal gradients/cracking
Degree of hydration
Moisture loss
Plastic shrinkage - cracks due to volume change.

19
Q

Factors for permeability (3)

A

Environmental conditions
Capillary size and interconnectivity
Hydrate structure

20
Q

What impacts capillary size and interconnectivity?

A

Aggregate size
W/C ratio

21
Q

What law can be used to calculate permeability?

A

Darcy’s law

22
Q

Factors for absorption (4)

A

Environmental conditions - moisture gradient
Capillary size
Hydraulic structure
Pore fluid content - degree of saturation

23
Q

Factors for diffusion (4)

A

Environment - ionic concentration gradient
Capillary size
Hydrate chemistry
Pore fluid chemistry

24
Q

Law for diffusion

A

Ficks First Law

Concrete (10 decks)

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