Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Construction Materials > Concrete part 2 > Flashcards

Concrete part 2 Flashcards

1
Q

How do we calculate compressive strength?

A 
fcu = Fu/A 
where:
fcu- compressive strength at 28 days
Fu- Force at failure at 28 days
A- cross-sectional area of the cylinder
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What shape can we also measure compressive strength on other than a cylinder?

A

Cubic samples when the load is applied the 45-degree cracks will interact with each other causing a higher strength.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What does strength development depend on? (6)

A

1) Cement composition
2) Water/cement ratio
3) Curing humidity
4) Curing temperature
5) Type of aggregates
6) Compaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the modulus of elasticity for ordinary concrete for PC?

A

Ec = 9.1fcu^0.33

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the elastic modulus Ec for 30MPa concrete?

A

9.1 x 30^0.33 = 26GPa

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the main degradation mechanisms of concrete?

A

1) Drying shrinkage
2) Freeze-thaw
3) Creep
4) Fatigue
5) Sulphur attack
6) Chloride attack
7) Carbonation
8) ASR alkali-silica reaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the cause of drying shrinkage?

A

During hydration, water is consumed through self-desiccation that causes shrinkage.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the cause of freeze thaw and sulphur attack?

A

Pressure from crystals forming and expanding in the pores.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is freeze-thaw?

A

Water turning into ice.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is a sulphate attack?

A

Monosulfoaluminate turning into ettringite.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What can free-thaw cause?

A

Fatigue due to its cyclic nature.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How can we avoid freez-thaw?

A

Introduce additional porosity with air-entraining admixtures.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How can we avoid sulphur attacks?

A

Use low-aluminium cement.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the cause of ASR?

A

Pressure from a phase expanding inside the pores.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What phase happens during ASR?

A

The gel formed by alkali ions that are usually present in the cement and react with amorphous aggregates.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How can we avoid ASR?

A

Use aggregates low in amorphous silica and use low alkali type of cement (more expensive).

17
Q

What is creep?

A

Stress and strain in concrete increase progressively overtime for years.

18
Q

What is the cause of creep?

A

Under stress, water layers in the nanostructure of C-S-H flow viscously.

19
Q

What is the effect of creep?

A

Excessive deformations can ultimately cause cracks and failure.

20
Q

What does creep depend on?

A

1) At what age the load/strain is applied
2) Humidity
3) Elastic modulus
4) Temperature

21
Q

What do both chloride attacks and carbonation induce?

A

Corrosion of the reinforcement of steel bars.

22
Q

What is a chloride attack?

A

The surface of steel reinforcement in concrete, soon after mixing, reacts with the solution and form a protective layer of iron oxide.

23
Q

What is carbonation?

A

CO2 from the atmosphere dissolves in the solution of concrete and reacts with CH to form calcium carbonate. Calcium carbonate reduces pH of the solution. At pH<9 corrosion starts.

24
Q

How well used is concrete?

A

The most widely used artificial material on earth with more than 3.5x10^9 tons produced per year.

25
Q

How expensive is concrete?

A

Not very expensive, £30 per ton.

26
Q

Is concrete high performer?

A

Yes, 30MPa strength, durable, fire-resistant.

27
Q

What is CEM I?

A

Pure Portland- more expensive and rarely used.

28
Q

What is CEM II to V?

A

Less expensive because some Portland is replaced by supplementary cementitious materials.

29
Q

Name two supplementary cementitious materials?

A

1) Ground granulated Blast-furnace Slag: a by-product of steel production.
2) Pulverised Fuel Ash- By-product of coal burning.

30
Q

Is the production of concrete environmentally friendly?

A

Yes per unit strength.

31
Q

How much concrete goes to downcycle, recycled & landfill?

A

Downcycle- 75%
Recycled- 20%
Landfill- 5%

Construction Materials (9 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions