CONCRETE TECHNOLOGY

Question 1

Concrete?

Answer 1

1. Corse Aggregate
2. Fine Aggregate
3. Cement
4. Water

+Optional Admixers

Can be described as stone, sand, cement and water

Question 2

Advantages of Concrete

Answer 2

• Low Cost
• Strong compressive strenght
• Flexible in Application
• Variety of Finishes
• Reinforcable

Question 3

Cement Process

To produce fine powder

Answer 3

1. Clay/Shale + Chalk/Limestone
2. Mixed in a kiln
3. Gypsum added (prevents flash setting)

Question 4

Types of Portland Cement

6

Answer 4

• Low Heat
• Rapid Hardening
• Sulphate Resistant
• Blast Furnace
• Plverised Fuel Ash
• White Portland Cement

Question 5

High Alumna Cement

Not A Portland

Answer 5

• Limestone and bauxite
• Very rapid hardening
• Acheives required strenght in 24 hours

Question 6

Low Heat PC

Answer 6

Mass concrete structures

Question 7

Rapid Hardening PC

Answer 7

Sets faster than OPC

Question 8

Sulphate Resistant PC

Answer 8

Sulphate bearing soils

Question 9

Blast Furnace Cement

Answer 9

OPC + Blast furnace slag

Question 10

Plverised Fuel Ash Cement

Answer 10

Coal power stations

Question 11

White Portland Cement

Answer 11

White china clay

Question 12

Concrete Performance Requirements

Answer 12

Workability
Compressive Strength
Durability

Question 13

Waiting days for Concrete Hardening?

Answer 13

28 Days

Question 14

Advantages of Using Aggregate

Answer 14

• Reduces costs
• Reduces shrinkage
• Can be used as decorative
• Improves fire resistance
• Versatile density qualities
• Produces palstic properties

Question 15

Aggregate Sizes

Answer 15

5mm - Screeds bellow 50mm
10mm - Thin sections
20mm - General concrete work
40mm - Mass road construction

(C, M, F) Grading

Question 16

Workability

PCF

Answer 16

Ability of concrete to be placed, compressed and finished

Tests for workability Include: Slump Test, Vebe Test, Compacting Factor Test, Cube Test

Question 17

Admixers

Answer 17

Materials other than cement, water, aggregates added to modify properties of the mix

Question 18

Types of Admixers

4

Answer 18

• Water reducing agents
• Superplasticizers
• Air- Entraining agents
• Accelerators

Question 19

Effects of Admixers

Answer 19

• Improve pumpability
• Increases strength
• Reduce permeability
• Improves durability
• Increase workability without changing the water content
• Reduce water content without changing the workability

Question 20

Causes of concrete deterioration

Answer 20

• Frost attack
• Sulphate attack
• Crystallisation damage
• Map cracking (concrete cancer)
• Corrosion of steel reinforcement

Question 20

Slump Test

Answer 20

• Concrete placed in 3 layers
• Tamped 25 times
• Usual results at 50mm - 75mm

Steel Slump Cone, Tamping Rod, Tamping Stick

Results: True, Shear, Collapsed

Question 21

Compacting Factor Test

Finds Compacting Factor

Answer 21

1. Concrete is gently loaded into hopper and allowed to vertically fall into lower hopper
2. Falls into cylinder
3. Concrete in cylinder is struck off and weighed
4. Cylinder is tipped empty, refilled then re-weighed with fully compacted concrete

Result: M. of partially compacted concrete/M. of fully compacted concrete

Question 22

Vebe Test