Conveying, Placement, and Finishing Concrete

Question 1

How do we consolidate the fresh concrete that is placed

Answer 1

1) Hand rodding or tamping
2) Internal Vibrator
3) External Vibrator (Vibrating Screed or Form Vibrator)

Question 2

What are the basic steps to finishing a concrete slab?

Answer 2

1) Strikeoff or Screeding (Sriking off excess concrete to bring the top surface to proper grade)
2) Bullfloating (Leveling to eliminate high and low spots)
3) Floating (Firmly embeds the aggregate to compact the surface and to remove any surface imperfection. Concrete must be able to sustain foot pressure with only slight indentation)
4) Troweling (Finishing to obtain a smooth dense surface)
5) Texturing (Finishing to obviation desired surface texture)

Question 3

How can we produce the different textures in the concrete surface?

Answer 3

Blooming to produce skid resistance surface

Question 4

What is an isolation joint

Answer 4

Joint to permit vertical and horizontal movement

Question 5

What is a construction joint

Answer 5

Joint for stopping places during construction

Question 6

What is a control joint

Answer 6

Joint to permit thermal shortening and drying shrinkage in the plane of slab

Question 7

Why is it important for concrete to properly cure?

Answer 7

• To keep concrete moist

- To control the temperature of the concrete

Question 8

What is sprinkling

Answer 8

Continuous sprinkling keeps the surface wet

Question 9

What is wet covering

Answer 9

Covering with moisture retaining fabrics (such as burlap or straw) and intermittent sprinkling

Question 10

What is ponding

Answer 10

retaining a pond of water by means of earth dikes

Question 11

What are waterproof covers

Answer 11

covering with waterproof paper or plastic sheets or spraying surface with a curing compound which acts as a water barrier

Question 12

What are the effects of using sea water as mixing water in concrete?

Answer 12

• Strength of concrete may be lower at later ages

- Increases the risk of corrosion of reinforcing steels

Question 13

What are the effects of hot weather on concreting?

Answer 13

• Increases rate of setting
• Slump loss earlier
• Increased possibility of plastic cracking
• Increased moisture loss during curing
• Difficulties in controlling entrained air content

Question 14

What are the appropriate measures to be taken in hot weather concreting?

Answer 14

• Cool the aggregate and the mixing water (ice can be used as mixing water)
• Reduce the time between placement and start of curing
• Cover the concrete during to reduce evaporation water
• Sprinkle additional water to the concrete during curing. Use tepid water to avoid thermal shocks

Question 15

What are the effects of cold weather on concrete?

Answer 15

• Lower rate of hydration at lower temperature

- Freezing of water will damage the concrete

Question 16

What measures should be taken in cold weather concreting?

Answer 16

• Use insulated forms
• use type III concrete or accelerating admixture
• use heaters to keep concrete warm
• Use air entrainment in concrete
• Allow longer curing time before stripping forms. Use the maturity method to relate curing history to the concrete cylinder to that of the in place concrete