Chapter 7 - Concrete Production

Question 1

Describe the properties of normal weight concrete

Answer 1

140-160 lb/cu*ft for design purposes 150 lb/cu ft

Question 2

Describe the properties of structural lightweight concrete

Answer 2

less than 120 lb/cu*ft. Aggregates used: Shale, Clay, etc.

Question 3

Describe the properties of insulating concrete

Answer 3

15 to 90 lb/cu ft used for thermal insulation with perlite as aggregate

Question 4

Describe the properties of heavy-weight concrete

Answer 4

180 to 400 lb/cu ft is mainly used for nuclear radiation shielding with barite as a heavy aggregate.

Question 5

Concrete components.
Describe concrete type 1

Answer 5

Used for general purposes

Question 6

Concrete components.
Describe concrete type 2

Answer 6

Good for piers or drainage systems due to its resistance to alkali attack

Question 7

Concrete components.
Describe concrete type 3

Answer 7

High early strength, used in cold weather. 150% heat hydration compare to normal cement

Question 8

Concrete components.
Describe concrete type 4

Answer 8

Low heat (40-60^ heat hydration compare to type 1). 55% cured in 7 days, good for dams.

Question 9

Concrete components.
Describe concrete type 5

Answer 9

Max resistance to alkali attacks.

Question 10

What are aggregates used in cement?

Answer 10

• 60% to 80% of concrete
• Ideally rounded or cubical in shape
• Strong & resistant to freeze and thaw
• Fine & coarse aggregates

Question 11

Why is water used in cement?

Answer 11

• water quality: drinking water
• water cement ratio - 40% to 70%
• used for cement hydration, the ratio defines the concrete strength

Question 12

Why do we use air-entering agents in cement?

Answer 12

Increase resistance to freezing and thawing

Question 13

Why do we use water-reducing agents in cement?

Answer 13

Increase slump or workability

Question 14

Why do we use retarders/accelerators in cement?

Answer 14

To slow down or speed up the setting time

Question 15

Mixer classification: what does 34E stand for? what would the letters S and M stand for?

Answer 15

A number indicates capacity: 34 cu.ft
E = paving, S= construction , M= mortar

Question 16

What is batching?

Answer 16

The process of proportioning cement, water, aggregates, and additives with an accuracy of 1% to 3% prior to mixing concrete

Question 17

Match the following moisture conditions of aggregate with the following terms:
Over dry, air dry, SSD, wet
More/equal/ less than potential absorption

Answer 17

oven-dry & air dry = less than
SSD = equal to
wet = more than

Question 18

What is the concrete paving process?

Answer 18

Haul trucks -> Slipform paver -> texture/tine -> curing -> Sawing joints

Question 19

What is a Slipform paver?

Answer 19

Used in airfields and highways to spread, consolidate and finish a concrete slab without conventional forms. Can also be used in canals, concrete gutters, concrete curbs and drainage systems.

Question 20

What is the max duration for hauling the concrete from the introduction of water?
What is the pace of the initial mixing in drum and the drum speed while travelling to the job,

Answer 20

90 minutes or 400 drum revolutions.
Initial: 20-22 from for 100 revolutions
Travelling speed: =< 2 rpm

Question 21

what is a consolidation?

Answer 21

The process of removing air voids as concrete is placed happens by shaking the concrete.
Can be done by using immersion-type vibrators (very common)

Question 22

Describe the finishing process.

Answer 22

It is done to make the concrete smooth.
Screeding -> floating -> troweling - > brooming