Chp 6

Question 1

Define the following terms:
- Cement paste
- Mortar
- Concrete

Answer 1

Cement paste: Cement + water.
Mortar: Cement paste + sand
Concrete: Cement paste + Sand + aggregate

Question 2

What are the 2 basic materials used in the production of cement?

Answer 2

• Calcareous: CaO such as limestone
• Argillaceous: Silica and alumina, can be obtained from shale, clay…

Question 3

What are the types of Portland Cement?

Answer 3

There are 5 types of portland cement:
1- Normal cement
2- Moderate sulfate resistance
3- Early Strength
4-Low heat of hydration
5-High sulfate resistance

Question 4

What is Soundness of Cement?

Answer 4

it refers to the ability of cement to retain its volume after setting.

Question 5

How is Soudness measured?

Answer 5

It is measured using the autoclave test where it is exposed to heat and pressure. The increase in volume should not surpass 0.8% for the cement to be be acceptable.

Question 6

What are the different types of voids?

Answer 6

• Interlayer hydration space: It is between CH gel. It does not effect the properties of strength and durability.
• Cappilary Voids
  When w/c ratio is too high.
  Esentially, this water will evaporate creating voids. The more water we add, the more the voids. This effects strength and durability.
  -Trapped Voids
  During mixing, air will get into concrete. We vibrate and compact the concrete to avoid this issue.
• Entrained air
  Microscopic bubbles causd by ad mixtures that improve the durability and helps in freeing conditions.

Question 7

Why are ready mix trucks prohibted from disposing their waste anywhere?

Answer 7

Because their waste is highly alkaline, thus it would effect the ph of the soil.

Question 8

Can sea water be used in cocnrete mix?

Answer 8

Yes it can be used if the cooncrete is not reinforced with steel rebars as sea water corrodes te steel rebards.

Question 9

What are Addmixtures for concrete?

Answer 9

Add mixtures are subtances added to concrete to improve a specefic quality of concrete.

Question 10

List all the Addmixtures:

Answer 10

• Air Entrainers
• Water reducers
• Accelerator
• Retarder
• Hydration controller
  -Specialty add mixtures

Question 11

Describe Air entrainers.

Answer 11

it is an add mixture that increases the durability of concrete. It creates voids that allow for the expansion of concrete in freezing conditions why avoiding creating internal stresses which reduce the durability of concrete. However, air entrainment reduces the strength of concrete. They also increase the workability of concrete.

Question 12

Describe water reducer.

Answer 12

They are admixture that increases the workability of concrete without adding water to it.

Question 13

What are the benefits of water reducers?

Answer 13

• increase strength
• reduce cost
• increase workability

Question 14

What are Retarders?

Answer 14

It is an add-mixture that delays setting time. It is used generally in hot conditions as usually in hot conditions the concrete sets rapidly.

Question 15

Define SCMs

Answer 15

They are materials used as partial replacement of portland cement to improve both fresh and hardened concrete properties.

Question 16

What are the benefits of using water reducers?

Answer 16

There are 3 benefits:
- Increase the compressive strength of concrete by adding water reducer, using the same amount of cement, and decreasing the
amount of water.
- Increase the workability by adding water reducer, and using the same amounts of cement and water.
- Reduce cost by adding a water reducer, and decreasing the quantity of both water and cement to maintain the w/c ratio.

Question 17

What are accelerators?

Answer 17

They are an add mixture used yo develop the early strength of concrete at a faster rate.

Question 18

Why are accelerators used?

Answer 18

They are used to increase the rate of strength gain, reduce the operation time, reduce curing time.

Question 19

What are hydration-control admixtures?

Answer 19

These admixtures can stop and reactivate the hydration process of concrete.
They consist of two parts: a stabilizer and an activator. Adding the stabilizer completely stops the hydration of the cementing materials for up to 72 hours,
while adding the activator to the stabilized concrete reestablishes normal hydration
and setting.

Question 20

List all type of SCMs.

Answer 20

• fly ash
• slag cement
• silica fume
• natural pozzolans

Question 21

what is silica fume and the effect of silica fume?

Answer 21

Silica fume is an SCM that is a by-product of the production of silicon metal. They increase strength and durability.

Question 22

What is slag cement and what are its effects?

Answer 22

Cement Slag cement is made from iron blast furnace slag. They can increase the strength of concrete.

Question 23

What are the effects of natural pozzolans?

Answer 23

• Increase workability
• Increase strength
• Increase durability
• decrease premability

Question 24

What are the 2 Cement Production Processes ?

Answer 24

There are 2 processes, the wet and dry process.
The wet process is more water and energy consumptive. It is more expensive.

It also causes water pollution.

Question 25

What are the 4 main chemical components of cement, and what are the role of each one?

Answer 25

C3S: Responsible for strength and durability.
C2S: Responsible for strength and durability.
C3A and C4AF: Responsible for lowering the required processing temperature in the kiln.