Chp 7 PC Conrete

Question 1

Early Volume Change:

Answer 1

This can happen due to 5 things:

• Curling:
  it is when the concrete becomes wavy due to the difference in curing. For example, curing the surface and not the bottom.
• Over-curing:
  It causes the concrete to swell (expand). it is negligible and it doesn’t harm the concrete.

Shrinkage
The 3 types of shrinkage are:
- Plastic shrinkage, occurs when the concrete is still in the plastic state.

• Dry Shrinkage
  It occurs after 3 days if the concrete is not properly cured causing cracks.

Thermal Cracks:
The heat of hydration gives of cement gives a lot of heat which may cause thermal cracks

Question 2

Define Creep

Answer 2

The gradual deformation of concrete due to sustained load over a long period of time.

Question 3

Define Permeability:

Answer 3

It is the interconnected voids inside the concrete that allow water and chemicals to enter.

Question 4

What are Factors that effet permability:

Answer 4

• Water cement ratio:
  increasing it will increase permeability exponentially.
• Air entraining agents:
  they reduce permeability indirectly because they allow the use of a lower w/c ratio.
• Age of concrete:
  age reduces permeability.

Question 5

Explain capping

Answer 5

Capping is applying a layer of gypsum on top of concrete cylinders to ensure that the load is equally distributed.

Question 6

How to increase the bond between Cement paste and aggregate in concrete:

Answer 6

• Have crushed angular aggregate to increase the interlocking.
• decrease the w/c ratio.

Question 7

Split Tension Test

Answer 7

This test is used to measure the tensile strength of concrete. It is impt because beams usually take compression at the top and tension in the button.
We carry out this test on cylinder samples.

The tension is indirect and it is applied through compression. It will cause the cylinder to split along its vertical diameter.

Question 8

What is Flectural Strength?

Answer 8

The maximum strength experienced by a material at the moment of yield.

Question 9

Why do we carry out Non-Destructive Tests?

Answer 9

• if the destructive test gives lower values, we apply these tests to see if we can avoid demolishing the building.
• If you don’t know the values of compression.
• To identify cheating
• To see if there are deflection and cracks.

Question 10

What is the Schmidt hammer test?

Answer 10

It is a test used to measure the strength by measuring the hardness of the surface which correlates to strength.

Question 11

Penetration Resistance Test:

Answer 11

It is similar to a shotgun. It shoots a probe that penetrates inside the concrete and measures its strength. The amount of penetration into the concrete is inversely related to the strength of the concrete.

Question 12

What is an ultrasonic pulse velocity test?

Answer 12

This test is used to measure the voids inside the concrete. The faster the transmission means there is no voids.

Question 13

What is the Maturity test?

Answer 13

It measures the hydratiojn of the concrete by measuring its temperature.
temp ^ , hydration^, strength^.

Question 14

X-ray test?

Answer 14

This is used to detect reinforcement in the concrete.

Question 15

Self Compacting Concrete

Answer 15

This type of concrete has very high slump and it does not require vibrating.
It was made for the labourers because over a long period of time they developed the syndrome of shaking.

It is also used where there is dense reinforcement.

Question 16

List all the NDTs

Answer 16

• Penetration test
• Schmidt Hammer
• X-ray
• Maturity test
• Ultrasonic velocity test

Question 17

List all the types of Concrete.

Answer 17

• Self compacted
• Flowable Fill
• Shotcrete
• Lightweight Concrete
• Heavyweight Concrete
• high-strength concrete
• shrinkage-compensating concrete
• polymers and concrete
• fiber-reinforced concrete
• roller-compacted concrete
• high-performance concrete
• previous concrete

Question 18

List LEED Considerations for Concrete.

Answer 18

• Development Density :
  Concrete can develop a very high-density community, reducing transportation as everything is within walking distance.
• Daylight
  Since concrete is strong, it can carry a lot of load which allows windows to be installed on the walls. This reduces the requirement for electrical lighting, reducing the cost.
• Heat Island Effect:
  This refers to urbanized areas that experience higher temperatures than outlying areas.
  Concrete can be used to reduce this effect as it has a high reflective index of above 20.
• Recycled Content:
  The LEED Requirement encourages the use of recycled materials and concrete can contain supplementary cementitious materials such as fly ash, silica fume, and slag cement.
• Regional Materials:
  The materials for concrete are sourced regionally within 800km which reduces transportation thus reducing the carbon footprint.
• Construction Waste Management:
  Concrete can be crushed and recycled into aggregate for road bases or construction fill.