G4 LT#1

Question 1

Concrete Slab construction consists of what key things?

Answer 1

A making of a form that defines the shape of the slab, a well compacted sub-grade that supports the slab and suitable reinforcing to keep the concrete slab stable and resist cracking.

Question 2

What is a monolithic slab?

Answer 2

A monolithic slab is poured with the perimeter footing and any other slab thickenings at the same time. It is mainly used in residential and isolated.

Question 3

What is one draw back of monolithic slabs?

Answer 3

One drawback is that the footing portion and the floor portion are under different building loads, which may cause stress cracks at these two points.

Question 4

When are the isolated slab on grades poured?

Answer 4

They are poured after the footings and walls have been placed.

Question 5

If the material under a slab is weak and loose, will the slab be strong?

Answer 5

A slab is only as strong as the material it is placed upon.

Question 6

If the existing soil is of suitable bearing for a slab on grade, what needs to be done?

Answer 6

It only needs to be excavated down to grade and leveled before placing the slab.

Question 7

If a sub-grade is not smooth enough, what is usually done?

Answer 7

A sub-base is usually laid down. This is usually a material that is more uniform in particle size.

Question 8

If the soil is not suitable at all, what is done?

Answer 8

It is removed and replaced in compacted lifts with proper granular fill specified in the drawings. Special attention must be given while compacting.

Question 9

How is compacting done in unsuitable soil?

Answer 9

With a plate roller or ram-type compacter

Question 10

What kind of materials are used to form slab on grades?

Answer 10

2 x 4 to 2 x 12

Question 11

What is needed to plumb and straighten slab on grade forms?

Answer 11

Wood or metal stakes and braces may all be all that is needed.

Question 12

What kind of formwork is needed for thicker edge forms?

Answer 12

For thicker edge forms, using plywood forms supported by studs and plates may be necessary. Strong backs and braces are used to plumb and straighten.

Question 13

What contributes to the strength and durability of slab on grade?

Answer 13

Controlling water/cement ratio (W:C ratio) contributes to both strength and durability.

Question 14

In commercial construction, who states the slab’s thickness, strength and design mix?

Answer 14

Professional Engineer

Question 15

In a slab on grade drawing, who designs the finish?

Answer 15

Architect

Question 16

The base preparation, compressive strength of the concrete mix, and proper curing are all directly related to what?

Answer 16

The strength of the slab.

Question 17

What is placed in the lower portion of the slab to protect it from tensile forces?

Answer 17

A mat of re-inforcing steel.

Question 18

The compressive strength, admixtures added and treatments after placing all are directly related to what?

Answer 18

The durability of the slab.

Question 19

Does a residential home necessarily need admixtures added into the concrete slab?

Answer 19

No, as it will only receive light traffic during its lifetime.

Question 20

What is added to the concrete slabs of industrial buildings to increase the durability against continuous traffic and heavy loads?

Answer 20

For interior slabs, admixtures may be added to the mix to protect from oils, greases and chemicals.

Question 21

What can be applied to the surface of the slab during finishing to harden the surface of the floor in high traffic areas?

Answer 21

Powdered or mechanical hardeners can be applied to the surface of the slab.

Question 22

What is done to all slabs which are exposed to freeze-thaw cycles?

Answer 22

Air entrainment

Question 23

What is air entrainment?

Answer 23

Air entrainment adds microscopic air bubbles to the concrete. It allows it to expand and contract without great risk of damage.

Question 24

Once the edge forms are installed, what’s the next step?

Answer 24

Edge forms need to be oiled with any accompanying screeds to make them easier to clean.

Question 25

Once the edge forms have been installed and oiled, what is next?

Answer 25

Polyethylene is barrier is placed on the sub-base. This will keep out moisture from migrating into the concrete below or keep soil gases from entering the building, or both.

Question 26

Once the polyethylene is in laid, what is placed on top before pour?

Answer 26

WIre mesh or re-inforcing steel will be placed on chairs over poly .

Question 27

What is the last step before pouring?

Answer 27

Check elevations of forms and check the strength, then go pour

Question 28

Does the BC building code require reinforcement for slab on grade?

Answer 28

No.

Question 29

When going above the minimum code and reinforcing, what is normally used to reinforce slabs?

Answer 29

Heavy wire mesh or reinforcing steel bar 3” off the ground

Question 30

What is often used to support reinforcement at the proper height?

Answer 30

Chairs, bricks, or rocks. Another option is hooking the reinforcement with a special tool once the concrete has been placed and lifting the reinforcement off the bottom of the slab.

*IF THE REINFORCEMENT IS ALLOWED TO LIE AT THE BOTTOM OF THE SLAB IT IS USELESS

Question 31

On which kind of surface should a slab-on-grade be placed?

Answer 31

Suitable bearing or compacted fill

Question 32

What factors affect the durability of slab-on-grade?

Answer 32

Protection from weather, W:C ratio, finishing

Question 33

What factors affect the strength of slabs-on-grade?

Answer 33

Base material, concrete mix, curing

Question 34

What should be done to walls or columns that pass through or beside slab-on-grade?

Answer 34

Isolation Joints

Question 35

Why is it important to compact the sub-grade?

Answer 35

Firm, even bearing.

Question 36

Why are screeds and forms oiled before concrete placement?

Answer 36

Easy cleaning.

Question 37

How long should slab forms remain in place after concrete placement?

Answer 37

As long as possible.