G4 - Slabs - LT# 1 Slabs-On-Grade

Question 1

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

Answer 1

1) Suitable bearing
2) Compacted fill

Question 2

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

Answer 2

1) Protection from weather
2) Finishing
3) W:C Ratio

Question 3

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

Answer 3

1) Base mix 2) Concrete curing 3) Concrete mix

Question 4

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

Answer 4

Provide Isolation joint

Question 5

Why is it important to compact the subgrade?

Answer 5

To give firm even bearing

Question 6

Why are screeds and forms oiled before concrete placement?

Answer 6

Easy cleaning

Question 7

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

Answer 7

As long as possible

Question 8

What is the minimum slope for drainage for an exterior slab?

Answer 8

1/8 per foot (1/96)

Question 9

What does a give-and-take strip allow for?

Answer 9

1)Expansion & contraction
2) Differential movement

Question 10

Describe pouring a monolithic slab.

Answer 10

Monolithic slab - Poured with the perimeter footing and any other slab thickenings at the same time.

Question 11

What is one setback of pouring a monolithic slab?

Answer 11

The footing portion and the floor portion are under different building loads, which may cause stress cracks at these locations.

Question 12

What is one advantage of a monolithic slab pour?

Answer 12

Economical and quick to form and place

Question 13

Describe pouring an isolated slab on grade.

Answer 13

Isolated slab is poured AFTER the walls and footing have been placed.

Question 14

Where does an isolated slab on grade have an isolation joint?

Answer 14

Usually between the slab and footings and an air and moisture barrier between the slab and wall

Question 15

A slab on grade is only as strong as ______

Answer 15

The material it is placed upon

Question 16

If existing soil (subgrade) is of suitable bearing, it only needs:

Answer 16

To be excavated down to a grade and levelled before placing the slab.

Question 17

If a subgrade is not smooth after grading and leveling, what is laid down?

Answer 17

A sub-base, is usually a material that is more uniform in particle size.

Question 18

If soil is not suitable for a slab on grade, then

Answer 18

It must be removed and replaced in compacted lifts with proper granular fill specified in the drawings

Question 19

What tool is used to provide a firm and even bearing?

Answer 19

Plate roller or a ram-type roller

Question 20

For forming a simple slab which is not too thick, what can be used as formwork?

Answer 20

Simple 2x4 to 2x12 depending on the thickness

Question 21

For thicker edge slab-on-grades, what material is used to form a slab-on-grade?

Answer 21

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 22

Controlling the ______ contributes to BOTH the strength and durability

Answer 22

Water:Cement ratio

Question 23

In commercial drawings, the slab thickness, strength, and design mix are stated in the drawings by whom?

Answer 23

The engineer

Question 24

The slab’s finish, depending on the use of the building, may be specified by whom?

Answer 24

The architect

Question 25

The strength of the slab is related to:

Answer 25

To the base preparation, compressive strength of the concrete mix, and proper curing.

Question 26

Rebar, admixtures specified by the engineer contribute to what?

Answer 26

The strength of the slab

Question 27

In residential construction, where can most compressive strength information can be cited where?

Answer 27

BCBC

Question 27

In residential construction, where can most compressive strength information can be cited where?

Answer 27

BCBC

Question 28

A mat of rebar is placed in the lower portion of the slab to protect it from:

Answer 28

Tensile forces

Question 29

The durability of a slab on grade is based on its:

Answer 29

1) Compressive strength (expressed in MPA) (Megapascals) 2) Admixtures added 3) Treatment after placing

Question 30

Industrial buildings require treatments why?

Answer 30

To increase durability against continuous traffic and heavy load

Question 31

For interior slabs, admixtures are sometimes added to the mix to protect from?

Answer 31

Chemicals, oils and greases

Question 32

What can be added to harden the surface of a floor in a high-traffic area?

Answer 32

Powered or mechanical hardeners can be applied to the surface of the slab during finishing

Question 33

What is specified for all exterior concrete exposed to free-thaw cycles?

Answer 33

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

Question 34

Does BCBC require reinforcement for slabs on grade?

Answer 34

No, many basement and garage floor slabs are not reinforced

Question 35

What forms can reinforcement take form in a slab on grade?

Answer 35

Heavy wire mesh, or grid of rebar

Question 36

For concrete in contact with te ground, rebar should be kept how far off the bottom of the slab?

Answer 36

3 " (75 mm) with good drainage below the slab and a polyethylene ground cover, the rebar may be as close as 30 mm to the bottom of the slab

Question 37

With good drainage below the slab, and a polyethylene ground cover, the reinforcement can be as close as:

Answer 37

30 mm to the bottom of the slab

Question 38

When attaching reinforcement on the bottom of a slab in contact with the ground, what techniques are used?

Answer 38

Chairs, bricks, and rocks are used to support the rebar to the proper height. Also a special hook tool.

Question 39

The surface of an exterior slab-on grade should be sloped how much per foot for drainage?

Answer 39

1/8" per foot (1:96)

Question 40

Interior floor slabs are required by BCBC to:

Answer 40

Have the bottom of the slab above the top of the perimeter drain pipe

Question 41

Elevations for slab can be set how?

Answer 41

Using screed boards or pipe with screed stakes.

Question 42

Where a slab meets a foundation wall, what is required?

Answer 42

A bond break in the form of an isolation joint. Preventing differential settlement.

Question 43

Additional expansion joints should be placed in slabs at least every

Answer 43

15 m (50') known as give-and-take strips,

Question 44

What is the purpose of a give-and-take strip?

Answer 44

Used to isolate one concrete member from another and allow vertical and horizontal movement

Question 45

Give-and-take strips are made from

Answer 45

Asphalt-impregnated fibreboard

Question 46

What is a control joint?

Answer 46

A weakening in the concrete slab that is designed to control the natural cracking of a concrete member due to shrinkage

Question 47

The spacing of control joints for driveways and garage floors may be spaced

Answer 47

As close as 3 m (10') apart

Question 48

Expansion joints may be spaced no farther than:

Answer 48

15 m apart

Question 49

How is a control joint made?

Answer 49

Tooled, cut in or formed by a two-part T-shaped plastic strip called a zip strip.

Question 50

How deep does a control joint need to be to be effective?

Answer 50

At least one-quarter the thickness of the slab

Question 51

What does a polyethylene barrier at the sub-base of the slab-on-grade do?

Answer 51

Keeps moisture from migrating into the concrete from below, or keeps soil gases from entering the building, or both.

Question 52

How does a high-rise get it's concrete?

Answer 52

Crane with a bucket

Question 53

How are gutters and curbs formed?

Answer 53

Hand-set the forms using planks and plywood or have a curb forming machine "slip-form" them