Chapter 3

Question 1

Granular subbases for slabs on ground can be compacted with the sheepsfoot rollers. T or F?

Answer 1

False

Question 2

In cold weather, the subgrade soil must be free of _____ before concrete placing begins.

Answer 2

Frost

Question 3

Before a concrete slab on ground is placed under severe drying conditions that threaten plastic shrinkage cracking, water should be sprayed on the subgrade until puddles are formed and the surface is soft. T or F?

Answer 3

False

Question 4

Before concreting, workers should check the elevation of the subbase by:
A. measuring down from a straightedge spanning between the side forms.
B. measuring the distance from the subbase surface to the top of both sets of side forms at 5ft intervals
C. using a surveyors level to measure the subbase elevation at the beginning and the endo fo the placement.
D. calculating the average elevation of the highest and lowest spots on the subbase surface and comparing that with the design elevation.

Answer 4

A. measuring down from a straightedge spanning between side forms

Question 5

If the surface of the subbase for a concrete slab on ground is too low, the slab is likely to be too thin. T or F?

Answer 5

False

Question 6

Which of the following placing sequences is not recommended?
A. adjacent lanes
B. alternate lanes
C. checkerboard

Answer 6

C. checkerboard

Question 7

Which of the following have the greatest effect on the floor levelness:
A. compaction of the subgrade and base
B. concrete slump
C. form setting and screeding
D. hand troweling slab edges

Answer 7

C. form setting and screeding

Question 8

When concrete will be placed directly on a vapor retarder, finishers should use a margin trowel to punch holes in the vapor retarder and thus decrease waiting time before the concrete can be finished. T or F?

Answer 8

false

Question 9

When specifications dont require a concrete slab to be in direct contact with the vapor retarder, the preferred method for reducing potential problems caused by slab curling is:
A. placing a 3in thick layer of uncompactible concrete sand on the vapor retarder before concrete placement.
B. Placing a 3in thick layer of compactible manufactured sand(containing rock dust) on the vapor retarder before concrete placement
C. Placing a 2in thick layer of lean concrete on the vapor rtarder before concrete placement
D. Placing a 3in thick layer of fly ash on the vapor retarder before concrete placement.

Answer 9

B. Placing a 3in thick layer of compactible manufactured sand(containing rock dust) on the vapor retarder before concrete placement

Question 10

The primary function of welded wire reinforcement in slabs on ground that are considered unreinforced is:
A. preventing slab cracking
B. keeping any slab cracks tightly closed
C. preventing plastic shrinkage cracking
D. providing tensile strength at the bottom of the slab

Answer 10

B. keeping any slab cracks tightly closed

Question 11

Instructions on drawings fro slabs-on-ground may require that:
A. reinforcing steel be discontinued(cut) so it doesn’t pass through the joint
B. every other bar or wire be discontinued(cut) so only half the steel passes though the joint
C. reinforcing steel area be doubled to reduce joint width
D. either A or B above

Answer 11

D. either A or B above

Question 12

Reinforcing steel should be located at or above mid-depth of slabs on ground so cracks will remain tightly closed at the surface. T or F?

Answer 12

true

Question 13

Load transfer at construction joints can be provided by smooth _____ _______ or other types of load transfer devices.

Answer 13

steel dowels

Question 14

Keyed construction joints are not recommended for slabs subject to heavy wheel traffic or for slabs less than _____ in thick.

Answer 14

six