Concrete NAVEDTRA 14043A

Question 1

Type V of Cement

Answer 1

Sulfate resistant and should be used where concrete is subjected to severe sulfate action. Reaches designed strength in 60 days.

Question 2

Type IV of Cement

Answer 2

Low heat of hydration and is intended for applications requiring a minimum rate and amount of heat hydration, strength develops at a slower rate. Reaches its designed strength in 90 days.

Question 3

Type III of Cement

Answer 3

High early strength that produces design strengths at an early age, usually 7 days or less. Use cautiously in concrete structures, having minimum dimension of 2 1/2’ or more, they will produce more heat which could cause shrinking or cracking

Question 4

Type II of Cement

Answer 4

Modified to resist moderate attack, generates less heat of hydration and at slower rate than Type I. Reaches its designed strength in about 45 days.

Question 5

Type I of Cement.

Answer 5

Cement is general purpose cement for concrete that does not require special properties, intended for concrete not subjected to sulfate attacks or damage by heat or hydration. Reaches strength in 28 days.

Question 6

Calculate for loss factor when ordering material

Answer 6

Add an additional 5% for jobs requiring 200 or more of cubic yards of concrete

Add 10% for smaller jobs.

Question 7

Concrete characteristics

Answer 7

A synthetic construction material made by mixing cement, fine aggregate (usually sand), coarse aggregate (usually gravel or crushed stone), and water in the proper proportions.

Question 8

Rule of thumb for calculating 1 cubic foot is 41 or 42

Answer 8

41 is used to calculate the quantity of material when the size of the coarse aggregate is not over 1”.

42 is used to calculate the quantity of material when the size of the coarse aggregate is over 1” but less than 2 1/2”.

Question 9

Converting CF to LBS

Answer 9

Using Rule of 41, multiple the quantity of course gravel in CF by 105 (average weight of dry compacted fine aggregate or gravel is 105 LBS per CF).

Question 10

Convert volume on CF to weights in LBS

Answer 10

Multiply the required CF of cement by 94 since 1 CF (or standing bag weights 94 LBS).

Question 11

Weight of Cement bag

Answer 11

94 LBS or about 1 CF by loose volume.

Question 12

Converting CF to LBS using Rule of 42.

Answer 12

Multiply the CF of rock by 100 since the average dry compacted weight of this rock is 100 LBS per CF.

Question 13

Conducting a Slump testing

Answer 13

Means of measuring the consistency of concrete using a slump cone

Question 14

What is a test cylinder?

Answer 14

1. Determine if the concrete meets the design requirements for specific compressive strength, known as design strength check.
2. Determine if the concrete that has been placed is of sufficient strength for the forms to be removed or for the concrete to be put into service, known as construction site control.

Question 15

What can cause form failure?

Answer 15

Inadequately tightening or securing form ties

Inadequate diagonal bracing or shores

Use of old, damaged, or weathered form materials

Use of undersized form material

Shoring not plumb

Failure to allow for lateral pressures on form work

Failure to inspect form work during and after concrete placement to detect abnormal deflections or other signs of imminent failure.

Question 16

Types of reinforcements?

Answer 16

Welded wire fabric, or wire mess, or reinforced steel, or rebar.

Question 17

Specifications for lapping wire fabric?

Answer 17

One complete lap is usually sufficient with a minimum of 2” between laps.

End lap method lap wire mess by overlapping one full piece to the end of the longitudinal wires in the adjacent piece. Then tie the 2 pieces with a snap tie at 1 1/2’ center

Side lap method place 2 longitudinal side wires one alongside and overlapping the other. Then tie the two pieces with a snap tie every 3’

Question 18

How to use reinforced steel in concrete forms?

Answer 18

Use a piece of burlap to clean the bars of rust, scales, grease, mud, or other foreign matter. Rebar must be tied together for the bars to remain in a desired arrangement during pouring. Tying also a means of keeping laps or spaces

Question 19

Types of rebar ties

Answer 19

Snap or simple tie
Wall ties
Double strand ties
Saddle ties
Saddle ties with a twist 
Cross or figure eight tie

Question 20

What is snap or simple tie?

Answer 20

Simply wrap the tie once around the two crossing bars in a diagonal manner with the two ends on top. Then twist the ends together with a pair of side cutters until they are very tight against the bars. Finally cut off the loss ends.

Used mostly on floor slabs.

Question 21

What is a wall tie?

Answer 21

Take one and one half turns around the vertical bar, then one turn diagonally around the intersection. Twist the two ends together until the connection is tight, then cut off the excess.

Used on light vertical mats of steel.

Question 22

What is double-strand single tie?

Answer 22

A variation of the simple. Is favored in some localities and is especially used for heavy work.

Question 23

What is a saddle tie?

Answer 23

Halfway around one of the bars on either side of the crossing bars and bring them squarely or diagonally around the crossing bar.

Question 24

What is a saddle tie with twist?

Answer 24

Carry the tie wire completely around one of the bars, then squarely across and halfway around the other, either side of the crossing bars, and finally bring the steel ends together and twist them either squarely or diagonally across

Used for heavy mats that are to be lifted by crane.

Question 25

What is cross or figure-eight tie?

Answer 25

Has the advantage of causing little or no twist in the bars.

Question 26

Ways to finish concrete surfaces?

Answer 26

Screeding
Broomed
Floated
Trowelled

Question 27

How to Screed concrete?

Answer 27

Brings the surface to the require elevation by striking off the excess concrete.

Question 28

Types of screeding

Answer 28

Hand screed and mechanical screed

Question 29

How to hand screed concrete.

Answer 29

Requires tool called a straightedge usually 2 x 4, having a straight lower edge to produce a flat surface or a curved surface. Move the screed back and forth across the concrete using a sawing motion. Hand screed up to 30ft wide.

Question 30

How to mechanical screed

Answer 30

A beam with a gasoline engine or electric motor and a vibrating mechanism mounted in the center. Used for in construction, highways, bridge decks, and deck slabs.

Question 31

What is hand tamping and when is it done

Answer 31

Also known as jitterbugging. Used to compact the concrete into a dense mass used to compact into a dense mass done after concrete has been screed.