Concrete NAVEDTRA 14043A Flashcards
Type V of Cement
Sulfate resistant and should be used where concrete is subjected to severe sulfate action. Reaches designed strength in 60 days.
Type IV of Cement
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.
Type III of Cement
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
Type II of Cement
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.
Type I of Cement.
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.
Calculate for loss factor when ordering material
Add an additional 5% for jobs requiring 200 or more of cubic yards of concrete
Add 10% for smaller jobs.
Concrete characteristics
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.
Rule of thumb for calculating 1 cubic foot is 41 or 42
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”.
Converting CF to LBS
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).
Convert volume on CF to weights in LBS
Multiply the required CF of cement by 94 since 1 CF (or standing bag weights 94 LBS).
Weight of Cement bag
94 LBS or about 1 CF by loose volume.
Converting CF to LBS using Rule of 42.
Multiply the CF of rock by 100 since the average dry compacted weight of this rock is 100 LBS per CF.
Conducting a Slump testing
Means of measuring the consistency of concrete using a slump cone
What is a test cylinder?
- Determine if the concrete meets the design requirements for specific compressive strength, known as design strength check.
- 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.
What can cause form failure?
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.
Types of reinforcements?
Welded wire fabric, or wire mess, or reinforced steel, or rebar.
Specifications for lapping wire fabric?
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’
How to use reinforced steel in concrete forms?
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
Types of rebar ties
Snap or simple tie Wall ties Double strand ties Saddle ties Saddle ties with a twist Cross or figure eight tie
What is snap or simple tie?
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.
What is a wall tie?
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.
What is double-strand single tie?
A variation of the simple. Is favored in some localities and is especially used for heavy work.
What is a saddle tie?
Halfway around one of the bars on either side of the crossing bars and bring them squarely or diagonally around the crossing bar.
What is a saddle tie with twist?
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.
What is cross or figure-eight tie?
Has the advantage of causing little or no twist in the bars.
Ways to finish concrete surfaces?
Screeding
Broomed
Floated
Trowelled
How to Screed concrete?
Brings the surface to the require elevation by striking off the excess concrete.
Types of screeding
Hand screed and mechanical screed
How to hand screed concrete.
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.
How to mechanical screed
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.
What is hand tamping and when is it done
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.
