Concrete Flashcards
What is the maximum that sheathing should be cut back on tendons?
1 inch
In stressing operations, the final stress should be pre-calculated to use an approximately what percentage of the full stroke of the jack on the final pull?
60 %
What is the purpose for post-tensioning concrete?
To increase compressive strength in the bottom of a joist or girder to offset tensile stress
Which of the below would be correct method of storing tendon coils?
Stored in a dry area on dunnage to keep the tendons off the ground
Which of the below would be proper way of unloading tendon coils?
Cradle coils by passing nylon straps through the center of coils
In most field applications the amount of force that will actually be applied to the strand will be approximately what percentage of the MUTS (Minimum Ultimate Tensile Strength) of the strand?
80 %
On concrete thickness up to about seven inches, which of the below are true about air content to slump?
Air content increases as slump increases
What is the maximum dosage of slag in concrete where exposed to deicing conditions?
50%
of the below would increase the abrasive strength of concrete?
1 – Low water-cement ratio
2 – Steel - troweled surface
3 – Harder aggregate
4 – All of these
What is the purpose of using vibrators when doing concrete work?
1 – Get rid of air voids
2 – Consolidates the concrete
3 – Moves fine aggregate to bottom
4 – Both 1 and 2
Usually air-entrained lightweight concrete has a slump of 2 to 4 inches, what would be the maximum slump you would seldom exceed?
5 Inches
– Tools used for finishing air-entrained concrete should be constructed from which of the below?
Aluminum or magnesium
What a method for strengthening reinforced concrete in which steel tendons are stretched through conduits and mechanically fastened is called what?
Post-tensioning
Normal weight and lightweight concrete exposed to freezing and thawing or deicing chemicals shall be ________.
Air entrained
Samples for strength test for each class of concrete placed each day shall be taken not less than once a day or less than once for each ___________ .
150 cubic yards
What would you use to keep concrete forms from spreading apart?
Snap ties and brackets
Hotter than normal temperatures when pouring concrete has what consequences (or “What is true” about pouring concrete in hot weather?)
1 – Increased slump loss
2 – Increased tendency for cracking
3 – Long term strength loss
4 – All of the above
temperatures have what effect (or it may have asked what is true) on fresh concrete.
Concrete that has been frozen will not be as impermeable as concrete that
wasn’t frozen
Retempered concrete or concrete that has been remixed after initial set shall not be used unless approved by?
Registered design professional
what is the minimum cover on #5 rebar where permanently exposed to earth?
3 inches
Once water is added to a concrete mix at the mixing plant, what is the maximum
time for delivery and discharge from truck?
1 ½ hours
The minimum strength of a concrete wall not exposed to the weather after 28 days is:
2500 psi
What is true about moisture in concrete?
1 – It is important to prevent moisture from leaving the concrete
2 – It is important to not prevent moisture from leaving the concrete
3 – Excessive moisture loss will result in concrete cracking
4 – Both 1 and 3
Steps in footings should be used when slope exceeds:
10 %
pumping concrete into tightly reinforced forms which of the below should be used?
Superplasticizers
What would you use to laterally support concrete forms?
Whalers and braces (tied and braced)
On concrete beams, what is the recommended distance between tendons/cables?
1 ½ inches
Concrete that is exposed to salt water, what is the correct mixture added to protect rebar?
Corrosion resistant mixture
How much concrete coverage is required when you have a # 10 rebar in a beam?
¾ inch
Low slump means that the concrete is;
Stiff
What is the minimum thickness required for a concrete slab placed against and permanently exposed to the earth?
3 ½ inches
Which of the following is not acceptable when grouting stressing pockets?
Having chlorides as an additive
When back stressing a barrier cable, the end anchor should be installed to a force of ___%
80 %
The maximum number of or .60 of an inch tendons / cables in a group is _____.
4
For an encapsulated post-tensioned system, the watertight cap should be installed less than____.
24 hours after stressing
If a tendon is stressed at both ends, what is the recommended length of tail to leave outside the edge form at each end?
12 inches
Which of the following is not a method to control plastic shrinkage?
Use of a richer mix design
High early strength concrete is made using Type _____ cement.
III
of the following are methods of curing concrete except _____.
1 – Keeping the surface moist
2 – Heated forms
3 – Covering with plastic sheets
4 - Using plastic forms
Which of the following concrete joints allows for both vertical and horizontal movement?
Isolation
For the strength of concrete to continue to increase with time, the relative humidity within the concrete should remain above____ percent.
80 %
Which of the following factors does not influence workability of concrete?
Calcium chloride
Durability of concrete can be related directly to:
Compressive strength
What is the most effective method for controlling shrinkage cracking in concrete?
Providing joints (contraction joints)
The resistance of hardened concrete to freezing and thawing is significantly improved by adding:
Air – entrainment
What is the effect of vibratory action on a concrete mixture?
1 – It permits the use of a stiffer mixture
2 – It causes the mix to be more liquid
3 – Removes trapped air
4 – All of the above
What is the effective period of time for increased workability that can be expected when placing concrete using super plasticizer?
30 to 60 minutes
What is most closely related to abrasive strength of concrete?
Compressive strength
How do higher temperatures at time of placement affect concrete?
Concrete has a lower slump
Besides the water to cement ratio, what else determines the final compressive strength of concrete?
Age
The most common plasticizer used in concrete is:
Lime
For the most part you do not need to add anything to the concrete mix other than the standard ingredients, but on occasion additives do help to make the job easier. Which of the below is not considered an additive?
1 – Air entraining powder
2 – Plasticizers
3 – Retarders
4 – Water
Concrete in which wires are tensioned on the jobsite after the concrete has been hardened by running the wires through ducts is called
Post-Tensioned concrete
What is the minimum 28 day compressive strength for lightweight aggregate concrete?
2500 psi
If you order and are pouring one cubic yard of concrete 4 inches thick, which of the following forms would it fill?
9 feet ½ inch x 9 feet ½ inch Design and Control of Concrete Mixtures Calculations
Divide 27 cubic feet (one yard) by inches (.33) and then square root to get the square dimensions. You may have to take answers given (if not square) and multiply and then multiply by inches and divide by 27
The concrete arrives on a construction project stiffer that needed and the workers add water to the mix. How will this affect the mix?
1 – Does not affect the mix
2 – Makes the mix weaker
3 – Increases the water to cement ratio
4 – Both 2 and 3
A footing needs to have a load supported on it of 252 kips, with a soil bearing capacity of 6,000 pounds. How many square feet will this footing have to be?
42 square feet
When placing concrete, what is the maximum distance it is allowed to fall before a tremie chute is required?
4 feet
What is the purpose for vibrating concrete?
1 – To remove trapped air
2 – To consolidate the concrete
3 – To separate the ingredients
4 – Both 1 and 2
When truck concrete mixers are used, the time between batching and complete discharge after water has been added to the cement and aggregates is ____ hours or before the drum has revolved ___times.
1 ½ hours and 300 revolutions
When mixing concrete, the reason for adding water to the cement is called:
Hydration
What temperature range would be considered a hot weather condition for concrete?
77 degrees to 90 degrees
What is the definition of creep in concrete?
The continuous deformation of the concrete due to continued sustained loads
If you have a pier or pier footing that is 7’0” x 7’0” by 1’6” deep using 4,000 psi concrete. The soil that this footing is sitting on has a bearing capacity of 2,000 pounds per square foot. What is the maximum load that soil can bear with this footing in kips?
98 kips
What is the definition of pre-cast concrete?
that is cast and poured off site and transported to its final position
What is the best temperature for curing concrete?
55 to 73 degrees (actually 50 to 70)
Which of the below would be the correct splice lap for splicing reinforcement rods (rebar) together in masonry?
40 times the bar diameter, minimum one foot of splice
What is the main reason for taking a slump test?
Check the workability and consistency of the concrete
When pouring concrete in hot weather, this is a condition that can occur:
1 – Shrinkage cracks
2 – Loss of strength
3 – Fast hydration (stiff very quickly)
4 – All of the above conditions
To resist the deterioration of concrete due to deicers, freezing and thawing, which of the following admixtures need to be added?
Air-entrainment
What is the purpose for using form ties when pouring concrete in forms?
To resist the lateral pressure of the concrete
4 – Neither of the above
When installing post tension cables, you are allowed to have 1 inch of the cable exposed in the concrete at the end tying into the form without plastic sheathing. What procedures are required if more than 1 inch is exposed?
Grease cable and tape
How can you stop reverse curvature of a post tension cable?
– Add additional cable supports
