Concrete Flashcards
Post-tensioned concrete
A variant of prestressed concrete where the tendons are tensioned after the surrounding concrete structure has been cast.
What is maximum size of coarse aggregate?
19mm or 25mm (3/4inch - 1 inch)
Aggregates make-up about ___ to ___ of the total volume of concrete.
60% to 75%
What are the proportion ranges of material used in concrete based upon volume?
Up to 8% Air
4-21% Water
7-15% Cement
23-35% Fine Aggregates
30-45% Coarse Aggregates
What are six advantages of reducing water to concrete?
- increased compressive and flexural strength
- lower permeability and increased water tightness
- increased durability and resistance to weathering
- better bond between concrete and reinforcement
- reduced drying shrinkage and cracking
- less volume change from wetting and drying
What are the six basic types of portland cement?
Type I - General Use
Type II - Moderate sulfate resistance
Type II (MH) - Moderate
Type III - High Early Strength
Type IV - Low Heat of hydration
Type V - High sulfate resistance
What is Type I Portland Cement?
Type I portland cement is a general-purpose cement suitable for all uses where the special properties of other cement types are not required. It uses in concrete include pavements, floors, reinforced concrete buildings, bridges, tanks, reservoirs, pipe, masonry units, and precast concrete products.
What is Type II Portland Cement?
Type II Portland cement is used where protection against moderate sulfate attack is necessary. It also contains no more than 8% tricalcium aluminate.
What is Type II(MH) Portland Cement?
Is often used in mass concrete structures, such as large piers, large foundations and thick retaining walls.
What is Type III Portland Cement?
Type III portland cement provides strength at an earlier age than other cement types. For example, strength may be achieved in a matter of days as compared to the typical requirements of 28 days.
What is Type IV Portland Cement?
Type IV cement is intended for use in massive concrete structures, such as large gravity dams.
What is Type V Portland Cement?
Type V portland cement is used in concrete exposed to sever sulfate environments - principally where soils or groundwaters have a high sulfate content.
What does air entrainment do for cement?
These cements can produce concrete with improved resistance to freezing and thawing. Air entrainment is achieved through the use of an air-entraining admixture added when batching concrete. (Ex. Type 1A)
What is white portland cement typically used for?
Primarily for architectural purposes in structural walls, precast, glass fiber reinforced concrete facing panels, terrazzo surfaces, stucco, cement paint, tile grout and decorative concrete.
All Portland and blended cements are ?
Hydraulic cements. Type GU (General Use)
What is the size and weight of a traditional concrete bag?
94lbs and 1 cubic foot.
What is Fly Ash?
The most widely used SCM in concrete in the US, is a byproduct of the combustion of pulverized coal in electric power generating plants. It is used in more than 50% of ready mixed concrete.
Seawater is generally suitable as mixing water for concrete not containing ______
Reinforcing steel.
Do acid waters with concentrations as high as 10,000ppm have an adverse effect on strength?
No
Mineral oil in concentrations greater than ____ by mass of cementitious materials may reduce strength by more than _____.
2.5% of mass
20% strength
Oils can also interfere with the action of air-entraining admixtures.
What is aggregate Maximum size?
The smallest sieve opening through which the entire amount of aggregate is required to pass. The smallest sieve size that requires 100% passing.
What is aggregate Nominal Maximum size?
The smallest sieve opening through which the entire amount of aggregate is permitted to pass. One sieve size smaller that the max.
The nominal maximum size aggregate should not exceed _____ the depth of slabs.
one third or
Dmax = 1/3T
When are materials harmful in aggregates?
When there are materials finer than the No. 200 sieve. It affects bond and increases the water requirement of the concrete.
Because of improved workability with entrained air, ____ and ____ content can be reduced significantly.
water and sand
What do high-range water reducers (superplasticizers) do?
Flowing concrete is by definition a cohesive concrete with a slump greater than 7.5 in., which includes self consolidating concrete that can be placed with little or no vibration or compaction while still remaining essentially free of excessive bleeding or segregation.
If a plasticizer is added to a concrete with a 3-in. slump, what will be the final slump?
Can easily produce a concrete with a 9-in. slump.
Calcium chloride is?
A highly effective accelerating admixture; it is limited to a dosage of 2% or less. Use with caution with:
- Reinforced steel
- Subjected to steam curing
The amount of pigments used in concrete should not exceed ____ of weight of the cement.
10%
What is the strength range of Grade 60 reinforcing steel?
60,000psi to 80,000psi
At what temperature and at what humidity of the concrete do hydration and strength gain stop?
80% humidity
14F
Difference between conventional concrete and low-density concrete in weights/cu ft?
Conventional concrete: 120-150 lb/cu.ft
Lightweight concrete: 70-12- lb/cu.ft
Contraction Joint
Controls shrinkage - are grooved, formed or saw cut into sidewalks at approximately 1/4 the concrete thickness
Isolation Joint
Separates a concrete placement from other parts of a structure to permit horizontal and vertical movements.
Construction Joint
Concrete work is concluded for the day.
Adding or subtracting 1 gallon (10lbs) of water per cubic yard of concrete can change the slump by?
1 inch
What is the minimum mixing time for every yard of concrete?
one minute plus 15 seconds for each yard added
Contraction joints in walls should be spaced not more than how many feet apart?
20
What is the approximate amount of mixing water for a trial batch of non-air entrained concrete with a 4” slump and a maximum size of 1” aggregate?
325 gallons
Structural lightweight aggregate concrete with a slump of ____ produces the best results for finishing.
2-4 inches
Contraction joints are to be cut-in on a concrete slab. This slab is 6” thick. Using 1/2” sized aggregates, the joints should be spaced not more than___feet.
12
A small job requires 1 cubic foot of air entrained concrete. How many pounds of wet fine aggregate is required when using a maximum sized 3/4” coarse aggregate.
42 lbs.
If the temperature of a freshly mixed concrete is increased from 50F to 100F, how much additional water is needed to maintain the same 3” slump?
11 lbs. per cubic yard
For corrosion protection for reinforced concrete exposed to chlorides from deicing salts, what is the maximum water-cementious material ratio by mass?
0.40
Cracking is possible with some concrete mixtures, such as those containing certain pozzolans, if the evaporation rate exceeds______.
0.1 pound per square foot per hour
After piles for each foundation are in place, they are cut off at about ____ inches above the bottom of the footing.
6”
What are concrete spandrel beams?
Edge or exterior beam that stretches horizontally from one column to another
What is a waffle slab?
A concrete slab made of reinforced concrete with concrete ribs running in two direction on its underside. The name waffle comes from the grid pattern created by the reinforcing ribs.
What is the minimum length of a spreader bar when hoisting rebar bundles?
1/2 the length of the bundle
What is the minimum concrete cover (outside bar to face of concrete) for where concrete is cast against the ground and on the bottoms of footings?
3”
What is the minimum concrete cover (outside bar to face of concrete) for bars larger than #5 exposed to weather or be in contact with the ground?
2”
What is the minimum concrete cover (outside bar to face of concrete) for ties and spirals in columns?
1-1/2”
What is the minimum concrete cover (outside bar to face of concrete) for #11 and smaller bars on top, bottom, and sides of joists and slabs where concrete surfaces are not exposed directly to the ground/weather?
3/4”
What is the minimum concrete cover (outside bar to face of concrete) for concrete not exposed directly to the ground or the weather?
3/4”
Lowering or raising the top/bottom bars by 1/2” more than specified in a 6” deep slab could reduce its load carrying capacity by ___%.
20%
Tolerance of rebar placement - longitudinal location of bends and ends
+/- 2 inches
Tolerance of rebar placement - as long as the total number of bars is maintained, a reasonable spacing tolerance in spacing individual bars is
+/- 3 inches
Tolerance of rebar placement - lap splice length
-1 inch
Tolerances in spacing bars in walls and solid slabs - should not be greater than three times the thickness of the slab or wall nor ___ inches.
18 inches
Tolerance in rebar stirrup spacing is?
+/- 1 inch
Rebars are ordinarily stocked in __ foot lengths
60 foot
Which size rebars requires mechanical splicing in lieu of lap splicing?
14 and #18 bars
Welded rebar splices are recommended for what size bar?
6 bars or smaller
What size of tie wire is typically used for for tying reinforcing bars?
No. 16-1/2 or No. 16 gauge black, soft annealed wire
When tying intersecting reinforcing bars, how often should they be tied?
Every fourth or fifth intersection
For concrete walls, ties should not be spaced more than _____ feet apart in either direction.
4 to 6 feet
What is a beam bolster (rebar)? And they are spaced at ___ feet OC max.
Used to support lower beam steal from the soffit form and are spaced at 5’ OC max.
What is a hickey tool (rebar)?
Hand tool with side opening jaw used in developing leverage for making bends on reinforcing bars at the jobsite.
This type of tie can be used to secure heavy mats that are lifted by a crane. This tie is a:
Wrap and Saddle Tie
What type of “chair” is made with a top wire formed with notches, or saddles, to support the two bars?
Joist Chair
What type of tie is usually used to secure reinforcing bars located within a vertical location?
Wrap and Snap Tie
What type of concrete is mixed partially in a stationary mixture and then completed in a truck mixer?
Shrink-mixed concrete
A slump test is used to measure the __________ of concrete.
Consistency
Long concrete chutes over _________ must discharge into a hopper before distribution to point of need.
20 feet
What is the approximate amount of mixing water for a trial batch of air entrained concrete with a 3” slump and a maximum size of 3/8” aggregate?
340 gallons
In a slump test, how many times should each layer be rodded?
25 times
Contraction joints are to be cut-in on a concrete slab. This slab is 8” thick. Using 3/4” sized aggregates, the joints should be spaced not more than _______.
20 feet
___________ is used to decrease the setting time of concrete.
Calcium chloride
What is the required slope range of the concrete mixing truck?
between 1:2 and 1:3
What is the desired effect of using a pumping aid, such as hydrated lime admixture, in concrete?
Increased bond strength
Crystaline hydrophilic polymers can be used as a __________-reducing admixture in concrete.
permeability
When using a 3/8” maximum size aggregate, what is the minimum cement requirement to be used in flatwork?
360 pounds per cubic yards
What tool/method leads to a smooth, hard and dense concrete surface.
Troweling.
For concrete floors placed by chute, the slump should not exceed a maximum of ______inches.
5 inches
What is the approximate amount of mixing water for a trial batch of non-air entrained concrete with a 3- 4” slump and a maximum size of 3/4” aggregate?
340 gallons
What is the approximate amount of mixing water for a trial batch of non-air entrained concrete with a 3- 4” slump and a maximum size of 1/2” aggregate?
365 gallons
What is the approximate amount of mixing water for a trial batch of non-air entrained concrete with a 3- 4” slump and a maximum size of 3/8” aggregate?
385 gallons
What is it called when the water-content ratio at the top surface of the concrete increases creating a weak layer with poor durability?
Excessive bleeding
In seismic category D1 locations, rebar in concrete cast against the earth shall have a minimum cover of _____ from the bottom of the footing.
3 inches
The minimum thickness of a bed joint at foundations is ___________.
1/4 inch.
The maximum thickness of bearing walls for a foundation or exterior basement shall not be less than______ inches.
7.5 inches
Development length for individuals bars within a bundle, in tension or compression, shall be that of the individual bar, increased _________________ for a four-bar bundle.
33 percent
What type of tie is usually used for securing column ties to vertical corner bars?
U Tie
