Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

EXAC EXAM 3 > 1. Final Project - Materials - Concrete > Flashcards

1. Final Project - Materials - Concrete Flashcards

1
Q

Formwork

A

Shapes and supports concrete until it cures enough to support itself

  • Formwork for a beam or slab is also a temporary working surface during construction
  • Must be strong enough to support weight concrete without deflection
  • Usually repeatedly used and must be protected
  • Coated with a form release compound that prevents adhesion of concrete to the form
  • Formwork is basically an entire temporary building that has to erected and demolished to construct the actual building. It’s a major cost of the project.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

most common form of forming material

A

plywood

  • usually 3.4” thick
  • coated with oil and water resistant glue or plastic to prevent water penetration into wood; help reusability of formwork
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

form ties

A

metal wires or rods used to hold opposite sides of the form together and also to prevent their collapse

-when the forms are removed the wires remain in the conrete; ecess wire is twisted or cut off

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

flying forms:

A

large fabricated sections of framework that are removed, once the concrete has cured, to be resued in forming an identical section above

-used in constuctung buildings with repetitive elements (e.g. hotels and apartments)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Form liner

A

conrete is shaped with liners of plastic, wood, or metal

  • parallel rib liners are common type
  • joints and form tie holes are treated as desired-either left exposed or patched
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are form ties? List 2 types

A

SNAP TIES
- have notches or crimps so they can be snapped off after forms are removed
SHE BOLTS
- waler rods (reused) threaded into inner rod which is left in concrete

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

formwork costs for self consolidating concrete may be higher than those for conventional concrete because

A

the greater fluid pressures exerted by the concrete require stronger and stiffer formwork

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Concrete: why reinforce it? (5)

A
  • Concrete resists compression very well, however it must be reinforced with steel so that it is more resistant to tension and shear.
  • Attach vertical and horizontal elements
  • Reinforce edges around openings
  • Reduce cracking due to shrinkage
  • Stabilize thermal expansion and contraction.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Concrete: advantages (4) and disadvantages (2) ?

A

Advantages :

  1. It can be given almost any possible shape.
  2. It can be provided with the most varied finishes and textures.
  3. Concrete frames are relatively cheap
  4. Concrete frames are fire resistant

Disadvantages:

  1. Density (2240kg/m3)
  2. Formwork necessary before setting it in place so that it sets and hardens.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Concrete = mixture of…? (3)

A
  1. Cement
  2. Various mineral aggregates
  3. Sufficient amount of water for the cement to set and bind the entire mass.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Concrete: why add admixtures?

Name 5 types of admixtures.

A

Admixtures can be added to a concrete paste to modify these properties or those of the cured product.

  1. Air-entraining admixture
  2. Accelerator or retarder
  3. Surface admixture
  4. Water reducer
  5. Dye
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Concrete: what is an air-entraining admixture? Roles (3)?

A

Disperses microscopic spherical air bubbles in the concrete paste to:

  • increase maneuverability
  • increase the resistance of the cured product to cracking caused by free thaw cycles or to spalling caused by de-icing chemicals
  • in larger quantities, to produce lightweight, insulating concrete.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Concrete: why add an accelerator and a retarder?

A
  • Accelerator: catalyzes the setting and the development of the resistance of a concrete paste -

Retarder: slows the setting of the concrete paste, allowing more time for placing and handling the concrete paste

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Concrete: why add a surface admixture?

A
  • Reduces surface tension of water added to concrete paste
  • Thus promotes the wetting and penetrating action of water or the emulsifying action and the dispersion of other additives in the dough.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Concrete: why add a water reducer (or superplasticizer)?

A
  • Reduces the amount of mixing water needed for proper workability of concrete paste or mortar.
  • By thus reducing the ratio between the proportions of water and cement, the strength of the concrete is generally increased.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Concrete: what determines the ratio between the quantity of water and cement?

Too much water = ?

Not enough water =?

Optimal ratio?

A

Determines: 1. Resistance… 2. durability… 3. waterproofing… … of the hardened concrete

The compressive strength of concrete is inversely proportional to the ratio of water to cement:

  • If there is too much water, the concrete paste will be weak and porous after drying.
  • If there is not enough water, the dough will be dense, but difficult to set up and handle.

In most cases, the ratio of water to cement should be

Water (L)/cement (kg) = 0.45 to 0.60.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

When specifuing small batches of conrete what does 1:2:5 mean?

A

it is the ratio of cement:sand:aggregate

C:S:A

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

concrete components

A
  • cement
  • fine and course aggregate
  • water

portalnd cement: binder; made of lime, silica, iron oxide, alumina

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

5 types of cement

A

type I: standard or normal cement (used for most construction)

type IA: Normal, air entraining

type II: modified cement; used in places when in contact with water with a high concentration of sulfates

type IIA:Moderate resistance, air entraining

type III:High early strength (hardens more quickly, used when reduced curing time is required)

type IIIA:High early strength, air entraining

type IV:Low heat of hydration (used in massive structures like dams, where heat emitted might raise the temperature of the concrete to damaging levels)

type V:High resistance to sulfate attack (used when in contact with water with a high concentration of sulfates) !

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Air Entraining Admixtures

A

Improved workability during placement

Increase the resistance of the cured concrete to damage caused by repeated cycles of freezing and thawing

Can create very lightweight non structural concretes with thermal insulating properties

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Air Entrained Cements

A

Contain ingredients that cause microscopic air bubbles to form in the concrete during mixing which give improved workability during placement, and greatly increases the resistance of the cured concrete to damage caused by repeated cycles of freezing and thawing

  • Commonly used for pavings and exposed architectural concrete in cold climates
  • Can reach the same structural strength a regular concrete
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

concrete strength

A

• Concrete cures/hardens due to hydration, where considerable heat is given off as the
cement combines with water to form strong crystals that bind the aggregates together

Concrete shrinks lightly during the process

• Designed on the basis of the s strength that is reaches after 28 days

7 day strength should be about 75% of the designed 28 day strength

  • Early strength concrete can reach normal 28 day strength in 7-14 days
  • Typical strength ranges from 3,000 psi - 10,000 psi
  • Nominal weight is 150 lbs per cubic foot
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Aggregates

A

Take up about 3/4 of the volume of concrete

• Structural strength is heavily dependent on the quality of its aggregates
• Must be stone, clean, resistant to freeze-thaw deterioration, chemically stable, and
properly graded for size distribution

• A range of sizes must be included and properly proportioned to achieve close packing of the particles

• The largest particle in a concrete mix must be small enough to easily pass between
the most closely spaced reinforcing bars and to fit easily into the formwork

• Maximum aggregate size should not be more than 3/4 of the clear spacing between
bars or 1/3 the depth of the slab

• 3/4” or 1 1/2” maximum is common for most slab and structural work

• Structural lightweight aggregates are made from minerals like shale and reduce the
density of concrete by about 20%
• Vermiculite or perlite used in non structural lightweight concrete (used for insulating
roof toppings) are less dense than expanded shale

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

The size of the aggregates in concrete is determiend by…

A

…the size of the forms and the spacing between the reinforcing

-in most cases, it should not be larger than 3/4 of the smallest distance between reinforcing bars or larger than 1/5 of the smallest dimension of forms, or more than 1/3 the depth of slabs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Methods used to specify the proportions of concrete mix:

A
  • ratio of cement to sand to gravel, such as 1:2:4; amount of water also has to be specified
  • specify weight of materials, including water, per 94 lbm bag of cement
  • for large batch quantities, define the weight of materials needed to make up one cubic yard of conrete
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Strength of final mix is specified by…

A

the compressive strength of concrete after it has cured and hardened for 28 days (known as the design strength of concrete)

-typical specified design strengths are indicated as 2000 psi, 3000 psi, and 4000 psi; 12000 is available but it’s more expensive

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Admixtures…

A

… are ingredients other than cement, aggregates, and water that are added to the mix to alter it in various ways

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Accelerating admixtures:

A

cause concrete to cure more rapidly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Hydration:

A

chemical reaction between water and cement which creates heat

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

High range water reducing admixtures (Superplasticizers):

A

Organic compounds that transform a stiff concrete mix into one that flows freely into forms, used to help place concrete in challenging circumstances, or to reduce the water content in a mix in order to increase its strength

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Water reducing admixtures:

A

Allow a reduction in the amount of mixing water while
retaining the same workability, results in a higher strength concrete

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Retarding admixture:

A

Slow curing to allow more time for working with wet concrete

help reduce the heat of hydration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Waterproofing admixtures:

A

decrease the permeability of the conrete

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

Fly ash:

A

A fine powder that’s a waste product from coal-fired power plants, which
increases concrete strength, decreases permeability, increase sulfate resistance, reduces temperature rise during curing, reduces mixing water, and improves workability

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

Silica fume (microsilica):

A

A powder 100x finer than portland cement, a byproduct of electronic semiconductor chip manufacturing that when added produces extremely high strength and low permeability

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

Blast furnace slag:

A

Byproduct of iron manufacture that improves workability, increases strength, reduce permeability, reduce temperature rise during curing, and improve sulfate resistance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

Pozzolans:

A

varicose natural/artificial material that react with calcium hydroxide in wet concrete to form cementing compounds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

Workability agents

A

Improve the plasticity of wet concrete to make it easier to place in forms and finishes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

Corrosion inhibitors:

A

Used to reduce rusting of rebar in structures that are exposed to road deicing salts or other corrosion causing chemicals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

Fibrous admixtures:

A

Short fibers of glass or steel added to a concrete mix to act as microreinforcing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

Freeze protection admixtures:

A

allow concrete to cure at temperatures as low as -6 C

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

Extend set control admixtures:

A

used to delay the curing reaction in concrete for up to 7 days.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

Coloring agents:

A

dyes and pigments used to alter the color of concrete

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

True or false.

Water used to mix with concrete must be potable

A

True.

Mixing water for concrete must be free of harmful substances, clay, salts, etc. If it’s good
enough to drink, it’s good enough to be in concrete.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

Self consolidating concrete (SCC)

A

can be placed purely by means of its own weight without the use of vibration

  • made posible with the use of superplasticizer admixture called polycarboxyplate polymer
  • placement is increased, less labor required, productivity increased
  • uniform smooth surface
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

carbon fiber conrete

A

Uses epoxy coated carbon fiber mesh in place of standard steel meash

  • carbon fiber is less corrosive requiring less conrete cover
  • resulting panels require smaller foundation and support structures
  • carbon fiber are bundled together to form pieces resembling yarn, called tows; tows laid perpendicular to each other, forming a grid; grid could have nearly seven times the tensile strength of standard steel mesh
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

poured gypsum deck

A

used for roofs and similar to conrete in that liquid is poured on a reinforcing form board

-Poured gypsum and concrete deck fill insulation are economical & applied directly to the corrugated steel decking and rough concrete decks, easily tapered during installation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

alkalinity in concrete can cause problems in two ways

A

high alkalinity on the surface of a slab can damage a tile installation by causing the adhesive to reemulsify

also responsible for the phenomenon known as alkali silica reaction (ASR); high alkaline cement begins to dissolve sand and rock within the concrete. this reaction produces a gel like materal that creates pressure in the pores of the conrete surface

-ASR can be reduced by specyfiying aggregates not suceptible to ASR, using low lime cement, proper curing not finishing conrete with a hard trowel surface

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

What cement would be used in slip form construction

type 1

type 2

type 3

type 4

A

type 3

type 3 is high early strength –the type needed for rapid slip form construction

type 1 is normal cement

type 2 is low heat and sulfate resistant

type 4 is slow setting and low heat for massive structures

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
50
Q

true or false.

the strength of concrete increases as the water cement ratio decreases

A

true

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
51
Q

calcium chloride is used as an admixture for concrete in order to…

A

accelerate the strengthening of concrete

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
52
Q

What is concrete mix comprised of?

A

+ CEMENT (PORTLAND)
+ WATER
+AGGREGATE

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
53
Q

Relationship of water-cement ratio to strength & ideal range

A
  • Compressive strength inversely proportional to ratio of water to cement.
  • IDEAL RANGE .45-.60
54
Q

Concrete mix contains __-__% aggregate.

A

60-80%

(Key to FR, Strength, Weight)

55
Q

Lightweight concrete made with _______ OR ___________.

A

Expanded shale or slate aggregate

56
Q

5 Types of concrete

A

TYPE I - normal
TYPE II - moderate portland cement
TYPE III - accelerated cure (cold weather)
TYPE IV - low heat
TYPE V - sulfate resistance (salty acidic soil)

57
Q

What kind of cement is portland cement and how is it made?

A

• HYDRAULIC CEMENT

1 - Burn clay & limestone in a kiln
2 - Pulverize into fine powder

58
Q

Insulating concrete made with _________

A

Prelite aggregate or foam agent.

59
Q

Size of fine & coarse aggregate.

What is the appropriate depth & thickness for a slab / walls?

A

FINE:
sand < 6mm

COARSE: (Abram’s Law)
must be <1/3 slab depth
must be <1/2 wall thickness

60
Q

Rule of thumb for estimating depth/width of a concrete beam:

A

Span / 16

Width: 1/3 to 1/2 of beam depth *equal or greater than width of column

*beam measured from top of slab

61
Q

One-way slab

A

Uniform thickness, reinforced in one direction, cast with parallel supporting beams

Short spans : 6’@18’

Slab thickness: span/30, 4” min, roof slabs span/36

62
Q

One-way joist slab

A

Joist or ribbed slab with perp beams

Spans : 15’@36’

Light to medium live loads

Slab thickness: span / 24, 3” - 41/2”

Joist width 5”-9”

Reusable pans 20” or 30”

Distribution rib for spans between 20’-30’

63
Q

Two way slab and beam

A

Reinforced in two directions, nearly square bays

*usually built as flat slabs without beams

Medium Spans : 15’@40’ square

Heavy live loads, high resistance to lateral forces

Slab depth: min 4”, slab perimeter/180

64
Q

Two way flat plate

A

Reinforced in two or more directions, columns without beams

Simple to form, low floor-to-floor height, flexibility in column placement : apartment / hotel

Short Spans : 12’@24’ square

Light to moderate loads

Slab depth: 5”-12”, span/33

Punching shear @ columns

65
Q

Two way flat slab

A

Flat plate thickened at column supports (drop panels)

Long Spans : 20’@40’ square

Heavy loads

Slab depth: 6”-12”, span/36

Drop panels @ columns : 0.25xslab thickness projection, 0.33 span = width

66
Q

Two way waffle slab

A

Reinforced by ribs in two directions

Long Spans : 24’@54’ square

Heavy live loads

Slab depth: 3”-4 1/2”, span/24

Square dome forms 19” or 30” - 2’ or 3’ module

Solid heads at column supports

Cantilever : 1/3 span

67
Q

What is prestressed concrete?

A

Pretensioning or posttensioning high-strength steel tendons to actively resist a service load.

Tensile stresses transferred to the concrete, placing entire member in compression

  • deflect less
  • carry greater load
  • span greater distance
68
Q

What is pretensioning?

A

Pretensioning is done in a precast plant.

Stretch the tendont before concrete is cast.

Member bents upwards & deflection makes it flat.

69
Q

What is posttensioning?

A

Pretensioning is done on site.

Stretch the tendont after concrete is cast.

Member bents upwards & deflection makes it flat.

Tend to shorten over time = expansion joints required

70
Q

What is needed on top of pre-cast slab units?

A

2”-3 1/2” concrete topping with steel fabric is required on top of pre-cast slabs.

71
Q

Grids for concrete columns:

12”

16”

20”

A

12” - 2000 sq.ft. - 44’x44’

16” - 3000 sq.ft. - 54’x54’

20” - 4000 sq.ft. - 63’x63’

*Note that span of floor would most likely dictate spacing

72
Q

Minimum concrete cover to protect reinforcement from fire & corrosion

A

1 1/2”

73
Q

epoxy coated reinforcing bars are used when …

A

…the concrete will be exposed to cholrides (salts) such as deicing salts and those in sea water.

-epoxy coating helps keep that salts from corroding the steel by chemical reaction

74
Q

Reinforcing

A

Is required because concrete has no useful tensile strength

  • Steel rebar is placed where there are tensile forces in a structural member, and concrete resist the compressive forces
  • Rebar is hot rolled like structural shapes, round in cross section with ribs for better bonding to concrete
  • Bars are numbered based on the number of eights of an inch the bar’s diameter is (Ex: number 6 rebar is 6/8” (or 3/4”) in diameter, number 8 rebar is 8/8” or 1”)

• Structural engineer knows how to calculate the amount of rebar required
for a given cross section and can be achieve with a few big bars or many small bars
• Rebar in structures exposed to salts like seawater are prone to rust

75
Q

two types of reinforcing steel for cast in place concrete

A

1 deformed bars

2 welded wire fabric

76
Q

rebar comes in 2 common grades

A

grade 40 and grade 60

  • these numbers refer to kips per square inch
  • grade 60 is the type most used in construction
77
Q

How to read rebar

A
  • top symbol: producing mill
  • second marking: size (given in eights of an inch)
  • Third marking: Manufacturing material ( “S” for carbon-steel or “W” for low- alloy steel)
  • bottom marking: Grade marking
78
Q

how to read welded wire fabric designations

A

example 6 x 6 -W1.4 x 1.4 means that the grid is 6 in by 6 in and the size of the wire is 1.4 hundredths of a square

-the letter preceding the gage is either W for smooth wire or D for deformed wire

79
Q

the designation for america standard sizes of rebar is based on…

A

…the number of eights of an inch in the nominal diameter of a bar, up to 1 inch

80
Q

In post tensioned concrete construction, what does it mean to drape reinforcing

A

reinforcing is draped (curved) along the length of a beam;

after tensioning, the drape creates for structural efficiency

81
Q

Minimum concrete coverage for reinforcement when exposed to earth?

A

3” min

82
Q

The best way to stop the migration of moisture though a conrete slab is with a vapor barrier placed…

A

directly below the conrete slab and on top of any sand cushion layer or subbase.

83
Q

vapor barrier

A

a thin sheet material, generally plastic, designed to prevent water vapor from passing though it.

permeance (measure of a materials resistance to water vapor transmission) not exceeding 0.04 perm

10 mils thick

perm is the passage of one grain of water vapor per hour through one square foot of material at a pressure differential of one inch of mercury between the two sides of the material

84
Q

vapor retarder

A

is not vapor proof; allows vapor to pass

it slows the rate of water vapor transmission

  • is a membrane of metal foil, plastic, or treated paper placed on the warm side of thermal insulation to prevent water vapor from entering the insulation and condensing into liquid
  • essential in colder climates to prevent moisture from accumulating within the insulation
85
Q

Capillary break

A

crused stone placed over compacted subsoil and serves as a drainage layer

86
Q

How to adequately place conrete?

A

If concrete slurry is vibrated excessively, dropped from a height, or moved too far horizontally in formwork its likely to segregate

• Aggregate works it way to the bottom of the form and water/cement to the top
• Result is non uniform and unsatisfactory, and typically has to be redone
• Segregation is prevented by depositing fresh from the mixer as close as possible to
the final position
• Should not be dropped more than 3’ - 4’
• If it must be moved to an inaccessible location, it should be pumped through hoses or
conveyed in buckets

87
Q

for concrete columns, piers, and walls, the maximum variation in plumb will be

A

plus ot minus 1/4 in in any 10 ft length.

-the same tolerances applies for horizontal elements

88
Q

the maximum variation out of plumb for the total height of the structure is

A

1 in for interior columns

1/2 in for corner columns for buildings up to 100 ft tall

89
Q

Ideally, concrete slabs should be allowed to cure and dry for a minimum of

A

six weeks before resilient flooring is installed

90
Q

If too much water is placed in a concrete mix, which of the following problems might develop:

laitance

efflorescence

hydration

segregation

A

laitance

laitance is the surface deposite of low strength material containing cement and fine aggregates (sand) brought to the surface of concrete. it is caused by having to much water in the concrete mix, which results in water bleeding to the top

91
Q

efflorescence

A

• Sometimes appears on the surface of a wall of brick, stone, or concrete masonry

• Consist of one or more water soluble salts that were originally present in the
masonry unit or in the mortar
• Brought to the surface and deposited there by water that seeped into the masonry,
dissolved the salts, then migrated to the surface and evaporated
• Can be avoided by choosing masonry units that are lab tested and don’t contain water soluble salts
• Will eventually diminish and disappear with time as the salt is gradually leached out of the wall

92
Q

expansion joints in concrete walks should be located at a maximum spacing of

A

expansion joints with a joint filler are placed a maximum of 20 ft

control joints placed where spearate sections of concrete are poured and in walks are placed 5 ft apart

93
Q

what is used to minimize cornner chipping of a concrete

A

chamfer strips

a chamfer strip is a small, triangular piece of material placed in the corners of forms to prevent sharp 90 corners, which are difficult to cast and have a tendency to break off during use or when the forms are removed

94
Q

at what temperature doe workers need to to take to protect concrete when cold weather is predicted?

A

around 4 deg C

A concrete pour can proceed at temperature below 4C. However the water and sand must be heated to ensure that none of the constituents have frozen, and the concrete must be heated for at least 7 days after placement, during the early curing stage

95
Q

during which period in the curing process does concrete gain the most compressive strength

A

0 to 3 days

  • concrete gains the most compressive strength during the first few days of curing
  • most critical time in curing process
  • the compressive strength of concrete is always referred to as its strength 28 days after it is palced
96
Q

chairs

A

small wire supports that help to keep rebar a specified distance from the outside of the concrete and help ensure adequate concrete cover

97
Q

four primary types of concrete joints:

A

1) control joints: joints that allow for shrinkage of large areas, and controls and inducescracking to occur along the joint: cut to a depth of 1/4 the slab thickness; intentionally created cracks that can open to accommodate shrinkage in surfaces made of concrete masonry
2) construction joints: occur wherever thera are two successive pours ( a new pour against a cured section of concrete); should be located at point of minimum shear; suceptible to water leakage, thus wa waterstop should be cast into the first pour
3) expansion joints:joints that allow free movement of adjacent parts due to expansion or contraction of concrete. Typically waterproof, watertight, filled with an elastic filler; Required at buildings over 200’ long, at joints of building wings, and additions
4) Isolation Joints: joints located at slab on grade, columns, or walls to allow for independent movement

98
Q

List the 3 most common precast concrete wall types

A

SOLID - 8’ width typ.
(max height 7m)

COMPOSITE - Rigid Foam @ center
(max height = 7m)

RIBBED - max rib depth 305mm
(max height = 14m)

99
Q

Autoclaved aerated conrete (AAC)

A

Precast concrete product manufactured by adding aluminum powder to conrete hardening it in molds, and then curing the molds in pressurazed steam chambers (autoclaves)

  • 1/5 the density of regular conrete
  • has good sound control qualities and thermal mass
  • not as strong thefore should only be limited to non load bearing application and low rise buildings
  • must be protected from weather
100
Q

Dimensions of three types of precast wall panels?

A
  1. Solid panels:
    height: 24’ max, thick: 3 1/2”-10”, width: 8’ typ.
  2. Composite panels:
    height: 24’ max, thick: 5 1/2”-12”, rigid foam insulation core with wire shear ties between concrete layers
  3. Ribbed panels:
    height: 48’ max, thick: 12”-24”, width: 8’ typ.
101
Q

what is the primary purpose of the voids in a cored slab?

a. to allow electrical services to be concealed in the slab
b. to make a more efficient load carrying member
c. to make erection easier
d. to minimize weight

A

b. to make a more efficient load carrying member

as with any beam, the deeper the member, the more efficient the beam. using a cored slap rather than a solid slab allows the depth to be increased without increasing the weight in the center of the beam where it is not needed

option A and D are also correct but B is the best choice

102
Q

Which of the following statements if FALSE?

a. type iii cememnt is often used for precast concrete members
b. precast concrete members can be a maximum of 14 ft wide
c. concrete used in precast members is typically 300 psi
d. conditions ar emosre controlled during the production of precast concrete members than they would be for similar structural systems

A

c. concrete used in precast members is typically 300 psi

concrete used in precast members is generally higher strength mix than the 300 psi concrete typically used for site cast applications

103
Q

How do you make precast panels on site?

A

Tilt-up construction

Pour on site & lift in place.

104
Q

Slump test

A

measures the consistency of the conrete

  • conrete is placed in a 12 in high cone and compacted with a rod
  • the distance the conrete slumps from the original 12 in is measured in inches
  • the amount of slump depends on how the conrete will be used (typically 2-6 in)
  • too much slump indicates too much water in the mix
105
Q

cylinder test

A

measures compresive strength

  • concrete is placed samples are put in cylinder molds that are 6 in diamter and 12 in high, and are moist cured and tested in the lab
  • cylinders are tested at specified number of days, normally 7 - 28 days; seven days are suually about 60-70% of the 28 day strength
106
Q

core cylinder test

A
  • used when a portion of the structure is placed and cured but needs to be tested
  • cylinder is drilled out of the conrete and tested in a lab to determie compressive strength
107
Q

kelly ball test

A
  • also known as the ball penetration test
  • a hemispheric mass of steel with a calibrated stem is dropped onto a slab of freshly laid concrete
  • the amount of penetartion of the ball into the concrete is measured and compared to one-half the values of the slump test
108
Q

impact hammer test

A
  • nondestructive way to test concrete strength after is has hardened
  • spring loaded plunger is smalled against a conrete surface, and the amount of rebound is measured.
  • the rebound gives an apporoximate measure of conrete strength
109
Q

k slump test

A
  • uses a 3/4 in tube that contains a floating scale
  • the tube is palced on the wet concrete and the scale is pushed into the mixture and released.
  • the distance the scale floats out is read directly and is a measure of the consitency of the conrete, comparable to the slump
110
Q

calcium chloride test

A

sometimes called the moisture dome test

  • used to measure moisture emission from conrete
  • a standard mass of calcium choloride is placed below a plastic cover and sealing it to the concrete floor
  • after the 60 to 72 hours the calcium chloride is weighed and compared to its pre test weight
111
Q

hygrometer

A
  • sometimes called the relative humidity test
  • determines the moisture emission by measuring the relative humidity of the atmosphere confined adjacent to the concrete floor
  • a pocket of air is trapped below a vapor impermeable box and a probe in the box measures RH
  • moisture sensitive flooring shouldn’t be installed unless RH is 75% or less
112
Q

polyethelene sheet test

A

qualitative test conducted by sealing an 18 in by 18 in sheet of plastic to the floor to trap excessive moisture

  • after a min. of 16 hours a visual inspection of the floor and sheet is performed
  • the presence of visible water indicates the concrete is insuficiently dry
113
Q

mat test

A

similar to polyethelene sheet test

a 24 in x 24 in smaple of vapor retardant floor finish is applied to floor with adhesive and edges are sealed with tape

  • after 72 hours, is floor is firmly bonded or difficult to remove, conrete is considered sufficiently dry
114
Q

electrical impedance test

A

-uses proprietary meaters to measure moisture by measuring conrete conductance and capacitance

115
Q

titration test

A

used to determine level of alkalinity in concrete

-involves grinding portions of the concrete, mixing with demineralized water and performing lab analysis to determine PH level

116
Q

scrubbed finish

A

the surface of the conrete is wetted and scrubbed with a wire or fiber bush to remove surface mortar and expose the coarse aggregate

117
Q

acid wash finish

A

the surface of the conrete is wetted with muriatic acid to expose and bring out the full color of the aggregate

118
Q

water jet finish

A

a high pressure water jet mixed with air is used to remove some of the mortar and expose the aggregate

119
Q

brush hammering

A

a brush hammer finish gives a rugged, heavy texture by removing a portion of the surface made with form liners

120
Q

grinding

A

finishing technique that smoothes out the surface of the concrete, similar to terrazzo in appearance

121
Q

applied finishes

A

appication of other materials, such as stucco

122
Q

sand blasted finish

A

produced by removing surface material of conrete

-exposes the fine and course aggregate to varying degrees

123
Q

smooth rubbed finish

A

concrete surface is wetted and rubbed with carborundum brick to produce a smooth uniform color

124
Q

grout cleaned

A

grout is applied over concrete and smoothed out

-conceals defects

125
Q

float finish

A
  • sandpaper like texture
  • appropriate of exterior surfaces
126
Q

light steel troweled finish

A

achieved by using a steel trowel several hours after floating

127
Q

hard steel troweled finish

A

continues the consolidation of the conrete and greatly densifies the top 1/8 in, making a very smooth surface

128
Q

broom finish

A
  • achieved by running a broom over the surface of the conrete
  • process dislodges fine aggregate and produces slip resistant surface on outdoor slabs
129
Q

super flat floor finish

A
  • hard steel trowl finish
  • used in industrial warehouses where forklift vehicles are used
  • vehicles must travel on very smooth and level floors.
130
Q

temperature sensitive materials, such as sealants should not be applied when the temperature dips below..

A

…4 C deg

EXAC EXAM 3 (14 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions