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Civi321 Midterm > Exam Midterm 1 > Flashcards

Exam Midterm 1 Flashcards

1
Q

What are the non-mechanical properties?

A
  • density and unit weight
  • thermal expansion
  • surface properties ——> abbrasion & wear resistance
    ——> surface texture
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2
Q

What is sustainable design in engineering

A

development that meets the needs of the present without
compromising the ability of future generations to
meet their own needs.

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3
Q

WHAT are the uses of
Aggregate in Civil Engineering Materials?

A
  • Represent 60-75% of volume concrete
  • made of gravel + sand
  • construction of asphalte, concrete, railroad,
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4
Q

WHY do we use Aggregate?

A
  • For Significant Economic Benefits for the final cost
  • Stable Aggregate results in Volume stability (stable in volume)
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5
Q

There are 2 types of aggregate. Name them

A
  • fine aggregate
  • coarse aggregate
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6
Q

What are the characteristics of fine aggregate

A
  • made of sand or crush stone
  • particle size <5mm
  • 35% to 45% of total mass or volume aggregate
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7
Q

What are the characteristics of coarse aggregate

A
  • gravel and crushed stone
  • particle size 5mm and more
  • typically between 9.5mm and 37.5mm
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8
Q

What is the Effect of Particle size on the Surface Area?

A

The smaller the Particle size, the higher the Surface Area

E.g : larger coarse aggregate results in lower surface area

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9
Q

What is the cement Requirement for large coarse aggregate ?

A

Less cement is required in mixtures having large coarse aggregate

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10
Q

What is the water requirement for larger coarse aggregate?

A

Less water is required in mixtures having large coarse
aggregate

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11
Q

What is the fineness modulus (FM) ?

A

the cumulative percentages of aggregate retained on each of standard sieves
and dividing the sum by 100

  • FM = 2.8 to 3.10 —> coarse
  • FM = 2.5 TO 2.8 —> MEDIUM
  • FM = 2.3 to 2.5 —> fine
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12
Q

What happen when different particle size of aggregate are put together ?

A

When different sizes are combined, the void-content decreases

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13
Q

Name some aggregate & concrete problems

A
  • D cracking : cracking caused by freeze-thaw and deterioration within concrete
  • harmful reactive substance
  • popouts : breaking away of a small fragment of concrete surface due to internal pressure
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14
Q

What are the 2 forms of Alkali- Aggregate Reactivity ( AAR )

A
  • Alkali-Silica Reaction (ASR) :

•Network of cracks
• Closed or spalled joints
• Relative displacements
• Fragments breaking out of the surface
(popouts)

  • Alkali-Carbonate Reaction (ACR ) : composition not very common

***ASR is of more concern than ACR because the occurrence of aggregates containing reactive silica minerals is more common

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15
Q

How To Control Alkali-Silica Reaction ASR ?

A

Add on the mixture :

•Non-reactive aggregates
•Limit alkali loading
• Lithium-based admixtures
• Supplementary cementing materials
•Limestone sweetening (~30% replacement of
reactive aggregate with crushed limestone

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16
Q

How To Control Alkali-Carbonate Reaction (ACR) ?

A

•Selective quarrying to avoid reactive aggregate

•Limit aggregate size to smallest practica

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17
Q

How do you keep aggregates in good state ?

A

• Store in a way to Avoid contamination & Avoid segregation

• Larger aggregates segregate more

• Store sizes separately to reduce segregation

• Dry aggregates segregate more

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18
Q

Explain the manufacture of portland cement

A

-Raw material Storage
-Raw material Grinding
-Raw material Blending
-Raw material Preheating
-Raw material Cooking in Kiln
-Clinker storage/cooling
-Gypsum addition
-Cement grinding
-Cement storage/loading

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19
Q

What are the 4 components of cement ?

A
  • lime
  • Silica
  • alumina
  • Iron oxide
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20
Q

During the manufacture of portland cement, what is happening inside the kiln at 700°C, 700-900°C, 1150-1200°C & 1200-1350°C

A
  • 700 °C : Raw materials are free-flowing powder. Solid particle with no reaction between particle
  • 700-900°C: Raw materials are free-flowing powder. Solid particle with no reaction between particle
  • 1150-1200°C : particle starting to become sticky & reaction between solid particle happen
  • 1200-1350°C : particles held together by the liquid as the particle agglomerate. Capilary forces of the liquid keep particle together
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21
Q

Inside the Kiln, calcium combines with other components of the
raw mix to form 4 principal compounds of cement, what are they??

A
  • Tricalcium silicate 3CaO•SiO2 (C3S)
  • Dicalcium silicate 2CaO•SiO2 (C2S)
  • Tricalcium aluminate 3CaO•Al2O3 (C3A)
  • Tetracalcium aluminoferrite 4CaO•Al2O3•Fe2O3 (C4AF)
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22
Q

What are the 5 Types of Cement?

A
  • type I : normal
  • type II : moderate sulfate resistance (lower C3A)
  • type III : high early strength (ground finer)
  • type IV : low heat of hydration (high C2S-C4AF and low C3S-C3A)
  • type V : High surface resistance (lower C3A)
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23
Q

What is the use of type I cement

A

For general use (90% of used cement)

Ex : concrete bridges, buildings, highway pavement

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24
Q

What is the use of type II & V cement ?

A

elements exposed to high surface soils

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25
Q

What is the use of type III cement

A

used where early concrete strength is needed

ex: cold weather concreting

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26
Q

What is White cement ?

A

It is a cement with low concentration of C4AF

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27
Q

What are the type of special cement ?

A
  • White cement (low C4HF)
  • Masonry cement
  • Oil Well Cement (use in high temp)
  • Finely-Ground Cements (Ultrafine Cements); strength for foundation
  • Expansive Cement; used when shrinkage a problem
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28
Q

What CSH means ?

A

It means calcium Silicate Hydrate

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29
Q

How do you apply cement test ?

A
  • —–Quality Control :
    chemical aspects
    Physical aspects

——-Performance of cement :
Fresh properties
Hardened properties

30
Q

What is causing the compressive strength of cement ?

A

—cement composition

— Fineness of the cement

31
Q

What is heat of hydration ?

A

Measures heat generared from cement as it hydrates

32
Q

Name 2 compounds of industrial pozzolans ?

A
  • Fly Ash
  • Silica fume
33
Q

Name 2 compounds of natural pozzolans ?

A
  • volcanic
  • Rice Husk
34
Q

What is pozzolanic reaction ?

A

it is the chemical reaction that occurs in Portland Cement upon the addition of pozzolans

35
Q

physical filler effect

A

SCMs with adequate particle size distribution can lead to a
physical filler effect (reduction of porosity between cement
grains).

36
Q

WHAT is Transition Zone?

A

Transition zone is a thin layer between the bulk hydrated cement
paste and the aggregate particles in concrete.

This zone is the
weakest component in concrete, and it is also the most permeable
area.

37
Q

Silica fume product forms ?

A

-As-produced powder
•Extremely fine and dusty
•Self-agglomerating /create small lumps

Silica fume slurry
50 - 52% solids (as-produced silica fume dispersed
in water)

Densified silica fume
•Reversible agglomeration process
•Bulk transportation economical

38
Q

how to calculate the strength activity index ?

A

Strength activity index = (A/B) × 100

A = average compressive strength of blended cement mixture cubes

B = average compressive strength of pure cement mixture cubes.

39
Q

What is the Benefits to use high strength concrete

A

Using high strength
concrete can lead to
savings in space and steel

40
Q

what are the 2 classes of fly ash ?

A

class F fly ash :
- low calcium oxide fly ash
- Produced by calcination of bituminous coal

High calcium oxide fly ash
• Produced by calcination of
subbituminous coal or lignite.
• Has pozzolanic + cementitious
properties

41
Q

what is the setting time
for fly ash ?

A

• Fly ash usually hydrates slowly
•Setting time is moderately or severely extended
depending upon properties of fly ash, temperature and
mixture proportions.
•Finer fly ash results …………………..shorter setting time
• Higher CaO content …………………..shorter setting time

42
Q

what’s the effect of flyash
on workability ?

A
  • Fly ash addition generally
    improve the workability of
    concretes.

-At similar slump fly ash
concrete is more workable
than normal concrete

43
Q

explain what slag is?

A

By-product of the metallurgical industry . the most used in cement is iron blast furnace slag

conventional slag is crystalline & used as aggregates

44
Q

what is the definition of admixture ?

A

Chemical admixtures are the ingredients in
concrete other than Portland cement,
water, and aggregate that are added to the
mix.

45
Q

what are the characteristic of admixture ?

A
  • Modify properties of hardened concrete
  • increase early strength ( accelerating admixture )
  • reduce water content ( water reducing ad mixture)
46
Q

what are the advantages of
admixture?

A
  • Modify the properties of hardened concrete
     Accelerating admixtures (Increase Early strength)
     Water-reducing admixtures (Reduce water content)
  • Reduce concrete construction cost
     Accelerating admixtures (Saving time)
     Water-reducing admixtures (Increase Workability)
  • Overcome emergencies during concrete operations
     Accelerating admixtures (Cold weather casting)
     Water-reducing admixtures (Narrow cross-sections)
47
Q

type of admixture

A
  • Air entrainement
  • Corrosion inhibitor
  • Asr inhibitors
  • shrinkage reducers
48
Q

what happen when adding
accelerating admixture ?

A

Accelerate the hydration rate so Early strength and setting

The faster the hydration reaction - - - - - - >The higher the strength &
The shorter the setting time

49
Q

what are the types of
accelerators ?

A

Types:
Alkali hydroxides
Silicates
organic compounds
Calcium nitrate,
Sodium chloride
Calcium chloride
…etc.

50
Q

when do we use an accelerator

A

It is used in cold weather to accelerate construction

it reduce :
- curing time
- formwork removal time

51
Q

what are the characteristic of calcium chloride ?

A
  • accelerate cement hydration
  • faster hardening and strength gain
    -The exact mechanism of this catalytic effect is not well understood
52
Q

what is the Effect of calcium chloride on Microstructure?

A

Change from fibrous structure of CSH to spherulite
or lace-like structure is reported by researchers

53
Q

what are the Effect of calcium chlor ide on Fresh properties?

A

• Increases the workability.
• Reduces significantly both initial and final setting
time)
• Reduces both bleeding rate and bleeding capacity

54
Q

what are the Effect of calcium chloride on Mechanical Properties ?

A

• Accelerates compressive strength gain at early stage.

• Most literature indicates that the long-term strength is lower than that of a non-accelerated control mixture.

55
Q

what is the effect of calcium chloride on durability ?

A

• Chlorides in CaCl2 increase corrosion of steel. CaCl2 usually banned in pre-stressed concrete.

• Drying shrinkage of concrete increases when CaCl2 is used.

• Alkali aggregate expansion is increased by addition of CaCl2

• Addition of CaCl2 leads to lower durability under sulfate attack

56
Q

what is non chloride accelerators?

A

Retarding admixture

57
Q

the main objective of water reducer admixture

A

_ reduce water - cement ratio

  • reduce cement content
58
Q

Effects of water reducer admixture on fresh concrete

A

• Workability is improved, less cold joints and air pockets
• Most water reducers decrease the bleeding rate and
capacity.
• Heat of hydration: Delay the rapid heat evolution

59
Q

Effects of water reducer admixture on durability

A

• Increase frost durability (39%)
• Less expansion under sulfate attack
• Decrease chloride diffusion and enhance corrosion
durability

60
Q

Effects of water reducer admixture on hardened concrete

A

• Early strength can be decreased due to retardingeffect, but 28 day strength is increased beyond what
could be expected from reduction of w/c ratio.

• Better dispersion of cement grains leads to better
particle packing and higher degree of hydration at later
ages.

61
Q

what is super- plasticirer?

A

Produce flowing concrete with high slump (≥ 190 mm

62
Q

what is cemment hydration ?

A

Chemical reactions between cement and water

63
Q

what is air-entraining admixture ?

A

The process by which small air bubbles are incorporated
into concrete at the mixing stage and remain dispersed in
concrete at the hard state.

64
Q

what’s the chemical composition of Air entraining?

A

surfactants (short for surface active substances)

Surfacactant is material whose molecules adsorb
strongly on air-water or air-solid interfaces.

65
Q

Factors Affecting Amount of AEA

A

• AEA dosage

• Finely divided materials (silica fume, etc.) cause a drop
in the EA: less water available for bubble formation +
AEA is adsorbed on high surface area

• Coarse aggregate: max size increases, air requirement
decreases.

• Fine aggregate: the higher the proportion of fine
aggregate in the total aggregate the more air generated

• Higher temperature
of concrete leads to
lower air content and
vise versa. Effect is
more clear at higher
slumps

66
Q

what is deterioration ?

A

• Physical manifestation of failure of a material (e.g., cracking,
spalling, delamination, pitting)

• Decomposition of material (disintegration, weathering)

67
Q

What are the causes
for concrete
Deterioration?

A

3 types

  • physical deterioration: frost, cracking, fire, abrasion

chemical deterioration : sulphate, sea water, leaching, AAR

Reinforcement corrosion : chlorides, carbonation

68
Q

Manifestation of Freeze/Thaw Deterioration

A

•Most common signs of freeze/thaw deterioration
Development of cracks sub-parallel to the surface
Cracks throughout the concrete (delamination)
Gaps around aggregates in the surface regions of concrete.

•Concrete is usually crumbled after prolonged exposure.

•Aggregate related damage (D-cracking) and paste related damage

•Scaling -surface deterioration

69
Q

How to Protect Concrete?

A

•Keep concrete dry (not always possible)
•Reduce the amount of freezable water (by reducing capillary
porosity, feasible)
•Provide a relief for pressure (air entrainment)
•Combinations of the above

70
Q

what is the freezing_thawing
cycle?

A
  • water filled crack
  • freezes to ice
  • rupture of structure
71
Q

what is the use of de-icing salts

A

Used because they reduce the melting temperature of ice and snow

72
Q

what is the cause of corosion?

A

chloride

Civi321 Midterm (1 decks)

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