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CIVE 202 > Concrete-General > Flashcards

Concrete-General Flashcards

1
Q

What is concrete?

A

Concrete is a particulate composite consisting of dispersed
particles (aggregates) surrounded and bound together by a
continuous matrix (hydrated cement paste)

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2
Q

How is concrete important

A

Concrete the most heavily used man-made material in the world.

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3
Q

cite the three phase of concrete

A

-hydrated cement paste (hcp)
-aggregates
-interfacial transition zone (itz)

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4
Q

Ingredients of concrete (4)

A
  • Portland Cement
  • Water
  • Aggregates
  • Admixtures and SCMs
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5
Q

what is paste mortar and concrete

A

paste=cement+water
mortar=paste+fine aggregate
concrete=mortar+coarse aggregate

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6
Q

important discoveries historically

A

greeks use lime
greeks use volcanic ash
romans use pottery and bricks as aggregate and ash- concrete hardens under water
dirty limestones (contain high proportions of clay)

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7
Q

Manufacture of Portland Cement
(raw materials (5categories + 5 steps)

A

Categories: calcium, silicates, aluminium, iron, sulphates)
Raw materials: Limestone, Sand, Clay and Iron Ore
Processing: quarrying, crushing and mixing
Firing: burned and calcined at 450°C (produces Clinker)
Gypsum is added
Grinding(1-100micrometer)
=Portland Cement

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8
Q

why use chains for heat exchanger

A

use heat exchanger chains to shorten the kiln length

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9
Q

Effect of tricalcium silicate

A

early strength (C3S)

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10
Q

Effect of dicalcium silicate

A

Ultimate strength (C2S)

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11
Q

Effect of tricalcium aluminate

A

Flux, Fast Set, Sulfate Reactive (C3A)

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12
Q

Effect of tetracalcium aluminoferrite

A

flux (C4AF)

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13
Q

Effect of Gypsum

A

Prevents Fast Set (CSH2)

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14
Q

Hydration of cement is

A

Exothermic

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15
Q

Calcium Silicates+Water

A

Calcium Silicate Hydrate+Calcium Hydroxide

(CSH+CH)

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16
Q

Tricalcium Alumiante + Gypsum + Water

A

Ettringite

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17
Q

Ettringite + Tricalcium Aluminate + Water

A

Monosulfoaluminate

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18
Q

Tetracalcium Aluminoferrite + Calcium Hydroxide + Water

A

Tetracalcium Aluminate Hydrate + Ferric-Aluminum Hydroxide
(Flux)

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19
Q

C-S-H influence

A

provide major cohesive force but weaker because of microporosity. dry concrete is stronger than wet (van der waals bonds)

very insoluble water in micropores does not freeze and has low mobility (low permeability)

water loss from micropores cause shrinkage on drying and creep on loading at room temp

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20
Q

calcium hydroxide influence

A

Contributes by reducing porosity. Cleavage may limit strength of high strength pastes

blocks capillary pores and hence lowers permeability. slowly leached by water which causes efflorescence and increases permeability.

is dimensionally stable will restrain c-s-h deformations

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21
Q

C4ASH12 influence

A

causes sulfate attack by reforming ettringite and causing expansion

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22
Q

unhydrated cement effects

A

restrains c-s-h deformations

renewed hydration may cause autogeneous healing of internal microcracks

23
Q

Capillary pores influence on concrete

A

total porosity is the major factor influencing strength.

fine pores contribute to shrinkage and creep

porosity influences permeability and diffusivity. large pores increase water flow through concrete.

24
Q

c3s influence

A

controls normal setting

temp rise during hydration

responsible for early strength

creep and shrinkage

leaching of Ca(OH)2

25
Q

c3a effects

A

cause premature stiffening

temp rise during hydration

minor effects on shrink and creep

26
Q

c2s effects

A

long term strength

major contribution to shrink and creep

27
Q

c3a effect

A

leads to sulfate attack

28
Q

interfacial transition zone

A

The microstructure of hcp is highly modified in the vicinity of
inclusions (aggregate, fiber, steel).
Primary features:
- Increased porosity
- Less unreacted cement

29
Q

wall effect

A

inability of cement particles to pack efficiently
in close proximity to the embedment.
Raises local W/C ratio at the interface. Further rise in W/C due to localized bleeding.

30
Q

Standard Portland Cement types

A

general purpose GU
moderate heat of hydration MH
moderate sulfate resistance MS
high early strength HE
low heat of hydration LH
sulfate resistance HS

31
Q

GU use

A

roads, bridges, floors, structures

(everything)

32
Q

MS or HS use

A

concrete exposed to sulfates in soil or water

33
Q

LH and MH types of cement used where

A

where there is lots of water (dam, dikes, buoys)

34
Q

what are mineral admixtures

A

Finely ground solid materials added to the concrete, either as a separate ingredient or blended with the cement.

35
Q

3 reasons to use admixtures

A
  1. Replace cement
  2. Improve workability
  3. Enhance durability
36
Q

3 categories of admixtures

A
  1. Pozzolanic
  2. Cementitious
  3. Non-reactive
37
Q

Supplementary cementing materials (SCM)

A

Mineral admixtures added to the concrete, either as a separate ingredient or blended with the cement, in which part of the cement is replaced by the mineral admixture.

38
Q

2 types of SCM

A
  1. pozzolanic
  2. cementitious
39
Q

Blast Furnace Slag

A

waste from steel blast furnaces, quenched
in water to form glass
Chemically react with water to produce aluminum-substituted calcium silicate hydrate
Will react with water alone

40
Q

most common types of pozzolanic SCMs

A

fly ash
silica fume
calcined clay

41
Q

how do pozzolanic SCMs work

A

Chemically react with calcium hydroxide and water to produce calcium silicate hydrate.
Will not react with water alone

42
Q

calcium silicates + water

A

calcium silicate hydrate + calcium hydroxide

43
Q

benefits of SCMs(6)

A

economics
environmentally friendly
lower heat of hydration
improved durability
improved workability
increased strength

44
Q

SCM replacement rate

A

Ranges from 5% to 70% of total cementitious material

45
Q

chemical admixtures

A

Materials added to the concrete in small amounts, usually dissolved in the mixing water, which bring about a desired effect on the physical properties of the fresh and/or hardened concrete.

46
Q

Common Types of chemical admixtures (4)

A

Water Reducing
Air Entraining
Set Retarding
Set Accelerating

47
Q

water reducing admixture

A

Surfactants which adsorb at the solid-water interface and prevent
the cement grains from flocculating in water

48
Q

two types of water reducing admixtures and explain

A

plasticizer- increase in workability at same w/c ratio

water reducer- decrease in w/c ratio at same workability

49
Q

air entraining admixtures

A

act at the air water interface causing water to foam during mixing.
bubbles remain stable and are locked into cement paste during hardening

50
Q

Advantages (4)
Disdvantage (1)

(air entraining)

A

Improves freeze/thaw resistance
Improves sulfate resistance
Improves workability (higher slump)
Reduces Segregation

Reduced Strength (10-20%)

51
Q

set retarding admixtures

A

Delay the setting of the concrete by slowing down the early hydration reactions and thus the rate of early strength development

52
Q

properties of set retarding admixtures (5)

A

does not affect ultimate strength
does not affect time to ultimate strength
may not affect slump loss

used for hot weather conditions
long delays between mixing and casting

53
Q

set accelerating admixtures

A

Accelerate the setting of concrete by speeding up the early hydration reactions and thus the rate of early strength development.

CIVE 202 (12 decks)

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