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CIVIL 250 - Phils > it > Flashcards

it Flashcards

1
Q

how much concrete used pp py

A

1 tonnes

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2
Q

concrete consists of

A

binder and filler

cement, water, fine and coarse aggregate

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3
Q

mortar consists of

A

cement, water, fine aggregate

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4
Q

grout consists of

A

cement, water, fine aggregates, small coarse aggregates

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5
Q

benefits of concrete

A 
high compressive strength
durable
cheap
can be cast on site and pre cast
fire resistant
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6
Q

negatives of concrete

A

low strength to weight ratio
brittle
low tensile strength
volumetric instability

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7
Q

usual density of concrete

A

2400kg/m^3

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8
Q

Early cement types

A 
Lime cement (non hydraulic) - harden upon drying, water resistance due to later reaction, Colloseum, Pont du Gard
Volcanic ash (hydraulic) - Pantheon
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9
Q

Process of making Portland cement (dry)

A

Combine limestone, clay/silt in furnace at temperature 1400-1600 (usually rotary furnace) to create clinker
gypsum added to clinker
ground to produce powder

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10
Q

Composition of clinker

A

calcium silicates, calcium aluminates

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11
Q

Clay/silt vs ______

A

vs pure silica
Pure silica expensive
Pure silica takes more energy to react (2000)
Pure silica creates a cement with fewer impurities (aluminium oxides etc) therefore stronger cement

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12
Q

Location of cement factories

A

Close to limestone quarries

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13
Q

Process of making Portland cement (wet)

A

mix raw ingredients and add water to form a slurry - ensures good and mechanically easy mixing of limestone and clay/silts
high energies needed to dry out slurry and turn to clinker

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14
Q

amount of global CO2 emissions

A

5%

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15
Q

gypsum

A

controls setting rate of compounds in cement (so as to not cause differential heating or boiling water)

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16
Q

rate of reaction and heat release of C3S, C2S, C3A, C4AF

A

C3S - medium, medium
C2S - low, low
C3A - high, high
C4AF - medium, medium

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17
Q

Cement production controlled in NZ by

A

NZS3122

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18
Q

GP

A

general purpose

mostly Portland cement (<10% SCMs)

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19
Q

GB

A

general blended

Portland cement plus >10% SCMs

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20
Q

SR

A

sulphate resisting concrete

C3A < 5%

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21
Q

SL

A

shrinkage limited cement

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22
Q

HE

A

high early strength
increase C3S
decrease C2S
OR grind better, increase SA

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23
Q

LH

A

low heat
decrease C3S and C2S
increase C3A and C4AF

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24
Q

Water that can’t be used in cement making

A 
water with dissolved solids
water with suspended solids
 - chlorides - increase ROR, corrosion of steel
 - sulphates - decrease strength
organic matter - leaves void
pH < 3
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25
Q

Important qualities of aggregates

A 
hard and strong
free of impurities (no slip planes)
chemically stable
thermally stable
durable
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26
Q

Types of aggregates

A

Natural
Crushed
Artificial

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27
Q

size between fine and coarse aggregates

A

4.75mm

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28
Q

fineness modulus equation

A

sum of cumulative % retained on sieves / 100

29
Q

How to describe aggregates

A

fineness modulus

size of largest aggregate (usually 19mm)

30
Q

FM large vs small

A

FM large means more fines

31
Q

Maximum aggregate size for given purpose

A

20% size of smallest part of mould

75% size of space between rebar

32
Q

States of saturation of aggregate

A

oven dry
air dry
saturated surface dry
wet

33
Q

AAR

A

alkali aggregate reactions

expansive reactions between alkali and aggregate which cause expansion of concrete and subsequent cracking

34
Q

ASR

A

alkali silica reactions

causes a gel to form which then absorbs water and causes expansion

35
Q

What is needed for an ASR reaction

A

moisture
alkalinity
reactive mineral or aggregate

36
Q

How to stop ASR

A

cant be stopped

don’t use high silicate aggregates during construction

37
Q

Like ipenz but for cement

A

Cement and Concrete Association (CCANZ)

38
Q

Main factors of concrete

A

economic viability
compressive strength
workability

39
Q

w/c?
w/c required for complete hydration?
why go less?

A

water-cement ratio (weight, not volume)
0.42
If this water-cement ratio is used then there will be quite a lot of void space left in the material once all the water has undergone hydration reactions which will decrease the strength of the concrete
Less water is used, knowing incomplete hydration, to improve the strength of the material

40
Q

Type of admixtures

A

Mineral - Pozzolans, cementitious materials
Chemical - Air entraining agents, Set controlling admixtures (Set retarders, Set accelerators, Set extenders), Plasticisers

41
Q

Benefits of mineral admixtures

A 
economic
workability
durability
reduced heat of hydration
environmental
42
Q

Examples of mineral admixtures

A

SCMs
Cementitious materials:
Slag
Pozzolans:
Fly Ash (coal power stations, Huntly) - increased durability and workability, decreased ROR
Silica fume (white silica, Rotorua) - fine particles of filling voids, increased durability and strength
Pumicite

43
Q

Pozzolan reaction

A

react and harden only when in contact the products of the ordinary cementitious hydration reaction
CS + H -> CSH + CH
CH + S + H -> CSH

44
Q

Examples of chemical admixtures

A

Air entraining agents:
air void for cold climates
increased workability, decreased strength

Set controlling admixtures:

Set retarders - slow the setting:
placing in hot conditions
exposed finish
account of delay between pours

Set accelerators:
placing in cold conditions
shotcreting
time critical
leaks

Set extenders - pause and restart setting:
transport over time times

Plasticiser:
reduce water required more workability
cement particles negatively charger so they repel each other and don’t clump together

45
Q

Stages of concreting

A

mixing
placing
vibration
curing

46
Q

Details to manufacturer

A 
compressive strength
durability requirements
maximum aggregate size/fineness modulus
nominal slump
pumped or not
site map/access
47
Q

How to place concrete

A

crane
truck
pump
conveyer

48
Q

Stopping segregation

A

No shaking
vertical fall less than 1 - 1.5m
low points first, pull towards

49
Q

Ensuring quality of concrete

A

slump test start, middle and end of load

average results

50
Q

Type of fluid concrete is

A

Bingham fluid

51
Q

Types of vibration

A

poker vibrator
vibrating screed
vibrating formwork

52
Q

What to do when using poker vibrator

A

don’t touch formwork
10 seconds
submerge as deep as if goes (fully)
don’t mix

53
Q

Effects of segregation

A

upper layer of cement paste

low abrasion resistance, strength and durability

54
Q

Curing examples

A

Controlling loss of water and temperature
Ponding and spraying water
Covering with plastic to prevent water escaping
Curing compound

55
Q

Bleeding definition

A

upward movement of water through concrete after it has been compacted but before it has set
bleeding is expected

56
Q

Issues with excessive bleeding

A

durability of top layer reduces due to increased w/c ratio
small pits due to bleed channels
rapid evaporation can form crazing

57
Q

How to decrease bleeding

A

decreased water content

increase fine aggregate

58
Q

Workability subsets

A

compatibility
mobility
stability (cohesive and homogenous)

59
Q

study of materials under stress

A

Rheology

60
Q

Types of shrinkage

A

carbonation
drying
plastic

61
Q

SR

A

sulfate resisting cement

lowering C3S content

62
Q

SL

A

shrinkage limit cement

small volumetric change

63
Q

cemetn guidelines

A

NZS3122-2009

64
Q

why not sea water to set concrete

A

chloride ions accelerate setting, leading to rapid strength gain, but sulfates reduce the strength of the concrete

65
Q

ASR condition

A

high silica content
gel is formed which absorbs water and then expands
ASR impossible to stop
sufficient moisutre, sufficient alkalinity, presence of reactive mineral/aggregate

66
Q

fineness modulus

A

sum of all cumulative % retained divided by 100

67
Q

maximum aggregate size

A

nominal value where 5-10% of aggregate is retained on this sieve size

68
Q

chemical symbols for compounds in cement

A

tricalcium silicate C3S
dicalcium silicate C2S
tricalcium aluminate C3A
dicalcium aluminate C2A

69
Q

workability

A

compactability
mobility
stability

CIVIL 250 - Phils (1 decks)

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