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ENCN221 > Bitumen and Asphalt Mixes > Flashcards

Bitumen and Asphalt Mixes Flashcards

1
Q

Asphalt Types

A
  • asphalt cements: generally refinery produced material, air blown asphalt cements
  • cutbacks: asphalt cements “cut” with petroleum solvents
  • emulsions: mixture of asphalt cement, water, and emulsifying agent
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2
Q

Problems with Asphalt Pavements

A
  • fatigue cracks
  • thermal cracks
  • transverse cracks
  • shoving
  • pothole and ravelling
  • bleeding
  • rutting
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3
Q

bitumen consistency

A

used to describe the degree of fluidity or plasticity of bitumen

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4
Q

soft asphalt

A

low viscosity - used in cold climates to avoid thermal cracking

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5
Q

hard asphalt

A

high viscosity - used in hot climates to avoid rutting

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6
Q

viscosity

A

ratio between applied shear stress and rate of shear

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7
Q

Penetration Testing: advantages

A
  • grades asphalt near average in-service temp.
  • fast
  • precision well established
  • temperature susceptibility can be determined
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8
Q

Penetration Testing: disadvantages

A
  • empirical test

- does not reflect differences in asphalts

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9
Q

Viscosity Testing: advantages

A
  • fundamental property
  • based on max. pavement surface temp,
  • test method precision established
  • temperature susceptibility is controlled
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10
Q

Viscosity Testing: disadvantages

A
  • not applicable for non-Newtonian materials (polymer modified binders)
  • wide range of properties for same grade
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11
Q

Ductility Test

A

measures the distance in centimeters that a standard briquette of asphalt cement will stretch before breaking

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12
Q

Softening Point Test

A

measures the temperature at which the bitumen will flow under its own weight

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13
Q

Solubility Test

A

used to measure the bitumen purity and quantify the amount of impurities

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14
Q

temperature susceptibility

A

the rate at which the consistency of bitumen changes with a change in temperature (denoted by A)

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15
Q

P.I

A
  • lower P.I. = higher temperature susceptibility
  • higher P.I. = less sensitive to temperature variation
  • most paving bitumens have P.I. between -1 and +1
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16
Q

viscosity-temperature susceptibility (VTS)

A
  • the slope of the log log (viscosity a 135oC) and log (temperature in K)
  • the higher the VTS, the higher the temperature susceptibility
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17
Q

Types of Mix Design

A
  • Marshall Mix Design
  • Hveem Mix Design
  • Superpave Mix Design
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18
Q

Marshall Mix Design

A
  • uses impact hammer to prepare specimens
  • determine stability with Marshall stabilometer
  • uses volumetrics to select optimum asphalt content
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19
Q

Hveem Mix Design

A
  • uses kneading compactor to prepare specimens
  • determine stability with Hveem stabilometer
  • visual observation, volumetrics and stability used to select optimum bitumen content
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20
Q

Superpave Mix Design

A
  • uses gyratory compactor to prepare specimens

- uses volumetric analysis to select optimum bitumen content

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21
Q

Vse

A

effective volume of aggregate

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22
Q

Vsb

A

bulk volume of aggregate

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23
Q

Vb

A

total volume of bitumen

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24
Q

Vba

A

volume of absorbed bitumen

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25
Q

Vbe

A

volume of effective bitumen

26
Q

Vmb

A

total or bulk volume of mix

27
Q

Vmm

A

volume that yields maximum specific gravity - voidless volume of mix

28
Q

Pb

A

percent of all bitumen by total weight of mix

29
Q

Pbe

A

percent of effective bitumen

30
Q

Pba

A

percent of absorbed bitumen

31
Q

Ps

A

percent of aggregate in total mix

Ps = 1 - Pb

32
Q

Gsb

A

bulk specific gravity of aggregate

33
Q

Gse

A

effective specific gravity of aggregate

34
Q

Gmb

A

bulk specific gravity of mix

35
Q

Gmm

A

maximum specific gravity of mix

36
Q

VFB

A

voids filled with bitumen

37
Q

VA

A

volume of air voids in mix

38
Q

VMA

A

volume of voids in mineral aggregate

39
Q

Key components of mix design

A
  • laboratory compaction of trial mix specimen
  • stability (strength) and volumetric testing
  • analysis of results
  • evaluation of moisture susceptibility
40
Q

Purpose of compaction

A

To simulate the inplace density of hot mix asphalt after it had endured several years of traffic

41
Q

Compaction Methods

A
  • impact compaction (Marshall Mix Design)
  • kneading compaction (Hveem Mix Design)
  • gyratory compaction (several forms available)
  • vibratory impact hammer
42
Q

Marshall Specimen

A

102mm diameter and 64mm height specimens

43
Q

Marshal mix aggregate size

A

max. 25mm

44
Q

marshall mix - bulk specific gravity determination

A 
calculated by finding:
- dry weight of specimen in air, A
- submerged weight of specimen in water, C
- Saturated Surface Dry (SSD) weight, B
Gmb = A/(B-C)
45
Q

marshall mix - Stability and Flow Test

A
  1. Immerse specimen in water bath (60oC) for 30 to 40 mins
    2, Make sure breaking head clean and well lubricated
  2. Remove specimen from water bath, towel dry and centre on breaking head
  3. apply constant rate of deformation 51mm/min and record max load to be Marshall stability and max deformation to be flow.
    (time from removing from water bath to end of testing
46
Q

Bitumen Testing

A
  1. Consistency Testing
  2. Durability
  3. Safety
  4. Purity
47
Q

Consistency Testing

A
  • Penetration Testing
  • Viscosity
  • Ductility
48
Q

Durability

A
  • Short Term Aging (RTFOT)

- Long Term Aging (PAV)

49
Q

Safety

A

Flash Point Cleveland Open Cup

50
Q

Purity

A

Solubility Test

51
Q

Short Term Binder Aging

A

Rolling Thin Film Oven (RTFO)

  • simulates aging from hot mixing and construction
  • bitumen kept in high temp and viscosity and penetration measured before and after testing
52
Q

Long Term Aging

A

Pressure Aging Vessel (PAV)

  • simulates aging of a bitumen binder after 7 to 10 years
  • specimen kept at high temperature and high pressure
53
Q

Asphalt Grading

A 
HISTORY
1. Penetration Grading
2. Viscosity Grading
3. Aged Residue Grading
CURRENT
Performance Grading (PG)
54
Q

Emulsion

A
  • mix of asphalt cement, water and emulsifier
  • emulsifier gives surface charge to asphalt droplets suspended in water medium
  • safe
  • cheap
  • -85oC (safe)
55
Q

anionic aggregate

A

limestones

56
Q

cationic aggregate

A

silica gravels

57
Q

Cutback

A
  • asphalt cement “cut” with petroleum solvents
  • bad for environment
  • flammable
  • expensive
  • high temperatures of application (150oC)
  • dangerous
58
Q

Asphalt Cements

A
  • generally refinery produced material

- air blown asphalt cements

59
Q

Newtonian Fluid

A

constant viscosity (water)

60
Q

non-Newtonian Fluid

A

changing viscosity

  • polymer modified binders
  • cornflour
61
Q

Compaction Viscosity

A

280+-30 MPa.s

62
Q

Mixing Viscosity

A

170+-20 MPa.s

ENCN221 (6 decks)

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