Bitumen and Asphalt Mixes Flashcards
(62 cards)
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
2
Q
Problems with Asphalt Pavements
A
- fatigue cracks
- thermal cracks
- transverse cracks
- shoving
- pothole and ravelling
- bleeding
- rutting
3
Q
bitumen consistency
A
used to describe the degree of fluidity or plasticity of bitumen
4
Q
soft asphalt
A
low viscosity - used in cold climates to avoid thermal cracking
5
Q
hard asphalt
A
high viscosity - used in hot climates to avoid rutting
6
Q
viscosity
A
ratio between applied shear stress and rate of shear
7
Q
Penetration Testing: advantages
A
- grades asphalt near average in-service temp.
- fast
- precision well established
- temperature susceptibility can be determined
8
Q
Penetration Testing: disadvantages
A
- empirical test
- does not reflect differences in asphalts
9
Q
Viscosity Testing: advantages
A
- fundamental property
- based on max. pavement surface temp,
- test method precision established
- temperature susceptibility is controlled
10
Q
Viscosity Testing: disadvantages
A
- not applicable for non-Newtonian materials (polymer modified binders)
- wide range of properties for same grade
11
Q
Ductility Test
A
measures the distance in centimeters that a standard briquette of asphalt cement will stretch before breaking
12
Q
Softening Point Test
A
measures the temperature at which the bitumen will flow under its own weight
13
Q
Solubility Test
A
used to measure the bitumen purity and quantify the amount of impurities
14
Q
temperature susceptibility
A
the rate at which the consistency of bitumen changes with a change in temperature (denoted by A)
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
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
17
Q
Types of Mix Design
A
- Marshall Mix Design
- Hveem Mix Design
- Superpave Mix Design
18
Q
Marshall Mix Design
A
- uses impact hammer to prepare specimens
- determine stability with Marshall stabilometer
- uses volumetrics to select optimum asphalt content
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
20
Q
Superpave Mix Design
A
- uses gyratory compactor to prepare specimens
- uses volumetric analysis to select optimum bitumen content
21
Q
Vse
A
effective volume of aggregate
22
Q
Vsb
A
bulk volume of aggregate
23
Q
Vb
A
total volume of bitumen
24
Q
Vba
A
volume of absorbed bitumen
25
Vbe
volume of effective bitumen
26
Vmb
total or bulk volume of mix
27
Vmm
volume that yields maximum specific gravity - voidless volume of mix
28
Pb
percent of all bitumen by total weight of mix
29
Pbe
percent of effective bitumen
30
Pba
percent of absorbed bitumen
31
Ps
percent of aggregate in total mix
| Ps = 1 - Pb
32
Gsb
bulk specific gravity of aggregate
33
Gse
effective specific gravity of aggregate
34
Gmb
bulk specific gravity of mix
35
Gmm
maximum specific gravity of mix
36
VFB
voids filled with bitumen
37
VA
volume of air voids in mix
38
VMA
volume of voids in mineral aggregate
39
Key components of mix design
- laboratory compaction of trial mix specimen
- stability (strength) and volumetric testing
- analysis of results
- evaluation of moisture susceptibility
40
Purpose of compaction
To simulate the inplace density of hot mix asphalt after it had endured several years of traffic
41
Compaction Methods
- impact compaction (Marshall Mix Design)
- kneading compaction (Hveem Mix Design)
- gyratory compaction (several forms available)
- vibratory impact hammer
42
Marshall Specimen
102mm diameter and 64mm height specimens
43
Marshal mix aggregate size
max. 25mm
44
marshall mix - bulk specific gravity determination
```
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
marshall mix - Stability and Flow Test
1. Immerse specimen in water bath (60oC) for 30 to 40 mins
2, Make sure breaking head clean and well lubricated
3. Remove specimen from water bath, towel dry and centre on breaking head
4. 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
Bitumen Testing
1. Consistency Testing
2. Durability
3. Safety
4. Purity
47
Consistency Testing
- Penetration Testing
- Viscosity
- Ductility
48
Durability
- Short Term Aging (RTFOT)
| - Long Term Aging (PAV)
49
Safety
Flash Point Cleveland Open Cup
50
Purity
Solubility Test
51
Short Term Binder Aging
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
Long Term Aging
Pressure Aging Vessel (PAV)
- simulates aging of a bitumen binder after 7 to 10 years
- specimen kept at high temperature and high pressure
53
Asphalt Grading
```
HISTORY
1. Penetration Grading
2. Viscosity Grading
3. Aged Residue Grading
CURRENT
Performance Grading (PG)
```
54
Emulsion
- mix of asphalt cement, water and emulsifier
- emulsifier gives surface charge to asphalt droplets suspended in water medium
- safe
- cheap
- -85oC (safe)
55
anionic aggregate
limestones
56
cationic aggregate
silica gravels
57
Cutback
- asphalt cement "cut" with petroleum solvents
- bad for environment
- flammable
- expensive
- high temperatures of application (150oC)
- dangerous
58
Asphalt Cements
- generally refinery produced material
| - air blown asphalt cements
59
Newtonian Fluid
constant viscosity (water)
60
non-Newtonian Fluid
changing viscosity
- polymer modified binders
- cornflour
61
Compaction Viscosity
280+-30 MPa.s
62
Mixing Viscosity
170+-20 MPa.s
