CHAPTER9 Flashcards
Behaviour of asphalt binder according to temperature
high : viscous
low : elastic
The characteristics of asphalt binder depends on
temperature and loading rate
3 types of asphalts used in pavements
- asphalt cement
- asphalt emulsion
- asphalt cutback
what is asphalt cement used for
HMA and patching
what is asphalt emulsion used for
cold mix & maintenance
what is asphalt cutback used for
cold mix & maintenance
characteristics of asphalt cement (binder)
- adheres well to most rock
- waterproof
- fairly durable
- resistant to rxn w most acids, alkalis & salts
- temperature sensitive (semi solid @ room temp)
what is asphalt cutback
asphalt cement + cutback
characteristics of asphalt cutback
- hazardous and volatile hydrocarbons are released
- cold mix maintenance, patching, chip seals, crack sealing, base and sub-base stabilization and surfacing low volume roads
what is asphalt emulsion
asphalt cement + water + emulsifying agent
asphalt emulsion is similar to _____ in its uses
asphalt cutback
advantages of asphalt emulsion over asphalt cutback
- safer
- environmentally better
- cost?
what is asphalt concrete?
asphalt binder + aggregate
what is asphalt binder used for?
sealing and waterproofing
what is asphalt concrete used for?
HMA pavement surfacing
describe the temperature susceptibility of asphalt
graph : log temperature (x) vs log viscosity (y). from too brittle (low temp) to too soft (high temp., low viscosity). DEGREES RANKING
low viscosity (soft) asphalt is used in where and for what
in cold climates to avoid thermal cracking
high viscosity (hard) asphalt is used where and for what
in hot climates to avoid rutting
Asphalt chemistry : the chemical composition depends on
- the oil source
- refining method
asphalt chemistry : composition
mostly hydrogen & carbon
some sulfur, nitrogen and oxygen
asphalt chemistry : whats more important than what
the molecular structure is more important than the composition
4 types of asphalt grading and which one is used now?
PEN : penetration grading
AC : viscosity grading
AR : aged residue grading
PG : performance grading (USED NOW)
what was created after the SHRP and define
Strategic Highway Research Program : creation of the superpave & performance grade binders
what is superpave + define
Superior Performing Asphalt Pavements
it’s a mix design method for asphalt concrete and a performance grading method for asphalt binder specification.
3 specific distresses
- rutting
- fatigue cracking
- thermal cracking
3 specific aging conditions
- unaged
- construction
- long term
define PG
intended to improve pavement performance by reducing potential to :
- permanent deformation
- fatigue cracking
- low temp cracking
- excessive aging from volatilization
- pumping & handling
nomenclature for PG
start with PG, followed by max & min pavement service temperatures in °C. (PG52-28)
where is the temperature measured for PG grading?
high is 20 mm (3/4”) below the pavement surface.
low at surface.
how is PG presented?
6°C increments for both high and low temperatures
what is a dynamic shear rheometer
- test complex shear modulus of binders
- - measures the resistance to shear deformation in the linear visco-elastic range
what data is taken for climate values?
2 stdv on each side
how are asphalt cutbacks graded?
RC : rapid curing (5-10 minutes)
MC : medium curing (few days)
SC : slow curing (few months)
higher grade for viscosity is more viscous
example : RC-70 or MC-3000
cutback nomenclature
MC-viscosity number
emulsion vs cutback : define
emulsion is preferred over cutback
- safer
- used with damp aggregates
- slightly more economic
- environmentally better
grading for asphalt emulsion
RS = rapid setting (5-10 min) MS = medium setting (several hours) SS = slow setting (few months)
what is anionic
negative charge
what is cationic
positive charge
emulsion nomenclature
CMS - 1h
first : C = cationic, HG = high float
second : medium, rapid or slow set
# : emulsion viscosity
third : hard asphalt residue or soft asphalt residue
what is HMA
asphalt binder + aggregates
HMA desirable properties
- stable (resists permanent deformations under load)
- fatigue resistant (under repeated loading)
- resistant to thermal cracking (due to contraction at low temps)
- resistant to hardening or aging (during production and in service)
- resistant to moisture induced damage (stripping asphalt from aggregate)
- skid resistant (by texturing surface)
- workable (ease of mixing, placing, compacting)
- economical
3 steps for asphalt concrete mix designb
- selection of design aggregate structure
- selection of design asphalt content
- evaluation of moisture sensitivity of mix
whats included in the selection of aggregate structure for the asphalt conrete mix design?
preliminary (gradation and consensus properties)
and
volumetric analysis of mixes
whats included in the selection of design asphalt content for th asphalt concrete mix design?
volumetric analysis of design aggregate structure at four binder contents
lab specimen preparation, 7 steps
- grade + weight aggregates & determine target asphalt content
- heat & mix aggregate and asphalt binder
- short term aging
- place material into mold & apply compactive force
- allow to cool and extrude from mold
- determine specific gravity + air voids
- mechanical tests
2 different types of compaction for AC mix design methods
superpave design mix : gyratory compactor
marshal mix design : marshall hammer
whats in the phase diagram?
gas – air
liquid – binder
solar – aggreagte
Specific gravity provides ____ b/n ____ & ____ properties of the ______.
Specifica gravity provides bridge b/n mass & volume properties of the hot mix.
volumetric code names nomenclature
X_12
steps for superpave mix design
a) aggregate selection
b) binder selection
c) determine design aggregate structure
d) determine design binder content
e) evaluate moisture susceptibility
a) aggregate selection. stockpiles are evaluated for
- soundness
- toughness
- deleterious materials
what are the blend requirements for the aggregate selection?
- coarse aggregate angularity (min)
- fine aggregate angularity (min)
- flat & elongated particles (max)
- sand equivalency (need clean aggregates)
- gradation 0.45 power chart (must pass through control points)
coarse aggregate angularity minimum requirements ____ as traffic increases
coarse aggregate angularity minimum requirements increase as traffic increases
why is the gradation called 0.45 power chart?
y : percent passing, from 0 to 100
x : sieve size, mm (raised to the power 0.45)
define
c) design aggregate structure
- evaluate three aggregate blends
- estimate asphalt content
- design aggregate structure (trial specimens w different aggregate gradations using gyratory compactor + uncompacted samples measure max theoretical specific gravity + volumetric analysis)
prepare design aggregate structure specimens
- for each of the three design aggregate structure blends.
- compact 2 or 3 samples using the superpave gyratory compactor
- prepare one sample to measure max theo specific gravity
- perform volumetric analysis
define VTM
voids in total mix
define VMA
voids in the mineral aggregate
measure of the asphalt film thickness (controls the minimum asphalt content)
define VFA
voids filled w asphalt
percent of the VMA filled w asphalt
define D/B
dust to binder ratio (percent stone passing #200, 0,075 mm)
VTM
4% for mix design
4-8% for construction
>2 % of the life of the pavement
what is DAS
design aggregate structure
define d) design binder content
prepare samples at four asphalt contents :
P_b -0.5
P_b
P_b + 0,5
P_b + 1.0
- perform volumetric analysis
- plot volumetric analysis vs asphalt content
- select P_b w 4% VTM
- select other volumetric param. at desired P_b
- compare to criteria
define e) evaluate moisture sensitivity
- using DAS & DBC prepare six compacted samples (compact to specific height, 7% air voids)
- reserve 3 samples
- condition 3 samples (sature, freeze/thaw)
- measure tensile strength
what is TSR
tensile strength ratio =
TSR = (avg. wet tensile strength)/(avg. unconditioned tensile strength)
what is stripping
loss of bond b/n asphalt & aggregate
how to evaluate moisture susceptibility
2 sets of specimens : control & conditioned
- evaluate strength before & after conditioning
- retained strength = conditioned strength/reference strength
- must have minimum retained strength
how to improve moisture susceptibility
- increase asphalt content
- higher viscosity asphalt
- aggregate clean of dust and clay
- change aggregate gradation
- add anti-stripping additives (liquid + portland cement or lime)
types of AC pavement failures
- rutting
- fatigue cracking (repeated bending)
- thermal cracking (temp. gradient)
- excessive surface roughness (aging)
- aging & oxidation of the binder (stiffening)
- stripping
the characterization of asphalt concrete is difficult because
AC is a nonlinear visco-elastic OR visco-elasto-plasti material
what is a triaxial cell used for?
simulate vehicle loads in three dimensions
3 tests that are still in research mode
- dynamic modulus (E*) test
- triaxial repeated load permanent deformation test (also known as flow number F_n test)
- triaxial static creep test (also known as Flow Time F_t test)
what is the dynamic modulus test for?
sinusoidal load
what is the static triaxial creep test for?
constant load
3 periods for static triaxial creep test
- primary
- secondary (creep over time, linear portion)
- tertiary (flow time when shear deformations begin, all falls apart)
look for longer Flow time and long linear portion (secondary)
what is the triaxial repeated test
thousands of load cycles (0.1 s load, 0.9 s unload)
components of the AC production and construction
- materials to plant
- plant (batch or drum type, mix asphalt to required proportions and discharge to truck for haul to job site)
- paver (place hot mix to desired thickness and smoothness)
- compactors (achieve desired density)
what is RAP
recycled asphalt pavement
advantages of AC recycling
- economy (25% savings in material cost)
- energy savings
- environmental
- maintains bridge & tunnel clearances
special considerations for using RAP
- evaluate quality
- mix design
- production (rely on heat transfer from virgin aggregate to RAP, moisture in RAP difficult to remove)
4 types of additives
- fillers
- extenders
- polymer modified asphalt
- antistripping agents
define additives : fillers
crushed fines, PC, lime, fly ash, carbon black.
to improve gradation, stability, binger-aggregate bond or to fill voids
define additives : extenders
sulfur & lignin to reduce amount of asphalt & therefore cost
define additives : polymer modified asphalt
most widely used : SBS (styrene butadiene styrene)
high range PG binders require modification to achieve required properties.
select asphalt w required low temp. properties. use modifier to achieve high and intermediate temperature properties.
SBS improves fatigue and rutting performance
additional cost justified through better performance
define additives : antistripping agents
lime, PC. improves bond b/n asphalt binder and aggregates for moisture resistance.
define additives : others
fibers, oxidants, antioxidants, hydrocarbons.
to improve strength and stiffness
warm mix : define
lower mixing and placing temperatures (reduction of 25-50 °C)
advantages of warm mix
- less energy required
- lower ghg
- less oxidation of the asphalt binder
- pave at lower temperatures
- longer haul distances possible
- extending paving season since the asphalt can be compacted at lower temperatures
asphalt binder =
asphalt cement
