Exam 3
What criteria must be considered when selecting an asphalt binder?
1. geographic area 2. air temperature 3. pavement temperature 4. loading type 5. reliability
How is the bulk specific gravity of the compacted HMA defined?
(compacted) mass of aggregates and asphalt divided by the volume of aggregates, asphalt, and air voids
How is the maximum specific gravity of the mixture defined?
(uncompacted) mass of aggregates and asphalt divided by the volume of aggregates and asphalt
How do you determine mixture properties?
-%Gmm at N initial, N design, and N maximum -determine % Va, % VMA, and % VFA @ N design -determine dust proportion -graph mixture properties vs. asphalt binder content
What is the Moisture Sensitivity Test?
-3 dry specimens -3 conditioned specimens (in water) -80% minimum tensile strength ratio -optional: freeze cycle, hot water soak
What is the Superpave Gyratory Compactor (SGC)?
-Texas equipment -French operational characteristics -150mm diameter (up to 37.5 mm nominal size -height recording -1.25 degrees -30 gyrations per minute
What are the major components of material selection?
-aggregates (coarse/fine/mineral filler) -asphalt binder -recycled asphalt pavement (RAP) -additives (lime, liquid anti-strip) -determine combined gradation using TxDOT Mix Design Program
What is N design based on?
-average design high air temperature -traffic level
How is the materials selection process performed?
-check aggregates and gradation for compliance with specification -check additives compliance with specification -determine specific gravity and absorption -use Excel Mix Design Program to develop a proposed blend of aggregate stockpiles -check aggregate classification of the combined blend
How do you determine the optimum asphalt content?
-determine VMA, Gr, and Ga at optimum asphalt content -if density and VMA are not within allowable, redesign mixture
How do you determine asphalt binder content?
-find design asphalt binder content that corresponds to 4% air voids -check % VMA, % VFA, %Gmm at N initial, %Gmm at Nmax and dust proportion -if satisfactory, proceed with moisture sensitivity test
How are mixtures evaluated?
-indirect tensile strength (specimens at 93% density -rut depth and number of passes (specimens at 93% density) by the Hamburg Wheel Test -if they are not within allowable ranges, redesign mixture
What do you need to input into the Excel Mix Design Program?
-material properties -bulk specific gravity -aggregate classification -combined gradation
What are the major components of TxDOT Mix Design?
-materials selection -preparation of laboratory samples -determine optimum asphalt content -mixture evaluation
How is the specimen prepared for the Superpave Gyratory Compactor (SGC)?
-mechanical mixer -short term oven aging (4 hours at 135 degrees C)
What is the general rule of field management of volumetric properties?
-mix design is only the starting point (adjustments will be necessary)
What factors are considered when selecting the PG grade in the superpave grading system?
-reliability -geographic location -loading type (time and amount) -temperature (air and pavement)
What are the major components of the preparation of laboratory samples?
-separate material into individual sieves for each stockpile -batch samples-mixing and compacting -determine percent density (Ga) at each asphalt content and input all data into TxDOT Mix Design program
What are the goals of compaction?
-simulate field densification (traffic & climate) -accommodate large aggregates -measure compactibility -conducive to quality control
What are the Superpave Mixture Requirements?
-specimen height -mixture volumetrics (air voids, voids in the mineral aggregate (VMA), voids filled with asphalt (VFA), and mixture density characteristics) -dust proportion -moisture sensitivity
What is the selection of mix type based on?
-traffic volumes -loading characteristics -design speed -desired performance characteristics -cost -previous experience
What are the main differences between TxDOT HMA Mix Design and Superpave Mix Design?
-type of mix -compactor type -weight or volume design -compaction level
What is involved in aggregate gradation for Superpave specifications?
0.45 gradation chart; blend different materials to create the proper gradation (3-4 materials)
What are two Superpave specifications of the designing the aggregate structure?
0.45 power chart and control points
What are the steps for Volumetric Superpave Mix Design?
1) Design aggregate structure 2) compute estimated binder content 3) computer design binder content 4) mix evaluation
What can VTM be increased by?
1) reducing asphalt content and 2) reducing dust
What can VMA be increased by?
1) reducing the dust or natural sand or 2) increasing the distance from the middle
What are two types of aggregate properties?
1. Consensus Properties (required) 2. Source Properties (optional)
What are the four steps of Superpave Mix Design after determining specification?
1. Materials Selection 2. Design Aggregate Structure (gradation) 3. Design Binder Content 4. Moisture Sensitivity (vertification)
What are three cutbacks?
1. Rapid Cure (RC); high volatility of solvent; tack coats and surface treatments 2. Medium Cure (MC); moderate volatility; stockpile patching mix 3. Slow Cure (SC); low volatility; prime coat and dust control good for fast projects, but not used because it's harmful for the environment
What are two binder aging methods?
1. Rolling Thin Film Oven (RTFO); simulates manufacture and construction aging 2. Pressure Aging Vessel (PAV); simulates long-term pavement aging
List five tests on bitumen (asphalt cement).
1. Rotational Viscometer (RV) 2. Dynamic Shear Rheometer (DSR) 3. Bending Beam Rheometer (BBR) 4. Direct Tension Test (DTT) [with Rolling Thin Film Oven (RTFO) or Pressure Aging Vessel (PAV) aging] 5. Flashpoint Test 6. Penetration Test 7. Absolute Viscosity Test
What are the four performance grade binder tests? What do they help simulate?
1. Rotational Viscometer (RV); temperature-viscosity relationship 2. Direct Shear Rheometer (DSR); rutting & fatigue cracking 3. Bending Beam Rheometer (BBR); low-temperature cracking 4. Direct Tension Tester (DTT); low-temperature cracking
List six desirable characteristics of aggregates to be used in asphalt concrete.
1. angularity (sharp) 2. cheap 3. available 4. good adhesion (chemical) 5. strong (toughness) 6. durable (soundness)
What are the three bituminous material types?
1. asphalt cement/hot mix asphalt 2. emulsified asphalt 3. cutback asphalt
What terms are involved in HMA volumetrics?
1. bulk specific gravity of compacted HMA 2. maximum specific gravity 3. air voids 4. effective specific gravity of aggregate 5. voids in mineral aggregate (VMA) 6. voids filled with asphalt (VFA)
What are four consensus properties of aggregates?
1. coarse aggregate angularity (CAA) 2. fine aggregate angularity (FAA) 3. flat, elongated particles (causes segregation) 4. clay content (want minimum for maximum bonding)
What are the steps of the bitumen production process?
1. drill/pump 2. store 3. heat 4. cool 5. sort
What are four major factors that you must consider when designing PCC mixes?
1. economy 2. workability 3. strength 4. durability
What are two types of polymer modifiers?
1. elastomers (stiff, but flexible) 2. plastomers (higher stiffness, but not as flexible)
What does a larger maximum aggregate size cause?
1. increases strength 2. improves skid resistance 3. increases volume and surface area of aggregate which decreases required asphalt cement content 4. improves rut resistance 5. increases segregation
What are the four steps of Superpave Mix Design?
1. materials selection 2. design aggregate structure 3. design binder content 4. moisture sensitivity
What are the tests performed on asphalt?
1. penetration 2. absolute viscosity 3. flashpoint 3. RV 4. DSR 5. BBR 6. DTT with aging methods: a) RTFO b) PAV see: https://engineering.purdue.edu/NCSC/library/video.htm
What specifications for petroleum asphalts developed?
1. penetration grade (scale of hardest to softest) 2. viscosity-graded specifications (scale of softest to hardest) 3. superpave binder specification
What are the basic steps of refinery operation?
1. pumping 2. storage 3. heating 4. distillation 5. condensing and cooling 6. separation
What does a smaller maximum aggregate size cause?
1. reduces segregation 2. reduces road noise 3. decreases tire wear
What are the desirable properties of aggregates for asphalt?
1. sharp edges (interlock) 2. size distribution (within gradation band) (permeability) 3. strong 4. durable 5. clean & free of organic material (for bonding) 6. round in shape (not flat or elongated) 7. cheap & locally available 8. chemical characteristics 9. good adhesion with the binder
Why would polymer modifiers be used?
1. stiffer mixes at high temperatures 2. stiffer mixes at low temperatures 3. improved fatigue resistance 4. reduced life-cycle costs
What are three source properties of aggregates?
1. toughness 2. soundness 3. deleterious materials
What are some characteristics of polymer modifiers?
1. used because of increased demand on HMA pavements (wider range of binder performance required) 3. disposal of waste products 4. willingness to pay more upfront for long-term benefit
How does the Texas Gyratory Press operate?
4": -6 degree angle-compact to given resistance, not fixed effort6": -6 degree angle -compact with constant pressure until rate of height change per revolution drops to specified level
What is the air void requirement for Superpave Mix Design?
4%
What is the minimum mixture density at N initial?
89%
What percentage of the weight and volume do aggregates make up?
95% and 70%
What is the maximum mixture density at N maximum?
98%
What is the principle of the test used for determining the low-temperature stiffness of bitumen with the Bending Beam Rheometer (BBR)?
A beam of asphalt is prepared. Then, a constant load is applied. Deflection is recorded. The BBR Test uses an equation for stiffness, based off of the beam's dimensions, the load, and the deflection. From the deflection, stiffness can be calculated. The negative slope in the graph of stiffness vs. time is due to relaxation. The slope of the graph of the stiffness vs. time is the m-value.
What are the advantages and disadvantages of using the PG specifications instead of the viscosity or penetration-based specifications for bitumen/asphalt?
Advantages: -performance-based -based on engineering properties (scientific), not empirical tests -adaptable to new applications -allows testing with results applicable to multiple temperatures (both high and low) Disadvantages: -require newer equipment (cost) -time/place for testing
List the main differences between asphalt/bitumen and tar.
Asphalt is a by-product of the petroleum industry (or naturally occurs) and it is soluble in petroleum products. Tar is a by-product of the coal industry and it is not soluble in petroleum products.
What is DTT?
Direct Tension Tester Test
What are asphalt emulsions and cutbacks? What are the advantages of using emulsions instead of cutbacks?
Emulsions are asphalt binder, water, and an emulsifying agent. Cutbacks are asphalt binder and petroleum solvent. Emulsions are more environmentally-friendly and cheaper than cutbacks.
How is specific gravity reported for superpave specifications?
G _ _ where the first blank is the material type: m-mixture b-binder s-stone and the second blank is the specific gravity type: a-apparent b-bulk e-effective m-maximum
What is involved in the DSR Test?
Gstar and sin(delta) are determined; rutting: Gstar divided by sin(delta) indicates high temperature stiffness (unaged or RTFO);fatigue cracking: Gstar multiplied by sin(delta) indicates intermediate temperature stiffness (PAV-aged)
What are the three special points on the %Gmm vs. Log Gyrations?
N initial, N design, and N max
How is the compactor type different between TxDOT and Superpave Mix Designs?
TxDOT has both the Texas Gyratory and Superpave Gyratory Compactors
How is the type of mix different between TxDOT and Superpave Mix Designs?
TxDOT has dense-graded, large stone, performance, permeable friction course, and stone matrix asphalt
Draw the phase volume diagram of asphalt concrete and identify all components.
________ [air] ________ [binder] ~~~~~~ [binder absorbed by aggregate] ________ [aggregate] ________
What is involved in the RTFO?
a bottle is coated through testing; mass loss must be within a certain range
What is a control chart?
a chart containing the data collected from a group of samples, with upper and lower specification limits (LSL and USL) and either the means or the ranges
What is involved in the BBR Test?
a constant load is applied and increasing deflection is observed; obtains a formula for creep stiffness, depending on load, length, width, thickness, and deflection; relaxation can be observed
What is lake asphalt?
a naturally-occurring asphalt on lake surface (Trinidad & Venezuela)
Why is viscosity an important test to perform on asphalt?
a relationship between temperature and viscosity can be determined, and there exist ranges of compaction and mixing
What is involved in the DTT Test?
a tension load is applied to a specimen; obtains stress-strain curve, including strain at peak stress and stress at failure; indicates low-temperature capacity to stretch
How does a weak aggregate structure compare to to strong aggregate structure on the %Gmm vs. Log Gyrations graph?
a weak aggregate structure has a shallower slope than a strong aggregate structure
What is the target gradation?
acceptable gradation band specified, with upper and lower gradation limits; mix design selects a job mix formula (JMF) which falls within band and meets design criteria; Superpave: 5 sieve size gradation specifications;
What were superpave specifications developed from?
air temperatures
What is the Rolling Thin Film Oven Method?
an aging method that simulates construction aging
What is the Pressure Aging Vessel Method?
an aging method that simulates long-term pavement aging
What are cutback asphalts composed of?
asphalt cement with petroleum solvent
What are emulsified asphalts composed of?
asphalt cement, water, and an emulsifying agent
What is VTM (air voids) most affected by?
asphalt content, dust, and proportions of course aggregate and fine aggregate
What is aging as it relates to asphalt?
asphalt is a petroleum product and oxidizes and hardens over time
What are the three components of asphalt?
asphaltenes, resins, and oils
What are two Superpave aggregate criteria?
based on aggregate blend and based on traffic and depth into pavement
What does a Superpave specification for aggregates look like?
based on the nominal maximum aggregate size; Ex. SM 12.5 means nominal maximum aggregate size is 12.5mm
How is the TxDOT Mix Design completed?
by Excel; requires inputting of: sieve analysis for each sieve, aggregate specific gravities, theoretical maximum specific gravity (Gr), percent density (Ga), and asphalt content (%); plots properties to ensure they satisfy specifications; aids in the selection of optimum asphalt content; prepares data in standard format for submittal
What affects the superpave specification? How does it affect it?
climate; the first number is the average 7-day maximum pavement temperature, and the second number is the minimum pavement temperature
What are the steps in determining design asphalt content?
compact design aggregate structure specimens -determine mixture properties -graph mixture properties vs. asphalt binder -select design asphalt binder content -check required criteria (VMA, VFA, etc.)
What is creep?
deformation from a sustained load
What are deleterious materials? What test measures the deleterious materials test?
deleterious materials are contaminants such as shale, wood, mica, and coal; wet sieve analysis determines; requirements for maximum
What is involved in the RV Test?
determine viscosity at both 135 degrees C and 165 degrees C; check for handling and pumping; develop a temperature-viscosity relationship
What is the Direct Shear Rheometer Test?
determines Gstar and delta, where Gstar (complex shear modulus) is the relationship between highest shear stress applied and highest resulting shear strain and delta (phase angle) is the time delay between the applied shear stress and the resulting shear strain; simulates rutting on unaged and RTFO specimens by determining high temperature stiffness and fatigue cracking on PAV specimens by determining intermediate temperature stiffness
What is the Penetration Test?
determines penetration, which is a measure of consistency
What is the Absolute Viscosity Test?
determines the absolute viscosity at 135 degrees C, which characterizes flow behavior and may be used for specification requirements; there is also a kinematic viscosity test with vacuum done at 60 degrees C
What is the Bending Beam Rheometer Test?
determines the deflection of an asphalt beam over time, which helps determine the stiffness and relaxation for use in determining low-temperature cracking
What is the Direct Tension Tester Test?
determines the stress-strain curve for asphalt and obtains the strain at peak stress and stress at failure, which helps determine the low-temperature capacity to stretch
What is the Flashpoint Test?
determines the temperature at which the asphalt catches fire; safety test
What is the Rotational Viscometer Test?
determines viscosity at 135 and 165 degrees C in order to check for handling and pumping and to develop a temperature-viscosity relationship
How is the effective specific gravity defined?
dry mass divided by effective volume
What is effective specific gravity?
excludes absorbed asphalt volume; includes the volume of solid particle and the volume of the pore volume that is not filled with asphalt
What is apparent specific gravity?
excludes the water permeable pore volume; includes only the volume of solid particle
What are some properties of uniformly-graded aggregates?
few points of contact; poor interlock (depending on shape); high permeability; not strong
How is low-temperature cracking addressed in the superpave binder specifications?
from BBR or DTT Tests; a minimum m value and a maximum S value OR a minimum failure strain because we want a soft and elastic binder that relaxes OR a stiff binder that will stretch
What is tar?
generally a by-product of coal production; resistant to petroleum products
What is asphalt?
generally a by-product of petroleum distillation; a complex hydrocarbon; soluble in petroleum products; can be naturally-occuring
What do emulsifiers do?
give surface charge to asphalt droplets suspended in water medium; anionic (limestone compatible) or cationic (siliceous gravel compatible); allow for bitumen to be mixed at lower temperatures; cheaper, safer, and better for the environment compared to cutbacks.
What are some properties of well-graded aggregates?
good interlock; low permeability; "densely-graded"
Why is gradation of aggregates important for HMA?
gradation determines packing; dense packing means lower permeability; permeable mix requires voids
How is pavement deformation addressed in the superpave binder specifications?
high temperature stiffness from DSR Test; early part of service life; a minimum value exists because a stiff, elastic binder is the goal
What is bulk specific gravity?
includes the bulk volume, which is the solid volume and the water permeable pore volume
How is fatigue cracking addressed in the superpave binder specifications?
intermediate temperature stiffness from DSR Test; later part of service life; a maximum value exists because a soft, elastic binder is the goal
What were the early specification for lake asphalts and for petroleum asphalts?
lake asphalts: -appearance -solubility in carbon disulfide petroleum asphalts: -consistency
What does specific gravity do?
like density, it relates mass and volume
How is a job mix formula gradation determined?
make the gradation fall between the control points
How is absorbed asphalt content defined?
mass concentration of asphalt absorbed by aggregate; used as a percentage by mass of total mix
How is asphalt content defined?
mass concentration of asphalt binder; used as a percentage by mass of total mix; effective asphalt+absorbed asphalt
How is effective asphalt content defined?
mass concentration of asphalt not lost to absorption; used as a percentage by mass of total mix
What is the Flat, Elongated Particles Test?
measured on larger particles; based on dimensional ratio of particles (usually 1:5); requirements of maximum percentage of flat and elongated particles depend on traffic level; flat, elongated particles cause non-uniformity and potential for segregation
What is the Coarse Aggregate Angularity Test?
measured on larger particles; based on fractured faces; requirements of minimum percentages of fractured faces depend on depth of layer within pavement and traffic level; sample grains, identify number of fractured faces (one or two+) because of interlock between grains; new test: funnel, let fall into cylinder, measure percent air voids
What is the Fine Aggregate Angularity Test?
measured on materials smaller than No. 8 sieve; based on air voids in loose sample; requirements of minimum air voids depend on depth of layer within pavement (higher stresses at lower depths) and traffic level; aggregates blended, put into funnel, place cylinder under funnel, let grains fall freely, calculate uncompacted voids; rounded particles pack tighter together, therefore there is less air
What is the Clay Content/Sand Equivalency Test?
measures how clean the sand is; measured on larger particles; based on sand equivalent value; requirements of minimum sand equivalent value depend on traffic level; get the sand reading and clay reading by putting the sand into a cylinder and mix it with calcium chloride solution and shake, then let it sit and measure the top of the coarse particles (sand reading) and the top of the clay particles (clay reading); higher number indicates cleaner sand; another test Methylene Blue Test exists, color of spot indicates higher or lower percentages of sand: 5-18 are acceptable; 20+ fails
What is maximum aggregate size?
one size larger than nominal maximum size
What is nominal maximum aggregate size?
one size larger than the first sieve to retain more than 10%
What are the two types of Superpave aggregates tests?
ones based on consensus properties and one based on source properties
What are some properties of gap-graded aggregates?
only limited sizes; good interlock; low permeability
What is asphalt aging?
oxidation of asphalt over time; RTFO & PAV; RTFO to simulate construction aging; PAV to simulate long-term aging
What is reliability as it relates to design temperature?
percent probability of not exceeding design temperature; area under the normal distribution curve to the left of the design temperature
How are voids filled with asphalt (VFA) defined?
percentage of VMA filled with asphalt
What is asphalt binder selection dependent on in superpave specifications?
performance (rutting, fatigue cracking, low temperature cracking)
What is the basic superpave specification?
performance grade (PG), which is based on physical properties
What is RAP?
reclaimed asphalt pavement (RAP) is recycled asphalt pavement; superpave transition was difficult due to grading difficulties and mixing difficulties, but partial blending occurs to a significant extent; may have to adjust the performance grade. see https://engineering.purdue.edu/NCSC/library/video.htm
What does superpave stand for?
superior performing pavement
How does testing for performance grade work?
test the same type of asphalt for multiple temperatures until the sample fails to meet the specification requirement; the asphalt belongs to the grade based on the last temperature that passed the specification
What is the dust proportion (DP)?
the % weight of the <0.075 (#200 sieve) material divided by the % weight of effective asphalt (should be between 0.8 and 1.6
How do the results of the Texas Gyratory Compactor compare to those of the Superpave Gyratory Compactor?
the Texas Gyratory Compactor is more variable and therefore less reliable; field mixes fair better than lab mixes
What is VMA most affected by?
the dust content
How is the weight or volume design different between TxDOT and Superpave Mix Designs?
the function of specific gravity of stockpiles is different
What do the VMA requirements depend on?
the nominal maximum aggregate size
How is the compaction level different between TxDOT and Superpave Mix Designs?
the number of gyrations of the Superpave Gyratory Compactor is different
What is proportion defective?
the percentage of samples from a normal dsitrbution that fall outside of the lower and upper limit; the percentage of samples that does not fall within the limits
What do the mixing and compaction temperatures depend on?
the performance grade (PG grade) of the binder
What do the requirements for the Hamburg Wheel Test depend on?
the performance grade (PG grade) of the binder
What is viscosity?
the ratio between the applied shear stress and the rate of shear strain
What is consistency?
the softness or hardness of a liquid; the stiffness; the way a liquid flows
What is phase angle?
the time difference between the applied shear stress and the resulting shear strain
What do the VFA requirements depend on?
the traffic level
What is consistency?
the way a liquid holds together; stiffness; softness or hardness
What limits the aggregate size?
thickness of layer
What is VFA?
voids filled with asphalt
How are air voids defined?
volume concentration of air voids; used as a percentage by volume of total mix
How are voids in mineral aggregate (VMA) defined?
volume concentration of intergranular void space in a compacted mix; used as a percentage by volume of total mix
When are modified binders used?
when the difference between the higher and lower temperatures is more than 90 or 92; "Rule of 90 or 92"
What are the results for the SGC?
you can determine the %Gmm vs. Log Gyrations
