Ms-25 Asphalt Binder Testing Manual

Maintain at the plant site a record system for all approved RAP stockpiles. Include at a minimum the following: Stockpile identification and a sketch of all stockpile areas at the plant site; all RAP test results (including asphalt content, gradation, and asphalt binder characteristics).

BK-50 Asphalt Binder Handbook, prepared by the Asphalt Institute, is a manual for asphalt binders and bitumen, and is a compilation of other AI publications including SP-1, MS-4, MS-5, MS-19 and MS-25 manuals.The fully-illustrated book contains information on Multiple-Stress Creep Recovery Test, testing variability and resolution, and the generation of mastercurves. MS-26 The Asphalt Binder Handbook The Asphalt Binder Handbook is a comprehensive manual that is devoted entirely to information about asphalt binders or bitumen.

Ms-25 Asphalt Binder Testing Manuals

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Asphalt binders, sometimes referred to as asphalt cement binders or simply asphalt cement,are an essential component of asphalt concrete—they are the cement that holds the aggregatetogether. Asphalt binders are a co-product of refining crude petroleum to produce gasoline,diesel fuel, lubricating oils, and many other petroleum products. Asphalt binder is producedfrom the thick, heavy residue that remains after fuels and lubricants are removed from crude oil.This heavy residue can be further processed in various ways, such as steam reduction and oxidation,until it meets the desired set of specifications for asphalt binders. For demanding, high-performanceapplications, small amounts of polymers are sometimes blended into the asphalt binder, pro-ducing a polymer-modified binder.Asphalt binders have been mixed with crushed aggregate to form paving materials for over100 years. They are a very useful and valuable material for constructing flexible pavement world-wide. However, asphalt binders have very unusual engineering properties that must be carefullycontrolled in order to ensure good performance. One of the most important characteristics ofasphalt binders that must be addressed in test methods and specifications is that their preciseproperties almost always depend on their temperature. Asphalt binders tend to be very stiff andbrittle at low temperatures, thick fluids at high temperatures, and leathery/rubbery semi-solids atintermediate temperatures. Such extreme changes in properties can cause performance problemsin pavements. At high temperatures, a pavement with a binder that is too soft will be prone torutting and shoving. On the other hand, a pavement that contains a binder that is too stiff at lowtemperatures will be prone to low-temperature cracking. Figure 3-1 illustrates the extreme changein modulus that occurs in asphalt binders over the range of temperatures likely to occur inpavements; at −30°C the modulus of this particular asphalt binder was about 37,000 times greaterthan its modulus at 50°C. Specifications for asphalt binders must control properties at high, low,and intermediate temperatures. Furthermore, test methods used to specify asphalt bindersusually must be conducted with very careful temperature control; otherwise, the results will notbe reliable. Asphalt binders are also very sensitive to the time or rate of loading. When tested ata fast loading rate, an asphalt binder will be much stiffer than when tested at a slow loading rate.Therefore, time or rate of loading must also be specified and carefully controlled when testingasphalt binders.Another characteristic of asphalt binders that complicates specification and testing of thesematerials is that, for various reasons, such binders tend to harden with time. For example, whenasphalt binders are heated to high temperatures, as happens when mixing and transporting HMA,some of the lighter volatile oil fractions of the asphalt vaporize, which can harden the remainingasphalt binder. At the same time, some of the chemical compounds making up asphalt binderscan oxidize, which can also result in an increase in stiffness. Some oxidation occurs during mixing,transport, and placement of the HMA. However, slow, long-term oxidation will continue tooccur in the asphalt binder in a pavement for many years, resulting in a slow but sometimes very15C H A P T E R 3Asphalt Binders

significant increase in stiffness. Sometimes asphalt binder age hardening can be so severe that itcan lead to serious premature surface cracking of the pavement surface. Several other types ofhardening occur in asphalt binders without any loss of volatiles or oxidation; these include sterichardening and physical hardening. These phenomena are not yet well understood, but appearto be caused by a slow rearrangement of the molecules in the asphalt binder over time, resultingin a gradual increase in stiffness. Unlike other types of hardening, steric hardening and physicalhardening are reversible—if the asphalt is heated until fluid and then cooled, all or most of thehardening will be removed. This is one of the reasons it is important to thoroughly heat and stirasphalt samples prior to performing any laboratory tests.Asphalt binders are complex materials that are difficult to specify and test. Pavement engineersand technicians have struggled for over 100 years to develop simple tests and effective specifica-tions for asphalt binders. One of the earliest tests for asphalt binders was the penetration test, inwhich a small lightly weighted needle was allowed to penetrate the asphalt for a set period of time(typically 5 or 60 seconds). The distance the needle penetrated into the asphalt was measuredand was used as an indication of its stiffness. Other such empirical tests were the ring and ballsoftening point temperature, and the ductility test. These tests were useful (many are still usedin specifications in Europe and other parts of the world), but had shortcomings. They did notmeasure any fundamental property of the asphalt binder, like modulus or strength. The resultswere also sometimes highly variable and were not always in close agreement from laboratory tolaboratory. In the 1960s, specifications based on viscosity measurements began to be adopted bymany highway agencies. Viscosity tests are superior to the earlier empirical tests—they provideinformation on a fundamental characteristic of the asphalt binder and provide reasonably repeatable results among laboratories. However, there are drawbacks to viscosity testing. First,it is best used at high temperatures, where the behavior of the asphalt binder approaches that ofan ideal fluid. At low and intermediate temperatures, viscosity tests become difficult to performand even more difficult to interpret. Second, viscosity tests only provide a limited amount of infor-mation on the flow properties of a material. Two different asphalt binders can have identical vis-cosity values at a given temperature but might behave very differently because of differencesin the degree of elasticity exhibited in their behavior. When loaded, the asphalt binders mightdeform the same amount, but when the load is removed, one might spring back, or recover, tonearly its initial shape. The other might hardly recover at all, staying in its deformed shape. Theasphalt binder that showed more recovery—that behaved in a more elastic fashion—would tendto provide better rut resistance in paving applications compared to the other binder with poorrecovery. However, viscosity tests provide no information about recovery or about the degree ofelasticity exhibited by a material under loading. The shortcomings in both older empirical testsand in the newer viscosity tests eventually led to the development of a more effective system16 A Manual for Design of Hot Mix Asphalt with Commentary1.E+041.E+051.E+061.E+071.E+081.E+09-40 -20 0 20 40 60 80Temperature, oCModulus, PaModulus at -30 oC is 37,000times the modulusat 50 oCFigure 3-1. Change in dynamic shear moduluswith temperature for typical asphalt binder (frequency = 10 rad/s).

of grading asphalt binders, as described in the remainder of this chapter. Photographs of thepenetration test and the capillary viscosity test are shown in Figure 3-2.Performance Grading of Asphalt Binders—OverviewPerformance grading of asphalt binders was developed during SHRP. The main purpose of thisway of classifying and selecting asphalt binders is to make certain that the binder has the correctproperties for the given environment. Performance grading was also meant to be based moresoundly on basic engineering principles—earlier methods of grading binders often used empiricaltests, which were useful but did not provide any information on the fundamental engineeringproperties of the binder. Performance grading uses various measurements of the binder’s flowproperties to establish its grade, which is expressed as two numbers, for example “PG 64-22.”In this example, the “64” represents the maximum pavement temperature for which this bindercan be used at low [moderate?] traffic levels. The second number, “−22,” signifies the minimumtemperature for which the binder can be used without likelihood of failure. It is essential tounderstand when using the performance grading system that the numbers in the grade designationrepresent the most extreme temperatures for which that binder is suited. For example, if agiven application requires a PG 58-16 binder, there are many other grades that could meet therequirements: PG 58-22, PG 58-28, PG 64-16, PG 64-22, etc. This is only a simple explanationof the basic features of performance grading; the details of the system are more complicated andare explained below.Performance Grading—Test MethodsMost of the tests used in performance grading of asphalt binders involve rheological tests.Rheology is the study of the way materials flow, so a rheological test is one that measures one ormore aspects of the way in which a material flows. The dynamic shear rheometer (DSR) and theAsphalt Binders 17(a) (b)Figure 3-2. Traditional test for asphalt binders: (a) penetration test; and (b) viscositytest on asphalt binders.

bending beam rheometer (BBR) both measure the flow properties of asphalt binders—the DSRat temperatures ranging from about 10 to 82°C, the BBR at temperatures ranging from −20 to 0°C.It may at first be surprising that asphalt binders flow at temperatures below 0°C, where it normally appears to be a brittle, glassy material. But asphalt binder will in fact flow even at verylow temperatures, although this flow might take months or even years before it is noticeable tothe naked eye.Asphalt binders can be characterized as they are produced at the refinery using these rheologicaltests. Unfortunately, this is not enough to give technicians and engineers a good idea of how abinder will perform in a pavement, since asphalt binders in a pavement harden during mixing,transport, and placement of the mix, and even after the pavement has been placed. Therefore,laboratory procedures are needed to estimate the amount of such age hardening. Two laboratoryage-hardening procedures are used in the performance grading system: the rolling-thin film oventest (RTFOT) and the pressure aging vessel (PAV). The way in which these aging tests are usedin combination with the rheological tests is illustrated in Figure 3-3. DSR tests at high temperatureare performed on both the unaged binder and on the residue from the RTFOT aging procedure.Residue from the RTFOT procedure is then aged in the PAV, and additional tests are performedon the residue from this procedure. The DSR test at intermediate temperature and the BBR testare always performed. An optional test, the direct tension test, is also sometimes performed onthe PAV residue. Unlike the other performance grading tests, the direct tension procedure doesnot measure flow properties, but instead measures the fracture properties of the asphalt binderat low temperatures. The direct tension test is useful for grading some modified binders withunusually high strength and toughness, since it will improve the low temperature grade.The sections below describe in additional detail each of the grading procedures. The agingprocedures are discussed first, followed by the actual binder tests. This is followed by a discussionof the grading procedure and a section covering practical aspects of performance grade selectionfor HMA mix design.18 A Manual for Design of Hot Mix Asphalt with CommentaryUnagedbinderDSR test athightemperatureRTFOTaging & mass lossdeterminationDSR test atintermediatetemperaturePAV agingBBR test atlowtemperatureDirect tensiontest at lowtemperature(optional)Figure 3-3. Flow chart for performance grading tests.

RTFOT AgingRTFOT aging is meant to simulate asphalt binder age hardening as it occurs during mixing,transport, and placement. In this procedure, 35 grams of asphalt are carefully weighed intoglass bottles, which are placed in a circular rack in a specially designed oven. The rack slowlyrotates the bottles while the oven maintains the test temperature of 323°C. During the test, a jetof air is blown into the bottles for a few seconds once every rotation. The test is continued for75 minutes; the bottles are then removed from the oven, cooled, and weighed. The percent massloss is calculated from the initial and final weight of the asphalt binder in the bottle. High values ofmass loss mean that a significant amount of light oils have volatized during aging and, as a result,the asphalt binder might be prone to excessive age hardening, shrinkage, and cracking. Currentperformance grading standards require that mass loss during RTFOT aging be no more than 1.0%.After mass loss determination, the bottles are heated, and the asphalt is poured either into a tinfor further testing, or into PAV pans for additional aging. Figure 3-4 shows an RTFOT oven.PAV AgingIn the PAV aging test, the technician fills 125-mm-diameter stainless steel pans with asphaltthat has already been aged in the RTFOT test. Six of these pans are placed in a vertical rack, whichis then placed in the pressure vessel, which in turn is placed inside an oven. The pressure vessel isa heavily constructed steel chamber, designed to withstand the high pressure and temperature usedin the PAV test. These high temperatures and pressures help accelerate aging of the asphalt binder.At the end of the PAV test, the asphalt binder has aged about as much as would typically occurin a pavement after several years of service. Figure 3-5 shows the various pieces of equipmentused in performing the PAV aging procedure.DSR Test at High TemperatureThe primary purpose of the DSR test at high temperature is to ensure that a properly specifiedasphalt binder will have the proper engineering properties at high temperature and, when usedin an HMA mix, will keep it from rutting and shoving under traffic. The DSR is a torsionaltest in which a thin specimen of asphalt binder is sheared between two circular plates. It is alsoAsphalt Binders 19Figure 3-4. RTFOT aging oven.

a dynamic test, meaning that the specimen is sheared very quickly in a back and forth cycle ofloading. In the high-temperature test, the steel plates are 25 mm in diameter, and the specimenis about 1-mm thick. Figure 3-6 is a sketch of the DSR test, showing both the high temperaturesetup and the smaller plates used for the intermediate temperature test (described in detail in thefollowing section). The applied strain varies depending on the stiffness of the binder. The test isperformed at various temperatures, depending on the grade of the asphalt: 46, 52, 58, 64, 70, 76,and 82°C are the standard temperatures for high-temperature DSR tests. The first number in aperformance grade is the standard high temperature for DSR testing for that binder. For example,one of the most common grades of asphalt binder is PG 64-22; the high-temperature DSR teston this binder would be performed at 64°C.The DSR test measures both modulus and phase angle. Modulus is a measure of stiffness—the higher the value, the stiffer the binder. Because the DSR test is a shear test, the modulus valueis called the dynamic shear modulus, abbreviated with the symbol G*. The “G” indicates that themodulus is a shear value, and the “*” indicates that it is a dynamic modulus. In rheological testslike the DSR, the phase angle is a measure of how fluid a material is. The more a material behaveslike a fluid, the higher the phase angle. Materials that behave like an elastic solid—that springback quickly after loading—have a low phase angle. Phase angle is often abbreviated using theGreek letter δ (“delta”). When a material with a high phase angle is loaded and deforms, andthe load is removed, the material will tend to stay in its deformed shape—it will not spring back.20 A Manual for Design of Hot Mix Asphalt with Commentary(a) (b)Figure 3-5. PAV aging test: (a) pan; and (b) rack filled with pans.8-mm plates forintermediatetemperature tests25-mm plates forhigh temperaturetestsFigure 3-6. Diagram of DSR test at high and intermediatetemperature.

Phase angle should not be confused with stiffness or modulus. A very stiff clay might have ahigher modulus than a soft rubber, but a higher phase angle. This means it will deform less thanthe rubber under loading, but will not recover any of this deformation once the load is removed.In the high-temperature DSR test, the quantity specified is G*/sin δ, in units of kPa. By usingboth G* and sin δ in the specification, the stiffness and elasticity of the asphalt binder are simul-taneously controlled. Stiff, elastic binders will have a higher G*/sin δ value than soft, fluid binders.Performance-graded binders must have a G*/sin δ value of at least 1.0 kPa at the specified gradingtemperature in the unaged condition, using a test frequency of 10 rad/s. After RTFOT aging,the minimum value of G*/sin δ is 2.2 kPa.DSR Test at Intermediate TemperatureThe DSR test at intermediate temperature uses the same basic principles as the high-temperaturetest, but there are a few important differences. The DSR test at intermediate temperatures isdesigned to prevent binders from becoming too stiff at intermediate temperatures, which cancontribute to premature fatigue cracking in pavements. This also helps to control the overallflow properties of the asphalt binder. Because the asphalt binder is much stiffer at the lower testtemperatures, the plates must be smaller and the specimen thicker, as shown in Figure 3-6. For theintermediate temperature test, 8-mm-diameter plates are used, and the specimen is 2 millimetersthick. Instead of G*/sin δ, the specified quantity for the intermediate temperature test is G* 0002 sin δ,since many pavement researchers have found a relationship between G* 0002 sin δ and fatigue resist-ance for HMA mixtures. The DSR test at intermediate temperatures is run after RTFOT andPAV conditioning, at temperatures ranging from 4 through 40°C, in 3° increments (4, 7, 10°C,etc). The maximum allowable value for G* 0002 sin δ is 5,000 kPa, at a frequency of 10 rad/s.BBR TestThe purpose of the BBR test is to make sure that asphalt binders do not become too stiff andbrittle at low temperatures, since this can contribute to transverse cracking in HMA pavements.The BBR test is a flexural stiffness test—a small beam of asphalt is loaded for 1 minute and thedeflection is measured. From the applied load and resulting deflection, the creep stiffness of theasphalt binder is calculated. In analyzing the BBR data, another quantity, called the m-value, isalso calculated. The m-value is the log-log slope of the creep curve at a given loading time. The BBRspecimen is 125 millimeters long, 12.5 millimeters wide, and 6.25 millimeters thick. The test canbe run at test temperatures of −36, −30, −24, −18, −12, −6 and 0°C. When performance grading anasphalt binder, the BBR test is run at a temperature 10°C higher than the low grading temperature.A performance 64-22 binder, for example, would be tested using the BBR at −12°C. The maxi-mum allowable stiffness in the BBR test is 300 MPa at 60 seconds, and the minimum m-valueis 0.300 at the same loading time. Figure 3-7 is a sketch of the BBR test.Direct Tension TestThe direct tension test is unique among the binder specification tests in that it is a fracture test,and not a rheological test. In this procedure, a small specimen of asphalt is slowly pulled apart intension until it fails. Figure 3-8 illustrates the direct tension test. This test should not be confusedwith the older ductility test, which is performed at higher temperatures at much higher strains,and is an empirical test that does not provide any useful information on engineering properties.The results of the direct tension test are strain and stress at failure, and the test is performed atlow temperatures at very low strains and strain rates. These results can be used to perform ananalysis of low-temperature thermal stresses that produces an estimated cracking temperaturefor the binder, as outlined in AASHTO Provisional Standard PP 42. This temperature is then usedAsphalt Binders 21

to determine the low-temperature performance grade for the given binder. The main advantageof the direct tension test and associated analysis compared to BBR grading is that many polymer-modified binders have enhanced fracture properties that will result in a lower grading temperatureusing the direct tension test compared to that produced by BBR grading.Performance Grading—SpecificationTable 3-1 lists the various requirements for performance-graded asphalt binders, as describedin AASHTO M 320 Table 1. In AASHTO M 320 Table 1, the low-temperature grade of thebinder is based on creep stiffness and the m-value of the binder from the BBR. If the binder hasa creep stiffness between 300 and 600 MPa, the direct tension failure strain requirement can beused in lieu of the creep stiffness requirement. There is also a Table 2 in AASHTO M 320 whichuses the critical low cracking temperature from the direct tension test to determine the low-temperature grade of the binder. AASHTO M 320 Table 1 is the most commonly used specifica-tion for PG binders.22 A Manual for Design of Hot Mix Asphalt with CommentaryFigure 3-7. Sketch of BBR test.(a) (b)Figure 3-8. Photographs of the direct tension test: (a) specimen and mold and (b) test device.

Asphalt Binders 23PG 46 PG 52 PG 58 Binder Performance Grade: −34 −40 −46 −10 −16 −22 −28 −34 −40 −46 −16 −22 −28 −34 −40Design high pavement temperature, °C: <46 <52 <58 Design low pavement temperature, °C: ≥34 ≥40 ≥46 ≥10 ≥16 ≥22 ≥28 ≥34 ≥40 ≥46 ≥16 ≥22 ≥28 ≥34 ≥40 Test on Original BinderFlash Point Temperature (T 48), Min., °C 230Viscosity (T 316) Maximum value of 3 Pa-s at test temperature, °C135Dynamic Shear (T 315) G*/sin δ, minimum value 1.00 kPa, at 10 rad/s and Test Temperature, °C46 52 58 Tests on Residue from Rolling Thin Film Oven (T 240)Mass Loss, Maximum, % 1.00Dynamic Shear (T315) G*/sin δ, minimum value 2.20 kPa, at 10 rad/s and Test Temperature, °C46 52 58 Tests on Residue from Pressure Aging Vessel (R 28)PAV Aging Temperature, °C 90 90 100 Dynamic Shear (T 315) G* sin δ, maximum value 5,000 kPa, at 10 rad/s and Test Temperature, °C10 7 4 25 22 19 16 13 10 7 25 22 19 16 13 Creep Stiffness (T 313) Stiffness, maximum value 300 Mpa m-value, minimum value 0.30, at 60 sec and Test Temperature, °C−24 −30 −36 0 −6 −12 −18 −24 −30 −36 −6 −12 −18 −24 −30Direct Tension (T 314) Failure strain, minimum value 1.0%, at 1.0 mm/min and Test Temperature, °C−24 −30 −36 0 −6 −12 −18 −24 −30 −36 −6 −12 −18 −24 −30PG 64 PG 70 Binder Performance Grade: −10 −16 −22 −28 −34 −40 −10 −16 −22 −28 −34 −40Design high pavement temperature, °C: <64 <70 Design low pavement temperature, °C: ≥10 ≥16 ≥22 ≥28 ≥34 ≥40 ≥10 ≥16 ≥22 ≥28 ≥34 ≥40 Tests on Original Binder Flash Point Temperature (T 48), Min., °C 230Viscosity (T 316) Maximum value of 3 Pa-s at test temperature, °C135Dynamic Shear (T 315) G*/sin δ, minimum value 1.00 kPa, at 10 rad/s and Test Temperature, °C64 70 Tests on Residue from Rolling Thin Film Oven (T 240) Mass Loss, Maximum, % 1.00Dynamic Shear (T 315) G*/sin δ, minimum value 2.20 kPa, at 10 rad/s and Test Temperature, °C64 70 Tests on Residue from Pressure Aging Vessel (R 28) PAV Aging Temperature, °C 100 100 (110) Dynamic Shear (T 315) G* sin δ, maximum value 5,000 kPa, at 10 rad/s and Test Temperature, °C31 28 25 22 19 16 34 31 28 25 22 19 Creep Stiffness (T 313) Stiffness, maximum value 300 Mpa m-value, minimum value 0.30, at 60 sec and Test Temperature, °C0 −6 −12 −18 −24 −30 0 −6 −12 −18 −24 −30Direct Tension (T 314) Failure strain, minimum value 1.0%, at 1.0 mm/min and Test Temperature, °C0 −6 −12 −18 −24 −30 0 −6 −12 −18 −24 −30Table 3-1. Specification for performance-graded asphalt binders.(continued on next page)

Critical Temperatures, Specification Values, and ReliabilityA unique feature of the performance grading system is that it is based not on the values of agiven property at a given temperature, but on at what temperature a critical value of that propertyis achieved. A PG 58-28 binder has a G*/sin δ value of at least 1.0 kPa at 58°C and 10 rad/s in theunaged condition and a maximum flexural creep stiffness of no more than 300 MPa at −18°C at60 s. The two numbers in the performance grade (PG) refer to extreme high and low pavementtemperatures at which the binder is expected to perform adequately. It is important to understandhow these extreme pavement temperatures are defined. The high temperature is defined asthe yearly, 7-day average maximum pavement temperature, measured 20 millimeters below thepavement surface (referred to as design high pavement temperature). This may seem straight-forward, but because high pavement temperatures are quite variable, the design high pavementtemperature will vary from year to year and cannot be defined in a precise, single value. Instead,statistical methods must be used through the concept of reliability. The reliability of a given highpavement temperature refers to the probability that it will not be exceeded in any given year.For example, in Saint Louis, MO, the average value of the design high pavement temperatureis 52.9°C. That means that in any given year, there is a 50% chance that the actual high pavementtemperature will be lower than this, and a 50% chance that it will be higher. Therefore, the designhigh pavement temperature at a 50% level of reliability for Saint Louis is 52.9°C. At a 98% level ofreliability, the design high pavement temperature is 60.0°C. In other words, in any given year thereis a 98% chance that the maximum pavement temperature in Saint Louis will be less than 60°C.The same approach is used in low-temperature performance grading. In this case, the lowpavement temperature is defined simply as the minimum pavement temperature at the pavement24 A Manual for Design of Hot Mix Asphalt with CommentaryPG 76 PG 82 Binder Performance Grade: −10 −16 −22 −28 −34 −10 −16 −22 −28 −34Design high pavement temperature, °C: <76 <82 Design low pavement temperature, °C: ≥10 ≥16 ≥22 ≥28 ≥34 ≥10 ≥16 ≥22 ≥28 ≥34 Tests on Original Binder Flash Point Temperature (T 48), Min., °C 230Viscosity (T 316) Maximum value of 3 Pa-s at test temperature, °C135Dynamic Shear (T 315) G*/sin δ, minimum value 1.00 kPa, at 10 rad/s and Test Temperature, °C76 82 Tests on Residue from Thin Film Oven (T 240) Mass Loss, Maximum, % 1.00Dynamic Shear (T 315) G*/sin δ, minimum value 2.20 kPa, at 10 rad/s and Test Temperature, °C76 82 Tests on Residue from Pressure Aging Vessel (R 28) PAV Aging Temperature, °C 100 (110) 100 (110) Dynamic Shear (T 315) G* sin δ, maximum value 5,000 kPa, at 10 rad/s and Test Temperature, °C37 34 31 28 25 40 37 34 31 28 Creep Stiffness (T 313) Stiffness, maximum value 300 Mpa m-value, minimum value 0.30, at 60 sec and Test Temperature, °C0 −6 −12 −18 −24 0 −6 −12 −18 −24Direct Tension (T 314) Failure strain, minimum value 1.0%, at 1.0 mm/min and Test Temperature, °C0 −6 −12 −18 −24 0 −6 −12 −18 −24Table 3-1. (Continued).

surface experienced at a given location in a given year. For Salt Lake City, UT, the average lowpavement temperature is −13.6°C. Thus, the design low pavement temperature at 50% reliabilityis −13.6°C. At a 98% reliability level, the design low pavement temperature at Salt Lake City is −21.3°C. It should be emphasized that the design low pavement temperature is not the same asthe minimum air temperature. Typically, the design low pavement temperature is significantlyhigher than the minimum air temperature for a given location. In Salt Lake City, for example,the average minimum air temperature is −19.6°C, 6 degrees colder than the average design lowpavement temperature.Figure 3-9 is a plot of performance grade reliability for design high and low pavement temperatures for Atlanta, GA. In the example illustrated in this plot, at a 65% reliability level, thedesign high pavement temperature is 54.7°C, and the design low pavement temperature is 7.1°C.Calculation of design high and low pavement temperatures at different reliability levels involvescompilation of a wide range of weather data and analysis of this data to produce both averagevalues and standard deviations for design high and low pavement temperatures for thousands ofsites throughout the United States and Canada. Fortunately, the software package LTPPBind hasbeen developed to perform these calculations for pavement engineers and technicians. The valuesin the examples given above were taken from LTPPBind, Version 2.1. LTPPBind also can generatevarious useful plots, including reliability plots like that shown in Figure 3-9. At the time thismanual was being compiled, a new version of LTPPBind—Version 3.0—was in beta release.This newer version of LTPPBind differs substantially from Version 2.1. The most importantof these differences is that in Version 3.0, critical high temperatures are based not just on pavementtemperatures calculated from historical weather data, but from damage analyses performed usinga newly developed rutting model. Version 3.0, once in full release, should provide better estimatesfor design high pavement temperatures in hot, dry climates—situations where earlier versions ofLTPPBind appeared to under-predict high pavement temperatures. The LTPPBind program canbe downloaded from the LTPPBind website maintained by the FHWA.An important question is what level of reliability should be used when selecting binders.Engineers and technicians should keep in mind that if a PG binder is selected at a 50% reliabilitylevel, there is a 50-50 chance in any year that the high and/or low pavement temperature will exceedthose for which the binder has been developed. That is, a pavement made using a binder selectedat a 50% reliability level is likely to exhibit rutting and or low-temperature cracking within a fewyears. Therefore, high reliability levels should be used when selecting binders. For lightly traveledrural and residential roads, reliability levels of at least 90% should be used. For interstate highwaysAsphalt Binders 2552586440 50 60 70 80 90 100Reliability, %Design High Pvmt. Temp., C-16-10-4Design Low Pvmt. Temp., Cdesign low pavementtemperaturedesign high pavementtemperature-7.1oC54.7oC65%Figure 3-9. Example of PG binder grade reliability for Atlanta, GA.

and other major construction projects, reliability levels of at least 95% should be used whenselecting performance-graded binders.Practical Selection of PG Binder Grades for HMA Mix DesignAlthough the LTPPBind computer program is very useful, in practice most highway agencieshave, through experience, developed their own systems for selecting binder performance gradesdepending on traffic level and location. This has been done in part because refineries are able toproduce only a limited number of binder grades, so engineers must determine two or three per-formance grades that can be used to meet most or all of the paving needs in a given region. This issometimes referred to as a “binder slate” for a given state or region. For example, a common binderslate in the Mid-Atlantic states involves only three performance grades: 58-28, 64-22, or 76-22.Other binders might be occasionally used in this region, but typically only for small demonstrationprojects. Engineers selecting performance-graded binders for paving applications should refer tothe appropriate specifications for their state or, if there are none, to those in neighboring states withsimilar climates and conditions. Binder producers may also be useful in providing informationconcerning what binder performance grades are available locally and which might be mostappropriate for a given application. Engineers and technicians using the LTPPBind programwithout referring to the binders used by the local highway agency may find that the binder theyhave specified for a given application is not locally available.In selecting performance-graded binders from an available slate, it must be remembered that agiven performance grade will meet the requirements of many less extreme situations. For example,in many areas of the Mid-Atlantic, LTPPBind (version 3.1) indicates that a PG 58-22 binder shouldbe used for light traffic. However, this binder may not be available in some Mid-Atlantic states.If the PG 58-22 binder cannot be found (or found at a reasonable price), a PG 64-22 binder wouldbe selected and would perform perfectly well, since its extreme high and low temperature ratingsmeet or exceed those for these applications. Care should however be used in selecting bindersthat are much stiffer than required for a given application. Recently, many highway agencies havenoticed an increase in surface cracking in HMA pavements. Although such top-down crackingis not yet fully understood, using unnecessarily stiff binders may contribute to the problem.Additional details concerning the selection of asphalt binders for HMA mixtures are given inChapter 8 of this manual.BibliographyAASHTO StandardsM 320, Performance-Graded Asphalt BinderM 323, Superpave Volumetric Mix DesignPP 42, Determination of Low-Temperature Performance Grade (PG) of Asphalt BindersR 28, Accelerated Aging of Asphalt Binder Using a Pressurized Aging Vessel (PAV)R 29, Grading or Verifying the Performance Grade of an Asphalt BinderR 35, Superpave Volumetric Design for Hot-Mix Asphalt (HMA)T 48, Flash and Fire Points by Cleveland Open CupT 49, Penetration of Bituminous MaterialsT 51, Ductility of Bituminous MaterialsT 53, Softening Point of Bitumen (Ring-and-Ball Apparatus)T 202, Viscosity of Asphalts by Vacuum Capillary ViscometerT 240, Effect of Heat and Air on a Moving Film of Asphalt (Rolling Thin-Film Oven Test)T 313, Determining the Flexural Creep Stiffness of Asphalt Binder Using the Bending Beam Rheometer (BBR)26 A Manual for Design of Hot Mix Asphalt with Commentary

T 314, Determining the Fracture Properties of Asphalt Binder in Direct Tension (DT)T 315, Determining the Rheological Properties of Asphalt Binder Using a Dynamic Shear Rheometer (DSR)T 316, Viscosity Determination of Asphalt Binder Using Rotational ViscometerOther PublicationsThe Asphalt Institute, Asphalt Binder Test Manual (MS-25).The Asphalt Institute (2007) The Asphalt Handbook (MS-4A), 7th Ed., 832 pp.The Asphalt Institute (2003) Superpave Performance Graded Asphalt Binder Specifications and Testing, 3rd Ed.,72 pp.Asphalt Binders 27

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