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Aggregates Usually refers to a soil that has in some way been processed or sorted. Soils are materials that are used as-is. An example would be a finished.

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Presentation on theme: "Aggregates Usually refers to a soil that has in some way been processed or sorted. Soils are materials that are used as-is. An example would be a finished."— Presentation transcript:

0 SUPERPAVE FHWA Condensed Superpave Asphalt Specifications
Lecture Series

1 Aggregates Usually refers to a soil that has in some way been processed or sorted. Soils are materials that are used as-is. An example would be a finished subgrade surface. Aggregates are materials that have been specifically sorted or processed to achieve given properties. This block will present general background information about how aggregates are obtained and processed.

2 Aggregate Size Definitions
100 90 72 65 48 36 22 15 9 4 100 99 89 72 65 48 36 22 15 9 4 Nominal Maximum Aggregate Size one size larger than the first sieve to retain more than 10% Maximum Aggregate Size one size larger than nominal maximum size For HMA pavements these are the definitions for gradations.

3 Sieve Size (mm) Raised to 0.45 Power
Percent Passing 100 max density line restricted zone control point nom max size max size To specify aggregate gradation, two additional features are added to the 0.45 chart: control points and a restricted zone. Control points function as master ranges through which gradations must pass. They are placed on the nominal maximum size, an intermediate size and the dust size. The restricted zone resides along the maximum density gradation between the intermediate size (either or 2.36 mm) and the 0.3 mm size. It forms a band through which gradations should not pass. Gradations that pass through the restricted zone have often been called “humped gradations” because of the characteristic hump in the grading curve that passes through the restricted zone. In most cases, a humped gradation indicates a mixture that possesses too much fine sand in relation to total sand. This gradation practically always results in tender mix behavior, which is manifested by a mixture that is difficult to compact during construction and offers reduced resistance to permanent deformation during its performance life. Gradations that violate the restricted zone possess weak aggregate skeletons that depend too much on asphalt binder stiffness to achieve mixture shear strength. These mixtures are also very sensitive to asphalt content and can easily become plastic. Sieve Size (mm) Raised to 0.45 Power

4 Superpave Aggregate Gradation
Percent Passing 100 Design Aggregate Structure The term used to describe the cumulative frequency distribution of aggregate particle sizes is the design aggregate structure. A design aggregate structure that lies between the control points and avoids the restricted zone meets the requirements of Superpave with respect to gradation. Superpave defines five mixture types as defined by their nominal maximum aggregate size: Sieve Size (mm) Raised to 0.45 Power

5 Superpave Mix Size Designations
Superpave Nom Max Size Max Size Designation (mm) (mm) 37.5 mm 25 mm 19 mm 12.5 mm 9.5 mm These are the five gradations developed for Superpave.

6 Gradations * Considerations: - Max. size < 1/2 AC lift thickness -
Larger max size + Increases strength + Improves skid resistance + Increases volume and surface area of agg which decreases required AC content + Improves rut resistance + Increases problem with segregation of particles Several factors need to be considered in selecting a desirable aggregate gradation. The maximum size of the aggregate needs to be at a minimum less than one half of the planned lift thickness. Current construction practices with Superpave gradations indicate that this needs to be changed to less than one-third of the lift thickness. Larger maximum size aggregate gradations have several advantages such as improved aggregate interlock, improved skid resistance and improved rut resistance. Local availability of aggregates will usually dictate the largest size aggregate. Also, the larger maximum size gradations also tend to have more problems with gradation separation (segregation) during construction. - Smaller max size + Reduces segregation + Reduces road noise + Decreases tire wear

7 Percent Crushed Fragments in Gravels
Quarried materials always 100% crushed Minimum values depended upon traffic level and layer (lift) Defined as % mass with one or more fractured faces The appropriate percentages of each aggregate stockpile are combined and then split on the 4.75 mm screen. The material retained on the 4.75 mm screen are used to determine the percent crushed faces

8 Percent Crushed Fragments in Gravels
0% Crushed % with 2 or More Crushed Faces This is a measurement of coarse aggregate angularity. The amount of crushing (angularity) is important because it determines the level of internal shear resistance which can be developed in the aggregate structure. Round, uncrushed aggregates tend to “roll” out from under traffic loads and therefore have a low rutting resistance.

9 Coarse Aggregate Angularity Criteria
Traffic Depth from Surface Millions of ESALs < 100 mm > 100 mm < 0.3 < 1 < 3 < 10 < 30 < 100  100 55/-- 65/-- 75/-- 85/80 95/90 100/100 --/-- 50/-- 60/-- 80/75 Superpave requirements are based on both the traffic level and the depth of the layer below the surface. The crushing requirements for low traffic volumes are low or none, regardless of depth. As traffic levels increase, so do the required percentages of crushed faces. There is a higher level of crushing required in the upper 100 mm of the pavement because this is the region which is subjected to the highest shear due to traffic loads. Higher shear forces require a higher level of resistance to shear. First number denotes % with one or more fractured faces Second number denotes % with two or more fractured faces

10 Background History of Specifications
Asphalt Cements Background History of Specifications This block of instruction will cover traditional penetration and viscosity grading systems used in the US. While the Superpave binder specification is quickly replacing these specifications in practice, the vast majority of the literature will refer to these standards. People in this industry also commonly ask “So, what AC grade is a PG 64-22?”. These traditional specifications will remain the baseline against which field experience is translated into an understanding of the new Superpave binder specification. At the conclusion of this block the student will understand: * How to use traditional binder specifications * The limitations of these specifications which led to the development of the Superpave binder specification. This material is covered in detail in Chapter 2 “Asphalt Refining, Uses, and Properties” in the recommended text book.

11 Background Tar Asphalt Resistant to petroleum products
Soluble in petroleum products Generally a by-product of petroleum distillation process Can be naturally occurring Tar Resistant to petroleum products Generally by-product of coke (from coal) production Students commonly use the words “asphalt” and “tar” interchangeably. However, asphalt is actually a waste product from the refining of petroleum crude oil while tar is a coal by-product. These chemical distinctions are important in a selecting the appropriate product for a given application. For example, if protection from oil and fuel spills is desired, then a coating which will not be dissolved by these products is needed. Since motor oils, fuel, and asphalt are all derived from petroleum, any spills on this pavement can damage the asphalt-based coating as well as the asphalt concrete. The old chemistry rule-of-thumb applies: Like dissolves like. Because tar is a coal rather than asphalt-based product, sealers from this material will not be damaged by petroleum product spills.

12 Penetration Testing Sewing machine needle
Specified load, time, temperature 100 g Initial Penetration in 0.1 mm After 5 seconds The penetration test started out using a No. 2 sewing machine needle mounted on a shaft for a total mass of 100 g. This needle was allowed to sink into (penetrate) a container of asphalt cement at room temperature (25 oC) for 5 seconds. The consistency (stiffness) of a given asphalt was reported as the depth in tenths of a millimeter (dmm) that the needle penetrated the asphalt.

13 Penetration Specification
Five Grades This test was used to standardize the penetration grading system approach for specifying asphalt cements. This specification uses the penetration of the original asphalt cement in the grade names. That is, a penetration grade asphalt will have a penetration value for the original asphalt of between 120 and 150 tenths of a millimeter.

14 Ductility This test evaluates the ability of an asphalt sample to stretch at a rate of 5 cm/min at 25oC. The distance the samples can be pulled is measured directly from the centimeter scale mounted to the top of the tank. The significance of the ductility test to indicate performance-related properties has been debated for a number of years due to its empirical nature and poor reproducibility of test results. In general, asphalts with lower ductility have a greater tendency to produce pavements which have excessive cracking

15 Typical Penetration Specifications
Flash Point, C Ductility, cm Solubility, % There are five penetration grades of asphalt cements with discrete ranges. That is, there is no overlap in penetration values between grades. It is possible to have an asphalt which will not meet any penetration grading requirement. This table presents two of these grades. Note the flash point decreases with increasing penetration. This is because softer asphalts usually have a higher percentage of lighter ends which will “flash” at lower temperatures. The specification allows for this difference. Since these fractions of the asphalt are also easily removed by heating, this means that there will be a higher percentage mass loss on aging. This greater loss of the softer asphalt components is reflected in the differences in requirements on the percent of the original penetration retained after aging. That is, the more light ends lost during aging, the greater the stiffening affect due to aging. This loss of the softer asphalt components is also reflected the ductility requirements. Retained Pen., % Ductility, cm NA

16 Viscosity Graded Specifications
These disadvantages led to the development of the viscosity grading system in the 1970's which is detailed in ASTM D This one ASTM standard actually contains three separate specifications designated as: Table 1, Table 2, and Table 3. The first two specifications are based on the original properties of the asphalt while the last table is based on the properties of the asphalt after rolling thin film oven aging. Each of these tables and differences between them will be discussed in the following slides.

17 Types of Viscosity Tubes
Two viscosity measurements are used in this specification: Absolute viscosity (60 oC) and kinematic viscosity (135 oC). Both use the principle of the rate of flow through a known area to measure viscosity. Because asphalt is still very thick (stiff) at 60 oC, a vacuum is needed to move the asphalt through the tube in a reasonable time. At 135 oC, gravity and a falling head pressure is sufficient to get the asphalt to flow. Zietfuchs Cross-Arm Tube Asphalt Institute Tube

18 Table 1 Example AC 2.5 AC 40 Visc, 60C 250 + 50 4,000 + 800
Penetration This table compares two of the viscosity graded Table 1 specifications. The viscosity grading system provides immediate information as to the mean anticipated viscosity at 60 oC. For example, an AC 25 will have a mean viscosity of 250 Poise (2.5 times 100). Because of the limited allowable range (coefficient of variance of 20 percent), there is no overlap between the AC grades. Visc, 60C <1, <20,000 Ductility

19 Penetration Grades Viscosity, 60C (140F) AC 40 40 50 100 AC 20 60 50
70 85 100 120 150 200 300 Penetration Grades AC 40 AC 20 AC 10 AC 5 AC 2.5 100 50 Viscosity, 60C (140F) This figure provides a general comparison of the various traditional specifications. While there is no direct relationship between the specifications, there is a general relationship between stiffness and viscosity. Higher penetration numbers correspond with lower viscosities. 10 5

20 Asphalt Cements New Superpave Performance Graded Specification
This block of instruction will cover the tests, concepts and use of the new Superpave binder specifications. At the end of this block the student will be familiar with the : * Concepts behind the PG binder grading system. * Tests used for determining performance-related binder properties. * Selection of an appropriate PG binder grade.

21 PG Specifications Fundamental properties related to pavement performance Environmental factors In-service & construction temperatures Short and long term aging The PG grading system was developed to address the short comings seen in the traditional asphalt cement specifications. This specification is referred to as a binder rather than an asphalt cement specification. The difference is that a binder can be either a neat (unmodified) or modified asphalt cement. The term “asphalt cement” usually refers to an unmodified asphalt cement.

22 High Temperature Behavior
High in-service temperature Desert climates Summer temperatures Sustained loads Slow moving trucks Intersections Viscous Liquid The viscous component of the binder response dominates its warm temperature behavior and is seen as permanent deformation. The magnitude of this deformation is increased with the time that the load is applied.

23 Pavement Behavior (Warm Temperatures)
Permanent deformation (rutting) Mixture is plastic Depends on asphalt source, additives, and aggregate properties Permanent deformation or rutting of the pavement is the result of non-recoverable or plastic deformation due to traffic loads. At the warmer temperatures, the aggregate structure carries a major portion of the loads. Stiffer binders help to keep the aggregate structure intact as well as help resist deformation in the binder matrix.

24 Permanent Deformation
Ruts can be very visible in extreme cases such as the one shown in this photo. Other places where rutting can be observed are at stop lights. In many cases, the crosswalk lines can highlight this type of distress. Courtesy of FHWA Function of warm weather and traffic

25 Low Temperature Behavior
Cold climates Winter Rapid Loads Fast moving trucks Elastic Solid At cold temperatures, or under very quick loads, the binder response is predominately elastic. Hooke’s Law s = t E

26 Pavement Behavior (Low Temperatures)
Thermal cracks Stress generated by contraction due to drop in temperature Crack forms when thermal stresses exceed ability of material to relieve stress through deformation Material is brittle Depends on source of asphalt and aggregate properties A length of pavement can be considered to be a semi-infinite constrained beam. As the temperature drops the asphalt concrete wants to contract but is restrained. This results in internal stresses building up as the temperature drops. Thermal cracks occur when the contraction-induced stresses exceed the tensile strength of the mixture. A number of researchers have shown that the low temperature behavior of the asphalt concrete pavement is highly dependent upon the properties of the binder.

27 Thermal Cracking Courtesy of FHWA
Thermal cracks are transverse cracks, usually at relatively evenly spaced intervals. The spacing gets closer together with increasing binder stiffness the colder the temperatures. Courtesy of FHWA

28 Superpave Asphalt Binder Specification
The grading system is based on Climate PG Min pavement temperature Performance Grade The binder designation is based on expected extremes of hot and cold pavement temperatures. Average 7-day max pavement temperature

29 Pavement Temperatures are Calculated
Calculated by Superpave software High temperature 20 mm below the surface of mixture Low temperature at surface of mixture Pave temp = f (air temp, depth, latitude)

30 Concentric Cylinder Rheometers
t Rq = Mi 2 p Ri2 L g = W R Ro - Ri The rotational viscosmeter (also referred to at a Brookfield viscometer) is a concentric cylinder rheometer. This means that one cylinder rotates inside of another. Viscosity is determined from the amount of torque needed to rotate a cylinder (called a spindle) with a known geometry. Viscosity, as defined earlier, is the ratio of the shear stress to the strain rate. This viscometer uses information about the torque, speed, and geometry to obtain these measurements.

31 Dynamic Shear Rheometer (DSR)
Shear flow varies with gap height and radius Non-homogeneous flow Parallel Plate tR = 2 M p R3 This type of rheometer has a parallel plate configuration. The stress and strain measurements are based on the assumption of a cylindrical geometry. This is why a great deal of effort is expended in preparing and trimming the specimen prior to starting the test. gR = R Q h

32 Short Term Binder Aging
Rolling Thin Film Oven Simulates aging from hot mixing and construction Short term aging is accomplished using the same RTFO oven as has been traditionally used in the AR viscosity graded specification.

33 Pressure Aging Vessel (Long Term Aging)
Simulates aging of an asphalt binder for 7 to 10 years 50 gram sample is aged for 20 hours Pressure of 2,070 kPa (300 psi) At 90, 100 or 110 C A pressure aging vessel (PAV) treatment of the RTFO binder is used to further age the binder. This simulates long term aging changes.

34 Bending Beam Rheometer
Computer Deflection Transducer Air Bearing Load Cell Fluid Bath This test applies a static load to a simply supported beam of asphalt cement. Temperature is held constant using a liquid bath. A computer provides both equipment control and data acquisition.

35 Direct Tension Test Load Stress = s = P / A D L sf D Le ef Strain
Regardless of the type of equipment used, a sample of binder is molded into a “dog bone” shape with a uniform center cross section. The sample is pulled until the it breaks in the middle. The stress and strain at failure are recorded. This test requires a minimum strain before the sample fails. ef Strain

36 Summary Low Temp Fatigue Cracking Cracking Construction Rutting [DTT]
[RV] [DSR] [BBR] This figure summarizes the testing required for the PG binder specification. RTFO Short Term Aging No aging PAV Long Term Aging

37 Superpave Binder Purchase Specification
One of the primary purposes of the Superpave binder testing is to use that data for the development of a purchase specification for asphalt binders.

38 Min pavement temperature Average 7-day max pavement temperature
Superpave Asphalt Binder Specification The grading system is based on Climate PG Min pavement temperature Performance Grade The binder designation is based on expected extremes of hot and cold pavement temperatures. Average 7-day max pavement temperature

39 Performance Grades ORIGINAL > 230 oC > 1.00 kPa > 2.20 kPa
CEC Avg 7-day Max, oC PG PG PG PG PG PG PG 82 1-day Min, oC ORIGINAL > 230 oC (Flash Point) FP < oC (Rotational Viscosity) RV (Dynamic Shear Rheometer) DSR G*/sin  > 1.00 kPa (ROLLING THIN FILM OVEN) RTFO Mass Loss < % (Dynamic Shear Rheometer) DSR G*/sin  > 2.20 kPa (PRESSURE AGING VESSEL) PAV This is the binder specification - it is defined by AASHTO MP -1. 20 Hours, 2.07 MPa (110) (110) (110) (Dynamic Shear Rheometer) DSR G* sin  < 5000 kPa 28 S < 300 MPa m > 0.300 ( Bending Beam Rheometer) BBR “S” Stiffness & “m”- value Report Value (Bending Beam Rheometer) BBR Physical Hardening > 1.00 % (Direct Tension) DT

40 How the PG Spec Works Spec Requirement Remains Constant
CEC Spec Requirement Remains Constant Avg 7-day Max, oC PG PG PG PG PG PG PG 82 1-day Min, oC 58 64 ORIGINAL > 230 oC (Flash Point) FP < oC (Rotational Viscosity) RV (Dynamic Shear Rheometer) DSR G*/sin  > 1.00 kPa (ROLLING THIN FILM OVEN) RTFO Mass Loss < % (Dynamic Shear Rheometer) DSR G*/sin  > 2.20 kPa (PRESSURE AGING VESSEL) PAV The approach to the PG system represents a change in philosophy. The specification requirement does not change; the temperature which the value has to meet changes with grade. 20 Hours, 2.07 MPa Test Temperature Changes (110) (110) (110) (Dynamic Shear Rheometer) DSR G* sin  < 5000 kPa 28 S < 300 MPa m > 0.300 ( Bending Beam Rheometer) BBR “S” Stiffness & “m”- value Report Value (Bending Beam Rheometer) BBR Physical Hardening > 1.00 % (Direct Tension) DT

41 PG Binder Selection PG 52-28 PG 58-22 PG 58-16 PG 64-10
> Many agencies have established zones PG 52-28 Many states have divided their territory into different regions. How many regions depends on the variation of climates. PG 58-22 PG 58-16 PG 64-10

42 Summary of How to Use PG Specification
Determine 7-day max pavement temperatures 1-day minimum pavement temperature Use specification tables to select test temperatures Determine asphalt cement properties and compare to specification limits This provides a brief summary of the steps needed to determine if an asphalt meets a particular PG specification.

43 Asphalt Concrete Mix Design
History This block will present background information on the traditional Marshall and Hveem mix design methods. At the conclusion of this block the student will have a general understanding of: The principal procedures and concepts used in Marshall and Hveem mix design techniques This material is covered in detail in Chapter 4 “Hot Mix Asphalt Mixture Design Methodology” of the recommended textbook.

44 Hot Mix Asphalt Concrete (HMA) Mix Designs
Objective: Develop an economical blend of aggregates and asphalt that meet design requirements Historical mix design methods Marshall Hveem New Superpave gyratory The objective of HMA mix design is to develop an economical blend of aggregates and asphalt. In the developing of this blend the designer needs to consider both the first cost and the life cycle cost of the project. Considering only the first cost may result in a higher life cycle cost. Historically asphalt mix design has been accomplished using either the Marshall or the Hveem design method. The most common method was the Marshall. It had been used in about 75% of the DOTs throughout the US and by the FAA for the design of airfields. In 1995 the Superpave mix design procedure was introduced into use. It builds on the knowledge from Marshall and Hveem procedures. The primary differences between the three procedures is the machine used to compact the specimens and strength tests used to evaluate the mixes. The current plan is to implement the Superpave procedures throughout the US for the design and quality control of HMA highway projects early in the next century. It appears that the Marshall method will continue to be used for airfield design for many years and that the Hveem procedure will continue to be used in California.

45 Requirements in Common
Sufficient asphalt to ensure a durable pavement Sufficient stability under traffic loads Sufficient air voids Upper limit to prevent excessive environmental damage Lower limit to allow room for initial densification due to traffic Sufficient workability No matter which design procedure is going to be used the HMA mixture that is placed on the roadway must meet certain requirements. The mix must have sufficient asphalt to ensure a durable, compacted pavement by thoroughly coating, bonding and waterproofing the aggregate. Enough stability to satisfy the demands of traffic without displacement or distortion (rutting). Sufficient voids to allow a slight amount of added compaction under traffic loading without bleeding and loss of stability. However, the volume of voids should be low enough to keep out harmful air and moisture. To accomplish this the mixes are usually designed by 4% VTM in the lab and compacted to less than 7% VTM in the field. Enough workability to permit placement and proper compaction without segregation.


47 Marshall Mix Design Developed by Bruce Marshall for the Mississippi Highway Department in the late 30’s WES began to study it in 1943 for WWII Evaluated compaction effort No. of blows, foot design, etc. Decided on 10 lb.. Hammer, 50 blows/side 4% voids after traffic Initial criteria were established and upgraded for increased tire pressures and loads Point out that the criteria has been modified since initial development; but, the basic process is the same as it was when it was initially developed.

48 Marshall Mix Design Select and test aggregate
Select and test asphalt cement Establish mixing and compaction temperatures Develop trial blends Heat and mix asphalt cement and aggregates Compact specimen (100 mm diameter) This slide outlines the major steps in the development of a Marshall mix design.

49 Marshall Design Criteria
Light Traffic Medium Traffic Heavy Traffic ESAL < < ESAL< ESAL > 106 Compaction Stability N (lb.) (750) 5338 (1200) (1800) Flow, 0.25 mm (0.1 in) to to to 14 Air Voids, % to to to 5 Voids in Mineral Agg. (VMA) Varies with aggregate size The criteria on this slide is that recommended by The Asphalt Institute. Most DOTs have their own requirements and they may vary some from that noted here.

50 Asphalt Concrete Mix Design
Superpave This block of instruction will cover the Superpave procedures. At the conclusion of this block the student will have a general understanding of: The principal procedures involved in the Superpave mix design. The relationship between these procedures and paving specifications. This material is covered in detail in Chapter 4 “Hot Mix Asphalt Mixture Design Methodology” of the recommended textbook.

51 Superpave Volumetric Mix Design
Goals Compaction method which simulates field Accommodates large size aggregates Measure of compactibility Able to use in field labs Address durability issues Film thickness Environmental The goals of the first new mix design procedure for HMA pavements in over 50 years were to have a procedure that would simulate the real world. In the past we may have “allowed the mold to design road”. The Marshall and Hveem procedures used 4 inch (100 mm) molds with Superpave using 150 mm molds to use larger aggregates. By monitoring compaction throughout the process, may provide a measure of how the mix will compact during construction. It was also desired to have equipment that could be used to for field quality control purposes.

52 Compaction Key Components of Gyratory Compactor height
measurement control and data acquisition panel reaction frame loading ram mold tilt bar These are the components of the machine. rotating base

53 Compaction Gyratory compactor Axial and shearing action
150 mm diameter molds Aggregate size up to 37.5 mm Height measurement during compaction Allows densification during compaction to be evaluated Ram pressure 600 kPa The compactor puts 600 kPa of pressure on the specimen and operates at 30 rpm. 1.25o

54 Three Points on SGC Curve
% Gmm Nmax Ndes Nini There are three critical points on the SGC compactor curve that are evaluated in Superpave. Ninital is of importance because it is desirable not to have mixes that compact too easily. Nmaximum is of importance to prevent having mixes that continue to compact under traffic loading. Log Gyrations

55 SGC Critical Point Comparison
%Gmm= Gmb / Gmm Gmb = Bulk Mix Specific Gravity from compaction at N cycles Gmm = Max. Theoretical Specific Gravity Compare to allowable values at: NINI : %Gmm < 89% NDES: %Gmm < 96% NMAX: %Gmm < 98%

56 Design Compaction Nmax Ndes based on Ndes Log Nmax = 1.10 Log Ndes
% Gmm Nmax Ndes based on average design high air temp traffic level Log Nmax = 1.10 Log Ndes Log Nini = 0.45 Log Ndes Ndes Nini The level of Ndesign is based on the climate and traffic levels. Log Gyrations

57 Superpave Testing Specimen heights Mixture volumetrics Dust proportion
Air voids Voids in mineral aggregate (VMA) Voids filled with asphalt (VFA) Mixture density characteristics Dust proportion Moisture sensitivity This data is available or must be calculated to complete the development of the Superpave mix design.

58 Superpave Mix Design Determine mix properties at NDesign and compare to criteria Air voids % (or 96% Gmm) VMA See table VFA See table %Gmm at Nini < 89% %Gmmat Nmax < 98% Dust proportion to 1.2 These properties are determined and compared to the specification criteria.

59 Gyratory Compaction Criteria
Superpave Mix Design Gyratory Compaction Criteria These properties are determined and compared to the specification criteria.

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