Superpave Asphalt Mixture Design Workshop Workbook

Transcription

1 Version 6.2 Updated July 1999 U.S. Department of Transportation Federal Highway Administration Superpave Asphalt Mixture Design Workshop Workbook "Superpave Asphalt Mix Design & Field Management" Demonstration Project No. 90

2 Superpave Asphalt Mixture Design Workshop Developed by the Asphalt Team Thomas Harman (202) Federal Highway Administration, HRDI Georgetown Pike, McLean, VA John D'Angelo (202) John Bukowski (202) Federal Highway Administration, HIPT 400 Seventh Street, S. W., Washington, DC In conjunction with Charles Paugh Carl Gordon With excerpts from Field Management of Asphalt Mixes - Summary of Simulation Studies, FHWA National Asphalt Training Center Training Manuals, Asphalt Institute MS & SP Series, & Superpave Lead States Guidelines.

3 This workshop is intended to demonstrate the Superpave asphalt mixture design system developed by the Strategic Highway Research Program (SHRP), along with the application of certain innovative concepts in field management of asphalt mixes. This workshop includes the latest recommendations of the Superpave Lead States and the Mixture, Binder, & Aggregate Expert Task Groups. Very Special Thanks To Dr. Aroon Shenoy, Ph.D. Editor & Friend

4 TABLE OF CONTENTS FOREWORD...1 INTRODUCTION...1 Background of SHRP...1 SHRP Implementation...2 SUPERPAVE OVERVIEW...3 Simulation Background...5 SELECTION OF MATERIALS...6 Binder Tests Required for Mixture Design...15 Aggregate Selection...19 CONSENSUS PROPERTY STANDARDS...20 Coarse Aggregate Angularity (ASTM D 5821)...20 Uncompacted Void Content of Fine Aggregate (AASHTO TP33)...21 Flat or Elongated Particles in Coarse Aggregate (ASTM D 4791)...21 Sand Equivalent Test (AASHTO T 176)...22 SOURCE PROPERTY STANDARDS...31 L.A. Abrasion (AASHTO T 96)...31 Sulfate Soundness (AASHTO T 104)...31 Clay Lumps and Friable Particles (AASHTO T 112)...32 SELECTION OF A DESIGN AGGREGATE STRUCTURE...33 SELECTION OF THE DESIGN ASPHALT BINDER CONTENT...63 EVALUATION OF MOISTURE SENSITIVITY AASHTO T APPENDICES...68 PROJECT SUMMARY...69 MIXING AND COMPACTION TEMPERATURE DETERMINATION...74

5 LIST OF TABLES Original: MP-2, Table 1 - Binder Selection on the Basis of Traffic Speed and Traffic Level...9 Current 01: MP-2, Table 1 - Binder Selection on the Basis of Traffic Speed and Traffic Level.10 Table: Superpave Performance Grades (PG)...11 Table: Binder Specification Test Results...13 Table: Aggregate Stockpiles...19 Table: Aggregate Tests...20 Original: MP-2, Table 4 - Coarse Aggregate Angularity Criteria (ASTM DX)...23 Original: MP-2, Table 5 - Uncompacted Void Content of Fine Aggregate Criteria (TP33)...23 Current 01: MP-2, Table 4 - Superpave Aggregate Consensus Property Requirements...25 Table: Simulation Study Test Results (ASTM D 5821), CAA...26 Table: Simulation Study Test Results (AASHTO TP 33), FAA...26 Table: Simulation Study Test Results (ASTM D 4791), F&E...27 Table: Simulation Study Test Results (AASHTO T 176), SE...27 Table: Superpave Aggregate Gradation Requirements...35 Table: Develop Trial Blends...36 Table: Summary of Trial Blend Percentages...39 Table: Summary of Actual Stockpile and Estimated Blend Properties...39 Table: Estimated Effective Specific Gravities...41 Table: Estimated Volume of Absorbed Binder...41 Table: Estimated Weight of Aggregate and Percent of Binder...42 Table: Required Tests...43 Original: PP-28, Table 2 - Gyratory Compaction Criteria...46 Current 01: PP-28, Table 1 - Superpave Gyratory Compaction Effort...47 Original: PP-28, Table 3 - Summary of Volumetric Design Criteria...48 Current 99: PP-35, Table 2 - Superpave Volumetric Mixture Design Requirements...49 Original: PP-35, Table 4 - Selection of a Design Aggregate Structure (Example)...50 Current 99: PP-28, Table 4 - Selection of a Design Aggregate Structure (Example)...51 Table: Summary of Project Volumetric Criteria...52 Table: Trial Blend No. 1: Specimen Compaction & Height Data...55 Table: Trial Blend No. 1 Compaction Results...55 Table: Trial Blend No. 1 Compaction Results...57 Table: Summary Superpave Gyratory Compaction Results...59 Table: Summary of Estimated Properties at 4 % V a...61 Table: Required Tests...63 Table: Compaction Test Results...64 Table: Volumetric Test Results at N design...65 Table: Summary of Design Mixture Properties at 5.4 % AC (P b )...65 Table: AASHTO T 283 Results...67

6 LIST OF FIGURES Figure: ASTM D Figure: AASHTO T Figure: Trial Blends 0.45 Power Chart...37 Figure: Gyratory Compaction Graph...53 Figure: Gyratory Compaction Data...57 Figure: Trial Blend Gyratory Compaction Curves...59 Figure: Design Gyratory Compaction Curves...64

7 Superpave Asphalt Mixture Design

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9 Workbook: Introduction Page 1 FOREWORD The focus of this workbook is to provide engineers and technicians with a detailed example of Superpave Volumetric asphalt mixture design. INTRODUCTION a. Background of SHRP The Strategic Highway Research Program (SHRP) was established by Congress in 1987 as a five-year, $150 million dollars, product driven, research program to improve the quality, efficiency, performance, and productivity of our nation's highways and to make them safer for motorists and highway workers. It was developed in partnership with States, American Association of State Highway and Transportation Officials (AASHTO), Transportation Research Board (TRB), Industry, and Federal Highway Administration (FHWA). SHRP research focused on asphalt (liquids and mixtures), concrete & structures, highway operations, and long-term pavement performance (LTPP).

10 Workbook: Introduction Page 2 b. SHRP Implementation As a follow-up program to SHRP, Congress authorized $108 million over six years as part of the Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991, to establish programs to implement SHRP products and to continue SHRP's LTPP program. The FHWA was given the responsibility of directing the implementation efforts to facilitate the application of the research findings. Several concurrent efforts were undertaken including: 1) Asphalt Technical Working Group (TWG) 2) Expert Task Groups: a) Asphalt Binder b) Asphalt Mixture c) Superpave Models - Now part of NCHRP ) Pooled Fund Equipment Buys - Nearly Completed 4) National Asphalt Training Center - Completed 5) Mobile Superpave Laboratories 6) Equipment Loan Program - Completed 7) Expert Technical Assistance 8) Superpave Regional Centers 9) Superpave Models Contract - Now NCHRP ) Superpave Lead States In 1998, Congress enacted the Transportation Equity Act for the 21 st Century (TEA21). Although TEA21 encourages the continued implementation of SHRP technologies, no specific funding is provided. To address this shortfall in funding the FHWA, AASHTO, TRB, and NCHRP approached the States to fund critical Superpave activities with NCHRP funding. The Asphalt TWG has been replace by the TRB Superpave Committee. The ETG s have also been transferred to TRB for management. FHWA will continue to provide expert technical assistance.

11 Workbook: Introduction Page 3 SUPERPAVE OVERVIEW The final product of the SHRP asphalt program area is Superpave. Superpave is an acronym which stands for: Superior Performing Asphalt Pavements. Superpave is a performance-related asphalt binder and mixture specification. Superpave is not just a computer software package, nor just a binder specification, nor just a mixture design and analysis tool. Superpave is a system which is inclusive of all these parts. Superpave mixture design provides for a functional selection, blending, and volumetric analysis of proposed materials, along with an evaluation of moisture sensitivity. There are four steps in mixture design: 1. Selection of Materials, 2. Selection of a Design Aggregate Structure, 3. Selection of the Design Asphalt Binder Content, and 4. Evaluation of Moisture Sensitivity of the Design Mixture. Criteria for materials selection and compaction are a function of three factors: a. Environment, b. Traffic, and c. Pavement Structure. Binder selection is based on environmental data, traffic level and traffic speed. Aggregate selection is based upon layer location, traffic level, and traffic speed. Selection of the design aggregate structure (design blend) consists of determining the aggregate stockpile proportions and corresponding combined gradations of the mix design. The design aggregate structure, when blended at the optimum asphalt binder content, should yield acceptable volumetric properties based on the established criteria. Selection of the design (optimum) asphalt binder content consists of varying the amount of asphalt binder in the design aggregate structure to obtain acceptable volumetric properties when compared to the established mixture criteria. It also provides a feel for the sensitivity of the design properties to changes in the asphalt binder content during production. Evaluation of moisture sensitivity consists of testing the design mixture by AASHTO T-283, or other State specified method, to determine if the mixture will be susceptible to moisture damage.

12 Workbook: Step 1- Selection of Materials Page 4 Simulation Background a. This simulated project is located in the city of Hot Mix, USA. b. The estimated, 20-year, design traffic for this project is 6,300,000 ESAL 80-kN, (18-kip ESAL = 80-kN ESAL). c. The posted traffic speed for the design section is 80 kilometers per hour, kph (50 mph). The estimated actual average speed for this section, accounting for speeding and rush hour, is 72 kph (45 mph). d. The mix is a surface course (such that the top of this pavement layer from the surface is less than 100 millimeters). The project location in conjunction with the Weather Database will provide the minimum pavement temperature, the maximum pavement temperature, and the maximum air temperature. The estimated traffic and project temperature data, in combination with the layer location will establish the material and compaction criteria. Update: All Superpave mixes are designed volumetrically. Currently under NCHRP study 9-19, Superpave Models Development, being conducted by the University of Maryland, a simple performance test is being identified/developed. The simple performance test will be used in conjunction with the Superpave volumetric mixture design. This test is intended to add an additional level of reliability to assure design mixes are able to resist the applied trafficking with minimal permanent deformation (rutting).

13 Workbook: Step 1- Selection of Materials Page 5 SELECTION OF MATERIALS The performance grade (PG) binder required for the project is based on environmental data, traffic level and traffic speed. The environmental data is obtained by converting historic air temperatures to pavement temperatures. The SHRP researchers developed algorithms to convert high and low air temperatures to pavement temperature: SHRP High-Temperature Models T(surf) = T(air) Lat ² Lat (1) where: T(surf) = High pavement temperature at the surface, C T(air) = Air temperature, C Lat = Latitude of the section, degrees T(d) = T(surf) ( d d ² d 3 ) (2) where: T(d) = High pavement temperature at a depth, d, in mm, C T(pav) = (T(air) Lat ² Lat ) (3) where: T(pav) High pavement temperature at 20 mm below the surface, C SHRP Low-Temperature Model T(d) = T(air) d d ² (4) where: T(d) = Low pavement temperature at a depth, d, in mm, C T(air) = Air temperature, C d = Depth in pavement in mm

14 Workbook: Step 1- Selection of Materials Page 6 The Lead States have recommended the adoption of the FHWA Long-Term Pavement Performance (LTPP) Program s new algorithms based upon the following rationale: Lead States Rationale The current SHRP low-pavement-temperature algorithm does not correctly determine the low pavement temperature from the air temperature. The FHWA LTPP program has developed a new low-pavement-temperature algorithm from their weather stations at over 30 sites all over North America. The Binder Expert Task Group feels the LTPP algorithm is far more accurate and should be used in all AASHTO documents. Data supporting the LTPP algorithm is presented in LTPP Seasonal Asphalt Concrete Pavement Temperature Models, FHWA-RD , September, The LTPP proposed algorithms are as follows: LTPP High-Temperature Model with Reliability T(pav) = T(air) Lat ² log 10 (H + 25)+ z ( σ air ²) ½ (5) where: T(pav) = High pavement temperature below the surface, C T(air) = High air temperature, C Lat = Latitude of the section, degrees H = Depth from surface, mm σ air = Standard deviation of the high 7-day mean air temperature, C z = From the standard normal distribution table, z=2.055 for 98% reliability LTPP Low-Temperature Model with Reliability T(pav) = T(air) Lat ² log 10 (H + 25)-z ( σ air ²) ½ (6) where: T(pav) = Low pavement temperature below the surface, C T(air) = Low air temperature, C Lat = Latitude of the section, degrees H = Depth from surface, mm σ air = Standard deviation of the high 7-day mean air temperature, C z = From the standard normal distribution table, z=2.055 for 98% reliability A complete report documenting the research is available entitled, LTPP Seasonal Asphalt Concrete (AC) Pavement Temperature Models. Publication No. FHWA-RD , September 1998.

15 Workbook: Step 1- Selection of Materials Page 7 The average 7-day maximum pavement temperature (T max ) and the minimum pavement temperature (T min ) define the binder laboratory test temperatures. A factor of safety can be incorporated into the performance grading system based on temperature reliability. The 50 % reliability temperatures represent the straight average of the weather data. The 98 % reliability temperatures are determined based on the standard deviations of the low (σ Low Temp ) and high (σ High Temp ) temperature data. From statistics, 98 % reliability is two standard deviations from the average value, such that: T max at 98% = T max at 50% + 2 * σ High Temp T min at 98% = T min at 50% - 2 * σ Low Temp Low Temperature Mean -18 degrees STD 3 degrees Pavement Temperature Distributions High Temperature Mean 52 degrees STD 2 degrees Normal Distribution Mean Mean % % % % Grades % 58 84% % % Page 12

16 Workbook: Step 1- Selection of Materials Page 8 Traffic level and speed are also considered in selecting the project performance grade (PG) binder either through reliability or grade bumping. A table is provided in AASHTO MP-2, Standard Specification for Superpave Volumetric Mix Design, to provide the designer with guidance on grade selection. The Lead States proposed a new table to better clarify the intent of grade bumping. Original: MP-2, Table 1 - Binder Selection on the Basis of Traffic Speed and Traffic Level TRAFFIC LOADING ADJUSTMENT TO BINDER PG GRADE Standing (< 20 km/h) Increase high temperature grade by 2 grades (12ºC). Use low temperature grade as determined in Section 5.4. Slow Transient (20 to 70 km/h) Increase high temperature grade by 1 grade (6ºC). Use low temperature grade as determined in Section 5.4. TRAFFIC LEVEL, ESAL ADJUSTMENT TO BINDER PG GRADE 1 x 10 7 to 3 x 10 7 Consideration should be given to increasing the high temperature grade by 1 grade (6ºC). Use low temperature grade as determined in Section 5.4. > 3 x 10 7 Increase high temperature grade by 1 grade (6ºC). Use low temperature grade as determined in Section 5.4

17 Workbook: Step 1- Selection of Materials Page 9 Current 03: MP-2, Table 1 - Binder Selection on the Basis of Traffic Speed and Traffic Level Adjustment to Binder PG Grade a Traffic Load Rate Design ESALs b (million) Standing c Slow d Standard e < 0.3 f to < to < to < f > a b c d e f Increase the high temperature grade by the number of grade equivalents indicated (one grade is equivalent to 6ºC). Use the low temperature grade as determined in Section 5. The anticipated project traffic level expected on the design lane over a 20 year period. Regardless of the actual design life of the roadway, determine the design ESALs for 20 years. Standing Traffic - where the average traffic speed is less than 20 km/h. Slow Traffic - where the average traffic speed ranges from 20 to 70 km/h. Standard Traffic - where the average traffic speed is greater than 70 km/h. Consideration should be given to increasing the high temperature grade by one grade equivalent. Note 4 - Practically, PG binders stiffer than PG 82-xx should be avoided. In cases where the required adjustment to the high temperature binder grade would result in a grade higher than a PG 82, consideration should be given to specifying a PG 82-xx and increasing the design ESALs by one level (e.g., 10 to <30 million increased to > 30 million). Author s Note The designer should use either reliability or the above table to address high traffic levels and slower traffic speeds. Both methods can effectively bump the performance grade such that the appropriate binder is used. However, using them in combination will result in an unnecessarily stiff binder, which in turn may cause problems during production and lay down.

18 Workbook: Step 1- Selection of Materials Page 10 Performance grades are delineated by 6 C increments. The following table shows the Superpave performance grade temperatures. A few State highway agencies have chosen to specify alternative performance grades. In Georgia, for example, the department of transportation specifies a PG This ensures the DOT of receiving an asphalt binder similar to what they have used historically, AC-30. Although highway agencies are not encouraged to alter the Superpave performance grades, Georgia is still receiving a performance grade asphalt. Binders provided to meet their modified specification still have to meet the Superpave test criteria, just at different temperatures. Table: Superpave Performance Grades (PG) Average 7-day Maximum Pavement Temperature (PG ##- ) 46ºC 52ºC 58ºC 64ºC 70ºC 76ºC 76º+ n6º Minimum Pavement Temperature (PG -##) +2ºC -4ºC -10ºC -16ºC -22ºC -28ºC -28º-n6º

19 Workbook: Step 1- Selection of Materials Page 11 For Hot Mix, USA, the following data is obtained from the project location and historical temperature data: a. Latitude is 41.1 degrees, b. 7-day average maximum air temperature is 33.0 C with a σ of 2 C, and c. 1-day average minimum air temperature is C with a σ of 3 C. From this data the high and low pavement temperature are determined at a depth of 20 mm: SHRP Algorithms LTPP Algorithms High pavement temperature Low pavement temperature 53.2 C C High pavement temperature Low pavement temperature 50.8 C C PG at 50% reliability PG at 98% reliability PG at 50% reliability PG at 98% reliability Q. For the pavement high temperature calculations, which algorithm produces the highest value? a. SHRP, or b. LTPP. Q. For the pavement low temperature calculations, which algorithm produces the lowest value? a. SHRP, or b. LTPP. Q. Does this make the new LTPP algorithms more or less conservative? a. More, or b. Less. Q. Does the project traffic level of 6.3 million ESAL s warrant an increase in the high temperature performance grade? a. Yes, or b. No. Q. Does the estimated, actual, average speed of 72 kph warrant an increase in the high temperature performance grade? a. Yes, or b. No. For Hot Mix, USA, the 50 % reliability LTPP performance grade is a PG The project traffic level and speed do not require grade bumping. However, the traffic speed is just above

20 Workbook: Step 1- Selection of Materials Page 12 the threshold for grade bumping and historically in this area pavements have shown susceptibility to low-temperature cracking. Such that, the agency shall require a PG Binder Selection The project asphalt binder is tested for specification compliance to the Superpave PG system. Project Binder: PG Binder Source: Asphalt is Us Table: Binder Specification Test Results Test Property Results Criteria Original Binder Flash Point n/a 310ºC > 230ºC Rotational Viscometer 135ºC Rotational Viscometer 165ºC Dynamic Shear Rheometer, G * /sin δ 58ºC Pa-s Pa-s 1.7 kpa < 3 Pa-s n/a > 1.0 kpa Mass Loss RTFO Residue - Aged Binder n/a 0.4 % < 1.0 % Dynamic Shear Rheometer, G * /sin δ 58ºC 2.8 kpa > 2.2 kpa RTFO + PAV Residue - Aged Binder Dynamic Shear Rheometer, G * sin δ 22ºC 3.4 MPa < 5 MPa Bending Beam Rheometer, Stiffness -12ºC 280 MPa < 300 MPa Bending Beam Rheometer, m-value -12ºC > 0.300

21 Workbook: Step 1- Selection of Materials Page 13 Binder ETG - Future Change The Superpave low temperature binder specification is being revised using a new scheme to determine the critical thermal cracking temperature. The main consideration in the new scheme is to unite the rheological properties obtained using the Bending Beam Rheometer (BBR) and the failure properties acquired from the new Direct Tension Test (DTT). The lowtemperature task group (LTTG), under the auspices of the Binder Expert Task Group, is evaluating the following scheme to define the new low-temperature criteria. The schematic in figure below shows the impact of S(60), m(60), and the failure strength on the thermal cracking behavior of asphalt binders. The thermal stress curve in the figure can be approximated using the BBR data, whereas the failure strength is obtained from the DTT. The critical temperature is determined, as shown, from the thermal stress curve and the strength. The LTTG is currently validating the new scheme using performance data from the Canadian Lamont sections. The Low-Temperature Binder Specification New Proposal Role of DTT and BBR Thermal stress curve (dotted line) is computed from BBR data. Failure Strength is measured using the DTT. Where they meet, determines critical cracking temperature, Tc. Stress Tcritical Strength from DTT Thermal Stress Curve From BBR Temperature Reserve Strength for Low and High m-value Role of S and m-value... Binder with low m-value has less reserve strength than high m-value binder and thus has less resistance to thermal fatigue. Stress High m Reserve Strength Strength Low m Temperature

22 Workbook: Step 1- Selection of Materials Page 14 Binder Tests Required for Mixture Design The rotational viscometer (Brookfield ), as part of the binder specification, is performed on the original/unconditioned binder at 135ºC. The specification recommends all binders to have a viscosity less than 3 Pascal-seconds (Pa-s). This is to ensure pump-ability during production. For mixture design, the rotational viscometer must be run at a second temperature, typically 160ºC. This is done in order to determine the proper mixing and compaction temperatures. SHRP adopted the Asphalt Institute mixing and compaction guidelines base on the temperatureviscosity relationship of the binder, where: Range for mixing =150 to 190 centistokes Range for compaction =250 to 310 centistokes The rotational viscometer measures viscosity in centipoises (cp) and the values are reported in Pascal-seconds (Pa-s). The conversion from centipoises to Pascal-seconds is as follows: 1 Pa-s = 1000 centipoises The relationship between centistokes and Pascal-seconds (or centipoises) is a function of the asphalt binder specific gravity. The specific gravity of an asphalt binder is a function of temperature. The asphalt binder specific gravity (G b ) is determined according to AASHTO T 228 and is typically measured at 25ºC. Tables of G b temperature correction factors have been developed to adjust G b over a range of temperatures. The following equation has been determined from these tables: Correction Factor, CF = (T test ) where: CF is the correction factor, and T test is the test temperature in ºC. Such that the conversion from centipoises or Pascal-seconds to centistokes is performed as follows: X cp = Y cst or X Pa-s * 1000 = Y cst (CF * G b ) (CF * G b )

23 Workbook: Step 1- Selection of Materials Page 15 The project PG provides the following test results: G b = Viscosity at 135ºC = 364 cp = Pa-s Viscosity at 160ºC = 100 cp = Pa-s Q. What are the equal-viscous mixing and compaction ranges for this asphalt binder? A. First the temperature correction factors for G b are calculated at the two test temperatures: CF 135ºC = (135ºC) = CF 160ºC = (160ºC) = The test results are then converted from Pascal-seconds to centistokes: Viscosity at 135ºC = 364 cp = 379 centistokes (0.933 * 1.030) Viscosity at 160ºC = 100 cp = 106 centistokes (0.918 * 1.030) This data is now analyzed graphically based on the Log-Log (base 10) of the viscosity in centistokes plotted against the Log (base 10) of the temperature in degrees Kelvin (273º + ºC), see figure. From the graph the following temperature data is determined: Range Temperature, _C Mixing 148ºC to? Compaction 138ºC to 142ºC

24 Workbook: Step 1- Selection of Materials Page 16 Temperature - Viscosity Chart Log - Log of Viscosity, shown in centistokes Compaction Range Mixing Range Log of Absolute Temperature, shown in C

25 Workbook: Step 1- Selection of Materials Page 17 Summary of Results Mixing Temperature Range 148ºC to 152ºC Compaction Temperature Range 138ºC to 142ºC Note: This relationship does not work for all modified asphalt binders. Note: See the Appendix for the mathematics required to perform the mixing and compaction temperature range determinations. Note: The conversion from centipoise to centistokes is important, however it is not required. Determining mixing and compaction temperatures based upon 150 to 190 centipoise and 250 to 310 centipoise ranges, respectively, will only effect the results by 1 to 2ºC.

26 Workbook: Step 1- Selection of Materials Page 18 Aggregate Selection Superpave utilizes a completely new system for testing, specifying, and selecting asphalt binders. While no new aggregate tests were developed, current methods of selecting and specifying aggregates were refined and incorporated into the Superpave design system. Superpave asphalt mixture requirements were established from currently used criteria. For this simulated project, four (4) stockpiles of materials consisting of two (2) coarse materials and two (2) fine materials are employed. Representative samples of the materials are obtained, and washed sieve analysis is performed for each aggregate. The gradation results are shown in the Aggregate Blending Section. The specific gravities (bulk G sb and apparent G sa ) are determined for each aggregate. The specific gravities are used in trial binder content and Voids in Mineral Aggregate (VMA) calculations. Table: Aggregate Stockpiles Aggregate Stockpile Bulk, G sb Apparent, G sa Coarse Aggregate Intermediate Aggregate Manufactured Fines Natural Fines In addition to sieve analysis and specific gravity determinations, Superpave requires certain consensus and source aggregate tests be performed to assure that the combined aggregates selected for the mix design are acceptable. The consensus property criteria are fixed in the Superpave design system; these are minimum requirements, which should be adhered to regardless of geographic location. The source property criteria are specified by the State highway agency. Superpave recommends three source property tests, which should be included in the aggregate selection process.

27 Workbook: Step 1- Selection of Materials Page 19 Table: Aggregate Tests Consensus Properties Coarse Aggregate Angularity (ASTM D 5821) Uncompacted Void Content of Fine Aggregate (AASHTO TP33) Flat & Elongated Particles (D 4791) Sand Equivalent (T 176) Source Properties (Set by SHA) Resistance to Abrasion (T 96) Soundness (T 104) Clay Lumps & Friable Particles (T 112) Superpave requires the consensus and source properties be determined for the design aggregate blend. The aggregate criteria are based on combined aggregates rather than individual aggregate components. However, it is recommended the tests be performed on the individual aggregates until historical results are accumulated and also to allow for the blending of the aggregates in the mix design. Author s Note An aggregate which does not individually comply with the criteria is not eliminated from the aggregate blend. However, its percentage of use in the total aggregate blend is limited. CONSENSUS PROPERTY STANDARDS Coarse Aggregate Angularity (ASTM D 5821) This property ensures a high degree of aggregate internal friction and aids in rutting resistance. It is defined as the percent by weight of aggregates larger than 4.75 millimeters with one or more fractured faces, ASTM D 5821, "Determining the Percentage of Fractured Particles in Coarse Aggregate." Where: Fractured Face, an angular, rough, or broken surface of an aggregate particle created by crushing, by other artificial means, or by nature (ASTM D 8). A face will be considered a fractured face only if it has a projected area at least as large as one quarter of the maximum projected area (maximum cross-sectional area) of the particle and the face has sharp and well defined edges; this excludes small nicks.

28 Workbook: Step 1- Selection of Materials Page 20 Fine Aggregate Angularity as Determined by: Uncompacted Void Content of Fine Aggregate (AASHTO TP33) -(Method A) Uncompacted void content is related to particle shape, angularity, and surface texture. These properties ensure a high degree of fine aggregate internal friction and aid in rutting resistance. Uncompacted void content is defined as the percent air voids present in loosely compacted aggregates smaller than 2.36 mm. Higher void contents correspond to higher fractured faces. A test procedure currently promulgated by the National Aggregates Association is used to measure this property. In the test, a sample of fine aggregate is poured into a small calibrated cylinder by flowing through a standard funnel. By determining the weight of fine aggregate (W) in the filled cylinder of known volume (V), void content can be calculated as the difference between the cylinder volume and fine aggregate volume collected in the cylinder. The fine aggregate bulk specific gravity (G sb ) is used to compute fine aggregate volume: Uncompacted Voids, U = W ( V - G sb ) V * 1 * 100 Flat/Elongated Particles as determined by: Flat or Elongated Particles in Coarse Aggregate (ASTM D 4791) This characteristic is the percentage by weight of coarse aggregates that have a maximum to minimum dimension-ratio greater than five. Elongated particles are undesirable because they have a tendency to break during construction and under traffic. The test procedure, ASTM D 4791, "Flat or Elongated Particles in Coarse Aggregate," is performed on coarse aggregate larger than 9.5 millimeters. The procedure uses a proportional caliper device (see figure below) to measure the dimensional ratio of a representative sample of aggregate particles. In the figure, the aggregate particle is first placed with its largest dimension between the swinging arm and fixed post at position A. The swinging arm then remains stationary while the aggregate is placed between the swinging arm and fixed post at position B. If the aggregate fits within this gap, then it is counted as a flat/elongated particle. Note: Superpave uses a single measurement be made for flat/elongated particles. The 5:1 ratio refers simply to the maximum to minimum dimension.

29 Workbook: Step 1- Selection of Materials Page 21 Figure: ASTM D :5 pivot point Fixed post (B) swinging arm fixed post (A) Clay Content as determined by: Sand Equivalent Test (AASHTO T 176) Clay content is the percentage of clay material contained in the aggregate fraction that is finer than a 4.75 mm sieve. It is measured by AASHTO T 176, "Plastic Fines in Graded Aggregates and Soils by Use of the Sand Equivalent Test." In this test, a sample of fine aggregate is placed in a graduated cylinder with a flocculating solution and agitated to loosen clay fines present in and coating the aggregate. The flocculating solution forces the clay material into suspension above the granular aggregate. After a period that allows sedimentation, the cylinder height of suspended clay and sedimented sand is measured (figure below). The sand equivalent value is computed as a ratio of the sand to clay height readings expressed as a percentage. Figure: AASHTO T 176 graduated cylinder flocculating solution Clay Content (Sand Equivalent, SE), mm SR SE = CR * * 100 SR - sand reading CR - clay reading suspended clay sedimented aggregate clay reading sand reading

30 Workbook: Step 1- Selection of Materials Page 22 The criteria for the consensus property standards as outlined in AASHTO MP-2 is as follows: MP-2 Table 5 - Coarse Aggregate Angularity Criteria (D 5821). MP-2 Table 5 - Fine Aggregate Angularity Criteria (T304, Method A). MP-2 Table5 - Sand Equivalent Minimum Criteria ( T176). MP-2 Section for Flat and Elongated Particles The aggregate shall meet the flat and elongated requirements specified in Table 5 measured according to D4791, with the exception that the material passing the 9.5-mm sieve and retained on the 4.75-mm sieve shall be included. The aggregate shall be measured using the ratio of 5:1, comparing the length (longest dimension) to the thickness (smallest dimension) of the aggregate particles. 6.6 When RAP is used in the mixture, the RAP aggregate shall be extracted using a solvent extraction (T164) or ignition oven (T308) as specified by the agency. The RAP aggregate shall be included in determinations of gradation, coarse aggregate angularity, fine aggregate angularity, and flat and elongated requirements. The sand equivalent requirements shall be waived for the RAP aggregate but shall apply to the remainder of the aggregate blend. Current 03: MP-2, Table 5 - Superpave Aggregate Consensus Property Requirements Design ESALs a (Million) Fractured Faces, Coarse Aggregate c Percent Minimum Uncompacted Void Content of Fine Aggregate Percent Minimum Sand Equivalent Percent, Minimum Flat and Elongated c Percent, Maximum Depth from Surface Depth from Surface < 100 mm > 100 mm <100 mm > 100 mm < /- -/ to < 3 75/- 50/ to < 10 85/80 b 60/ < 30 95/90 80/ > / / c b a The anticipated project traffic level expected on the design lane over a 20-year period. Regardless of the actual design life of the roadway, determine the design ESALs for 20 years. 85/80 denotes that 85 percent of the coarse aggregate has one fractured face and 80 percent has two or more fractured faces. This criterion does not apply to 4.75-mm nominal maximum size mixtures. Note 7- If less than 25 percent of a construction lift is within 100 mm of the surface, the lift may be considered to be below 100 mm for mixture design purposes.

31 Workbook: Step 1- Selection of Materials Page 23 Table: Simulation Study Test Results (ASTM D 5821), CAA Stockpiles/Blends 1 + Fractured Criterion 2 + Fractured Criterion Coarse Aggregate 99 % % min 97 % % min Intermediate Aggregate 80 % 60 % This test is commonly only performed on the coarse aggregates during the initial screening of materials, even though the fine aggregate stockpiles may contain a small percentage retained on the 4.75 millimeter sieve. This test should also be run on the plus 4.75 millimeter material of the final design aggregate blend. Q. Based on the Current 03 table, what is the criterion for this surface mixture with an estimated traffic of 6,300,000 ESALs, (fill in the above table)? Do both stockpiles meet the criteria, (Y/N)? If the answer is no, what does this mean? (1) Stockpile cannot be used. or (2) Percentage of stockpile in blend is limited. Table: Simulation Study Test Results (AASHTO TP 33), FAA Stockpiles/Blends % Air Voids Criterion Manufactured Fines 48 Natural Fines 42 > Q. Based on the Current 01 table, what is the criterion for this surface mixture with an estimated traffic of 6,300,000 ESALs, (fill in the above table)? Do both stockpiles meet the criteria, (Y/N)? If the answer is "no," what does this mean? a. Stockpile cannot be used. or b. Percentage of stockpile in blend is limited. Author s Note Fine aggregates with higher angularity may aid in the development of higher voids in mineral aggregate (VMA).

32 Workbook: Step 1- Selection of Materials Page 24 Table: Simulation Study Test Results (ASTM D 4791), F&E Stockpiles/Blends % Elongated Criterion Coarse Aggregate 9 % % Intermediate Agg. 2 % Q. Based on the Current 01 table, what is the criterion for this surface mixture with an estimated traffic of 6,300,000 ESALs, (fill in the above table)? Do both stockpiles meet the criteria, (Y/N)? If the answer is "no," what does this mean? a. Stockpile cannot be used. or b. Percentage of stockpile in blend is limited. Table: Simulation Study Test Results (AASHTO T 176), SE Stockpiles/Blends Sand Equivalent Criterion Manufactured Fines Natural Fines Intermediate Aggregate 51 % 39 % 45% % Q. Based on the Current 01 table, what is the criterion for this surface mixture with an estimated traffic of 6,300,000 ESALs, (fill in the above table)? Do both stockpiles meet the criteria, (Y/N)? If the answer is "no," what does this mean? a. Stockpile cannot be used. or b. Percentage of stockpile in blend is limited. Q. For this project, did any of the criteria change from using the Current 01 table versus the original standards in AASHTO MP-2? Consensus Standard Original Criteria Current 01 Criteria CAA FAA F&E SE 85 / /

33 Workbook: Step 1- Selection of Materials Page 25 Lead States Recommendations Aggregate Consensus Properties - If Superpave criteria allow the use of aggregates with lower quality than previously used in a state, consideration should be given to maintaining the states more stringent requirements until all Superpave validation work is complete. With respect to specific aggregate consensus properties, the following is offered: Coarse Aggregate Angularity - Previous references in SHRP reports and elsewhere to the Pennsylvania Department of Transportation Test Method No. 621 for determining coarse aggregate angularity have been revised in AASHTO MP2, Standard Specification for Superpave Volumetric Mix Design to reference ASTM D5821, Standard Test Method for Determining the Percentage of Fractured Particles in Coarse Aggregate, to more critically discriminate between aggregates. Fine Aggregate Angularity - Fine aggregate angularity should be determined in accordance with AASHTO TP-33, Uncompacted Void Content of Fine Aggregate, method A. The Lead States recommend the current Superpave fine aggregate angularity requirement of 45 at greaterthan 3 million ESALs and 40 at less-than 3 million ESALs be specified. It should be noted that the aggregate s bulk specific gravity is a critical factor in the determination of the fine aggregate angularity, therefore, this value should be determined on a frequency appropriate for the variability of the source.

34 Workbook: Step 1- Selection of Materials Page 26 Flat-and-Elongated Particle Content - Excessive amounts of flat-and-elongated particles in a mixture can potentially lead to production and placement problems. This includes problems with volumetrics (both during design and production), aggregate degradation, and compaction. Current Superpave requirements (and other documentation) establish a 10% maximum flatand-elongated particle content on material coarser than the 4.75 mm sieve when using a ratio of 5:1. This ratio is determined by comparing the maximum to minimum dimension. These dimensions should be visualized by circumscribed rectangular prisms around the aggregate. Testing is performed in accordance with ASTM D 4791, Flat Particles, Elongated Particles, or Flat and Elongated Particles in Coarse Aggregate. It should be noted D 4791 requires testing to be performed on material coarser than the 9.5 mm sieve. Many believe testing aggregate passing the 9.5 mm sieve and retained on the 4.75 mm sieve will be very difficult and results highly variable. While this discrepancy is being addressed through AASHTO and ASTM, the Lead States recommend the states be aware of this issue and base specifications on their judgement of potential risks. Many states have expressed concern that this criteria may not adequately discriminate between suitable and unsuitable aggregates and a 3:1 ratio should be specified. However, the relationship between flat-and-elongated particle content and performance has not been clearly established. There are currently several on-going research efforts attempting to establish this relationship. Before changing the flat-and-elongated particle criteria to a 3:1 ratio, the Lead States recommend that past specifications and performance be considered. Further, until information is obtained relating flat-and-elongated particle content to performance, the maximum allowable value should not be set lower than 20%. This value is consistent with existing SMA criteria and has been used successfully in the past. Caution should be exercised when considering this change as it may significantly affect the use of certain materials which may otherwise prove to be suitable.

35 Workbook: Step 1- Selection of Materials Page 27 Mixture ETG Discussion Under the auspicious of the Mixture expert task group, stockpile data collected as part of DP 90 was offered for discussion of the use of the 3:1 ratio. 27 Stockpiles from 12 different projects sites located in: California, Nevada, Alabama, Maine, Louisiana, Missouri, Illinois, South Carolina, Connecticut, Texas, Wisconsin, Minnesota, and Oklahoma. 30 Flat & Elongated Particles Percent Passing :1 Ratio 3:1 Ratio Stockpile Flat & Elongated Particles Percent of Data within Criteria Criteria (Maximum) 30 3:1 Ratio 5:1 Ratio The stockpile data is sorted above by increase F&E values. The plot to the left shows the percent of these stockpile that would fail a range of criteria. In this case, all of the 27 stockpiles meet a 5:1 maximum criteria as tight as 5 % and 98% of the stockpiles meet a 3:1 maximum criteria of 25%. It is recommended each specifying agency should perform a market analysis to access the impact of specifying a 3:1 source property standard.

36 Workbook: Step 1- Selection of Materials Page 28 SOURCE PROPERTY STANDARDS Toughness as determined by: L.A. Abrasion (AASHTO T 96) Toughness is the percent loss of materials from an aggregate blend during the Los Angeles Abrasion test. The procedure is stated in AASHTO T 96, "Resistance to Abrasion of Small Size Coarse Aggregate by Use of the Los Angeles Machine." This test estimates the resistance of coarse aggregate to abrasion and mechanical degradation during handling, construction, and service. It is performed by subjecting the coarse aggregate, usually larger than 2.36 mm, to impact and grinding by steel spheres. The test result is percent loss, which is the weighted percentage of coarse material lost during the test as a result of the mechanical degradation. Maximum allowable loss values typically range from approximately 35 to 45 percent. Soundness as determined by: Sulfate Soundness (AASHTO T 104) Soundness is the percent loss of materials from an aggregate blend during the sodium or magnesium sulfate soundness test. The procedure is stated in AASHTO T 104, "Soundness of Aggregate by Use of Sodium Sulfate or Magnesium Sulfate." This test estimates the resistance of aggregate to weathering while in-service. It can be performed on both coarse and fine aggregate. The test is performed by alternately exposing an aggregate sample to repeated immersions in saturated solutions of sodium or magnesium sulfate each followed by oven drying. One immersion and drying is considered one soundness cycle. During the drying phase, salts precipitate in the permeable void space of the aggregate. Upon re-immersion the salt rehydrates and exerts internal expansive forces that simulate the expansive forces of freezing water. The test result is total percent loss over various sieve intervals for a required number of cycles. Maximum allowable loss values typically range from approximately 10 to 20 percent for five cycles.

37 Workbook: Step 1- Selection of Materials Page 29 Deleterious Material as determined by: Clay Lumps and Friable Particles (AASHTO T 112) Deleterious materials are defined as the weight percentage of contaminants such as shale, wood, mica, and coal in the blended aggregate. This property is measured by AASHTO T 112, "Clay Lumps and Friable Particles in Aggregates." It can be performed on both coarse and fine aggregate. The test is performed by wet sieving aggregate size fractions over prescribed sieves. The weight percentage of material lost as a result of wet sieving is reported as the percent of clay lumps and friable particles. A wide range of maximum permissible percentage of clay lumps and friable particles is evident. Values range from as little as 0.2 percent to as high as 10 percent, depending on the exact composition of the contaminant.

38 Workbook: Step 1- Selection of Materials Page 30 SELECTION OF A DESIGN AGGREGATE STRUCTURE The FHWA 0.45 Power gradation chart is used to define permissible gradations. This chart uses a unique graphing technique to judge the cumulative particle size distribution of a blend. The ordinate (y axis) of the chart is percent passing. The abscissa (x axis) is an arithmetic scale of sieve size opening in microns, raised to the 0.45 power. To select the design aggregate structure, trial blends are established by mathematically combining the gradations of the individual materials into a single blend. The blend is then compared to the specification requirements for the appropriate sieves. Gradation control is based on four control sieves: the maximum sieve, the nominal maximum sieve, the 2.36 mm sieve, and the mm sieve. Definitions: Nominal Maximum Sieve Size: One standard sieve size larger than the first sieve to retain more than 10 percent. Maximum Sieve Size: One standard sieve size larger than the nominal maximum size. The 0.45 power maximum density line is draw from the origin to 100 percent passing the maximum size. Standard Sieves 50.0 mm 37.5 mm 25.0 mm 19.0 mm 12.5 mm 9.50 mm 4.75 mm 2.36 mm 1.18 mm 0.60 mm 0.30 mm 0.15 mm mm

39 Workbook: Step 2- Selection of a Design Aggregate Structure Page 31 Q. Match the English Sieves to their Standard equivalents: English Sieves (1) No. 100 (2) No. 4 (A) (B) Standard Sieves 50.0 mm 37.5 mm (3) 1/4 inch ( C) 25.0 mm (4) 1 inch (5) No. 200 (6) No. 80 (7) No. 50 (8) ½ inch (9) No. 16 (10) No. 20 (11) No. 40 (D) (E) (F) (G) (H) (I) (J) (K) (L) (M) 19.0 mm 12.5 mm 9.50 mm 4.75 mm 2.36 mm 1.18 mm 0.60 mm 0.30 mm 0.15 mm mm A. (1)L, (2)G, (3)*, (4)C, (5)M, (6)*, (7)K, (8)E, (9)I, (10)*, (11)* * - English sieve is not part of the Standard sieve stack.

40 Workbook: Step 1- Selection of Materials Page 32 There is also a recommended "restricted zone." The restricted zone is an area on either side of the maximum density line generally starting at the 2.36 millimeter sieve and extending to the millimeter sieve. The minimum and maximum values required for the control sieves change (as does the restricted zone) as the nominal size of the blend changes. The following table defines the control points and recommended restricted zones for different nominal maximum sieve sizes. Table: Superpave Aggregate Gradation Requirements Standard Percent Passing Criteria (Control Points) Sieve (mm) Nominal Maximum Sieve Size 9.5 mm 12.5 mm 19 mm 25 mm 37.5 mm Sieve Recommended Restricted Zone All trial blend gradations (washed in accordance to AASHTO T-11) must pass between the control points established. In addition, they should be outside of the area bounded by the limits set for the restricted zone.

41 Workbook: Step 2- Selection of a Design Aggregate Structure Page 33 Typically the State highway agency will specify the nominal maximum size required for the pavement layer. For our simulation study, the specified size is 19.0 mm. It is recommended that three trial blends be initially developed. Table: Develop Trial Blends A g g r e g a t e s Trial No. 1 Trial No. 2 Trial No. 3 46% 51% 25% Coarse Agg. Intr. Agg. Man. Fines Natr l. Fines 24% 15% 15% 25% 15% 9% 24% 23% 28% Sieve Stockpile Gradations No. 1 No. 2 No mm 25.0 mm 19.0 mm 12.5 mm 9.5 mm 4.75 mm 2.36 mm 1.18 mm 0.60 mm 0.30 mm 0.15 mm mm Nominal Maximum Sieve Size: One standard sieve size larger than the first sieve to retain more than 10 percent. The first sieve to retain more than 10 percent for all blends is the 12.5 millimeter. On sieve larger is the 19.0 millimeter. Such that the nominal maximum sieve size is the 19.0 millimeter. Maximum Sieve Size: One standard sieve size larger than the nominal maximum size. Such that the 25.0 millimeter is the maximum sieve size.