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Suggested Citation:"Front Matter." National Research Council. 2021. Validation of a Performance-Based Mix Design Method for Porous Friction Courses. Washington, DC: The National Academies Press. doi: 10.17226/26333.
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NCHRP Web-Only Document 305: Validation of a Performance-Based Mix Design Method for Porous Friction Courses Nam Tran Fan Gu Donald Watson National Center for Asphalt Technology Auburn University Auburn, AL Contractor’s Final Report for NCHRP Project 20-44/Task 18 Submitted June 2021 NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed, and implementable research is the most effective way to solve many problems facing state departments of transportation (DOTs) administrators and engineers. Often, highway problems are of local or regional interest and can best be studied by state DOTs individually or in cooperation with their state universities and others. However, the accelerating growth of highway transportation results in increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of cooperative research. Recognizing this need, the leadership of the American Association of State Highway and Transportation Officials (AASHTO) in 1962 initiated an objective national highway research program using modern scientific techniques—the National Cooperative Highway Research Program (NCHRP). NCHRP is supported on a continuing basis by funds from participating member states of AASHTO and receives the full cooperation and support of the Federal Highway Administration (FHWA), United States Department of Transportation, under Agreement No. 693JJ31950003. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, FAA, FHWA, FTA, GHSA, NHTSA, or TDC endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP. DISCLAIMER The opinions and conclusions expressed or implied in this report are those of the researchers who performed the research. They are not necessarily those of the Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; the FHWA; or the program sponsors. The information contained in this document was taken directly from the submission of the author(s). This material has not been edited by TRB.

The National Academy of Sciences was established in 1863 by an Act of Congress, signed by President Lincoln, as a private, non- governmental institution to advise the nation on issues related to science and technology. Members are elected by their peers for outstanding contributions to research. Dr. Marcia McNutt is president. The National Academy of Engineering was established in 1964 under the charter of the National Academy of Sciences to bring the practices of engineering to advising the nation. Members are elected by their peers for extraordinary contributions to engineering. Dr. John L. Anderson is president. The National Academy of Medicine (formerly the Institute of Medicine) was established in 1970 under the charter of the National Academy of Sciences to advise the nation on medical and health issues. Members are elected by their peers for distinguished contributions to medicine and health. Dr. Victor J. Dzau is president. The three Academies work together as the National Academies of Sciences, Engineering, and Medicine to provide independent, objective analysis and advice to the nation and conduct other activities to solve complex problems and inform public policy decisions. The National Academies also encourage education and research, recognize outstanding contributions to knowledge, and increase public understanding in matters of science, engineering, and medicine. Learn more about the National Academies of Sciences, Engineering, and Medicine at www.nationalacademies.org. The Transportation Research Board is one of seven major programs of the National Academies of Sciences, Engineering, and Medicine. The mission of the Transportation Research Board is to provide leadership in transportation improvements and innovation through trusted, timely, impartial, and evidence-based information exchange, research, and advice regarding all modes of transportation. The Board’s varied activities annually engage about 8,000 engineers, scientists, and other transportation researchers and practitioners from the public and private sectors and academia, all of whom contribute their expertise in the public interest. The program is supported by state transportation departments, federal agencies including the component administrations of the U.S. Department of Transportation, and other organizations and individuals interested in the development of transportation. Learn more about the Transportation Research Board at www.TRB.org.

C O O P E R A T I V E  R E S E A R C H  P R O G R A M S  CRP STAFF FOR NCHRP WEB-ONLY DOCUMENT 305 Christopher J. Hedges, Director, Cooperative Research Programs Lori L. Sundstrom, Deputy Director, Cooperative Research Programs Edward T. Harrigan, Senior Program Officer Anthony P. Avery, Senior Program Assistant Natalie Barnes, Director of Publications Kathleen Mion, Senior Editorial Assistant NCHRP PROJECT 20-44/Task 18 PANEL Field of Special Projects Shihui Shen, Pennsylvania State University, Altoona, Altoona, PA Mylinh Lidder, Nevada DOT (retired), Reno, NV Tanya M. Nash, Asphalt Testing Solutions and Engineering, Jacksonville, FL Richard S. Gribbin, Jas. W. Glover Ltd., Honolulu, HI .

iv Summary Porous Friction Course (PFC) mixtures have an open aggregate structure with high in-place air voids for increased permeability. They are typically placed on a pavement surface to improve roadway safety, especially in wet weather conditions. PFC mixtures are also effective in reducing the tire/pavement noise and improving water runoff. However, according to a survey conducted in NCHRP Project 01-55, the potential issues of poor durability and short service life diminish the use of PFC in a number of states. Thus, to improve the durability of PFC mixtures, a performance-based mix design procedure for PFC was proposed in NCHRP Project 01-55, and described in NCHRP Research Report 877: Performance-Based Mix Design of Porous Friction Courses. This performance-based mix design procedure included a series of performance tests to evaluate the resistance of a PFC mixture to raveling, moisture susceptibility, and drain down (with optional tests for cracking and rutting), while still maintaining an air void structure that provides adequate permeability. The determination of optimum asphalt content was based on the following tests and criteria. Except for the draindown test that is conducted on loose mix samples, all the tests are conducted on specimens compacted to 50 gyrations with a Super pave gyratory compactor.  Air voids: Air voids may be determined by either the Vacuum Sealing method (AASHTO T 331) or by the dimensional method. The recommended air void range is 15-20 percent if the vacuum seal method is used, or 17-22 percent if the dimensional method is used.  Draindown: the draindown test is conducted in accordance with AASHTO T 305 and a maximum of 0.3 percent is recommended.  Cantabro stone loss: The Cantabro stone loss is determined using AASHTO TP 108. Unaged specimens are typically used and the maximum loss is 20 percent.  Permeability: The Florida permeability method FM 5-565 is used to determine permeability and a minimum threshold of 50 m/day is recommended.  Moisture susceptibility: A modified version of AASHTO T 283 is used to determine resistance to moisture damage. A minimum of 50-psi conditioned tensile strength is recommended along with a minimum tensile strength ratio (TSR) value of 0.70.  Rutting (optional): The Hamburg Wheel Tracker (HWT) is used for the optional rutting susceptibility test and the number of cycles to failure (12.5 mm rut depth) is based on the asphalt binder grade used. – PG 64 Min. 10,000 passes – PG 70 Min. 15,000 passes – PG 76 or higher Min. 20,000 passes  Cracking (optional): The Illinois Flexibility Index Test (I-FIT) is used according to Illinois Test Procedure 405. A minimum Flexibility Index (FI) value of 25 is recommended. NCHRP Project 20-44(18), “Validation of the PFC Performance-Based Mix Design Method,” was conducted with an objective of assisting state highway agencies (SHAs) in implementing the proposed performance-based mix design procedure, verifying if the thresholds proposed in the procedure could be achieved, and refining the procedure if needed. To accomplish the research objective, the project team worked with three state highway agencies, including Georgia (GDOT), South Carolina (SCDOT) and Alabama (ALDOT) Departments of Transportation, to evaluate their PFC mix designs and construct the PFC sections. Based on results of the implementation effort, the following conclusions were drawn in this study.

v  Two state agencies recently added gradation limits for 9.5 mm PFC mixtures to their specifications as this finer aggregate gradation appears more durable while still maintaining good permeability.  The thresholds proposed in the performance-based mix design procedure can be achieved based on the mix designs provided by the three SHAs.  The plant-produced mixtures had lower asphalt contents than the respective optimum asphalt contents in the mix designs; thereby, the Cantabro losses of the PMLC specimens were higher than those of the LMLC specimens.  One state agency recently added a maximum Cantabro loss requirement of 15 percent as the Cantabro test was found to be an adequate indicator of PFC mixture durability. (Some state agencies indicated in the previous NCHRP Project 01-55 survey that they had success with a Cantabro loss requirement of 20 percent).  Extended silo storage and haul time at elevated temperatures may significantly influence the Cantabro loss, , and adversely affect mixture durability in the field especially when absorptive aggregate is used. To facilitate the implementation process, the project team recommends refining the performance-based mix design procedure based in the following tests and criteria. All test specimens are compacted to 50 gyrations with a Superpave gyratory compactor, except for the draindown test, which is conducted on a loose mix sample.  Air voids: The minimum and maximum air voids are 15 to 20 percent if the vacuum seal method is used, or 17 to 22 percent if the dimensional method is used.  Draindown: The maximum binder draindown is 0.3 percent.  Cantabro stone loss: The maximum Cantabro stone loss is changed from 20 percent to 15 percent.  Permeability: The minimum falling head permeability is 50 m/day.  Moisture susceptibility: The minimum conditioned tensile strength is 50 psi with a minimum TSR value of 0.70. A lower threshold of 15 percent for Cantabro loss was originally set based on the NCHRP Project 01- 55 data for the proposed minimum air void requirement (i.e., 15 percent), but it was suggested later to change it to 20 percent so that the same criterion could be used for both mix design and production testing when taking into account production tolerances. However, the data collected under NCHRP Project 20- 44(18) suggested that plant mixes could yield the same Cantabro loss results as lab mixes when the plant mixes were produced within allowable production tolerances. Thus, it is proposed that the maximum Cantabro stone loss requirement is changed to 15 percent, and this requirement can be used for both mix design and production testing. In addition, even though HWT was not included in the implementation effort under NCHRP Project 20- 44(18), it can be used to evaluate PFC mixtures if rutting is a concern. Also, both I-FIT and the Indirect Tensile Asphalt Cracking Test (IDEAL-CT, ASTM D8225) can be used to evaluate the cracking resistance of PFC mixtures, but further research is needed to validate their correlations to field performance and acceptance thresholds. The Texas Overlay Test has also been used in other studies with a minimum criterion of 200 cycles to failure.

vi C O N T E N T S CHAPTER 1. INTRODUCTION ............................................................................................................. 1  Background ........................................................................................................................................................ 1  Objective ........................................................................................................................................................... 1  Scope of Work ................................................................................................................................................... 2  CHAPTER 2. STATE OF PRACTICE .................................................................................................... 3  Findings of NCHRP Project 01‐55 Survey ............................................................................................................. 3  Reported Distresses .................................................................................................................................................. 3  PFC Mix Design .......................................................................................................................................................... 3  Construction and Maintenance ................................................................................................................................ 5  Implementation of Performance‐Based Mix Design ............................................................................................ 5  Case Studies of implementation ............................................................................................................................... 7  CHAPTER 3. EXPERIMENTAL DESIGN ........................................................................................... 10  Experimental Plan ............................................................................................................................................. 10  Materials and Agency’s PFC Mix Designs ........................................................................................................... 11  Test Methods and Proposed Design Thresholds ................................................................................................. 12  Binder Content and Aggregate Gradation of Plant‐Produced Mixture ................................................................... 13  Specimen Air Voids ................................................................................................................................................. 13  Draindown .............................................................................................................................................................. 13  Cantabro Test .......................................................................................................................................................... 14  Tensile Strength Ratio ............................................................................................................................................. 14  CHAPTER 4. RESULTS AND ANALYSIS .......................................................................................... 15  GDOT Project .................................................................................................................................................... 15  SCDOT Project ................................................................................................................................................... 16  ALDOT Project ................................................................................................................................................... 18  CHAPTER 5. CONCLUSIONS .............................................................................................................. 23  REFERENCES .......................................................................................................................................... 25  APPENDIX A. DETAILED TEST RESULTS ...................................................................................... 26

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Porous Friction Course (PFC) mixtures are designed with an open aggregate structure to yield high inplace air voids (i.e., typically between 15 and 20 percent). This allows rainwater to drain horizontally through the layer toward the edge of the pavement structure, thereby improving pavement surface friction.

The TRB National Cooperative Highway Research Program's NCHRP Web-Only Document 305: Validation of a Performance-Based Mix Design Method for Porous Friction Courses is designed to assist state highway agencies in implementing the proposed performance-based mix design procedure, verify if the thresholds proposed in the procedure could be achieved, and refine the procedure if needed.

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