TRANSPORTATION RESEARCH BOARD 2024 EXECUTIVE COMMITTEE*
OFFICERS
CHAIR: Carol A. Lewis, Professor, Transportation Studies, Texas Southern University, Houston
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___________________
* Membership as of May 2024.
NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM
NCHRP RESEARCH REPORT 1105
Use of Marginal and
Unconventional-Source
Coal Ashes in Concrete
Christopher Shearer
SOUTH DAKOTA SCHOOL OF MINES AND TECHNOLOGY
Rapid City, SD
Lisa Burris
THE OHIO STATE UNIVERSITY
Columbus, OH
R. Douglas Hooton
UNIVERSITY OF TORONTO
Toronto, ON
Prannoy Suraneni
UNIVERSITY OF MIAMI
Coral Gables, FL
Subscriber Categories
Bridges and Other Structures • Materials • Pavements
Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration
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.
The Transportation Research Board (TRB) of the National Academies of Sciences, Engineering, and Medicine was requested by AASHTO to administer the research program because of TRB’s recognized objectivity and understanding of modern research practices. TRB is uniquely suited for this purpose for many reasons: TRB maintains an extensive committee structure from which authorities on any highway transportation subject may be drawn; TRB possesses avenues of communications and cooperation with federal, state, and local governmental agencies, universities, and industry; TRB’s relationship to the National Academies is an insurance of objectivity; and TRB maintains a full-time staff of specialists in highway transportation matters to bring the findings of research directly to those in a position to use them.
The program is developed on the basis of research needs identified by chief administrators and other staff of the highway and transportation departments, by committees of AASHTO, and by the FHWA. Topics of the highest merit are selected by the AASHTO Special Committee on Research and Innovation (R&I), and each year R&I’s recommendations are proposed to the AASHTO Board of Directors and the National Academies. Research projects to address these topics are defined by NCHRP, and qualified research agencies are selected from submitted proposals. Administration and surveillance of research contracts are the responsibilities of the National Academies and TRB.
The needs for highway research are many, and NCHRP can make significant contributions to solving highway transportation problems of mutual concern to many responsible groups. The program, however, is intended to complement, rather than to substitute for or duplicate, other highway research programs.
NCHRP RESEARCH REPORT 1105
Project 10-104
ISSN 2572-3766 (Print)
ISSN 2572-3774 (Online)
ISBN 978-0-309-70984-2
Library of Congress Control Number 2024938425
© 2024 by the National Academy of Sciences. National Academies of Sciences, Engineering, and Medicine and the graphical logo are trademarks of the National Academy of Sciences. All rights reserved.
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, APTA, FAA, FHWA, FTA, GHSA, or NHTSA 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.
Cover figure: Electron micrograph of one coal ash. Photo by Ying Wang (University of Miami).
NOTICE
The research report was reviewed by the technical panel and accepted for publication according to procedures established and overseen by the Transportation Research Board and approved by the National Academies of Sciences, Engineering, and Medicine.
The opinions and conclusions expressed or implied in this report are those of the researchers who performed the research and are not necessarily those of the Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; the FHWA; or the program sponsors.
The Transportation Research Board does not develop, issue, or publish standards or specifications. The Transportation Research Board manages applied research projects which provide the scientific foundation that may be used by Transportation Research Board sponsors, industry associations, or other organizations as the basis for revised practices, procedures, or specifications.
The Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; and the sponsors of the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade or manufacturers’ names or logos appear herein solely because they are considered essential to the object of the report.
Published research reports of the
NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM
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The National Academy of Sciences was established in 1863 by an Act of Congress, signed by President Lincoln, as a private, nongovernmental 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.
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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 program divisions of the National Academies of Sciences, Engineering, and Medicine. The mission of the Transportation Research Board is to mobilize expertise, experience, and knowledge to anticipate and solve complex transportation-related challenges. The Board’s varied activities annually engage about 8,500 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.
COOPERATIVE RESEARCH PROGRAMS
CRP STAFF FOR NCHRP RESEARCH REPORT 1105
Waseem Dekelbab, Deputy Director, Cooperative Research Programs, and Manager, National Cooperative Highway Research Program
Inam Jawed, Senior Program Officer
Mireya Kuskie, Senior Program Assistant
Natalie Barnes, Director of Publications
Heather DiAngelis, Associate Director of Publications
Claire Aelion-Moss, Editor
NCHRP PROJECT 10-104 PANEL
Field of Materials and Construction—Area of Specs, Procedures, and Practices
Tommy E. Nantung, Indiana Department of Transportation, West Lafayette, IN (Chair)
Harvey Dale DeFord, Florida Department of Transportation, Gainesville, FL
Harikrishnan Nair, Virginia Transportation Research Council, Charlottesville, VA
Andy Naranjo, Texas Department of Transportation, Austin, TX
Karthik H. Obla, National Ready Mixed Concrete Association, Alexandria, VA
Tyson D. Rupnow, Louisiana Department of Transportation and Development, Baton Rouge, LA
Lawrence L. Sutter, Michigan Technological University, Houghton, MI
Robert P. Spragg, FHWA Liaison
AUTHOR ACKNOWLEDGMENTS
This research was performed under NCHRP Project 10-104 by the Department of Civil and Environmental Engineering at South Dakota School of Mines and Technology; the Department of Civil and Architectural Engineering at University of Miami; the Department of Civil, Environmental and Geodetic Engineering at The Ohio State University; and the Department of Civil and Mineral Engineering at University of Toronto. South Dakota School of Mines and Technology was the lead contractor for this study, with its Office of Research Affairs serving as fiscal administrator.
Christopher Shearer, associate professor of civil and environmental engineering at South Dakota School of Mines and Technology, was the project director and principal investigator. The other authors of this report are Prannoy Suraneni, assistant professor of civil and architectural engineering at University of Miami and co-principal investigator; Lisa Burris, assistant professor of civil, environmental, and geodetic engineering at The Ohio State University; and R. Douglas Hooton, professor of civil and mineral engineering at the University of Toronto, along with the following students and researchers: Ying Wang, Cansu Acarturk, Yujia Min, Erin Stewartson, Mahmod Yahya, Olga Perebatova, Jill Rotherham, Duncan Pilling, and Jetsun Ty Thinley. The work was done under the general supervision of Professors Shearer, Suraneni, Burris, and Hooton.
FOREWORD
By Inam Jawed
Staff Officer
Transportation Research Board
NCHRP Research Report 1105: Use of Marginal and Unconventional-Source Coal Ashes in Concrete proposes changes to current methods for selecting coal ash for concrete construction so that ashes presently deemed not to meet standards could be considered and evaluated for use in concrete. The proposed changes focus on ash properties that impact concrete performance rather than other factors or characteristics. The findings of this report should be particularly useful to state DOTs and others involved in selecting concrete materials for their highway infrastructure projects.
There is a growing concern among concrete users and producers about the scarcity of high-quality coal ash, arguably the most common supplementary cementitious material used in concrete to enhance its durability and prevent or mitigate alkali-silica reactivity. Electric power plants are increasingly using gas in place of coal, leading to a decreased supply of coal ash. Environmental regulations for air pollution keep on tightening, adversely impacting the quality of the ash coming out of coal-fired power plants. The situation will almost certainly intensify with time, leaving the concrete industry with no other option but to rethink ashes that, until now, were considered unacceptable. This includes marginal ashes that do not meet the current specification and those disposed of in landfills or impoundments. There is a growing realization that these ashes should not be rejected simply because they do not meet the historical specifications adopted when high-quality coal ash was available in abundance; rather, they should be evaluated and considered if concrete made with them meets performance requirements. To support this, the current specification could be revisited to include marginal and unconventional-source coal ashes. More importantly, it may be useful to consider basing new specifications on measuring and evaluating ash properties that impact the performance of the concrete.
Under NCHRP Project 10-104, “Recommendations for Revision of AASHTO M 295 Standard Specification to Include Marginal and Unconventional Source Coal Fly Ash,” South Dakota School of Mines and Technology was tasked to propose how current specifications could be revised so off-specification coal ashes could be considered for use in concrete without any negative impact on concrete performance. These off-specification ashes included ashes that are currently discarded in landfills and impoundments. Following a literature review on the state of the practice, with particular reference to marginal and unconventional-source coal ashes, a new specification based on the impact of ash on concrete performance was proposed. An extensive testing program involving a large suite of standard and unconventional coal ashes was subsequently developed and executed to evaluate the proposed specification and demonstrate its applicability. Based on this evaluation, draft language is proposed for consideration by AASHTO to incorporate the research results in
the next update of the AASHTO M 295 Standard Specification to include marginal and unconventional-source coal ash. The report includes a step-by-step guide for state DOTs and other users on a plan of action, including mitigation strategies for any negative effects, to allow the use of coal ashes previously considered noncompliant with specifications for the intended construction applications.
CONTENTS
Reactivity and Paste Testing Methods
Chapter 3 Findings and Applications
Modifications of SAI and Development of BRI
Assessment of Uniformity, Sampling, and Testing Frequency of Unconventional Coal Ash
Chapter 4 Conclusions and Proposed Draft Language for Specification
Proposed Draft Language for AASHTO M 295 Standard Specification
Appendix A Details of Statistical Methods Used for Analysis of Uniformity
Appendix B Using Off-Specification Coal Ashes in Highway Concrete Applications
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