U.S. Department of Agriculture Stabilization Selection Forest Service National Technology & Guide for Aggregate- Development Program 7700—Transportation Mgmt and Native-Surfaced 0877 1805—SDTDC March 2009 Low Volume Roads OF TRAN NT S E PO T SER M R ES VI T T OR CE R A F A T P I O E N D D E E U A R P N C U I I A R T T R TMENT OF AGRICU L ED E S AM TATES OF Cover photo: Alan Anderson, Black Hills National Forest Stabilization Selection Guide for Aggregate- and Native-Surfaced Low-Volume Roads Maureen A. Kestler, Civil Engineer, Forest Service, San Dimas Technology & Development Center March 2009 Information contained in this document has been developed for the guidance of employees of the U.S. Department of Agriculture (USDA) Forest Service, its contractors, and cooperating Federal and State agencies. The USDA Forest Service assumes no responsibility for the interpretation or use of this information by other than its own employees. 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TABLE OF CONTENTS CHAPTER 1—OVERVIEW Introduction ................................................................................................ 1 Purpose ...................................................................................................... 2 Scope of Guide .......................................................................................... 2 General Information and Background ........................................................ 5 How To Use This Guide ............................................................................. 6 CHAPTER 2—CHEMICAL STABILIZATION Selecting A Traditional Chemical Additive .................................................. 7 Selecting A Nontraditional Chemical Additive .......................................... 13 CHAPTER 3—MECHANICAL STABILIZATION Introduction .............................................................................................. 19 Selecting a Mechanical Stabilization Technique ...................................... 19 Background and Design Theory .............................................................. 24 CHAPTER 4—CONSTRUCTION HINTS ................................................................ 33 REFERENCES .................................................................................................... 37 APPENDIX A—Definitions APPENDIX B—Traditional Chemical Stabilizers: Simplified method of selecting and determining quantities (including FWHA 2005) APPENDIX C—Traditional Chemical Stabilizers: UASCE method of selecting and determining quantities APPENDIX D—ASTM Soil Tests APPENDIX E—pH and Sulfate Tests APPENDIX F—Evaluation of Stabilizers APPENDIX G—Nontraditional Stabilizers (FHWA 2005) APPENDIX H—Mechanical Stabilization Techniques (FHWA 2005) APPENDIX I—Geosynthetics ACKNOWLEDGMENTS This publication is the result of a partnership between the National Technology and Development Program of the Forest Service, U.S. Department of Agriculture and the U.S. Department of Transportation Federal Highway administration (FHWA) Coordinated Federal Lands Highway Technology Improvement Program. We would like to acknowledge Pete Bolander and Douglas Scholen for providing the foundation from which this guide was developed, Gordon Keller for his recommendation of updating former selection guides to include recent developments and new information on stabilizers that has come about during the past few years, Alan Yamada and Mike Mitchell for their guidance, and Charles Aldrich for providing helpful information. The author also thanks Jeb Tingle at the U.S. Army Corps of Engineers Engineer Research and Development Center, Mike Voth and his colleagues at the Central Federal Lands, Minnesota Local Road Research Board, the Transportation Research Board, and also reviewers Bill Vischer, Pete Bolander, and Gordon Keller, those who provided photographs, the editors, and ever-so-many other Forest Service representatives who contributed toward the development of this updated stabilization guide. Overview INTRODUCTION Soil stabilizers can be used to treat the upper several inches of soil or aggregate surfaces of low-volume roads (LVRs) when the strength or other properties of the in-place soil do not meet the desired or required levels for anticipated traffic. Soil can be either modified or stabilized by many methods, including chemical, mechanical, thermal, and electrical (Danyluk 1986; Martel et al. unpublished). Modification is generally short term and includes benefits such as improvement in workability (expediting construction and saving time and money). Stabilization generally results in a longer term strength gain. q Chemical stabilization is achieved by mixing chemicals, such as cement, lime, fly ash, bitumen, or combinations of these materials, with soil to form a stronger composite material. Selection of the type and percentage of additive is a function of the soil classification and the degree of improvement desired. Chemicals and/or emulsions can be used as: m Compaction aids to soils. m Binders and water repellents. m A means of modifying the behavior of clay to form a stronger composite material. Chemical stabilization can aid in: m Dust control. m Water-erosion control. m Fixation and leaching control of both waste and recycled materials (Das 2000). q Mechanical modification/stabilization involves mixing (two or more soils to obtain a material of desired specification), draining, and/or compacting soil. Alternately, fibrous or other nonbiodegradable reinforcing materials, such as geosynthetics/geocomposites/fibers, can be mixed in or physically placed with the geomaterial to improve strength. CHAPTER ONE q Thermal stabilization involves heating or freezing soil. m Heating the soil to 600 °C can irreversibly dehydrate or fuse soil particles. m Freezing can strengthen the soil by solidifying water content. q Electrical stabilization involves applying a direct electrical current to the soil. This causes water to migrate out of the soil to an electrode. Overview 1 CHAPTER ONE This guide focuses on chemical and mechanical methods. Definitions used in conjunction with stabilization are provided in appendix A. PURPOSE The purpose of this guide is to facilitate the selection of modification/stabilization agents and techniques for aggregate- surfaced and native/unsurfaced LVRs. The objective is to provide low-cost alternatives that reduce aggregate wear and loss, reduce road-surface maintenance (i.e., blading out ruts), and reduce the time period between major rehabilitation (i.e., between adding new aggregate or the total reconditioning of the road pavement). This guide provides information on available stabilizing agents, appropriate conditions for use, selection procedures, quantity determination, and contact information for manufacturers/suppliers. Emphasis is on the modification/stabilization of existing in-place road surface materials, but many of the methods can be used in the construction of new roads. Construction procedures for application are also presented. The intended audience includes road managers, engineers, and technicians involved in road maintenance, construction, and reconstruction. Those involved in trail maintenance and construction also may find the guide beneficial, as stabilizers used on trails, particularly accessible trails, help provide a smooth, durable surface. Information on the use of synthetics for trails can be found in the Forest Service, U.S. Department of Agriculture, publication “Geosynthetics for Trails in Wet Areas” by Groenier (2008). Information on accessible trails is provided in another Forest Service publication, “Soil Stabilizers on Universally Accessible Trails” (Bergmann 2000). SCOPE OF GUIDE This guide focuses primarily on chemical and mechanical methods. It serves as an updated sequel to two reports prepared in the 1990s, “Non-Standard Stabilizers” (Scholen 1992) and “Stabilization with Standard and Nonstandard Stabilizers” (Bolander 1995), and incorporates applicable tables from the “Surfacing Selection Guide” recently developed by the U.S. Department of Transportation, Federal Highway Administration (FHWA), Central Lands Federal Highway Division (FHWA 2005), and tables from the Transportation Research Board (TRB) (Petry and Sobhan 2005). The guide also incorporates procedures from the U.S. Army Corps of Engineers (USACE), and reflects discussions with engineers and contractors,