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Reduction of Sulfate Swell in Expansive Clay Subgrades in The

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Reduction of Sulfate Swell in Expansive Clay Subgrades in The Technical Report Documentation Page L Report No. I 2. Government AccesSIOn No. 3. Recipient's Catalog No. TX-9511994-5 4. Title and Subtitle 5. Report Date REDUCTION OF SULFATE SWELL IN EXPANSIVE CLAY November 1994 SUBGRADES IN THE DALLAS DISTRICT Revised: May 1995 6. Performing UIganization Code 7. Author(s) IS.Pertomung orgaruzaaon Keport No. Sanet Bredenkamp and Robert L. Lytton Research Report 1994-5 9. Performmg Organizatton Name and Address 10. Work Urut No. (TRAIS) Texas Transportation Institute The Texas A&M University System 1 L Contract or (jrant No. College Station, Texas 77843-3135 Study No. 7-1994, Task 16 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Texas Department of Transportation Interim: Research and Technology Transfer Office September 1993 - August 1994 P. O. Box 5080 14. sponsoring Agency Code Austin, Texas 78763-5080 1:>. ::.upplementary Notes Research performed in cooperation with the Texas Department of Transportation. Research Study Title: Highway Planning and Operation for District 18 Phase III 16. Abstract The addition of hydrated lime to clay soils is one of the most common methods of soil stabilization. However, when sulfates are present in the soil, the calcium in the lime reacts with the sulfates to form ettringite, an expandable mineral. This expansion causes a considerable amount of economical as well as structural problems. Sulfate related heave has been experienced along IH 45 and FM 1382. In this research, a field test method was developed to locate sulfate bearing soils. A permittivity probe was used to measure the electrical conductivity of the in situ soil. The electrical conductivity was then related to sulfate content in soils. Expansion tests were performed to determine the amount of expansion that occurs when lime is added to soils with different sulfate contents. A model that relates the amount of expansion of clay soils to electrical conductivity was proposed. The use of low calcium fly-ashes were investigated and proposed as an alternative form of stabilizer for sulfate bearing soils. 17. Key Words 1IS. DlStnbutton Statement Sulfate Swell, Ettringites, Low Calcium Fly-Ash No restrictions. This document is available to Stabilizers the public through NTIS: National Technical Information Service 5285 Port Royal Road Springfield, Virginia 22161 19. Security Classif.(of this report) 20. Security Classif.(ot ms page) 21. No. of Pages Unclassified 1 Unclassified 124 Form DOT F 1700.7 (8-72) ReproductioD of completed page authonzed REDUCTION OF SULFATE SWELL IN EXPANSIVE CLAYSUBGRADES IN THE DALLAS DISTRICT by Sanet Bredenkamp Research Assistant Texas Transportation Institute and Robert L. Lytton Research Engineer Texas Transportation Institute Research Report 1994-5 Research Study Number 7-1994, Task 16 Research Study Title: Highway Planning and Operation for District 18 Phase III Sponsored by the Texas Department of Transportation November 1994 Revised: May 1995 TEXAS TRANSPORTATION INSTITUTE The Texas A&M University System College Station, Texas 77843-3135 IMPLE:MENT ATION STA TE:MENT Sulfate related heave was experienced along FM 1382 and rn: 45. The mechanism of the heave and a proposed solution to the problem are described in this report. A field measurement procedure to determine an estimated amount of sulfate related heave before and after lime stabilization is described. Electrical conductivity is related to sulfate content and can, therefore, be used to determine whether substantial amounts of sulfates are present and whether they will cause a problem upon lime stabilization. Three different low calcium fly-ashes were used as alternative stabilization methods for sulfate bearing soils. The fly-ashes performed well and their results are described in this report. The field measurement procedure developed in this project is sufficiently promising to warrant pilot and subsequently full implementation by those district laboratories which must contend with sulfate swelling subgrades. A step-by-step procedure to determine sulfate related expansion in clay soils is included in the implementation section at the end of this report. v DISCLAIMER The contents of this report reflect the views of the authors who are responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Texas Department of Transportation. This report does not constitute a standard, specification, or regulation. vii TABLE OF CONTENTS Page LIST OF FIGURES ..... ',' ...................................... xiii LIST OF TABLES .............................................. xvi SUMMARY .................................................. xix CHAPTER 1 INTRODUCTION . .. 1 CHAPTER 2 liTERATURE REVIEW .............................. 5 Introduction ............................................... 5 Conductivity of Soils ......................................... 5 Electrical Conductivity in Soils ............................. 5 Conventional Methods for Measuring Soil Electrical Conductivity ................................... 6 Relation of Conductivity to Salt Content and Osmotic Pressure .................................... 8 The Effect of Soil: Water Ratios on the ,Electrical Conductivity ................................... 8 The Effect of Temperature on Conductivity ........ .. 8 Electrical Conductivity Measurements with Permittivity Probe ...................................... 13 Mineralogy of Clay Soils ..................................... 13 Stabilization of Base Courses with Lime . .. 18 Formation of Ettringites ..................................... 18 CHAPTER 3 METHODOLOGY .................................. 21 Introduction .............................................. 21 Method for Determination of Expansion of Sulfate Bearing Clay Soils .................................... 22 Method for Determining Electrical Conductivity with Permittivity Probe and the EPA Method No. 9050 ................................................. 25 ix Page Method for Investigating Several Low Calcium Fly-Ashes as Alternative Stabilizers ..................................... 28 Methods by which Supplementary Tests were Performed ................................................ 28 Cation Exchange Capacity Determination .................... 28 Method for Determination of Soluble Sulfate Content ........... 29 Method for Determination of Dielectric Constants ............. 29 CHAPTER 4 RESULTS FROM EXPANSION TESTS ................ ,. 31 Introduction .............................................. 31 Results of Expansion Tests Performed on Samples from IH 45 and FM 1382 . .. 31 Results of Expansion Tests Performed on Clay Soil Samples .......................................... 39 Conclusions ............................................... 42 CHAPTER 5 RESULTS FROM ELECTRICAL CONDUCTIVITY MEASUREMENTS ............................................. 43 Introduction .............................................. 43 Results from Soluble Sulfate Determination ....................... 43 Results from Electrical Conductivity Measurements on Soil Samples Obtained from IH 45 and FM 1382 . .. 45 Results from Electrical Conductivity Measurements on Four Clay Soils .............................. 45 Water Content of the In Situ Soil .............................. 54 Conclusions ............................................... 55 CHAPTER 6 RESULTS OF SUPPLEMENTARY TESTS ............... 57 Introduction .............................................. 57 Results from Cation Exchange Capacity Determination .............. 57 Results of Dielectric Constant Measurements ...................... 59 Conclusions ............................................... 63 x Page CHAPTER 7 RESULTS OF LOW CALCIUM FLY-ASH STABILIZATION .............................................. 65 Introduction .............................................. 65 Results of Low Calcium Fly-Ash Stabilization on Four Clay Soils . .. 65 Results of Low Calcium Fly-Ash Stabilization on FM 1382 Site No 7 ......................................... 69 Evaluation of Different Low Calcium Fly-Ashes as Stabilizers ...................................... 70 Conclusions ............................................... 71 CHAPTER 8 INTERACTIVE DISCUSSION OF ALL RESULTS ......... 73 Introduction .............................................. 73 Modell: Regression Modeling with % Expansion without Lime as Response Variable for the Four Clay Soil Samples ............... 73 Model 2: Regression Modeling with % Expansion with 6% Lime as Response Variable for the Four Clay Soil Samples ............... 76 Model 3: Regression Modeling with % Expansion without Lime as Response Variable for Soil Samples from FM 1382 and IH 45 ....... 77 Model 4: Regression Modeling with % Expansion with 6% Lime as Response Variable for Soil Samples from FM 1382 and IH 45 ....... 79 Model for Determination of Amount of Expansion Experienced by Sulfate Bearing Clay Soils ................................ " 81 Conclusions ............................................... 82 CHAPTER 9 CONCLUSION ..................................... 85 Overall Conclusions ......................................... 85 Subjects Proposed for Further Investigation ....................... 86 CHAPTER 10 IMPLEMENTATION OF RESULTS .................... 89 REFERENCES ................................................ 93 xi Page APPENDIX A . .. 97 Locations from which Soil Samples Were Taken Along FM 1382 ....... 99 Locations from which Soil Samples Were Taken Along IH 45
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