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Chemical Stabilization of Subgrades

Learn about soil subgrade stabilization techniques using lime, cement, and kiln dust for long-lasting results. Understand when and how much stabilizer to use, along with detailed procedures for lime and cement stabilization. Field testing methods for strength and durability assessment are also covered.

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Chemical Stabilization of Subgrades

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  1. Chemical Stabilization of Subgrades Section Engineers’ Meeting Lake Cumberland State Resort Park March 5-7, 2013

  2. Why should soil subgrades be stabilized? Improve Bearing Capacity CBR of Clays Soils are 1 to 5 CBR of Silts 4 to 10 Silts Very Susceptible to Changes in Moisture Stabilized Subgrade Will Last for Many Years 85% of Soils in Kentucky are Silts and Clays

  3. Types of chemical stabilization Lime: Lean to Fat clays Plastic Index Predominantly > 15 Cement: Sandy and Silty Soils Plastic Index <20 PI 15 to 25: Lime or Cement may be used Lime Kiln Dust: Clays Cement Kiln Dust: Sandy Soils Kiln Dust is byproduct from cement and lime manufacturing Cheaper but more may be needed Good for drying wet soils (modification)

  4. Types of chemical stabilization Lime: takes longer (mellowing period initial and final mixing) Cement: Mixed and compacted within a few hours Kiln Dust: Lower Cost; not as much active calcium available

  5. When should soil subgrades be stabilized? 15 samples CBR of Clays Soils are 6 or less

  6. When should soil subgrades be stabilized? CBR of Clays Soils are 6 or less

  7. How much stabilizer should be used Eads and Grim Test (ASTM D 6276) The lowest amount needed to reach a pH of 12.4

  8. How much stabilizer should be used Unconfined Compressive Strength, Qu, test on lime stabilized sample

  9. How much stabilizer should be used? The lowest amount needed to reach a specified strength

  10. Procedures (Lime Stabilization) Construct subgrade to plan elevation

  11. Sampling before starting • Send samples (1 per 1,000 feet min.) to Geotechnical Branch at least 3 weeks before starting stabilization • Proctor tests may take 2 weeks • If you think a soil needs stabilization call Geotech

  12. CaO + H2o Ca(OH)2 Procedures (Lime Stabilization) Quick Lime is delivered and transferred to mixing (slaking tank) Quick Lime is converted to Hydrated Lime

  13. Procedures (Quick Lime Stabilization) Lime Slurry is transferred to dispensing truck

  14. Procedures (Quick Lime Stabilization) Scarify Subgrade

  15. Procedures ( Quick Lime Stabilization) Apply lime slurry to scarified subgrade

  16. Procedures (Quick Lime Stabilization) Apply lime slurry to scarified subgrade

  17. Procedures (Lime Stabilization) Mix slurry and soil to specified depth

  18. Procedures (Lime Stabilization quick lime) Mix slurry and soil to specified depth

  19. #4 Sieve, 1 Inch Sieve, 2 Inch Sieve

  20. Procedures (Lime Stabilization) Lightly Compact

  21. Clay will have a silty texture Procedures (Lime Stabilization) Mellow for one day and mix again

  22. Procedures (Lime Stabilization) Mellow for one day and mix again

  23. Procedures (Lime Stabilization) Final Compaction (24- 72 hours)

  24. Procedures (Hydrated Lime Stabilization) Dry (hydrated lime) application Ca(OH)2 Hydrated lime is delivered in tanker Transported to spreader truck

  25. Procedures (Hydrated Lime Stabilization) Dry (hydrated lime) application Ca(OH)2 Hydrated lime spread on subgrade

  26. Dry (hydrated lime) application Water added during mixing Compaction same as for quick lime

  27. Procedures (Lime Stabilization) Check compaction

  28. Procedures (Lime Stabilization) Cut to final grade

  29. Procedures (Lime Stabilization) Cut to final grade

  30. Procedures (Lime Stabilization) Check Depth of chemical stabilization

  31. Lime Testing • Soil sampler

  32. Depth Testing • Phenolthalein lime testing solution

  33. Procedures (Lime Stabilization) Depth of chemical stabilization

  34. Procedures (Lime Stabilization) Depth of chemical stabilization

  35. Procedures (Lime Stabilization) Keep moist

  36. Procedures (Lime Stabilization) Apply an asphalt seal No additional moisture is needed after sealing Typical cure time is seven days maximum

  37. Molecular Weight CaO Ca 40.08 x 1 = 40.08 O 16.00 x 1 = 16.00 Total 56.08 CaO + H2o CaO + H2O Ca(OH)2 Ca(OH)2 Why is quick lime paid at 1.25 times actual quantity? Quick lime is delivered and transferred to mixing (slaking tank) quick lime is converted to hydrated lime Molecular Weight Ca(OH2) Ca 40.08 x 1 = 40.08 O 16.00 x 2 = 32.00 H 1.00 x 2 = 1.02 Total 74.10 Close to 1.25? 74.10/56.08 = 1.32

  38. Truck being filled with Cement

  39. Procedures (Cement Stabilization) Dry application Mix one time and compact soon

  40. Water Applied to Soil

  41. Procedures (Cement Stabilization) Water can be applied to mixer directly Typical cure time sometimes shortened

  42. Procedures (Cement Stabilization) Water applied to mixer directly

  43. Field testing to determine long-term strengths And durability of chemically stabilized subgrades

  44. Field testing to determine long-term strengths And durability of chemically stabilized subgrades

  45. SPT TESTS

  46. Coring a stabilized subgrade using compressed air as cooling medium

  47. Core of stabilized subgrade and asphalt about 30 years old

  48. Shelby Tubes of stabilized subgrade (special tubes made) and layer below the stabilized subgrade

  49. Field CBR test on stabilized subgrade and below stabilization

  50. Percentile Test Value In Situ CBR From University of Kentucky Transportation Center

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