Sensitivity of Selected Colorado Soils to Form Ettringite/Thaumasite When Treated With Calcium-Based Stabilizers and When Soluble Sulfates Are Available

Details

• Creators:
  Little, Dallas N. ; Nair, Syam
• Corporate Creators:
  Colorado. Department of Transportation. Applied Research & Innovations Branch
• Corporate Contributors:
  United States. Department of Transportation. Federal Highway Administration
• Subject/TRT Terms:
  Alumina Calcium Hydroxide Calcium Sulfates Calorimeters Differential Scanning Calorimeter Ettringite Gibb's Free Energy Mineralogy Portland Cement Silica Soil Mineralogy Soil Stabilization Sulfate-induced Heave Sulfates Swelling Soils Thermodynamics

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• Publication/ Report Number:
  CDOT-2007-14
• Resource Type:
  Tech Report
• Geographical Coverage:
  United States ; Colorado
• Edition:
  Final Report
• Corporate Publisher:
  Colorado Department of Transportation. Applied Research & Innovations Branch
• Abstract:
  The sensitivity of five Colorado soils, which were selected to represent the variety of soils likely to be treated with calcium-based chemical stabilizers such as hydrated lime or Portland cement, to the formation of potentially expansive minerals are evaluated using thermodynamic principles based on Gibb's free energy and direct measurements. Phase diagrams are used to predict the threshold levels of soluble sulfates that favor the formation of the expansive mineral ettringite, which is most widely blamed for deleterious expansion in sulfate bearing soils treated with calcium-based stabilizers. The results of the thermodynamic, phase diagram evaluation are checked against direct measurement of ettringite using differential scanning calorimetry (DSC), and the results agree well. The conclusions derived from this research are that, as expected, mineralogical differences among the soils affect the threshold level of soluble sulfates that trigger the development of ettringite and that the presence of soluble silica and the form of alumina present have a dominant effect. The research validates previous research that a safe lower limit of soluble sulfates is approximately 3,000 ppm as long as additional soluble sulfates do not migrate into the soil. A methodology is presented for using the DSC to directly assess the threshold level of sulfates for a particular soil. However, refinement of the method is a key goal of on-going research.
• Format:
  PDF
• Funding:
  80.25
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  urn:sha-512:937ab781cc26f872b57199cb6add63cd80e3a4ff59d2e2cfb114a8661753c62a3b8769f49f5adf2209b0ec0a5e8aabc49d7a0eb1ad069d9650312819b713e343
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/92964/dot_92964_DS1.pdf
• File Type:
  [PDF - 3.14 MB ]