Mechanical and Physical Properties of Edmonton Stiff Clay Treated With Cement and Fly Ash

• Author / Creator

  Luis Goncalves, Adriana E

• Cementitious binders have been widely used to improve the mechanical, hydraulic, and physical properties of soft soils by deep soil mixing and jet grouting in the past 50 years. However, the majority of previous investigations are limited to the stabilization of very soft clays in marine environments or sandy soils, which are often mixed with cement contents lower than 15%. This research considers a context where the soil-cement mix (soilcrete) would be produced with stiff clays as a deep foundation to support heavy loads that require cement contents higher than 20% to meet the design requirements for strength. The objective of the present research is to determine the mechanical properties of Edmonton stiff clay mixed with binders composed by cementitious additives. Two binders were used for the investigation, which contained 100% Portland cement and a mix of 90% Portland cement and 10% fly ash. In the first phase of this research, unconfined compressive strength tests were carried out at different curing ages on soilcrete specimens produced with different cement contents. The results demonstrate that soilcrete with cement contents near 22% continue developing strength at a faster rate after 28 days, when compared to soilcrete with greater cement content. Soilcrete behaves similar to an overconsolidated clay, and reaches peak strength at strains lower than 1% at mature age (>56 days). Scanning electron microscope images show the main differences in the microstructure of soilcrete between the binders. In the second phase of this research, mechanical properties of specimens produced in the laboratory were investigated through isotropically consolidated–undrained triaxial tests, confined to a pressure ranging from 100 kPa to 3 MPa. Effects of consolidation and shear failure on the soilcrete permeability were quantified. The microstructures of soilcrete failure surface and outer surface were inspected with scanning electron microscope. Computed tomography (CT) scanned images of the soilcrete were analyzed and a method was proposed to estimate the porosity of the specimen and porosity distribution. The results show strain softening behaviour on all the specimens, and suggest the breakage of cement bonds with confining pressure over 1 MPa. The peak friction angle is the same for both soilcrete, with greater cohesion in specimens with cement only. Significant cohesion remained at the fully-softened state. The new method of analyzing CT scanned images predicted the soilcrete porosities that match the lab-estimated porosity very well.

• Subjects / Keywords

  • Mechanical properties
  • Cemented clay
  • CT scan
  • SEM
  • Soilcrete
  • Unconfined compression
  • Triaxial test
  • Porosity

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3DB7W445

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.