Beneficial Use of Off-Specification Fly Ashes to Increase the Shear Strength and Stiffness of Expansive Soil-Rubber (ESR) Mixtures

The use of off-specification fly ashes to increase the shear strength and stiffness of an expansive soil-rubber (ESR) mixture is investigated systematically in this study. The off-specification fly ashes used include a high-sulfur content and a high-carbon content fly ash. A class C fly ash is used as a control to develop a basis for comparison. The ESR mixture consists of high-plasticity clay blended with 20% 6.7-mm granulated rubber. The fly ash content necessary to develop pozzolanic reactions is determined based on the concept of lime fixation point and kept constant for all ESR-fly ash mixtures. Specimens are prepared at a single relative compaction level and curing times of 7 and 14 days. Unconfined compression testing was performed to validate the fly ash content selected and assess the development of pozzolanic reactions. Undrained triaxial compression tests are performed to evaluate the effect of the fly ash type and curing time at mean effective stress levels of 50, 100 and 200 kPa. Stiffness is evaluated at large strains during undrained compression and at very small strains using bender elements. Results indicate shear strength and stiffness are improved by the addition of the fly ashes, with the off-specification fly ashes performing as well as or better than the standard class C fly ash.

  • Record URL:
  • Record URL:
  • Supplemental Notes:
    • This document is disseminated under the sponsorship of the Department of Transportation, University Transportation Centers Program.
  • Corporate Authors:

    Colorado State University, Fort Collins

    Department of Civil and Environmental Engineering
    Fort Collins, CO  United States  80525

    Mountain-Plains Consortium

    North Dakota State University
    Fargo, ND  United States  58108

    Research and Innovative Technology Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Authors:
    • Wiechert, Ethan P
    • Carraro, J Antonio H
  • Publication Date: 2011-7


  • English

Media Info

  • Media Type: Print
  • Features: Figures; References; Tables;
  • Pagination: 108p

Subject/Index Terms

Filing Info

  • Accession Number: 01354564
  • Record Type: Publication
  • Report/Paper Numbers: MPC Report No. 11-235
  • Files: UTC, NTL, TRIS, USDOT
  • Created Date: Oct 21 2011 7:38AM