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

摘要

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 to 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 200kPa. 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 or better than the standard class C fly ash.