Beneficial Use of Off-Specification Fly Ash to Improve the Small-Strain Stiffness of Expansive Soil-Rubber Mixtures

摘要

The potential use of off-specification fly ash to increase the small-strain stiffness of expansive soil-rubber (ESR) mixtures was investigated systematically in this study. Both high-sulfur content and high-carbon content off-specification fly ashes were tested. A standard Class C fly ash was also used as a control fly ash. The ESR mixture consisted of high-plasticity clay blended with 20% 6.7-mm granulated rubber (by dry weight). The off-specification fly ash content required to develop pozzolanic reactions was determined based on the lime fixation point concept and kept constant for all ESR-fly ash mixtures. At this selected off-specification fly ash content, ESR-fly ash mixtures were tested at a single relative compaction and curing time of seven days. Changes in small-strain stiffness due to fly ash addition were evaluated at mean effective stresses equal to 30, 50, 100 and 200 kPa using a bender element device incorporated to a conventional triaxial apparatus. Results suggest the small-strain stiffness improvement imparted by off-specification fly ashes is equal to or better than the improvement imparted by a standard Class C fly ash. Beneficial use of off-specification fly ashes restores the small-strain stiffness of the ESR mixtures to levels similar to or higher than those reported for the soil without rubber.