Wiechert, Ethan Patrick, authorCarraro, J. Antonio H., advisorGuggemos, Angela A., committee memberShackelford, Charles D., committee member2007-01-032007-01-032011http://hdl.handle.net/10217/47424The potential use of off-specification fly ashes to increase the shear strength and stiffness of an expansive soil-rubber (ESR) mixture was investigated systematically in this study. The off-specification fly ashes used included a high sulfur content fly ash and a high carbon content fly ash. A standard Class C fly ash was also used as a control fly ash to develop a basis for comparison of the effects of the off-specification fly ashes. The ESR mixture consisted of high-plasticity clay blended with 20% 6.7-mm granulated rubber (by weight). The fly ash content required to develop pozzolanic reactions was determined based on the concept of lime fixation point and kept constant for all ESR-fly ash mixtures. At this selected fly ash content, ESR-fly ash mixtures were tested at a single relative compaction level and curing times of 7 and 14 days. Unconfined compression testing was performed on compacted specimens to validate the fly ash content selected and the effect of curing time on the development of pozzolanic reactions. The effect of the fly ash type, curing time and mean effective stress was evaluated by performing isotropically consolidated undrained triaxial compression tests on saturated specimens at mean effective stress levels of 50, 100 and 200 kPa. Stiffness changes due to fly ash addition were evaluated during undrained compression. Large-strain stiffness was measured using conventional external displacement transducers. Very-small strain stiffness was evaluated from shear wave velocity measurements using a bender element apparatus. Results suggest that the shear strength and stiffness improvements imparted by the off-specification fly ashes is similar to or better than the improvements imparted by conventional Class C fly ash.born digitalmasters thesesengCopyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.expansive soiloff-specification fly ashscrap tire rubbershear strengthstiffnesstriaxialText