Unconfined Compressive Strength of Synthetic and Natural Mine Tailings Amended with Fly Ash and Cement

Abstract

The objectives of this study were to evaluate the effect of binder amendment on the unconfined compression strength (UCS) of mine tailings and assess applicability of using the amended materials in earthworks. Natural and synthetic (i.e., laboratory prepared) mine tailings were used to assess the effects of tailings particle size and tailings solids content on UCS. Two types of off-specification fly ashes and Types I and II portland cement were used as cementitious binders. Tailings and fly ash mixtures were prepared at 70, 80, and 90% solids content and amended with 10 or 20% binder. Unconfined compression strength tests were conducted on specimens cured for 7 days. In general, UCS increased with an increase in tailings particle size, solids content, and/or increase in CaO-to-SiO2 ratio of fly ash for amended tailings specimens. A multivariate regression model was developed to predict UCS of tailings amended with fly ash as a function of (1) tailings water content, (2) water-to-binder ratio, and (3) CaO-to-SiO2 ratio of fly ash. The model was developed using data from synthetic tailings specimens and validated via tests on natural tailings and data compiled from literature. The model is applicable for estimating the UCS of candidate fly ash amended hard rock mine tailings and low plasticity soils (i.e., liquid limit<50). The UCS of high plasticity materials was underpredicted with the model.