Mixtures of colliery spoils and fluidized bed bottom ash: strength and swelling behavior under compressive stress in isolated conditions

Abstract

AbstractThe amount and variety of waste materials used in civil engineering are steadily increasing due to the depletion of natural resources and the implementation of environmental policies. A new mixture of colliery spoils and fluidized bed bottom ash was recently developed in Poland, which proved to be prone to excessive, long-term swelling, potentially damaging structures such as road embankments. Numerous papers discuss the heaving mechanisms in spoils or fluidized bed ash. However, no reports analyzing the expansion of their mixture seem to be available. The purpose of this paper is to fill this void. The experiment involved measurements of linear swelling of mixture samples stored inside CBR test molds and isolated from moisture loss/gain. Material expansion is caused by the reactivity of the fluidized bed ash; its content in the mix correlates positively with the final swelling strain. At the same time, colliery spoils provide an environment particularly conducive to the phenomenon’s occurrence. A linear swelling strain of 0.3–3.2% was observed after 6 months (disregarding the first 24 h of rapid volume growth). The expansion of mixtures was also measured under constant compressive stress of 0–100 kPa to better represent their actual working conditions. Based on the results, it is proposed to adapt a mathematical model developed for anhydrite-rich rock to describe the load-swelling relationship in mixtures of colliery spoils with fluidized bed bottom ash. Such a model can be potentially used, e.g., in numerical analyses, to assess the impact of the material’s expansion on embankments.