Phase transformation and strength of hydrated circulating fluidised bed combustion ash sediment in an open environment over 15 years: implications for the long-term stability of ash waste plateaus

Abstract

Low-temperature circulating fluidised bed combustion (CFBC) of oil shale results in Ca-rich ashes with low pozzolanic properties, raising concerns regarding the long-term stability of ash depositories. This paper presents findings from a long-term field study investigating the mineral and chemical transformations of total CFBC ash sediments over a 15-year period. The study reveals that the pozzolanic properties of CFBC ashes are primarily influenced by the formation of Ca-Al sulphate mineral ettringite and the compactness of sediment. The compaction of ashes during deposition contributes to the development of a dense microstructure, providing uniaxial compressive strength that exceeds 20 MPa. Our findings suggest that compacted and hydrated CFBC ashes are sufficiently stable in ash deposits, holding promise as a sustainable alternative for cement-free construction materials.

Keywords

• cfbc ashes
• strength development
• long-term stability