Strength and compressibility of sedimented ash beds treated with chemical columns

Abstract

This paper reports the strength and compressibility properties of sedimented ash beds treated with chemical columns. Sedimented model ash beds were prepared by simulating the natural sedimentation process in a laboratory environment and allowing them to undergo consolidation under the self-weight for a period of 30 days. Then, the ash beds were treated with three different configured chemical columns of sodium hydroxide (NaOH) with a concentration of 18 M for 60 days. After the 60 days of treatment, the in-situ dry unit weight, moisture content, bearing resistance, collapse potential, compressibility properties, and pore structure at different locations of the treated ash beds were examined. The contours of the bearing resistance were found to be bell-shaped with larger spreading towards the bottom end of the columns. The magnitude of the strength development was found to diminish rapidly with an increase in the radial distance from the column surface. After 60 days, the void ratio and collapse potential values in the column’s peripheral region of the ash beds treated with full, ½, and 1/4 columns were found to be 0.89, 0.93, and 0.95 and 0.75%, 0.89%, and 0.97%, respectively, compared to 1.64 and 7.46% of an untreated ash bed. These changes were attributed to the development and distribution of reaction products, which are functions of the column configuration and sampling location. The void ratio gradually increased with an increase in the radial distance from the chemical column. The decrease in void ratio was attributed to the blockage of the capillary pores by the reaction products. Primarily sodium- and calcium-based reaction products were observed along with hybrid compounds of sodium-calcium-based alumino-silicates. These reaction products encapsulated the ash particles within the matrix structure, thus modifying the bearing resistance, collapse potential, and compressibility properties of the sedimented ash beds. The morphology of the stabilized ash specimens showed a mixture of partially reacted ash particles, semi-crystalline structures, and reacted gel phase as the geopolymerization products.