The mathematical models to describe alkali assisted dissolution of ground fly ash following shell-core behavior under finite solution volume condition were developed. An analytical solution was obtained for the model based on pseudo steady state diffusion, whereas the model based on unsteady state diffusion was converted by the finite integral transform technique to a system of first order coupled ordinary differential equations, which are then solved by numerical methods using the Gear method available in Numerical Algorithms Group (NAG) library. The alkali dissolution data of fly ash under finite solution volume condition were obtained using Fourier Transformed Infra-Red (FTIR) spectrophotometer analysis. The two models were tested with actual fly ash dissolution data and yield comparable results. (C) 2016 Elsevier B.V. All rights reserved.