Enhanced series-parallel model for estimating the time-dependent thermal conductivity of fly ash soil mixtures

© 2015, Springer-Verlag Berlin Heidelberg. An enhanced series-parallel (S-II) model of one-dimensional conductive heat flow through a unit cell was developed to estimate the time-dependent thermal conductivity of Class C fly ash stabilized soils. The unit cell is composed of three separate heat flow paths: a continuous path through solid contacts (soil contacts, fly ash contacts, and soil fly ash contacts) in parallel arrangement, a series-parallel path of solids in a series arrangement with a parallel arranged path of solid-miniscule pores (miniscule portion of solid water and miniscule portion of solid air), and a continuous path through water and air in parallel arrangement. The solid-miniscule pores volume fraction and the fluid/air volume fraction changes during pozzolanic reaction were modeled by estimating the interparticle pore water consumption rate. In addition, the time-dependent thermal conductivity characteristics of the fly ash soil mixtures were investigated by conducting experimental tests. Based on the test observations and parametric analysis, interparticle voids, fly ash percentage and degree of cementation, volume change of the interparticle liquids, and curing time were all found to play critical roles on the effective thermal conductivity of fly ash soil mixtures. The predicted thermal conductivity using the enhanced S-II model was compared with the experimental test data with good agreement, suggesting that the enhanced S-II model is a robust tool for estimating the global effective thermal conductivity of Class C fly ash stabilized soils.