Dimensional analysis of ionic transport problems in hydrated cement systems - Part 1. Theoretical considerations

The validity of the local equilibrium assumption in hydrated cement systems that a particular chemical reaction is instantaneous with respect to trans port is examined using a dimensional analysis of electrochemical transport in cementitious materials. The transport equation parameters are scaled, re sulting in a dimensionless equation. The dimensionless coefficient for each reaction/transport term determines its relative contribution to the overal l process. The diffusion of ions in a reactive porous medium can be fully d escribed on the basis of six independent dimensionless numbers. The analysi s demonstrates that the kinetics of the reaction determine the appropriate time constant for the analysis. The formalism is applied to the dissolution of calcium hydroxide under an electrochemical potential gradient. The resu lts are in agreement with previous observations and demonstrate quantitativ ely the local equilibrium hypothesis is valid in most practical cases where ions are transported by diffusion through a saturated material. (C) 2001 E lsevier Science Ltd. All rights reserved.