Mesoscale numerical simulation of chloride ion penetration in geopolymer concrete under the externally applied electric field

This paper presents a numerical investigation on the penetration of chloride ions in a saturated geopolymer concrete under the action of externally applied electric field. The chloride ion transport model in geopolymer concrete is established, and the interactions between different ionic species such as potassium ions, sodium ions, hydroxide ions, and chloride ions are considered. By solving the modified mass conservation equation and the Poisson equation of individual ionic species, the concentration and electrostatic potential of different ions at any position and at any time are obtained. Results show that under the action of externally applied electric field, the ion electromigration plays a leading role, which is characterized by a rectangular wave in the concentration distribution curve. In addition, the average chloride ion penetration depth obtained from the numerical simulations agrees well with that measured from the experiment in the cited literature. Moreover, the transmission speed of the two positively charged ions (or the two negatively charged ions) are almost the same. While there is a striking difference in the transmission speed between the positively charged ions and the negatively charged ions, indicating that the electrostatic potential gradient is not constant, and is region related.