Modeling of Chloride Transport Resistance in Cement Hydrates by Focusing on Nanopores

Abstract

This study proposes reasonable models to evaluate chloride ion ingress in cementitious materials with dense micropore structures. Salt water immersion tests with mortar specimens, including low water-to-cement (W/C) ratio materials, were conducted. The results show that chloride ion ingress is so slow in specimens with low W/C ratios that existing models cannot follow experimental trends, and pores in the nanometer range may have significant effects on the total extent of chloride ion transport. Two phenomena related to chloride ion ingress in nanopores were considered and installed in the existing system: a threshold radius regarding the chloride ion movement, and a reacting friction force along the pores against the water movement pressure. Measured chloride ion distributions with salt water immersion tests were used to verify the proposed models. By conducting additional numerical simulations, the possible mechanisms of high resistivity against chloride ingress were studied.

Numerical Simulations of Chloride Transport in Concrete Considering Connectivity of Chloride Migration Channels in Unsaturated Pores

“…where W thre is the amount of liquid water existing in the pores with a radius not greater than the threshold pore radius r thre (Takahashi and Ishida 2016), and W ink is the liquid water in the ink-bottle pores.…”

“…It is supposed that chloride ions in a pore with a radius smaller than the threshold pore radius, r thre , cannot pass through the pore even if the pore is filled with liquid water. This r thre is set as 10 nm based on the results of sensitivity analyses (Takahashi and Ishida. 2016).…”

Assessing the Performance and Transport Properties of Concrete using Electrical Property Measurements

“…The reduced pore interconnectivity will reduce ionic mobility and, therefore, increase the resistance of the concrete to ionic (i.e. chloride) ingress (Takahashi and Ishida 2016). At the end of the test period, the formation factor (± 5) increases in the order PC (315); GGBS/35 (545); GGBS/50 (835) and GGBS/65 (1040).…”

Future of multiscale modelling of concrete - Toward a full integration of cement chemistry and concrete structural engineering

“…Recently, the chloride ion transport model has been enhanced by introducing the threshold pore radius of chloride ion transport and the water transport friction to consider the stagnation effect of chloride ions in low water-cement ratio cases with OPC [24]. However, this enhanced model still overestimates the extent of long-term chloride ingress for fly ash blended concrete (Fig.…”