The Impact of Tortuosity on Chloride Ion Diffusion in Slag-Blended Cementitious Materials

Abstract

The purpose of this study is to determine the tortuosity of cementitious materials containing blast furnace slag (BFS). Furthermore, the influence of tortuosity on multi-species transport into these materials is studied. The porosity and diffusivity of calcium silicate hydrate (C-S-H) were predicted using a three-dimensional spatial distribution model, which were then fitted to Archie's law to determine tortuosity. The tortuosity increased with the slag replacement ratio, suggesting that the diffusion path for ions becomes complicated and lengthy due to slag addition. Thermoporometry was used to determine the pore size distribution of hydrated slag-blended cement. A partial replacement of ordinary Portland cement (OPC) with BFS modified the mineralogy (especially in the types of C-S-H), resulting in changes to the pore structure. The determined tortuosity and porosity were used in a reactive transport model to predict multi-species transport. Experimentally measured and simulated chloride profiles were in good agreement for hydrated OPC and slagblended cements exposed to sodium chloride solutions. The causes for the low penetration rate of chloride in slagblended cementitious materials are discussed considering their pore structure and surface electrical properties. The role of tortuosity on Cl -/OH -for the evaluation of chloride induced corrosion was also discussed.

Physical, chemical, and mineralogical characteristics of blast furnace slag on durability of concrete

“…Backscattered electron image (BEI), energy dispersive X-ray spectrometry (EDX), electron probe microanalyzer (EPMA), micro-elastic modulus, and thermoporometry measurements were conducted on the cured and exposed specimens. The details of the composition of raw materials and their physical properties as well as the experimental techniques are described in our previous paper [6].…”

Gas Diffusion in Cement Pastes: An Analysis using a Fluctuating Diffusivity Model

“…It is an undeniable fact that cementitious materials are inherently porous in nature, possessing pores of various scales. Diffusion, the primary mode of mass transport, has been comprehended by devising effective diffusion coefficients which properly reflect the characteristics of the pore network structure (tortuosity, connectivity, constrictivity, formation factor [10,11,12,13,14,15]) and by utilizing them to solve the diffusion equation. It is obvious that the probabilistic displacement distribution is Gaussian when the conventional diffusion equation is resolved [16,17].…”

“…Yamaguchi et al refined the empirical relationship by assessing the accessible capillary pores, and demonstrated that the modified model is efficacious in describing the effective diffusion coefficient of tritiated water [69]. Furthermore, the empirical effective diffusive coefficient has been adapted to include semi-empirical parameters that characterize the morphology of the pore network (tortuosity, connectivity, constrictivity, formation factor) [10,11,12,13,14,15]. There has been extensive research aimed at relating these parameters to the actual pore topology obtained from imaging techniques, rather than simply adjusting bulk diffusion coefficients to effective diffusion coefficients [70,71,10,66,72,13,15].…”

A multi-species reactive transport model based on ion-solid phase interaction for saturated cement-based materials

“…In the current RTMs [10,[12][13][14], the ion mass transport is performed only through free water space, whereas the ions in the EDL are considered stagnated ions, which means that part of cations is neglected in the ion mass transport calculation. In addition, the ion mass transport in porous materials strongly depends on temperature [23], composition and ionic strength of pore solution [24,25], and pore structure [26,27]. Pore solution composition, phase assemblage, and pore structure will continuously vary in a cement-based material due to exposure to long-term environmental actions.…”