The chloride diffusivity of concrete is an important parameter for assessing the long-term durability of coastal concrete structures. The purpose of this paper is to present a three-dimensional random walk algorithm (RWA) for estimating the chloride diffusivity of concrete. By analyzing the size distribution of aggregates, the equivalent interfacial transition zone (ITZ) thickness is derived in an analytical manner. Each aggregate is combined with the surrounding ITZ to construct an equivalent aggregate model (EAM) and the chloride diffusivity is formulated. It is found that the equivalent ITZ thickness decreases with the increase of practical ITZ thickness and aggregate volume fraction. The aggregate gradation influences the equivalent ITZ thickness to a certain extent. The relative chloride diffusivity of the equivalent aggregate is almost directly and inversely proportional to the equivalent ITZ thickness and the aggregate radius, respectively. The numerical results show that, when the EAM is adopted, the computational time is greatly reduced. With the EAM, concrete can be modeled as a two-phase material and the chloride diffusivity is estimated by applying the RWA. It is shown that, with the increase of mean square displacement and number of Brownian particles, the average chloride diffusivity of concrete approaches a stable value. Finally, through comparison with experimental data, the validation of the RWA is preliminarily verified.
Concrete is a multiphase composite material composed of coarse aggregate, cement mortar, and interface transition zone (ITZ). It is of great significance to study the effect of ITZ and coarse aggregate on chloride microscopic diffusion behavior for predicting the service life of reinforced concrete (RC) structures. By introducing the random distribution function, a random coarse aggregate model considering the randomness of the thickness of the ITZ was established. Furthermore, a two-dimensional (2D) chloride ion diffusion mesoscopic model was developed by specifying different diffusion properties for different phase materials of concrete. Moreover, the effects of coarse aggregate rate, ITZ thickness, and ITZ diffusion property on chloride ion diffusion behavior were investigated in this paper. The research showed that the aggregate has hindrance and agglomeration action on chloride ion diffusion. Although the volume content of the ITZ was very small, less than 0.2% of the total volume of concrete, the effect of the ITZ on the chloride diffusion in concrete cannot be ignored. More importantly, the mechanism of promoting chloride diffusion in the ITZ was revealed through the chloride diffusion trajectory. The research revealed the transmission mechanism of chloride ions in the meso-structure of concrete and provides theoretical support for the design of RC structures in coastal areas.
A two-step scheme is presented for estimating the chloride diffusivity of pure cement paste. In the scheme, gel pores are included in the solid skeleton composed of CH, unhydrated cement, and CSH while capillary pores and the solid skeleton constitute pure cement paste. In combination with percolation theory, the effective medium method is modified to formulate sequentially the chloride diffusivities of the solid skeleton and pure cement paste. A detailed analysis is conducted to calibrate the percolation exponent for the high-diffusivity phase and the chloride diffusivity of pore solution. Finally, comparisons are made to verify the scheme with various test data. Compared with existing analytical methods, the physical properties, volume fractions, and morphological relationship of various phase constituents and the shapes, percolation behavior, and different roles of gel and capillary pores are all taken into account simultaneously. The calibrated chloride diffusivity of pore solution is considerably closer to that derived by molecular dynamics simulation, suggesting that the scheme represents a more realistic pure cement paste. The scheme can reasonably evaluate the chloride diffusivity of pure cement paste with middle- and long-curing ages.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.