A prediction method for chloride ion diffusion coefficient of hardened cement paste based on fractal theory

Chloride ion diffusion coefficient is a common index to evaluate the durability of cement-based materials. In this paper, Mercury Intrusion Porosimetry (MIP) was used to verify the fractal characteristics of fly ash-cement system, silica fume-cement system and fly ash-silica fume-cement system. Meanwhile, fractal theory and X-ray Computed Tomography (CT) imaging technology were used to characterize the microstructure of cement-based materials, and the effective diffusion coefficient was obtained through finite element simulation. Thus, a prediction method for chloride ion diffusion coefficient of hardened cement paste was established. Results indicated that the three types of hardened cement pastes exhibited the fractal characteristics of solid phase volume within a certain range of pores. There was a linear correlation between the average effective porosity (f_eff) obtained by CT modeling and the porosity (f_mip) obtained by MIP (f_mip = 1.58f_eff – 0.12). The results from modeling were in good agreement with the results obtained from Rapid Chloride Migration (RCM) tests. The approximate relationship between f_mip and the simulated value of chloride diffusion coefficient (D_eff) was defined as D_eff = 2.75 – 16.34f_mip + 86.7f_mip².