Experimental investigation and numerical simulation for chloride diffusivity of cement paste with elliptical cement particles

The shape of cement particle affects the hydration process of cement through its specific surface area and dispersion morphology, and then exerts great effects on the pore structure characteristic and the chloride ingression of cement paste, while it is generally simplified as the sphere in most of the vector models of cement hydration. To reveal the influence of cement particle shape on chloride diffusivity, a numerical method for quantitative analysis was proposed in this work. According to the size distribution curve and periodic distributions of cement particles, a representative fresh cement paste with elliptical inclusions was firstly constructed. According to the regulations of uniform increase of the thickness of hydration layer around the surface of quasi ellipse and the interference effects induced by hydration layer overlapping, a vector-based model of cement hydration was established and the influence of aspect ratio of cement particles on the hydration degree was discussed. By considering the diffusion properties of the multi-phase composite cement paste, the first-passage theory suited to two-dimensional pixel model was proposed, and the corresponding Brownian motion algorithm was applied. Using high power microscope, the average aspect ratio of cement particles was calculated. By full comparison of eight groups of experimental results, the effectiveness of this estimation method was verified. At last, the influence of the aspect ratio of elliptical cement particles on chloride diffusivity was drawn.