Fractal model for simulating the space-filling process of cement hydrates and fractal dimensions of pore structure of cement-based materials

Abstract

A fractal model is established for simulating the space-filling process of cement hydrates in cement paste. Based on this model, it is predicted that the fractal dimension D of the pore structure of hardened cement paste (hcp) is between 0 and 3, and that the water-to-cement ratio, degree of hydration of cement, and the addition of pozzolanic materials will affect the value of D. With the mercury intrusion porosimetry (MIP) technique, the fractal dimensions D of the pore structure of hcp can be determined; the quantitative relationship between D, accumulative volume V∗ of pores as defined in the paper, and the radius of pores ϱ is established as V∗ = tϱ3−D (where t is a constant). The experimental results of the pore size distribution of hcp from MIP were used to verify the equation, and the D value is calculated. It is experimentally found that the value of D for pores in fine diameter range is smaller than that in large diameter range. The experimental results also suggest that the higher the strength of concrete, the smaller the value of D in both the small and the large pore diameter ranges.