Preliminary investigation on the pore structure of Portland cement paste by means of multifractal measure method

Concrete is a complex material with a multi-scale structure which plays a critical role concerning permeability and durability. In this paper, a two-dimensional pore structure of the cement paste is considered as a media showing an intermittency phenomenon. On this basis, a multifractal (MF) measure method is employed to analyze the pore structure characteristics, using a digital cross section image acquired by scanning electric microscopy (SEM). The results suggests that the pore structure of cement paste displays special mutiple scaling properties. As investigation scale increases, the spatial distribution characteristics display a transition from random type in low scales to scaling properties in high scales with the existing of a critical scale. More specifically, as for the selected image sample with size (256x256) pixels, the acquired multifractal index spectrum displays quasi-bifractal characteristics, showing two different fractal singularities as scales change. Finally, the multifractal property of pore structure is attributed collective nonlinear physical and chemical interactions in the hydration process.