Abstract

Pore structure characteristics,including porosity,pore size distribution,pore connectivity and tortuosity,play an important role in the durability of cementbased materials.The gradual improvement of computational capabilities has enabled nondestructive imaging methods such as X-ray computed microtomography(X-ray μCT)to yield high-resolution,threedimensional(3D)representations of pore spaces.In this paper,X-rayμCT was used to derive the 3D images of hardened cement paste specimens with water-tocement(W/C)ratios of 0.3,0.4 and 0.45 at curing ages of 1,3,7,28 days at the resolution of 1μm/voxel.By defining the upper threshold value in the basis of the inflection point of the cumulative volume fraction curve,the pores were distinguished from solid phases(i.e.hydration products and unhydrated cement grains)in the microtomography images of each specimen[1-3].The 3D pore structures of cement-based materials were obtained and the pore structure characteristics were analyzed in detail by the application of the segmentation and 3D reconstruction software Avizo.The pore characteristics by X-ray μCT were compared with the results from other experiment methods,including mercury intrusion porosimetry(MIP),backscattered electron(BSE),N2 adsorption,vapor adsorption,vacuum water saturation[4],nuclear magnetic resonance(NMR)[5]and small-angle Xray scattering(SAXS)[6,7].Furthermore,chloride ion diffusion test was conducted to investigate the relationship between the pore structure and chloride diffusivity of cement-based materials.Based on the pore structure characteristics obtained by experiment methods,chloride ion transmission coefficient yielded from chloride diffusion was analyzed qualitatively and quantitatively,by which we identified the most critical factors affecting chloride ion transmission coefficient in pore structure characteristics.In the meanwhile,by fitting the experiment data on a theoretical basis,a more optimized model for the relationship between pore structure characteristics and chloride ion transmission coefficient was proposed.