Pore Structure Characterization of Cement Paste by XCT and FIB/SEM

Abstract

Many durability properties of cement-based materials, such as water permeability, chloride diffusivity and CO₂ diffusivity, are closely related to their pore structures. As a porous material, cement paste has a wide range of pore size distribution. One single observation method cannot fully characterize the pore structure of cement paste. In this paper, mercury intrusion porosimetry (MIP), focused ion beam/scanning electron microscopy (FIB/SEM) and X-ray computed tomography (XCT) were used to comprehensively characterize the pore structure of cement paste with different water-cement ratios, different ages and different admixtures. A series of important parameters of pore structure were obtained, such as representative elementary volume (REV), porosity, pore shape and orientation, pore size distribution (PSD), connectivity and tortuosity. Five different methods were used to obtain different types tortuosity of cement paste, namely geometrical tortuosity by direct shortest-path search method (DSPSM, τ_gD), pore centroid method (PCM, τ_gP), and transport-related tortuosity by hydraulic flow (τ_h), electrical conduction (τ_e) and diffusion (τ_d). Compared with MIP, the PSD results of FIB/SEM and XCT showed limited pore ranges, and other pore parameters between FIB/SEM and XCT revealed certain differences, indicating that a single FIB/SEM or XCT sample cannot represent cement paste.