Evaluation of Microstructure and Transport Properties of Deteriorated Cementitious Materials from Their X-ray Computed Tomography (CT) Images

Abstract

Pore structure, tortuosity and permeability are considered key properties of porous materials such as cement pastes to understand their long-term durability performance. Three-dimensional image analysis techniques were used in this study to quantify pore size, effective porosity, tortuosity, and permeability from the X-ray computed tomography (CT) images of deteriorated pastes that were subjected to accelerated leaching test. X-ray microtomography is a noninvasive three-dimensional (3D) imaging technique which has been recently gaining attention for material characterization. Coupled with 3D image analysis, the digitized pore can be extracted and computational simulation can be applied to the pore network to measure relevant microstructure and transport properties. At a spatial resolution of 0.50 μm, the effective porosity (φe) was found to be in the range of 0.04 to 0.33. The characteristic pore size (d) using a local thickness algorithm was found to be in the range of 3 to 7 μm. The geometric tortuosity (τg) based on a 3D random walk simulation in the percolating pore space was found to be in the range of 2.00 to 7.45. The water permeability values (K) using US NIST Permeability Stokes Solver range from an order of magnitudes of 10−14 to 10−17 m2. Indications suggest that as effective porosity increases, the geometric tortuosity increases and the permeability decreases. Correlation among these microstructure and transport parameters is also presented in this study.

Quantitative disentanglement of nanocrystalline phases in cement pastes by synchrotron ptychographic X-ray tomography

“…Since the pioneering work of Bentz et al (2000), absorptioncontrast X-ray computed tomography has been widely used for investigating PC hydration and to study several parameters under different conditions, including the pore and void network (Gallucci et al, 2007;Moradian et al, 2017), tortuosity (Promentilla et al, 2009(Promentilla et al, , 2016, leaching alterations (Sugiyama et al, 2010), alkali-silica reactions (Marinoni et al, 2012; Voltolini et al, 2011; Herná ndez-Cruz et al, 2016), early hydration microstructure evolution (Gastaldi et al, 2012;Parisatto et al, 2015) and uranium encapsulation in grout (Stitt et al, 2017(Stitt et al, , 2018. As of today, these tomographic investigations have limited spatial resolution (usually 500 nm at best) and it is extremely difficult to distinguish between different hydrated phases as they have very similar X-ray absorption values (Deboodt et al, 2017) yielding poor contrast.…”

Numerical simulation of the effect of cement particle shapes on capillary pore structures in hardened cement pastes

“…Among these capillary pore structure parameters, numerous studies [28,36,37] have attached great importance to tortuosity in cement paste 3D microstructure for understanding aggressive species transport process in capillary pores.…”

“…A range of voxel-based (or pixel-based) algorithms have been proposed to measure tortuosity in porous material structures including medial axis [39], Dijkstra algorithm [40], A-star algorithm [41] and fast marching method thin-line skeleton [42]. In this work, a 3D random walk simulation [28,36,37] of simulating selfdiffusion behavior along with a home-made program is employed to compute tortuosity by the mean square displacement (MSD) of randomly walking "ants" in the percolating capillary pore voxels as a function of time. The programming mechanism is as follows: sufficient "ants" used to model diffusion specimen in pore structure migrate on the pore voxel selected randomly, as the start position of the lattice walk trial at integer time equals to 0.…”

X-ray micro computed tomography characterization of cellular SiC foams for their applications in chemical engineering

“…μ-CT characterization of cellular foams was also carried out with the main focus on exploring morphometric properties and mechanical behaviors of materials [3,[23][24][25][26][27][28][29][30][31] Transport and hydrodynamic properties of cellular foams are related closely to their morphological properties such as the cell size, porosity, strut thickness, etc. To date, only a few works endeavored to interpret μ-CT data of cellular foams for continuous-flow chemical applications [2,3,5,32,33].…”