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Porosity is an intrinsic property of many cementitious materials. This study uses a new centrifugation-based low-melting-point metal intrusion technique to characterize and analyze the shape of pores in cementitious materials. Low energy electrons with ultra-long beam dwell time are used to obtain nano meter level resolution of the pore shape. Three descriptors, namely circularity, solidity, and aspect ratio, are proposed to represent the area-perimeter relationship, hydration and packing and 3D shape of the pores, respectively. Circularity is found to hold a consistent power correlation with pore size. Based on this correlation, the Washburn’s equation is modified to correct the biased prediction of pore size using mercury intrusion porosimetry (MIP). Solidity, is found to decrease with increased pore size, denser packing of cement particles and more hydration products. Aspect ratio of the observed pores is found to average at about 2 representing an oblate ellipsoid shape of pore in 3D space. [ABSTRACT FROM AUTHOR]

• Reconstructing 3D micropore structure of silty clay from 2D images. • Microstructure-based permeability prediction via numerical simulation. • Enhancing the understanding of processing–structure–property linkage for earth materials. • 3D imaging characterisation of silty clay's pore structure. The porous structure of hydrated cement has a significant effect on its governing properties, such as strength, density, ion-diffusion, acoustic performance etc. However, direct observation of the 3D pore structure is limited by high stochasticity and multiscale features. We constructed a statistically equivalent 3D micropore structure using a digital concrete model that used a probabilistic map derived from 2D cross-sections and parameter sets calibrated via a deep learning neural network. Based on the replica of cement pore structure, image analyses and virtual mercury intrusion porosimetry (MIP) tests were compared with experimental outcomes. In particular, the pore size distribution curves matched well for both MIP and image analysis approaches. However, although the fractal dimension derived from each 2D image linearly correlated with the corresponding porosity, it tended to underestimate the complexity of the pore structure. Correspondingly, the 3D fractal dimension showed a periodic pattern to voxel size in log-scale and was slightly higher than the MIP results. The tortuosity factor also had a linear correlation to voxel size, resulting in an overestimation of the pore structure's tortuosity. We demonstrated that the digital concrete model could serve as an alternative approach to studying the microstructural pore analysis of cementitious material through such a comparison. This study's outcome helps to understand the structure–property link in cement with the potential to transform traditional analytical processes of cementitious materials. [ABSTRACT FROM AUTHOR]

Abstract Nano-engineering cement binder using a hybrid of carbon nanotubes (CNTs) and graphene oxide (GO) combines the superior mechanical properties of CNTs and the good dispersibility and affinity of GO. Ultrasonication is a key process implemented in the dispersion of CNTs and GO. The present study characterizes the effect of ultrasonication on the dispersion and size of the GO/CNT particles by using an ultraviolet spectrophotometer and Zetasizer μV detector, respectively. The mechanical properties of GO/CNT-OPC pastes treated with different ultrasonication time and power levels were tested and their microstructure was investigated using scanning electron microscopy and mercury intrusion porosimetry. The results of this study not only reveal that differences in ultrasonication can cause the mechanical properties of the GO/CNT-OPC composite to vary by −11.7–78.8% but also show that the effect of the amount of ultrasonication energy can vary significantly when different ultrasonication time or power levels are adopted. The porosity of the composite is found to have a nonlinear correlation with the ultrasonication. The findings of this study can promote understanding of GO/CNT-OPC composites and help to guide the implementation of ultrasonication in the future. [ABSTRACT FROM AUTHOR]

The effects of graphene oxide (GO) on the early-age hydration process and mechanical properties of Portland cement paste were experimentally investigated in this study. Based on an isothermal calorimeter measurement, the hydration rate of cement was observed to increase with the increase of GO content by nucleation effect. On the other hand, the electrical resistivity development of GO-cement paste was monitored using a non-contact electrical resistivity device. The result showed that electrical the resistivity of GO-cement paste was evidently higher than that of plain cement paste. However, cement paste with excessive amounts of GO exhibited a decreased electrical resistivity due to the massive ion diffusion caused by GO. Compared to plain cement paste, the GO-cement paste exhibited obviously higher compressive and flexural strengths, but the enhancements in compressive strength began to decline when the GO amount was greater than 0.04%. The microstructure characterization indicated that GO can apparently densify the cement pastes with less porosity and hydrates networking, which is consistent with the results of hydration acceleration and strength enhancement. [ABSTRACT FROM AUTHOR]