The pore structures of hardened Portland/slag cement pastes (>75 wt% slag content), and the initial capillary absorption of moisture through these pores, were monitored using ex situ synchrotron X-ray computerised microtomography and in situ quantitative neutron radiography. The pore structure becomes more constricted as the cement hydrates and its microstructure develops. This mechanism was effective even at a slag content as high as 90 wt% in the cementitious blend, where the lowest total porosity and a significant pore refinement were identified at extended curing ages (360 d). By combining this information with neutron radiographic imaging, and directly quantifying both depth and mass of water uptake, it was observed that 90 wt% slag cement outperformed the 75 wt% slag blend at 90 days in terms of resistance to capillary water uptake, although the higher-slag blend had not yet developed such a refined microstructure at 28 days of curing. The assumptions associated with the "sharp front model" for water ingress do not hold true for highly substituted slag cement pastes. Testing transport properties at 28 days may not give a true indication of the performance of these materials in service in the long term.

Magnesium potassium phosphate cements (MKPC) were investigated to determine their efficacy towards retardation of reactive uranium metal corrosion. Optimised low-water content, fly ash (FA) and blast furnace slag (BFS) blended MKPC formulations were developed and their fluidity, hydration behaviour, strength and phase assemblage investigated. In-situ time resolved synchrotron powder X-ray diffraction was used to detail the early age (similar to 60 h) phase assemblage development and hydration kinetics, where the inclusion of BFS was observed to delay the formation of struvite-K by similar to 14 h compared to FA addition (similar to 2 h). All samples set within this period, suggesting the possible formation of a poorly crystalline binding phase prior to struvite-K crystallisation. Longterm corrosion trials using metallic uranium indicated that MKPC systems are capable of limiting uranium corrosion rates (reduced by half), when compared to a UK nuclear industry grout, which highlights their potential application radioactive waste immobilisation.

This study reports the development and application of a digital image cross correlation based approach to resolve contiguous microstructural volumes of interest in X-ray microtomography data, collected in fluid suspensions that undergo significant microstructural changes over time, using fresh cementitious pastes as an example. This computational method provides a high precision both for cementitious pastes that sediment only slightly (i.e. are cohesive), and for those that undergo significant sedimentation and/or settlement within the first few minutes of reaction. The normalised cross correlation algorithm presented here enables the observation of an identical volume of interest, i.e., one which contains a contiguous particle group, from the first seconds of observation onwards with excellent accuracy. This method enables segmentation of the same cluster of particles to be almost entirely automated and resolved in large sets of sequentially collected data, therefore enabling particle reaction to be observed directly while removing effects due to sedimentation. (C) 2020 Elsevier Ltd. All rights reserved.