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Many methods have been proposed to analyse SEM‐EDS hypermaps of hydrated cementitious materials but none can fit all purposes. In this presentation, we review existing methods for phase identification, stoichiometry quantification, and microstructure quantification in cementitious materials and related materials. We first discuss the unique contribution of SEM‐EDS with respect to the outstanding scientific challenges towards sustainable construction materials. We then compare the SEM‐EDS and image analysis techniques which contribute to answering these challenges. Convergence and divergence in current methods and workflows, and knowledge gaps are highlighted in terms of the specificities of the material (phase assemblage complexity, grain sizes, mixtures, etc.). The discussion is weighted by the required expert knowledge for the sample preparation, microscope operation, and data analysis. We conclude by discussing how microscopy and image analysis integrate into the overall experimental toolkit to investigate and improve cementitious materials. LAY DESCRIPTION: Concretes, mortars and hardened cement pastes are very complex and heterogeneous. As such, the visualisation of phases in the microstructure is often necessary to understand the processes by which this microstructure forms and evolves. Scanning electron microscopy coupled with energy dispersive spectroscopy (SEM‐EDS) is one of the techniques that allows studying these materials at the micron‐scale level, by forming images combining the elemental composition. But the analysis of the data is challenging due to the heterogeneity of the material. This article is a review of the latest advancements in the analysis of SEM‐EDS data for cementitious materials. It focuses on two aspects, the most successful applications of SEM‐EDS to study the microstructure of hardened cementitious materials; and some of the main methods used to analyse the dataset. The discussion aims to highlight the requirements of each method and each application, so that readers can pick and mix methods to answer their own scientific questions. [ABSTRACT FROM AUTHOR]

Constitutive laws to predict long-term deformation of solution-mined caverns and radioactive-waste repositories in rock salt play an important role in the energy transition. Much of this deformation is at differential stresses of a few megapascals, while the vast majority of laboratory measurements are at much higher differential stress and require extrapolation. This can be much improved by including microstructural data of samples deformed in natural laboratories. Deformation of rock salt can occur by dislocation creep and grain-size-dependent dissolution–precipitation creep processes (pressure solution); this mechanism is not commonly included in current engineering predictions. Here we show evidence for large grain-size-dependent differences in rock salt rheology based on microstructural observations from Zechstein rock salt cores of the northern Netherlands that experienced different degrees of tectonic deformation. We studied the relatively undeformed horizontally layered Zechstein 2 (Z2) salt (Stassfurt Formation) from Barradeel and compared it with a much more strongly deformed equivalent in diapiric salt from Winschoten, Zuidwending, and Pieterburen. We used optical microscopy of thin gamma-irradiated sections for microtectonic analysis, recrystallized grain-size measurements and subgrain-size piezometry, electron microscopy with energy-dispersive X-ray spectroscopy, and X-ray diffraction analysis for second-phase mineralogy. Subgrain-size piezometry shows that this deformation took place at differential stresses between 0.5 and 2 MPa. In the undeformed, layered salt from Barradeel we find centimetre-thick layers of single crystalline halite (Kristalllagen or megacrystals) alternating with fine-grained halite and thin anhydrite layers. The domal salt samples are typical of the well-known "Kristallbrockensalz" and consist of centimetre-size tectonically disrupted megacrystals surrounded by fine-grained halite with a grain size of a few millimetres. We infer high strains in the fine-grained halite as shown by folding and boudinage of thin anhydrite layers, as compared to the megacrystals, which are internally much less deformed and develop subgrains during dislocation creep. Subgrain size shows comparable differential stresses in Kristallbrocken as in matrix salt. The fine-grained matrix salt is dynamically recrystallized to some extent and has few subgrains and microstructures, indicating deformation by solution–precipitation processes. We infer that the finer-grained halite deformed dominantly via pressure solution and the megacrystals dominantly by dislocation creep. The samples show that the fine-grained matrix salt is much weaker than Kristallbrocken because of different dominant deformation mechanisms. This is in agreement with microphysical models of pressure solution creep in which grain size has a significant effect on strain rate at low differential stress. Our results point to the importance of pressure solution creep in rock salt at low differential stresses around engineered structures but also in most salt tectonic settings. We suggest that including results of microstructural analysis can strongly improve engineering models of rock salt deformation. We recommend that this mechanism of grain-size-dependent rheology is included more consistently in the constitutive laws describing the deformation of rock salt. [ABSTRACT FROM AUTHOR]

Constitutive laws of rock salt are required for the prediction of long-term deformation of radioactive waste repositories and solution mined caverns, which are used for energy storage and play an important role in the energy transition. Much of this deformation is at differential stresses of a few MPa. The vast majority of laboratory measurements of salt creep are at much higher differential stress and require extrapolation over many orders of magnitude. This extrapolation can be made more reliable by including microphysical information on the deformation mechanisms in the laboratory samples, integrated with microstructural analysis of samples deformed in natural laboratories at low differential stress. Rock salt can deform at widely different rates at the same temperature and deviatoric stress, depending on state variables such as grain size, solid solution- and second phase-impurities, crystallographic preferred orientation, water content and grain boundary structure. Both dislocation creep and dissolution-precipitation creep processes are common, but dissolutionprecipitation creep (pressure solution) is not commonly included in current engineering predictions. Here we show evidence for large grain size-dependent differences in halite rheology based on microstructural observations from Zechstein rock salt cores of the Northern Netherlands that experienced different degrees of tectonic deformation. We studied the relatively undeformed Z2 (Stassfurt Formation), horizontal-layered salt from Barradeel, and compare it with much stronger deformed equivalent in diapiric salt form Winschoten, Zuidwending, and Pieterburen. We used optical microscopy of Gamma-irradiated thin sections for microtectonic analysis, recrystallized grain size measurements and subgrain size piezometry, SEM-EDX and XRD for second phase mineralogy. Subgrain size piezometry shows that this deformation took place at differential stress between 0.5 and 2 MPa, providing a natural laboratory. In the undeformed, layered salt from Barradeel we find cm-thick layers of single crystalline halite (Kristalllagen) alternating with fine-grained halite and thin anhydrite layers. The domal salt samples are typical of the well-known "Kristallbrocken" salt, and consist of cm-size tectonically disrupted megacrystals surrounded by fine-grained halite with grain size of a few mm. We infer high strains in the fine-grained halite as shown by folding and boudinage of thin anhydrite layers, as compared to the megacrystals, which are internally much less deformed and develop subgrains during dislocation creep. Subgrain size shows comparable differential stresses in Kristallbrocken than in matrix salt. The fine-grained matrix salt is dynamically recrystallized, has few subgrains and microstructures indicating deformation by solution-precipitation processes. We infer that the finer grained halite deformed dominantly via pressure solution and the megacrystals dominantly by dislocation creep. This provides evidence that the fine-grained matrix salt is much weaker than Kristallbrocken because of different dominant deformation mechanisms. This is in agreement with microphysical models of pressure solution creep in which grain size has a significant effect on strain rate at these low differential stress. Our results on the operation of pressure solution creep in rock salt at differential stress of a few MPa point to the importance of this mechanism at low differential stresses around engineered structures but also in most salt tectonic settings. We suggest that including results of microstructural analysis can strongly improve engineering models of rock salt deformation. We recommend that this mechanism of grain size dependent rheology is included more consistently in the constitutive laws describing deformation of engineered structures in rock salt. [ABSTRACT FROM AUTHOR]

Burning of clinker is the most influencing step of cement quality during the production process. Appropriate characterisation for quality control and decision‐making is therefore the critical point to maintain a stable production but also for the development of alternative cements. Scanning electron microscopy (SEM) in combination with energy dispersive X‐ray spectroscopy (EDX) delivers spatially resolved phase and chemical information for cement clinker. This data can be used to quantify phase fractions and chemical composition of identified phases. The contribution aims to provide an overview of phase fraction quantification by semi‐automatic phase segmentation using high‐resolution backscattered electron (BSE) images and lower‐resolved EDX element maps. Therefore, a tool for image analysis was developed that uses state‐of‐the‐art algorithms for pixel‐wise image segmentation and labelling in combination with a decision tree that allows searching for specific clinker phases. Results show that this tool can be applied to segment sub‐micron scale clinker phases and to get a quantification of all phase fractions. In addition, statistical evaluation of the data is implemented within the tool to reveal whether the imaged area is representative for all clinker phases. [ABSTRACT FROM AUTHOR]

A microphysics-based understanding of mechanical and hydraulic processes in clay shales is required for developing advanced constitutive models, which can be extrapolated to long-term deformation. Although many geomechanical laboratory tests have been performed to characterize the bulk mechanical, hydro-mechanical and failure behaviour of Opalinus Clay, important questions remain about microphysics: How do microstructural evolution and deformation mechanisms control the 15 complex rheology over time scales not accessible in the laboratory. In this contribution, Scanning Electron Microscopy (SEM) was used to image microstructures in an Opalinus Clay sample deformed in an unconsolidated-undrained triaxial compression test at 4 MPa confining stress followed by Argon Broad Ion Beam (BIB) polishing. Axial load was applied (sub-) perpendicular to bedding until the specimen failed. The test was terminated at an axial strain of 1.35 %. Volumetric strain measurements showed bulk compaction throughout the compression test. Observations on the cm- to μm-scale showed that deformation 20 localized by forming a network of μm-thick fractures. In BIB-SEM at the grain scale, incipient deformation zones show dilatant inter- and intragranular micro-cracking, granular flow, plastic deformation and bending of phyllosilicate grains, and pore collapse in fossils. Outside these zones, no deformation microstructures were observed indicating localized damage. Thus, microphysics of deformation appear to be controlled by both brittle and ductile processes along preferred orientations. Anastomosing networks of deformation bands develop into the main deformation bands along which the sample fails. 25 Microstructural observations and the stress-strain behaviour were integrated into a deformation model with three different stages of damage accumulation representative for the deformation of the compressed Opalinus Clay sample. Results on the microscale explain how the sample locally dilates while bulk measurement shows compaction, with an inferred major effect on permeability evolution. Comparison with the microstructure of highly strained Opalinus Clay in fault zones shows minor similarity and suggest that during long-term deformation additional solution-precipitation processes operate. [ABSTRACT FROM AUTHOR]

A comprehensive characterization of clay shale behavior requires quantifying both geomechanical and hydromechanical characteristics. This paper presents a comparative laboratory study of different methods to determine the water permeability of saturated Opalinus Clay: (i) pore pressure oscillation, (ii) pressure pulse decay and (iii) pore pressure equilibration. Based on a comprehensive data set obtained on one sample under well-defined temperature and isostatic effective stress conditions, we discuss the sensitivity of permeability and storativity on the experimental boundary conditions (oscillation frequency, pore pressure amplitudes and effective stress). The results show that permeability coefficients obtained by all three methods differ less than 15 per cent at a constant effective stress of 24 MPa (k mean = 6.6E-21 to 7.5E-21 m2). The pore pressure transmission technique tends towards lower permeability coefficients, whereas the pulse decay and pressure oscillation techniques result in slightly higher values. The discrepancies are considered minor and experimental times of the techniques are similar in the range of 1–2 d for this sample. We found that permeability coefficients determined by the pore pressure oscillation technique increase with higher frequencies, that is oscillation periods shorter than 2 hr. No dependence is found for the applied pressure amplitudes (5, 10 and 25 per cent of the mean pore pressure). By means of experimental handling and data density, the pore pressure oscillation technique appears to be the most efficient. Data can be recorded continuously over a user-defined period of time and yield information on both, permeability and storativity. Furthermore, effective stress conditions can be held constant during the test and pressure equilibration prior to testing is not necessary. Electron microscopic imaging of ion-beam polished surfaces before and after testing suggests that testing at effective stresses higher than in situ did not lead to pore significant collapse or other irreversible damage in the samples. The study also shows that unloading during the experiment did not result in a permeability increase, which is associated to the persistent closure of microcracks at effective stresses between 24 and 6 MPa. [ABSTRACT FROM AUTHOR]