A new 3D-microscopy method, focused ion beam-nanotomography (FIB-nt), has been applied to the statistical particle shape analysis and for topological characterization of granular textures in cement samples. Because of its high resolution (15 nm), FIB-nt reveals precise microstructural information at the submicrometer scale, which cannot be obtained with conventional tomography methods. It is demonstrated that even from complex granular textures with dense agglomerates, it is possible to identify the individual sub-grains. This is the basis for reliable statistical shape analysis. For this purpose, moments of inertia were determined for particles from five different grain size fractions of a given cement, which provides important input data for future modeling of rheology and hydration processes. In addition, FIB-nt was used for topological characterization of the particle-particle interfaces in the dense and fine-grained granular textures. The unique 3D-data obtained with FIB-nt thus open new possibilities for quantitative microstructure analysis and the data can be used as structural input for object-oriented modeling.

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SummaryCryo-FIB-nanotomography is a novel high-resolution 3D-microscopy technique, which opens new possibilities for the quantitative microstructural analysis of complex suspensions. In this paper, we describe the microstructural changes associated with dissolution and precipitation processes occurring in a fresh cement paste, which has high alumina and sulphate contents. During the first 6 min, precipitation of ettringite leads to a general decrease of the particle size distribution. In the unhydrated cement paste almost no particles smaller than 500 nm are present, whereas after 6 min this size class already represents 9 vol%. The precipitation of ettringite also leads to a significant increase of the particle number density from 0.294 * 10 9 /mm 3 at t 0min to 20.55 * 10 9 /mm 3 at t 6min . Correspondingly the surface area increases from 0.75 m 2 /g at t 0min to 2.13 m 2 /g at t 6min . The small ettringite particles tend to form agglomerates, which strongly influence the rheological properties. The particular strength of cryo-FIB-nt is the potential to quantify particle structures in suspension and thereby also to describe higher-order topological features such as the particle-particle interfaces, which is important for the study of agglomeration processes.

Based on high resolution 3D-microsturctural data from FIB-nanotomography tl1e pore stmcture in the sub-m range can now be described quantitatively. This is demonstrated for a 28 days old cement paste. In contTast to the discontinuous pore size distribution (PSD) which results from mercmy intrusion porosimehy, the data from FIB-3D-analysis reveals an exponential PSD at radii larger than 50 nm. Using extended image analysis techniques, porosity in hadley grains and the capillary pore network in tl1e interstitial groundmass can be distinguished and the cormectivity between them can be quantified. In the 28 days old cement paste, 34 % of the total pore volume are located within the liadley grains. The connection with the capilla1y pores in the groundmass is dominated by numerous but small patl1ways (intersections). The average radius of these intersections is below 100 nm. The average intersection density is 0.75 intersections per 111 2 of phaenograin surface. The intersections occupy only 2% of the interface between the phaenograins and the groundmass. In summary, the new 3D-rnicroscopy teclmique not only provides infonnation about pore size distribution of the bulk microstructure, but it also enables to distinguish different types of pores and to characterize the co1111ectivity between them. This infonnation is considered to be a prerequisite for establishing microstmctural models that can predict penneability properties in cement pastes.

SummarySurface roughness affects the results of nanomechanical tests. The surface roughness values to be measured on a surface of a porous material are dependent on the properties of the naturally occurring pore space. In order to assess the surface roughness of hardened cement paste (HCP) without the actual influence of the usual sample preparation for nanomechanical testing (i.e. grinding and polishing), focussed ion beam nanotomography datasets were utilized for reconstruction of 3D (nanoscale resolution) surface profiles of hardened cement pastes. 'Virtual topographic experiments' were performed and root mean square surface roughness was then calculated for a large number of such 3D surface profiles. The resulting root mean square (between 115 and 494 nm) is considerably higher than some roughness values (as low as 10 nm) reported in the literature. We suggest that thus-analysed root mean square values provide an estimate of a 'hard' lower limit that can be achieved by 'artefact-free' sample preparation of realistic samples of hardened cement paste. To the best of our knowledge, this 'hard' lower limit was quantified for a porous material based on hydraulic cement for the first time. We suggest that the values of RMS below such a limit may indicate sample preparation artefacts. Consequently, for reliable nanomechanical testing of disordered porous materials, such as hardened cement paste, the preparation methods may require further improvement.