Limitation in obtainable surface roughness of hardened cement paste: ‘virtual’ topographic experiment based on focussed ion beam nanotomography datasets

Abstract

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.

A Coupled Nanoindentation/SEM‐EDS Study on Low Water/Cement Ratio Portland Cement Paste: Evidence for C–S–H/Ca(OH)2 Nanocomposites

“…These points were excluded from the coupled nanoindentation/SEM-EDS analysis. No evidence for pore filling by surface detritus 31 was observed.…”

Local elastic moduli of simple random composites computed at different length scales

“…Roughly speaking, the results of these models can be stated that by an SV size of about one half the diameter (41 voxels) of the spherical building block of the models, one could not identify more than one peak from any of the models. However, such small indents may be impossible on some composite materials such as cement paste, since the intrinsic surface roughness of the paste might be of the same size and cannot be polished out in a nanoindentation experiment [43]. Third, the local ''probe'' used in this paper was ideal, while that used in experiment has uncertainties associated with it in terms of quantities such as assumed shape and calculated penetration depth [6][7][8].…”

“…The type of materials that the analysis of this paper could apply include any multi-phase composite material. Examples would include cement paste [8,42,43] or concrete [46], or a polycrystalline, poly-phase material like steel [47,48] or other alloys. Polymers filled with an inorganic powder would also lend themselves to this kind of analysis.…”

Experimental Investigation on Quantitative Nanomechanical Properties of Cement Paste

“…The RMS value can be used to evaluate the surface roughness because there is no standard criterion of roughness of cement pastes for nanomechanical testing due to the inherent roughness of hardened cement pastes, particularly which would be applicable to the three methods presented. 29 For nanoindentation, the most commonly used method for nanomechanical characterization of cement hydration products is Miller et al, 30 who reported the RMS roughness measured over an area with one side 200 times the average depth of indenta-tion should be less than one fifth of the average indentation depth. The roughness of the samples tested in this study is sufficiently low and is comparable to those obtained by other investigators.…”