@article {590, title = {Production of H 2 by water radiolysis in cement paste under electron irradiation: A joint experimental and theoretical study}, journal = {Cement and Concrete Research}, volume = {100}, year = {2017}, month = {Oct-2017}, pages = {110 - 118}, abstract = {

Long-term confinement of nuclear waste is one of the main challenges faced by the nuclear industry. Fission products such as Sr-90 and Cs-137, both beta(-) emitters known to induce serious health hazards, represent the largest fraction of nuclear waste. Cement is a good candidate to store them, provided it can resist the effects of irradiation over time. Here, we have investigated the effects of beta(-) decay on cement by performing electron irradiation experiments on different samples. We show that H-2 production in cement, the main effect of water radiolysis, depends strongly on composition and relative humidity. First-principles calculations indicate that the water-rich interlayer regions with Ca2+ ions act as electron traps that promote the formation of H-2. They also show that holes localize in water-rich regions in low Ca content samples and are then able to participate in H-2 production. This work provides new understanding of radiolysis effects in cements.

}, issn = {00088846}, doi = {10.1016/j.cemconres.2017.05.022}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0008884617302065}, author = {Le Caer, Sophie and Dezerald, Lucile and Boukari, Khaoula and Laine, Maxime and Taupin, s{\'e}bastien and Kavanagh, Ryan M. and Johnston, Conrad S.N. and Foy, Eddy and Charpentier, Thibault and Konrad J. Krakowiak and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Tribello, Gareth A. and Kohanoff, Jorge J. and Andres Sa{\`u}l} } @article {196, title = {Mesoscale texture of cement hydrates}, journal = {Proceedings of the National Academy of Sciences}, volume = {113}, year = {2016}, month = {Feb-23-2016}, pages = {2029 - 2034}, abstract = {

Strength and other mechanical properties of cement and concrete rely upon the formation of calcium\–silicate\–hydrates (C\–S\–H) during cement hydration. Controlling structure and properties of the C\–S\–H phase is a challenge, due to the complexity of this hydration product and of the mechanisms that drive its precipitation from the ionic solution upon dissolution of cement grains in water. Departing from traditional models mostly focused on length scales above the micrometer, recent research addressed the molecular structure of C\–S\–H. However, small-angle neutron scattering, electron-microscopy imaging, and nanoindentation experiments suggest that its mesoscale organization, extending over hundreds of nanometers, may be more important. Here we unveil the C\–S\–H mesoscale texture, a crucial step to connect the fundamental scales to the macroscale of engineering properties. We use simulations that combine information of the nanoscale building units of C\–S\–H and their effective interactions, obtained from atomistic simulations and experiments, into a statistical physics framework for aggregating nanoparticles. We compute small-angle scattering intensities, pore size distributions, specific surface area, local densities, indentation modulus, and hardness of the material, providing quantitative understanding of different experimental investigations. Our results provide insight into how the heterogeneities developed during the early stages of hydration persist in the structure of C\–S\–H and impact the mechanical performance of the hardened cement paste. Unraveling such links in cement hydrates can be groundbreaking and controlling them can be the key to smarter mix designs of cementitious materials.

Fig. 1.

}, issn = {0027-8424}, doi = {10.1073/pnas.1520487113}, author = {Katerina Ioannidou and Konrad J. Krakowiak and Mathieu Bauchy and Christian G. Hoover and Enrico Masoero and Sidney Yip and Franz-Josef Ulm and Pierre E. Levitz and Roland Jean-Marc Pellenq and Emanuela Del Gado} } @article {151, title = {Inference of the phase-to-mechanical property link via coupled X-ray spectrometry and indentation analysis: Application to cement-based materials}, journal = {Cement and Concrete Research}, volume = {67}, year = {2015}, month = {Jan-2015}, pages = {271 - 285}, abstract = {

A novel approach for the chemo-mechanical characterization of cement-based materials is presented, which combines the classical grid indentation technique with elemental mapping by scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDS). It is illustrated through application to an oil-well cement system with siliceous filler. The characteristic X-rays of major elements (silicon, calcium and aluminum) are measured over the indentation region and mapped back on the indentation points. Measured intensities together with indentation hardness and modulus are considered in a clustering analysis within the framework of Finite Mixture Models with Gaussian component density function. The method is able to successfully isolate the calcium-silica-hydrate gel at the indentation scale from its mixtures with other products of cement hydration and anhydrous phases; thus providing a convenient means to link mechanical response to the calcium-to-silicon ratio quantified independently via X-ray wavelength dispersive spectroscopy. A discussion of uncertainty quantification of the estimated chemo-mechanical properties and phase volume fractions, as well as the effect of chemical observables on phase assessment is also included.

}, issn = {00088846}, doi = {10.1016/j.cemconres.2014.09.001}, author = {Konrad J. Krakowiak and Wilson, William and James, Simon and Musso, Simone and Franz-Josef Ulm} } @article {150, title = {Nano-chemo-mechanical signature of conventional oil-well cement systems: Effects of elevated temperature and curing time}, journal = {Cement and Concrete Research}, volume = {67}, year = {2015}, month = {Jan-2015}, pages = {103 - 121}, abstract = {

With ever more challenging (T,p) environments for cementing applications in oil and gas wells, there is a need to identify the fundamental mechanisms of fracture resistant oil well cements. We report results from a multi-technique investigation of behavior and properties of API class G cement and silica-enriched cement systems subjected to hydrothermal curing from 30\ \°C to 200\ \°C; including electron probe microanalysis, X-ray diffraction, thermogravimetry analysis, electron microscopy, neutron scattering (SANS), and fracture scratch testing. The results provide a new insight into the link between system chemistry, micro-texture and micro-fracture toughness. We suggest that the strong correlation found between chemically modulated specific surface and fracture resistance can explain the drop in fracture properties of neat oil-well cements at elevated temperatures; the fracture property enhancement in silica-rich cement systems, between 110\° and 175\ \°C; and the drop in fracture properties of such systems through prolonged curing over 1\ year at 200\ \°C.

Fig.1. Particle size distribution of the silica flour (ground quartz) incorporated{\textellipsis}

Fig.2. Location of the {\textquotedblleft}chemical poles{\textquotedblright} of the cement clinker and cement hydration{\textellipsis}

Fig.3. Simplified schematic of: (a) the cement paste microstructure cured at room{\textellipsis}

Fig.4. A schematic of the effect of adding an extra dimension, Al, to the statistical{\textellipsis}

Fig.5. X-ray powder diffraction spectra with qualitative analysis of the major phases{\textellipsis}

Fig.6. Thermal gravimetric analysis (TGA) carried out on samples cured in the{\textellipsis}

}, issn = {00088846}, doi = {10.1016/j.cemconres.2014.08.008}, author = {Konrad J. Krakowiak and Jeffrey J. Thomas and Musso, Simone and James, Simon and Ange-Therese Akono and Franz-Josef Ulm} } @article {72, title = {Combinatorial molecular optimization of cement hydrates}, journal = {Nat Commun}, volume = {5}, year = {2014}, month = {Sep-24-2014}, pages = {Article Number: 4960}, abstract = {

Despite its ubiquitous presence in the built environment, concrete\â\€$(1s (Bmolecular-level properties are only recently being explored using experimental and simulation studies. Increasing societal concerns about concrete\â\€$(1s (Benvironmental footprint have provided strong motivation to develop new concrete with greater specific stiffness or strength (for structures with less material). Herein, a combinatorial approach is described to optimize properties of cement hydrates. The method entails screening a computationally generated database of atomic structures of calcium-silicate-hydrate, the binding phase of concrete, against a set of three defect attributes: calcium-to-silicon ratio as compositional index and two correlation distances describing medium-range silicon-oxygen and calcium-oxygen environments. Although structural and mechanical properties correlate well with calcium-to-silicon ratio, the cross-correlation between all three defect attributes reveals an indentation modulus-to-hardness ratio extremum, analogous to identifying optimum network connectivity in glass rheology. We also comment on implications of the present findings for a novel route to optimize the nanoscale mechanical properties of cement hydrate.

Figure 1

}, doi = {10.1038/ncomms5960}, author = {Mohammad Javad Abdolhosseini Qomi and Konrad J. Krakowiak and Mathieu Bauchy and Stewart, K.L. and Rouzbeh Shahsavari and Jagannathan, D. and Brommer, D.B. and Alain Baronnet and Markus J Buehler and Sidney Yip and Franz-Josef Ulm and Krystyn J. Van Vliet and Roland Jean-Marc Pellenq} } @article {110, title = {Simultaneous assessment of phase chemistry, phase abundance and bulk chemistry with statistical electron probe micro-analyses: Application to cement clinkers}, journal = {Cement and concrete Research}, volume = {55}, year = {2014}, month = {Jan-2014}, pages = {35-48}, type = {Article}, abstract = {

According to recent developments in cement clinker engineering, the optimization of chemical substitutions in the main clinker phases offers a promising approach to improve both reactivity and grindability of clinkers. Thus, monitoring the chemistry of the phases may become part of the quality control at the cement plants, along with the usual measurements of the abundance of the mineralogical phases (quantitative X-ray diffraction) and the bulk chemistry (X-ray fluorescence). This paper presents a new method to assess these three complementary quantities with a single experiment. The method is based on electron microprobe spot analyses, performed over a grid located on a representative surface of the sample and interpreted with advanced statistical tools. This paper describes the method and the experimental program performed on industrial clinkers to establish the accuracy in comparison to conventional methods. (C) 2013 Elsevier Ltd. All rights reserved.

SEM micrographs of coarsely ground sample C-C4. (a) The 500{\texttimes} magnification ...
Ca vs. Si representation for bulk samples (a) B-C2 focused on the entire range ...
(a) SEM micrograph of clinker C4 at 1000{\texttimes} magnification: the spacing between ...
Additional representations of the clustered results for bulk samples: Fe vs. Si ...
Si vs. Ca representation for coarsely ground samples (a) C-C2a and (b) C-C4b and ...
}, keywords = {Characterization, Clinker, EPMA, X-ray diffraction}, issn = {0008-8846}, doi = {10.1016/j.cemconres.2013.09.013}, author = {Wilson, William and Konrad J. Krakowiak and Franz-Josef Ulm} } @article {257, title = {Multitechnique Investigation of Extruded Clay Brick Microstructure}, journal = {Journal of the American Ceramic Society}, volume = {94}, year = {2011}, month = {Sept-2011}, pages = {3012 - 3022}, abstract = {

Despite the omnipresence of clay brick as construction material since thousands of years, fundamental knowledge about the link between composition, microstructure, and mechanical performance is still scarce. In this paper, we use a variety of advanced techniques of experimental mechanics and material characterization for extruded clay brick for masonry, that range from scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy, mercury intrusion porosimetry, to instrumented nanoindentation and macroscopic strength and durability tests. We find that extruded clay brick possesses a hierarchical microstructure: depending on the firing temperature, a \“glassy\” matrix phase, which manifests itself at submicrometer scales in form of neo-crystals of mullite, spinel-type phase, and other accessory minerals, forms either a granular or a continuum matrix phase that hosts at submillimeter scale the porosity. This porous composite forms the backbone for macroscopic material performance of extruded brick, including anisotropic strength, elasticity, and water absorption behavior.

}, doi = {10.1111/jace.2011.94.issue-910.1111/j.1551-2916.2011.04484.x}, author = {Konrad J. Krakowiak and Lourenco, Paulo B. and Franz-Josef Ulm} }