Suchergebnisse

The origin of different stability of crystalline calcium silicate hydrates was investigated. The tobermorite crystal has been used as an analog of cement hydrate that is being mostly manufactured material on earth. Normal tobermorite is thermally unstable and transforms to amorphous at low pressure. Meanwhile, anomalous tobermorite with high Al content does not significantly transform under high pressure or high temperature. Conducted X-ray absorption spectroscopy explains the weak stability of normal tobermorite which was originally hypothesized by the role of zeolitic Ca ions in the cavities of silicate chains. Atomic simulations reproduced the experimentally observed trend of pressure behavior once the ideal structures were modified to account for the Al content as well as the chain defects. The simulations also suggested that the stability of tobermorite under stress could be rationalized as a self-healing mechanism in which the structural instabilities were accommodated by a global sliding of the CaO layer. ; J.M. acknowledges support by a grant (20SCIP-C159063-01) from Construction Technology Research Program funded by Ministry of Land, Infrastructure and Transport of Korean government. H.M. acknowledges the financial support from the Gobierno Vasco (project IT912-16). The work in San Sebastián (R.D., J.S.D, A.A) was supported by the Spanish Ministry of Science and Innovation with RTI2018-098554-B-I00, PID2019-105488GB-I00 and PCI2019-103657 research grants, the Gobierno Vasco UPV/EHU (Project No. IT-1246-19), and the European Commission from the NRG-STORAGE project (GA 870114). The Institute of Engineering Research in Seoul National University provided research facilities for this work. The Ca-XAS and HPXRD experiments were performed at XAFCA beamline in Singapore Synchrotron Light Source (SSLS) and 12.2.2 beamline in Advanced Light Source (ALS), respectively. The ALS supported by a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231 and the Consortium for Materials Properties Research in Earth Sciences under NSF Cooperative Agreement EAR 1606856. ; Peer reviewed

. Seventy-eight graphs were plotted to describe and analyze the dependences of the height and roughness irregularities on the water-to-cement ratio and on the porosity of the cement hydrates. The results showed unambiguously that the water-to-cement ratio or equivalently the porosity of the specimens has a decisive influence on the irregularities of the fracture surfaces of this material. The experimental results indicated the possibility that the porosity or the value of the water-to-cement ratio might be inferred from the height irregularities of the fracture surfaces. It was hypothesized that there may be a similarly strong correlation between porosity and surface irregularity, on the one hand, and some other highly porous solids, on the other, and thus the same possibility to infer porosity from the surfaces of their fracture remnants.

Shortly after mixing cement grains with water, a cementitious fluid paste is formed that immediately transforms into a solid form by a phenomenon known as setting. Setting actually corresponds to the percolation of emergent network structures consisting of dissolving cement grains glued together by nanoscale hydration products, mainly calcium-silicate-hydrates. As happens in many percolation phenomena problems, the theoretical identification of the percolation threshold (i.e. the cement setting) is still challenging, since the length scale where percolation becomes apparent (typically the length of the cement grains, microns) is many times larger than the nanoscale hydrates forming the growing spanning network. Up to now, the long-lasting gap of knowledge on the establishment of a seamless handshake between both scales has been an unsurmountable obstacle for the development of a predictive theory of setting. Herein we present a true multi-scale model which concurrently provides information at the scale of cement grains (microns) and at the scale of the nano-hydrates that emerge during cement hydration. A key feature of the model is the recognition of cement setting as an off-lattice bond percolation process between cement grains. Inasmuch as this is so, the macroscopic probability of forming bonds between cement grains can be statistically analysed in smaller local observation windows containing fewer cement grains, where the nucleation and growth of the nano-hydrates can be explicitly described using a kinetic Monte Carlo Nucleation and Growth model. The most striking result of the model is the finding that only a few links (~12%) between cement grains are needed to reach setting. This directly unveils the importance of explicitly including nano-texture on the description of setting and explains why so low amount of nano-hydrates is needed for forming a spanning network. From the simulations, it becomes evident that this low amount is least affected by processing variables like the water-to-cement ratio and the presence of large quantities of nonreactive fillers. These counter-intuitive predictions were verified by ex-professo experiments that we have carried out to check the validity of our model. ; This study was carried out under the umbrella of the BASKRETE initiative and supported by the Basque Government under the ELKARTEK Program (project SUPER). Te computing facilities of TECNALIA, DIPC, and the Supercomputing Center of Galicia CESGA are likewise acknowledged. A.P. acknowledges fnancial support from the TIFER program of TECNALIA and S.A.-I. acknowledges the fnancial support from project IT-654-13 by the Basque government.

Shortly after mixing cement grains with water, a cementitious fluid paste is formed that immediately transforms into a solid form by a phenomenon known as setting. Setting actually corresponds to the percolation of emergent network structures consisting of dissolving cement grains glued together by nanoscale hydration products, mainly calcium-silicate-hydrates. As happens in many percolation phenomena problems, the theoretical identification of the percolation threshold (i.e. the cement setting) is still challenging, since the length scale where percolation becomes apparent (typically the length of the cement grains, microns) is many times larger than the nanoscale hydrates forming the growing spanning network. Up to now, the long-lasting gap of knowledge on the establishment of a seamless handshake between both scales has been an unsurmountable obstacle for the development of a predictive theory of setting. Herein we present a true multi-scale model which concurrently provides information at the scale of cement grains (microns) and at the scale of the nano-hydrates that emerge during cement hydration. A key feature of the model is the recognition of cement setting as an off-lattice bond percolation process between cement grains. Inasmuch as this is so, the macroscopic probability of forming bonds between cement grains can be statistically analysed in smaller local observation windows containing fewer cement grains, where the nucleation and growth of the nano-hydrates can be explicitly described using a kinetic Monte Carlo Nucleation and Growth model. The most striking result of the model is the finding that only a few links (~12%) between cement grains are needed to reach setting. This directly unveils the importance of explicitly including nano-texture on the description of setting and explains why so low amount of nano-hydrates is needed for forming a spanning network. From the simulations, it becomes evident that this low amount is least affected by processing variables like the water-to-cement ratio and the presence of large quantities of nonreactive fillers. These counter-intuitive predictions were verified by ex-professo experiments that we have carried out to check the validity of our model. ; This study was carried out under the umbrella of the BASKRETE initiative and supported by the Basque Government under the ELKARTEK Program (project SUPER). Te computing facilities of TECNALIA, DIPC, and the Supercomputing Center of Galicia CESGA are likewise acknowledged. A.P. acknowledges fnancial support from the TIFER program of TECNALIA and S.A.-I. acknowledges the fnancial support from project IT-654-13 by the Basque government. ; Peer Reviewed

8 páginas; 8 figuras; 3 tablas ; The nanostructure of the main binding phase of the hydrated cements, the calcium silicate hydrates (C–S–H), and their structural changes due to aqueous carbonation have been characterized using TEM, nitrogen physisorption, and SAXS. Synthetic C–S–H has been used for this purpose. Two different morphologies were identified, similar to the high density and low density C–S–H types. When submitting the sample to a CO2 flux, the low density phase was completely carbonated. The carbonation by-products, calcium carbonate, and silica gel were also identified and characterized. The precipitation of the silica gel increased the specific surface area from 95 to 132 m2/g, and its structure, formed by particles of ~5 nm typical radius, was observed by small angle X-ray scattering. In addition, the resistance of the high density C–S–H to carbonation is reported, and the passivating effect of the precipitated calcium carbonate is also discussed. Finally, the results have been compared with carbonation features observed in Portland cement carbonated experimentally at downhole conditions. ; We acknowledge the ESRF for provision of the synchrotron radiation facilities, and would like to especially thank Dr. F. Fauth for his assistance in using the beamline BM16. We also acknowledge the technical services of the Instituto de Ciencia de Materiales de Sevilla (CSIC-US) for its help with characterization measurements. This study was funded by the European Union through a Marie Curie grant within the GRASP project MRTN-CT-2006-035868. Finally, we would like to thank Dr. J. N. Rouzaud for his help with the TEM micrographies, Mr. Yves Pinquier with his help with the teflon reactor, and Dr. Nicolas de la Rosa-Fox for discussion and his wise ideas. ; Peer reviewed

The beneficial effects of pozzolans on cement manufacture have encouraged theiruse in that industry. Tradit ional natural pozzolan have become less available oflate, however, due to a decline in quarrying intensity aimed at minimizing theimpact on the landscape. At the same time, environ mental policies pursue thereduction or elimination of spoil heaps by valorizing industrial waste and by-pro-ducts as raw materials, in keeping with the principles of the circular economy.The quest for new types of waste and by-products with pozzolanic properties hasconsequently become a priority line of resear ch. This study explored the valoriza-tion of one such by-product, the ceramic sludge resulting from fired clay industrymilling and glazing, as a component in new, more eco-sustainable cements. Thesludge was characterized physically, chemically, morphologically, and mineralogi-cally to determine its suitability as a pozzolanic addition in cement. The findingsshowed that ceramic sludge consists in clustered particles ranging in size from100 lmto1lm. SiO2,Al2O3, and Fe2O3together comprise over 70% of the totalcomposition, while the reactive silica content is greater than the 25% required bythe existing legislation. The predominant minerals are quartz, kaolinite, and mus-covite, with some zircon. A study of pozzolanic reaction kinetics in the ceramicsludge/lime system revealed that over time this waste can fix lime, generatingproducts such as calcium aluminate hydrates and C–S–H gels. The cements madewith ceramic sludge proved to be standard-compliant in terms of water demand,setting, drying shrinkage and mechanical strength ; Peer reviewed

4 pages.-- Final full-text version of the paper available at: http://dx.doi.org/10.1111/j.1551-2916.2007.02034.x. ; Fly Ash Belite Cement (FABC) pastes with and without nanosilica additions have been prepared and maintained in sulfate solutions (Na2SO4 0.5M) for 180 days. The mechanical performance and the changes in microstructure have been monitored at 28, 90, and 180 days by compressive strength, X-ray diffraction (XRD), and 29Si MAS NMR measurements. We have found that, unexpectedly, and contrary to what happens in Ordinary Portland Cements (OPC), the addition of nanosilica particles induces an initial decline in the compressive strength of the samples. Only in samples maintained for a long time (180 days) does the nanosilica addition improve the mechanical properties. Our XRD and 29Si NMR experiments have revealed that although nanosilica additions trigger the consumption of Belite phases, this is not always accompanied by formation of longer calcium–silicate–hydrate (C–S–H) gel structures. Only at a long time (180 days), and due to a mechanism that seems to be controlled by the pH of the samples, do the nanosilica additions lead to high-polymerized C–S–H gels. ; This work was financially supported by the Spanish Government (Projects no. MAT 2002-04023-CO1-CO2-CO3 and MAT2005-03890). ; Peer reviewed

The first edition of the Handbook of Clay Science published in 2006 assembled the scattered literature on the varied and diverse aspects that make up the discipline of clay science. The topics covered range from the fundamental structures (including textures) and properties of clays and clay minerals, through their environmental, health and industrial applications, to their analysis and characterization by modern instrumental techniques. Also included are the clay-microbe interaction, layered double hydroxides, zeolites, cement hydrates, genesis of clay minerals as well as the history and teaching of clay science. The second edition adds new infomation from the intervening six years and adds some important subjects to make this the most comprehensive and wide-ranging coverage of clay science in one source in the English language. Provides up-to-date, comprehensive information in a single sourceCovers applications of clays, as well as the instrumental analytical techniquesProvides a truly multidisciplinary approach to clay science

The present study focuses on the interaction between cement mortar (OPC-based CEM-II) and the FEBEXbentonite; this interaction takes place at a small spatial scale (~1 cm/~1 cm; compacted cement mortar/compacted bentonite thickness) within a timeline of 6 and 18 months. This work was designed to determine the early interaction processes and compare them with large-scale FEBEX in situ underground research laboratory experiments. The study aimed at the primary reactions that occurred at the interface in a small spatial scale (nm- μm scale). The experimental device consisted of a composite column containing the cement mortar/bentonite materials. A granitic groundwater solution was injected through the cement mortar/bentonite system and collected out of the column in sequential syringes for analysis of the chemical composition evolution. For the study of the post-mortem samples, an innovative use of grazing incidence X-ray diffraction was performed to determine the phases produced at the interface. Scanning electron microscopy coupled to energy dispersive X-rays and local specific surface area measurements were also applied. The main results showed the initial development of a Mg perturbation in FEBEX-bentonite at the interface related to the formation of 7 Å precursors of Mg-clay 2:1 sheet silicates as the main neogenic phases expected in the long term. Additionally, a Ca-carbonation skin (calcite) occurred in cement mortar at the interface. The specifications of the reaction products observed at small scales of time and space (μm) are highly promising for the development of reaction concepts and support modelling in the future, which could offer a useful perspective for advancement in the upscaling of concrete/bentonite interface perturbation. ; This work was supported by funding from the European Union's Horizon 2020 Research and Training programme from EUROATOM [H2020-NFRP 2014, 2015] under grant agreement nº662147; CEBAMA

Bentonite is a key barrier for the isolation of high-level radioactive waste within Deep Geological Repository. However, bentonite may be altered by contact with cementitious materials and their alkaline pore fluids. This study offers an extensive morphological and semi-quantitative characterization of the bentonite surface exposed to three types of alkaline pore fluids released by different cement-based materials. The bentonite surfaces were studied using a thorough scanning electron microscopy exploration and analysed using an energy-dispersive ꭕ-ray detector (SEM-EDX). In addition, statistical, element mappings, ꭕ-ray diffraction and infrared spectroscopy analyses were performed. The aim was to have a picture of the morphological and chemical alterations of bentonite at very early stages in accordance with the integrated approach necessary to address bentonite stability in the long-term. As a consequence of the reactivity, two types of morphologies stood out in the matrix of bentonite: platelets and coatings-like crusts characterized by their high Mg and Ca content. These alterations presented a different scope depending on the type of alkaline pore solution involved and suggested the precipitation of authigenic magnesium silicate hydrates (M-S-H) and/or trioctahedral clay minerals and Ca‑carbonates. The knowledge of the performance of bentonite subjected to these alkaline solutions can help in the evaluation of the most suitable cement-based materials to be used next to bentonite ; The experimental work was supported by funding from the European Union's Horizon 2020 Research and Training programme from EURATOM [H2020-NFRP 2014, 2015] under grant agreement n◦662147; CEBAMA

The composition and structure of Calcium-Silicate-Hydrate (C-S-H) phases depends on various reaction parameters leading to its formation. Molecular Dynamic simulation studies probing the formation and structure of C-S-H are generally computationally expensive and can reach only very short time scales. Herein, we propose a coarse graining approach to model the formation of C-S-H, using patchy particles and a modified Patchy Brownian Cluster Dynamics algorithm. The simulations show that patchy particle systems can recover the qualitative kinetic evolution of C-S-H formation, and the obtained final structures were comparable to previously reported molecular dynamics studies and experiments. The model was extended to study the effect of water in the polymerization of tetraethoxysilane oligomers, the principal component of an impregnation treatment for deteriorated concrete surfaces. The intermediate system properties predicted by the simulations, such as viscosity and gel time, and structure were found to be well in accordance with the tailored experiments. ; The work described in this manuscript has been performed under InnovaConcrete EC project, supported by funding from the European Union's Horizon 2020 Research and Innovation Programme under Grant Agreement N◦760858. AP and JSD also acknowledge the support received from the BASKRETE initiative and the Joint Transborder Lab-oratory (LTC) "Aquitaine-Euskadi Network in Green Concrete and Cement-based Materials

The interest of this study is the formulation and characterization of 3D printing cementitious mortars. This research work has been carried out in the frame of the MATRICE Project, co-funded by the region "Hauts de France" and the European Union with the European Regional Development Fund. Specifications for a cementitious printable material are first set based on three criteria: extrudability, buildability and conserving the compressive strength of the printed material. Two printable mortars are formulated using simple tests on a laboratory scale. The first, with slow setting, is composed of a Portland-based binder (OPC). The second, with accelerated setting, is composed of a mixed binder (93% OPC and 7% sulfoaluminous cement (CSA)). Real scale prints are then realized in the frame of the project MATRICE allowing the validation of the printability of each mortar upon its application. The chemical behavior of Portland cement and sulfoaluminate cement mixes is then studied experimentally. The heats of hydration measured by isothermal calorimetry increase with the CSA dosage (2% to 10%) and are higher than those of cement pastes containing 100% OPC and 100% CSA. The comparison of the hydrates identified in the mix mad of 7% CSA to those present in the two other cement pastes of each cement alone shows that the presence of gypsum and lime from the Portland cement lead to a faster hydration of the ye'elimite from CSA and to an early formation of ettringite. However, the nature of hydrates is not affected. The rheological behavior, in particular the thixotropy, of the cement pastes made of Portland cement and sulfoaluminate cement (up to 10%) is then studied in function of different formulation parameters during the first hour. The increase in CSA dosage (0% to 10%) leads to an almost linear increase of the structuration coefficient (Athix) of theses mixes. For mixes with 7% CSA and 100% OPC, the influence of the W/C ratio and superplasticizer on the thixotropy is then studied. The increase in W/C ratio leads to an ...

The main objective of this research has been the valorisation of a waste from the TiO2 production process (sulphate method), called red gypsum, in the production of cements. This waste is mainly formed by di-hydrate calcium sulphate and iron hydroxides. To cover this objective it has been necessary to perform the physico-chemical characterisation of the red gypsum as well as the main components in the production of cements and of the new cements generated. Moreover, for the red gypsum, has been analyzed its radioactive content because it is generated in a NORM (Naturally Occurring Radioactive Materials) industry. Finally, the most important properties of the obtained cements with different proportions of red gypsum in their composition have been studied by comparing them with the standard ones obtained in a Portland cement. Lastly, we have demonstrated that the new cements fulfil all the quality tests imposed by the European legislation. ; El objetivo de esta investigación ha sido analizar la valorización de un residuo generado en el proceso de producción de dióxido de titanio (vía sulfato), denominado yeso rojo, en la producción de cementos. Dicho residuo está compuesto fundamentalmente por sulfato de calcio di-hidratado e hidróxidos de hierro. Para ello, ha sido necesaria la caracterización físico-química del yeso rojo, así como la de los otros componentes fundamentales en la fabricación de cementos y de los cementos generados con el mencionado residuo. Además, en el caso del yeso rojo, se ha analizado su contenido radiactivo al generarse éste en una industria NORM (Natural Occurring Radioactive Materials). Posteriormente, se han estudiado las propiedades más importantes de los cementos producidos con diferentes porcentajes de yeso rojo añadido, comparando estas mezclas con las propiedades de un cemento Portland comercial, comprobándose que se cumplen todas las normas Europeas de calidad exigibles.

El objetivo de esta investigación ha sido analizar la valorización de un residuo generado en el proceso de producción de dióxido de titanio (vía sulfato), denominado yeso rojo, en la producción de cementos. Dicho residuo está compuesto fundamentalmente por sulfato de calcio di-hidratado e hidróxidos de hierro. Para ello, ha sido necesaria la caracterización físico-química del yeso rojo, así como la de los otros componentes fundamentales en la fabricación de cementos y de los cementos generados con el mencionado residuo. Además, en el caso del yeso rojo, se ha analizado su contenido radiactivo al generarse éste en una industria NORM (Natural Occurring Radioactive Materials). Posteriormente, se han estudiado las propiedades más importantes de los cementos producidos con diferentes porcentajes de yeso rojo añadido, comparando estas mezclas con las propiedades de un cemento Portland comercial, comprobándose que se cumplen todas las normas europeas de calidad exigibles. ; The main objective of this research has been the valorisation of a waste from the TiO2 production process (sulphate method), called red gypsum, in the production of cements. This waste is mainly formed by di-hydrate calcium sulphate and iron hydroxides. To cover this objective it has been necessary to perform the physicochemical characterisation of the red gypsum as well as the main components in the production of cements and of the new cements generated. Moreover, for the red gypsum, has been analyzed its radioactive content because it is generated in a NORM (Naturally Occurring Radioactive Materials) industry. Finally, the most important properties of the obtained cements with different proportions of red gypsum in their composition have been studied by comparing them with the standard ones obtained in a Portland cement. Lastly, we have demonstrated that the new cements fulfil all the quality tests imposed by the European legislation. ; This work has been supported by the PROFIT Project "Valorization of red gypsum from the industrial production of titanium dioxide" (CIT-310200-2007-47).