Effect of hydration on the dielectric properties of C-S-H gel

9 páginas, 7 figuras, 1 tabla.-- Trabajo presentado a la "Gordon Research Conference: Water & Aqueous Solutions" celebrada en EE.UU. del 8 al 13 de agosto de 2010.The behavior of water dynamics confined in hydrated calcium silicate hydrate (C-S-H) gel has been investigated using broadband dielectric spectroscopy (BDS; 10−2–106 Hz) in the low-temperature range (110–250 K). Different water contents in C-S-H gel were explored (from 6 to 15 wt%) where water remains amorphous for all the studied temperatures. Three relaxation processes were found by BDS (labeled 1 to 3 from the fastest to the slowest), two of them reported here for the first time. We show that a strong change in the dielectric relaxation of C-S-H gel occurs with increasing hydration, especially at a hydration level in which a monolayer of water around the basic units of cement materials is predicted by different structural models. Below this hydration level both processes 2 and 3 have an Arrhenius temperature dependence. However, at higher hydration level, a non-Arrhenius behavior temperature dependence for process 3 over the whole accessible temperature range and, a crossover from low-temperature Arrhenius to high-temperature non-Arrhenius behavior for process 2 are observed. Characteristics of these processes will be discussed in this work.Authors gratefully acknowledge the support of Consolider (CSD2006-00053) and Etortek program. S.C. gratefully acknowledge the support of CSIC (200860I021) and S.C. S.A-I, A.A and J.C. gratefully acknowledge the support of the DYNACOP program and the Basque Government, and project IT-436-07 and the Spanish Ministry of Education, project MAT-22007-63681.Peer reviewe

Effect of hydration on the dielectric properties of C-S-H gel

9 páginas, 7 figuras, 1 tabla.-- Trabajo presentado a la "Gordon Research Conference: Water & Aqueous Solutions" celebrada en EE.UU. del 8 al 13 de agosto de 2010.The behavior of water dynamics confined in hydrated calcium silicate hydrate (C-S-H) gel has been investigated using broadband dielectric spectroscopy (BDS; 10−2–106 Hz) in the low-temperature range (110–250 K). Different water contents in C-S-H gel were explored (from 6 to 15 wt%) where water remains amorphous for all the studied temperatures. Three relaxation processes were found by BDS (labeled 1 to 3 from the fastest to the slowest), two of them reported here for the first time. We show that a strong change in the dielectric relaxation of C-S-H gel occurs with increasing hydration, especially at a hydration level in which a monolayer of water around the basic units of cement materials is predicted by different structural models. Below this hydration level both processes 2 and 3 have an Arrhenius temperature dependence. However, at higher hydration level, a non-Arrhenius behavior temperature dependence for process 3 over the whole accessible temperature range and, a crossover from low-temperature Arrhenius to high-temperature non-Arrhenius behavior for process 2 are observed. Characteristics of these processes will be discussed in this work.Authors gratefully acknowledge the support of Consolider (CSD2006-00053) and Etortek program. S.C. gratefully acknowledge the support of CSIC (200860I021) and S.C. S.A-I, A.A and J.C. gratefully acknowledge the support of the DYNACOP program and the Basque Government, and project IT-436-07 and the Spanish Ministry of Education, project MAT-22007-63681.Peer reviewe

Radiative Cooling Properties of Portlandite and Tobermorite: Two Cementitious Minerals of Great Relevance in Concrete Science and Technology

Although concrete and cement-based materials are the most engineered materials employed by mankind, their potential for use in daytime radiative cooling applications has yet to be fully explored. Due to its complex structure, which is composed of multiple phases and textural details, fine-tuning of concrete is impossible without first analyzing its most important ingredients. Here, the radiative cooling properties of Portlandite (Ca(OH)2) and Tobermorite (Ca5Si6O16(OH)2·4H2O) are studied due to their crucial relevance in cement and concrete science and technology. Our findings demonstrate that, in contrast to concrete (which is a strong infrared emitter but a poor sun reflector), both Portlandite and Tobermorite exhibit good radiative cooling capabilities. These results provide solid evidence that, with the correct optimization of composition and porosity, concrete can be transformed into a material suitable for daytime radiative cooling

Wer ist heute 'Ehrenmann' und 'Ehrenfrau'? Ethische und jugendkulturelle Aspekte des deutschen Jugendworts des Jahres

Eine Jury des deutschen Langenscheidt-Verlags wählt jedes Jahr das sogenannte 'Jugendwort des Jahres'. 2018 fiel diese Wahl auf 'Ehrenmann' bzw. 'Ehrenfrau' im Sinne von 'jemand, der etwas (Besonderes) für einen tut'. In der Folge fand jedoch weder eine öffentliche Auseinandersetzung über die Herkunft des Begriffs statt noch darüber, was Ehre für Jugendliche heute bedeutet. Der Artikel möchte daher zunächst darstellen, was Ehre ist und welche soziale Funktion sie erfüllt, und anschließend die besondere Bedeutung von Ehre für Jugendliche in Migrationssituationen reflektieren. Schließlich folgen eine pop- und jugendkulturelle Analyse der Herkunft und Verwendung des Ausdrucks 'Ehrenmann' (und 'Ehrenfrau') sowie eine abschließende kritische Reflexion der Jurywahl.Every year, a jury of the German Langenscheidt-Verlag chooses the so-called 'youth expression of the year' (Jugendwort des Jahres). In 2018, this choice fell on 'man/woman of honour' (Ehrenmann/Ehrenfrau), in a sense of ‚someone doing something (special) for somebody‘. Interestingly, no public discourse followed to examine the origin of this unusual expression or the meaning of 'honour' for today's youth. The article, therefore, aims to outline what honour is and which social functions it fulfils, and then to reflect the particular significance of honour for adolescents with a migrant background. This is followed by a pop- and youth-cultural analysis of the origin and use of the expression 'man of honour' as well as a concluding critical reflection of the jury's choice

Cause of the fragile-to-strong transition observed in water confined in C-S-H gel

In this study, the rotational dynamics of hydration water confined in calcium-silicate-hydrate (C-S-H) gel with a water content of 22 wt.% was studied by broadband dielectric spectroscopy in broad temperature (110-300 K) and frequency (10-1-108 Hz) ranges. The C-S-H gel was used as a 3D confining system for investigating the possible existence of a fragile-to-strong transition for water around 220 K. Such transition was observed at 220 K in a previous study [Y. Zhang, M. Lagi, F. Ridi, E. Fratini, P. Baglioni, E. Mamontov and S. H. Chen, J. Phys.: Condens. Matter 20, 502101 (2008)] on a similar system, and it was there associated with a hidden critical point of bulk water. However, based on the experimental results presented here, there is no sign of a fragile-to-strong transition for water confined in C-S-H gel. Instead, the fragile-to-strong transition can be explained by a merging of two different relaxation processes at about 220 K. © 2013 AIP Publishing LLC.The support from the Basque Government through the Nanoiker project (Grant No. E11-304) under the ETORTEK Program is acknowledged. S.C. also acknowledges the support of the Spanish Ministry of Education, project MAT2012-31088 and the Basque Government, and project IT-654-13 and Professor J. Colmenero for helpful discussions. H.J. acknowledges the Swedish Research Council Formas for financial support.Peer Reviewe

New kinetic Monte Carlo model to study the dissolution of quartz

Quartz dissolution is a frequent process in geochemistry and materials science. It is controlled at the atomic scale by the sequential hydrolysis reactions and breakage of siloxane bonds, the surface topography, and the Gibbs free energy difference ΔG between the solid and the solution. Atomistic simulations have provided valuable topographic information about quartz dissolution and reaction energy barriers. However, with the current interpretation of the data, serious discrepancies persist between the predicted dissolution rates Rdis and the macroscopic dissolution activation energy Ea compared to their experimental counterparts. In this work we show that both quantities can be reconciled using a kinetic Monte Carlo (KMC) atomistic model based on bond-by-bond reactions and Rdis and Ea can be jointly reproduced. In addition, the obtained etch pit shapes for different quartz planes are in agreement with the experimentally reported ones: V-shape striations in {001}, rectangular pyramidal pits in {100}, and trapezoidal semipyramidal pits in {101}. We also study the dissolution rate dependence with ΔG by introducing chemical reversibility in the KMC model, obtaining again results in good agreement with experiments. This work highlights the importance of understanding the mechanisms taking place at the nanoscale to describe macroscopic properties and provides the basic ingredients to extend this study to other minerals and/or dissolution conditions.Peer reviewe

Aging and durability of ternary cements containing fly ash and activated paper sludge

This research work deals with durability aspects of ternary cements containing 79 wt.% ordinary Portland cement (CEM I), 10.5 wt.% coal fly ash and 10.5 wt.% thermally activated paper sludge. Aging tests were performed to study the resistance of the new ternary cement matrixes to the following aggressive exposure conditions: accelerated freeze/thaw cycles, marine environment and Spanish plateau climate conditions. Ternary cements revealed a high resistance to accelerated freeze/thaw cycles. In addition, after 18 months of exposure, they exhibited enhanced performance under marine conditions and similar resistance to Spanish plateau’s climate, compared to ordinary Portland cement.Peer reviewe

Comparative study of the effects of micro silica and nano silica in concrete’,

6 well recognized to enhance the properties of concrete. Silica induces a pozzolanic reaction that results in a reduction of the amount of calcium hydroxide in concrete, and silica fume reduces porosity and improves durability. Recent studies (1) have shown that the addition of silica nanoparticles to cement paste could effectively reduce the degradation rate as well as its negative consequences. The aim of this study was to examine the nanomechanical properties of cement pastes with and without silica fume and nanosilica additions. Nanoindentation has been used successfully by researchers to determine the local mechanical properties of cementitious materials (2-10). This paper examines the nanomechanical properties of significant phases of cement paste microstructure and concrete by using a special type of nanoindenter called a Triboindenter. EXPERIMENTAL DETAILS Materials Used and Sample Preparation Cement paste samples were made by using type I portland cement (Lafarge). The chemical composition of the cement is SiO 2 , 20.4%; CaO, 65.3%; Al 2 O 3 , 4.8%; Fe 2 O 3 , 2.8%; C 3 S, 68%; and C 3 A, 8%. The Blaine surface area was 365 m 2 /kg. The specification of ASTM C305 was followed during the mixing of the cement pastes. Samples were cured under water for 1 month at 25°C. To study the effects of silica fume on the nanomechanical properties of the pastes, Force 1000D silica slurry from W. R. Grace was used. Silica slurry is a predispersed mix of silica fume powder in water with 50% total solid by weight. To prepare the paste samples, 15% of cement by weight was replaced by silica fume. The percentage of water present in the slurry was considered to maintain an effective water-to-binder (cement + silica fume) ratio of 0.5. Samples were cured under water for 1 month at 25°C. Comparative Study of the Effects of Microsilica and Nanosilica in Concrete Paramita Mondal, Surendra P. Shah, Laurence D. Marks, and Juan J. Gaitero It is well recognized that the use of mineral admixtures such as silica fume enhances the strength and durability of concrete. This research compares the effects of adding silica fume and nanosilica to concrete and provides a better understanding of the changes in the concrete nanostructure. Nanoindentation with scanning probe microscopy imaging was used to measure the local mechanical properties of cement pastes with 0% and 15% replacement of cement with silica fume. A reduction in the volume fraction of calcium hydroxide in a sample with silica fume provides evidence of pozzolanic reaction. Furthermore, replacing 15% cement by silica fume increased the volume fraction of the high-stiffness calcium silicate hydrate (C-S-H) by a small percentage that was comparable with the decrease in the volume fraction of calcium hydroxide. A parallel study of cement pastes with nanosilica showed that nanosilica significantly improves durability of concrete. This research provides insight into the effects of nanosilica on cement paste nanostructure and explains its effect on durability of concrete. The nanoindentation study showed that the volume fraction of the high-stiffness C-S-H gel increased significantly with addition of nanosilica. Nanoindentation results of cement paste samples with similar percentages of silica fume and nanosilica were compared. Samples with nanosilica had almost twice the amount of high-stiffness C-S-H as the samples with silica fume. Concrete is a porous material with pore sizes ranging from a few nanometers to a few millimeters. These pores are generally filled with a basic (pH > 12.5) pore solution of calcium dissolved in water. Therefore, environmental conditions with lower pH disturb equilibrium and are detrimental to concrete. During the degradation process, known as calcium leaching, caused by exposure to lower pH, cement hydrates progressively dissolve to reestablish the equilibrium concentration of the minerals contained in the pore solution. The dissolution rates of hydration products depend on the calcium-to-silicon ratio of the products, and rates are different for each of the hydrates. Furthermore, the response of each of the hydration products to the attack is also different. Although the phenomenon of calcium leaching has been widely studied, a suitable method to stop it is still unknown. The use of mineral admixtures such as silica fume (SF) is P. Mondal

Synthesis and addition of Al-substituted tobermorite particles to cement pastes

The last generation of cement hydration accelerators relies on the seeding effect induced by amorphous calcium silicate hydrate particles. However, little is known about the effect of variables, such as the degree of crystallinity and morphology, on their performance. In this work, particles with a Ca/(Si+Al) molar ratio of 0.83 and different proportions of aluminum substitution for silicon were synthesized under hydrothermal conditions. X-ray diffractograms, nuclear magnetic resonance spectra, and scanning electron microscopy images showed that this altered the degree of crystallinity, structure, and morphology of the particles. Nevertheless, the addition of the synthesis products to cement pastes and their subsequent study by isothermal calorimetry and mechanical tests showed that the variables with the largest impact on cement hydration are the dosage and the proper dispersion of the particles. In fact, the use of a dispersing agent is highly recommended while drying of the particles should be avoided to prevent irreversible agglomeration processes from taking place.This study was carried out under the umbrella of the BASKRETE initiative and the Laboratory for Transborder Cooperation“Aquitaine-Euskadi Network in Green Concrete and Cement-based Materials” (LTC-Green Concrete). Economic support was providedby the Basque Government under the ELKARTEK Program [project NEOMAT (KK-2021/00059)]. In addition, Marta Diez-Garcia is grateful to the University of the Basque Country (UPV/EHU) and the University of Bordeaux for her pre-doctoral fellow-ship, within the framework of the Cross-Border Euroregional Campus of International Excellence IDEX Bordeaux–Euskampus. Francisco B. Aguirre acknowledges the funding received from Tecnalia to carry out his Ph.D. in cotutelle between the University of the Basque Country (UPV-EHU) and University of Bordeaux within the framework of the Cross-Border Euroregional Campus of International Excellence IDEX Bordeaux–Euskampus. Theauthors wish also to express their gratitude to the SAREN Re-search Group (IT-1619-22, Basque Government) and MCIN/AEI/10.13039/501100011033/ FEDER, UE (PID2021-124203OB-I00).Peer reviewe

Corrosion rate of a high strength steel by AFM

Trabajo presentado en la 59th Annual Meeting of the International Society of Electrochmistry, celebrada en Sevilla (España), del 7 al 12 de septiembre de 200