Download or read book A Study of Retarding Effects on Cement and Tricalcium Silicate Hydration Induced by Superplasticizers written by Thomas Sowoidnich and published by . This book was released on 2015 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Superplasticizers are utilized both to improve the fluidity during the placement and to reduce the water content of concretes. Both effects have also an impact on the properties of the hardened concrete. As a side effect the presence of superplasticizers affects the strength development of concretes that is strongly retarded. This may lead to an ecomomical drawback of the concrete manufacturing. The present work is aimed at gaining insights on the causes of the retarding effect of superplasticizers on the hydration of Portland cement. In order to simplify the complex interactions occurring during the hydration of Portland cement the majority of the work focuses on the interaction of superplasticizer and tricalcium silicate (Ca3SiO5 or C3S, the main compound of Portland cement clinker). The tests are performed in three main parts accompanied by methods as for example isothermal conduction calorimetry, electrical conductivity, Electron Microscopy, ICP-OES, TOC, as well as Analytical Ultracentrifugation. In the first main part and based on the interaction of cations and anionic charges of polymers, the interactions between calcium ions and superplasticizers are investigated. As a main effect calcium ions are complexed by the functional groups of the polymers (carboxy, sulfonic). Calcium ions may be both dissolved in the aqueous phase and a constitute of particle interfaces. Besides these effects it is furthermore shown that superplasticizers induce the formation of nanoscaled particles which are dispersed in the aqueous phase (cluster formation). Analogous to recent findings in the field of biomineralization, it is reasonable to assume that these nanoparticles influence the crystal growth by their assembly process. Based on the assumption that superplasticizers hinder either or both dissolution and precipitation and by that retard the cement hydration, the impact on separate reactions is investigated. On experiments that address the solubility of C-S-H phases and portlandite, it is shown that complexation of calcium ions in the aqueous phase by functional groups of polymers increases the solubility of portlandite. Contrary, in case of C-S-H solubility the complexation of calcium ions in solution leads to decrease of the calcium ion concentration in the aqueous phase. These effects are explained by differences in adsorption of polymers on C-S-H phases and portlandite. It is proposed that adsorption is stronger on C-S-H phases compared to portlandite due to the increased specific surface area of C-S-H phases. Following that, it is claimed that before polymers are able to adsorb on C-S-H phases the functional groups must be screened by calcium ions in the aqueous phase. It is further shown that data regarding the impact of superplasticizers on the unconstrained dissolution rate of C3S does not provide a clear relation to the overall retarding effect occurring during the hydration of C3S. Both increased and decreased dissolution rate with respect to the reference sample are detected. If the complexation capability of the superplasticizers is considered then also a reduced dissolution rate of C3S is determined. Despite the fact that the global hydration process is accelerated, the addition of calcite leads to a slower dissolution rate. Thus, a hindered unconstrained dissolution of C3S as possibly cause for the retarding effect still remains open for discussion. In the last section of this part, the pure crystallization of hydrate phases (C-S-H phases, portlandite) is fathomed. Results clearly show that superplasticizers prolong the induction time and modify the rate of crystal growth during pure crystallization in particular due to the complexation of ions in solution. But this effect is insufficient to account for the overall retarding effect. Further important factors are the blocking of crystal growth faces by adsorbed polymers and the dispersion of nanoscaled particles which hinders their agglomeration in order to build up crystals. In the last main part of the work, the previously gathered results are utilized in order to investigate hydration kinetics. During hydration, dissolution and precipitation occur in parallel. Thereby, special attention is laid on the ion composition of the aqueous phase of C3S pastes and suspensions in order to determine the rate limiting step. All in all it is concluded that the retarding effect of superplasticizers on the hydration of tricalcium silicate is based on the retardation of crystallization of hydrate phases (C-S-H phases and portlandite). Thereby, the two effects complexation of calcium ions on surfaces and stabilization of nanoscaled particles are of major importance. These mechanisms may partly be compensated by template performance and increase in solubility by complexation of ions in solution. The decreased dissolution rate of C3S by the presence of superplasticizers during the in parallel occuring hydration process can only be assessed indirectly by means of the development of the ion concentrations in the aqueous phase (reaction path). Whether this observation is the cause or the consequence within the dissolution-precipitation process and therefore accounts for the retarding effect remains a topic for further investigations. Besides these results it is shown that superplasticizers can be associated chemically with inhibitors because they reduce the frequency factor to end the induction period. Because the activation energy is widely unaffected it is shown that the basic reaction mechanism sustain. Furthermore, a method was developed which permits for the first time the determination of ion concentrations in the aqueous phase of C3S pastes in-situ. It is shown that during the C3S hydration the ion concentration in the aqueous phase is developed correspondingly to the heat release rate (calorimetry). The method permits the differentiation of the acceleration period in three stages. It is emphasized that crystallization of the product phases of C3S hydration, namely C-S-H phases and portlandite, are responsible for the end of the induction period.
Download or read book Superplasticizers written by Vangipuram Seshachar Ramachandran and published by Natural Resources Canada, Canada Centre for Mineral and Energy Technology. This book was released on 1997 with total page 436 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book has been prepared with the aim of integrating information about the chemistry and application of concrete superplasticizers in a manner relevant to concrete engineers and technologists. The opening chapter introduces basic aspects of concrete science as background for what follows. Chapters 2-4 discuss the chemical synthesis of superplasticizers, methods used to characterize those chemicals, and techniques for evaluation of their effect in cementitious systems. Subsequent chapters cover: the influence of superplasticizers on hydration of cement materials; rheology of cementitious systems; issues related to the mode of action and compatibility of superplasticizers; the effect of superplasticizers on fresh concrete; mechanical properties and durability of concrete; innovative applications of superplasticizers in concrete; superplasticizer dispensing, specifications, and standards; patents related to superplasticizers; and current and future trends in the use of superplasticizers in concrete.
Download or read book Study on Microstructure and Rheological Properties of Cement Chemical Admixtures Water Dispersion System at Early Stage written by Yanrong Zhang and published by Springer. This book was released on 2017-07-25 with total page 271 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis studies the effects of superplasticizers, polyacrylate latexes and asphalt emulsions, which differ in molecular/particle size from nanometers to microns, on the rheological properties of fresh cement pastes (FCPs), as well as the action mechanisms involved. It systematically investigates the rheological properties and microstructure of cement-based materials, and elucidates the adsorption behaviors of polycarboxylate polymers with different functional groups and their effects on cement hydration. Moreover, it reveals how the working mechanism of naphthalene sulfonate formaldehyde (NSF) differs from that of polycarboxylate ether-based (PCE) superplasticizers. Lastly, it develops a conceptual microstructure model and two rheological equations. These findings lend theoretical support to the development of new chemical admixtures and new, higher-performance, cement-based composites.
Download or read book Developments in the Use of Superplasticizers written by V. M. Malhotra and published by . This book was released on 1981 with total page 582 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Influence of Superplasticizers on the Early Hydration of Portland Cement and Cement Compounds written by Christopher John Duston and published by . This book was released on 1982 with total page 124 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Hydration Products of Tricalcium Silicate written by William John Padavona and published by . This book was released on 1968 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Publications of the National Institute of Standards and Technology Catalog written by National Institute of Standards and Technology (U.S.) and published by . This book was released on 1990 with total page 424 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Effect of Water to cement Ratio on Hydration Kinetics of Tricalcium Silicate Cements Testing the 2 step Hydration Hypothesis written by David Kirby and published by . This book was released on 2011 with total page 108 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Science and Technology of Concrete Admixtures written by Pierre-Claude Aïtcin and published by Woodhead Publishing. This book was released on 2015-11-12 with total page 668 pages. Available in PDF, EPUB and Kindle. Book excerpt: Science and Technology of Concrete Admixtures presents admixtures from both a theoretical and practical point-of-view. The authors emphasize key concepts that can be used to better understand the working mechanisms of these products by presenting a concise overview on the fundamental behavior of Portland cement and hydraulic binders as well as their chemical admixtures, also discussing recent effects in concrete in terms of rheology, mechanics, durability, and sustainability, but never forgetting the fundamental role played by the water/binder ratio and proper curing in concrete technology. Part One presents basic knowledge on Portland cement and concrete, while Part Two deals with the chemical and physical background needed to better understand what admixtures are chemically, and through which mechanism they modify the properties of the fresh and hardened concrete. Subsequent sections present discussions on admixtures technology and two particular types of concrete, self-consolidating and ultra-high strength concretes, with final remarks on their future. Combines the knowledge of two leading authors to present both the scientific and technology of admixtures Explains what admixtures are from a chemical point-of-view and illustrates by which mechanisms they modify the properties of fresh and hardened concrete Presents a fundamental, practical, and innovative reference book on the topic Contains three detailed appendices that can be used to learn how to use admixtures more efficiently
Download or read book Impact of Small Organic Molecules on the Nucleation of Calcium Silicate Hydrate written by Lina Bouzouaid and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Superplasticizers are nowadays commonly employed in concrete to improve its workability and mechanical performance. They generally have the side effect of retarding the hydration of Portland cement which results from two simultaneous reactions: the dissolution of cement grains and the precipitation of cement hydrates. The mechanisms responsible for this retardation and thus delay the setting time of cement remain however largely unexplained. The present work intended to tackle this puzzle from the perspective of cement hydrate formation and employing four small organic molecules as model for superplasticizers. In particular, the impact of these organics on the homogeneous nucleation of calcium silicate hydrate (C-S-H) was studied in detailed. The work further focused on the determination of the driving force of the nucleation (and dissolution) and thus on the determination and modeling of the ion speciation and organic complex formation with calcium, silicate and hydroxide aqueous species. The selected organics whether charged or neutral were all found to form a rich zoo of mono- and poly-nuclear complexes not only with calcium and hydroxide ions but also with silicate species. They were further successfully modeled with the speciation program PHREEQC. This allowed to compare and quantify the impact of the selected organic molecules on the nucleation rate of C-S-H. The nucleation rate was correlated to the complexation power of the organics. A modification of the C-S-H nucleation pathway induced by the organics was found for which the organic complexation with silicate and calcium ions seems to play a crucial role. More generally, the retardation power of the molecules on the hydration of alite, the main mineral phase of Portland cement, was found to correlate well with their impact on the nucleation rate of C-S-H.
Download or read book Effect of Chemical Admixtures on Portland Cement Hydration written by I. Odler and published by . This book was released on 1987 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: The effect of selected chemical admixtures on the progress of portland cement hydration, composition of the hydration products, and strength development was studied. Calcium chloride (CaCl2) accelerated the hydration of both tricalcium silicate (C3S) and tricalcium aluminate (C3A) and increased the calcium oxide/silicon dioxide (CaO/SiO2) ratio of the formed calcium-silicate-hydrate (CSH) phase. In the presence of zinc oxide (ZnO), Na-lignosulfonate, and a melamine resin, the hydration of both C3S and C3A was retarded, while in the presence of sucrose only that of C3S. The effect of all these additives was more pronounced if pure C3S rather than portland cement was employed. Regardless of the kind and amount of admixture added (except high amounts of CaCl2) and hydration time, the bound water content, amount of liberated calcium hydroxide, and compressive strength were linear functions of the amount of hydrated C3S.
Download or read book Adsorption of High range Water reducing Agents on Selected Portland Cement Phases and Related Materials written by D. R. Rossington and published by . This book was released on 1989 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt: The quantities of high-range water-reducing agent (superplasticizer) adsorbed from their aqueous solutions by portland cement, tricalcium silicate, silica fume, wollastonite, and calcium silicate hydrate gel were determined using an ultraviolet spectrophotometer. The two superplasticizers (sulfonated melamine formaldehyde and sulfonated naphthalene formaldehyde) produced generally similar results. Wollastonite, a calcium silicate that does not react with water, produced no measurable adsorption of superplasticizer. The adsorption of superplasticizer by tricalcium silicate was similar to the adsorption by portland cement. From these results, it appears that superplasticizer is not adsorbed by anhydrous silica or anhydrous calcium silicate, but rather by calcium silicate hydrate gel. Additional studies are recommended for improving the understanding of the adsorption of superplasticizer by portland cement.
Download or read book Cement and Concrete Chemistry written by Wieslaw Kurdowski and published by Springer Science & Business. This book was released on 2014-04-24 with total page 705 pages. Available in PDF, EPUB and Kindle. Book excerpt: This monograph describes cement clinker formation. It covers multicomponent systems, clinker phase structures and their reactions with water, hydrate composition and structure, as well as their physical properties. The mineral additions to cement are described as are their influence on cement-paste properties. Special cements are also discussed. The microstructure of concrete is then presented, and special emphasis is given to the role of the interfacial transition zone, and the corrosion processes in the light of cement-phase composition, mineral additions and w/c ratio. The admixtures' role in modern concrete technology is described with an emphasis on superplasticizer chemistry and its cement-paste rheological modification mechanism. Cement with atypical properties, such as calcium aluminate, white, low energy and expansive cements are characterized. The last part of the book is devoted to special types of concrete such as self compacting and to reactive powders.
Download or read book Nucleation Theory written by V.I. Kalikmanov and published by Springer. This book was released on 2012-11-28 with total page 319 pages. Available in PDF, EPUB and Kindle. Book excerpt: One of the most striking phenomena in condensed matter physics is the occurrence of abrupt transitions in the structure of a substance at certain temperatures or pressures. These are first order phase transitions, and examples such as the freezing of water are familiar in everyday life. The conditions at which the transformation takes place can sometimes vary. For example, the freezing point of water is not always 0°C, but the liquid can be supercooled considerably if it is pure enough and treated carefully. The reason for this phenomenon is nucleation. This monograph covers all major available routes of theoretical research of nucleation phenomena (phenomenological models, semi-phenomenological theories, density functional theories, microscopic and semi-microscopic approaches), with emphasis on the formation of liquid droplets from a metastable vapor. Also, it illustrates the application of these various approaches to experimentally relevant problems. In spite of the familiarity of the involved phenomena, it is still impossible to calculate nucleation accurately, as the properties and the kinetics of the daughter phase are insufficiently well known. Existing theories based upon classical nucleation theory have on the whole explained the trends in behavior correctly. However they often fail spectacularly to account for new data, in particular in the case of binary or, more generally, multi-component nucleation. The current challenge of this book is to go beyond such classical models and provide a more satisfactory theory by using density functional theory and microscopic computer simulations in order to describe the properties of small clusters. Also, semi-phenomenological models are proposed, which attempt to relate the properties of small clusters to known properties of the bulk phases. This monograph is an introduction as well as a compendium to researchers in soft condensed matter physics and chemical physics, graduate and post-graduate students in physics and chemistry starting on research in the area of nucleation, and to experimentalists wishing to gain a better understanding of the efforts being made to account for their data.
Download or read book Chemical Admixtures for Concrete written by Sandra Senft and published by CRC Press. This book was released on 1999-06-24 with total page 456 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chemical admixtures are used in concrete mixtures to produce particular engineering properties such as rapid hardening, water-proofing or resistance to cold. Chemical Admixtures for Concrete surveys recent developments in admixture technology, explaining the mechanisms by which admixtures produce their effects, the various types of admixtures avail
Download or read book Concrete Admixtures written by V.H. Dodson and published by Springer Science & Business Media. This book was released on 2013-06-29 with total page 218 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Effects of Superplasticizer Retarding Agent and Silica Fume on the Air Permeability of High Performance Concrete written by R. Gagné and published by . This book was released on 1998 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: The aim of this research is to evaluate how transport properties at the surface and in the core of high-performance concrete (HPC) slabs are affected by silica fume and by superplasticizer and retarding agent dosages. The transport properties were evaluated by measuring the air permeability at two depths under the surface finished with a wooden trowel. The experimental program is based on eight different high-performance concrete mixtures (77 to 93 MPa) made with a water-to-binder ratio of 0.30. An ordinary portland cement (OPC) and a blended silica-fume cement (SF) were used to compare the effect of silica fume on the air permeability of surface and core concrete. Four mixtures were produced with a retarding agent to assess the effect of set retardation on the surface properties of high-performance concrete. For each combination of cement type and retarding agent dosages, the superplasticizer dosage was selected to produce two slump levels of 100 ± 10 mm and 200 ± 20 mm.
