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Jeffrey J. Thomas - One of the best experts on this subject based on the ideXlab platform.
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the instantaneous apparent activation energy of Cement Hydration measured using a novel calorimetry based method
Journal of the American Ceramic Society, 2012Co-Authors: Jeffrey J. ThomasAbstract:A new calorimetry-based method for calculating the activation energy of Cement Hydration is described. The method requires a scanning calorimeter that can change the sample temperature relatively quickly and has a stable baseline, but the technique is straightforward to perform. Activation energy values can be calculated at multiple Hydration times from a single specimen, allowing any changes with time to be assessed. With this method, the measured activation energy at a given time does not depend on the previous microstructural development, as is the case with traditional methods of calculating the activation energy from parallel specimens hydrated isothermally at different temperatures. For tricalcium silicate (C3S) hydrated in pure water or in a calcium chloride solution, the activation energy remains statistically constant from the earliest times until the degree of Hydration exceeds 0.65, with an overall average value of (51.1 ± 1.8) kJ/mol. For Cement Hydration, the activation energy is also constant until well past the main Hydration peak, with slightly lower average values. These results suggest that the rate-controlling step in the Hydration process does not change during the early Hydration period (the first few days after mixing), as different reaction steps tend to have different activation energies.
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mechanisms of Cement Hydration
Cement and Concrete Research, 2011Co-Authors: Jeffrey W. Bullard, George W. Scherer, Hamlin M. Jennings, Richard A. Livingston, André Nonat, Karen Scrivener, J S Schweitzer, Jeffrey J. ThomasAbstract:The current state of knowledge of Cement Hydration mechanisms is reviewed, including the origin of the period of slow reaction in alite and Cement, the nature of the acceleration period, the role of calcium sulfate in modifying the reaction rate of tricalcium aluminate, the interactions of silicates and aluminates, and the kinetics of the deceleration period. In addition, several remaining controversies or gaps in understanding are identified, such as the nature and influence on kinetics of an early surface hydrate, the mechanistic origin of the beginning of the acceleration period, the manner in which microscopic growth processes lead to the characteristic morphologies of Hydration products at larger length scales, and the role played by diffusion in the deceleration period. The review concludes with some perspectives on research needs for the future. Published by Elsevier Ltd.
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Mechanisms of Cement Hydration
Cement and Concrete Research, 2011Co-Authors: Jeffrey W. Bullard, George W. Scherer, Hamlin M. Jennings, Richard A. Livingston, André Nonat, Jeffrey Schweitzer, Karen Scrivener, Jeffrey J. ThomasAbstract:Abstract The current state of knowledge of Cement Hydration mechanisms is reviewed, including the origin of the period of slow reaction in alite and Cement, the nature of the acceleration period, the role of calcium sulfate in modifying the reaction rate of tricalcium aluminate, the interactions of silicates and aluminates, and the kinetics of the deceleration period. In addition, several remaining controversies or gaps in understanding are identified, such as the nature and influence on kinetics of an early surface hydrate, the mechanistic origin of the beginning of the acceleration period, the manner in which microscopic growth processes lead to the characteristic morphologies of Hydration products at larger length scales, and the role played by diffusion in the deceleration period. The review concludes with some perspectives on research needs for the future.
Xiangming Kong - One of the best experts on this subject based on the ideXlab platform.
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a comparative study of the effects of two alkanolamines on Cement Hydration
Advances in Cement Research, 2021Co-Authors: Xiangming Kong, D Jansen, Chaoyang ZhangAbstract:The effects of two alkanolamines, triethanolamine (TEA) and diethanol-isopropanolamine (DEIPA), on Cement Hydration were comparatively investigated by several techniques including calorimetry, in s...
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retardation effect of pce superplasticizers with different architectures and their impacts on early strength of Cement mortar
Cement & Concrete Composites, 2019Co-Authors: Xiangming Kong, Liran Zhang, Xia Miao, Shimin ZhouAbstract:Abstract As the most effective superplasticizer, the comb-like PCE polymers also severely retard early Cement Hydration and hence decelerate early strength growth of concrete, which is undesired in some applications. In this study, a series of PCEs with different molecular architectures, including varied side chain length and density were synthetized by co-polymerizing acrylic acid and α-methallyl-ω-hydroxy poly(ethylene glycol) ether. Impacts of the obtained PCEs on Cement Hydration and early strength of mortar were investigated. Results show that adsorption of PCEs on Cement grains is highly dependent on polymer architectures. Higher side chain length and density lead to lower adsorption amount and consequently higher early strength of mortar. It is interestingly found that the retardation effect of the PCEs on Cement Hydration is simply proportion to their absolute adsorption amounts on Cement surface, while the complexation of R−COO− group with Ca2+, which is independent on polymer architectures, plays a minor role.
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the early Hydration of opc investigated by in situ xrd heat flow calorimetry pore water analysis and 1h nmr learning about adsorbed ions from a complete mass balance approach
Cement and Concrete Research, 2018Co-Authors: D Jansen, Xiangming Kong, Ch Naber, D Ectors, F Goetzneunhoeffer, J NeubauerAbstract:Abstract In-situ XRD, heat flow calorimetry, pore water analysis and 1H NMR were used in order to gain more detailed understanding for Cement Hydration within the first hours of Hydration. All methods used show very satisfying accordance. All information gained from the different methods were used in order to calculate absolute mass balance for several ions in order to get an idea about ionic reservoirs adsorbed on surfaces during Cement Hydration. Sulfate and aluminum adsorption show impact on sulfate depletion, calcium does not.
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influences of styrene acrylate latexes on Cement Hydration in oil well Cement system at different temperatures
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2016Co-Authors: Xiangming Kong, Biqin Dong, Ziming Wang, Yanrong Zhang, Yi Cai, Qing Zhang, Feng XingAbstract:Abstract Influences of styrene-acrylate (SA) latexes on Cement Hydration were investigated by isothermal calorimetry and the mechanism wasdiscussed. Super-retardation phenomenon caused by addition of SA latexes on oil well Cement Hydration was found at 80 °C by setting time measurement. Quantitative analysis of hydrolysis of SA latexes in Cementitious systems and their effect on Cement Hydration were investigated by FTIR, zeta potential and surface charge density measurements. Results show that the hydrolysis of ester groups in acrylate units is significantly accelerated by elevated temperature in alkaline condition. The continuous production of carboxyl groups promotes the adsorption of polymer particles on the surface of Cement grains and/or leads to continuous Ca 2+ sequestration from pore solution. These two aspects are the causes of the super-retardation effect. It is concluded that unless special chemistry is involved in the preparation of SA latexes, such as construction of core-shell structure of the colloidal particles, SA latexes with high content of acrylate units, due to the severe hydrolysis of the ester groups in the polymer chains, are not recommended to be used in oil well Cement system.
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correlations of the dispersing capability of nsf and pce types of superplasticizer and their impacts on Cement Hydration with the adsorption in fresh Cement pastes
Cement and Concrete Research, 2015Co-Authors: Yanrong Zhang, Xiangming KongAbstract:Abstract Comparative study of NSF and PCE superplasticizers was carried out aiming at correlating the adsorption in fresh Cement pastes (fcps) with their dispersing capability and the impacts on Cement Hydration. Results show that the adsorption of NSF follows a typical Langmuir monolayer adsorption model while PCE exhibits a multi-layer adsorption. The fluidity of fcps containing NSF and the retardation effect of NSF on Hydration are directly proportional to the surface coverage of NSF on Cement grains. As full coverage is achieved, the fluidity enhanCement and the retardation effect reach maximum by addition of NSF. By contrast, the fluidity of fcps with PCE is related to the coverage of the first adsorbed layer and the secondary adsorbed layer does not contribute to the enhanCement of fluidity. Both the adsorbed PCE and the PCE remaining in aqueous phase participate in retarding Cement Hydration because of the complexation effect of COO − with Ca 2 + .
Xin Cheng - One of the best experts on this subject based on the ideXlab platform.
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fabrication and properties of piezoelectric composites designed for process monitoring of Cement Hydration reaction
Materials Chemistry and Physics, 2012Co-Authors: Dongyu Xu, Shifeng Huang, Xin ChengAbstract:Abstract A series of receiving type piezoelectric composites were designed and fabricated by cutting and filling technique. The piezoelectric composites were also optimized from such aspects as matrix phase, functional phase and composite connectivity. The researches show that these piezoelectric composites have larger piezoelectric voltage factor, thickness electromechanical coupling coefficient and lower acoustic impedance than the pure piezoelectric ceramic. The early Cement Hydration reaction process monitoring result indicates that the ultrasonic wave receiving ability of the piezoelectric composite is obviously better than that of the pure piezoelectric ceramic. Therefore, these kinds of piezoelectric composites have potential application prospect in Cement Hydration reaction process monitoring.
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an exploration of 1 3 Cement epoxy resin based piezoelectric composite in Cement Hydration reaction process monitoring
Advanced Materials Research, 2011Co-Authors: Lei Qin, Shifeng Huang, Xin ChengAbstract:1-3 type Cement/epoxy resin based piezoelectric composite was designed and fabricated aiming at providing a new method for Cement Hydration monitoring. Combining with piezoelectric impedance technology, the Cement Hydration reaction process was monitored by using the composite. The research results show that in the initial Cement Hydration period, the resistance-frequency curves of the sensor drift toward low frequency direction, while the anti-resonance resistance value decreases gradually. With increasing Cement Hydration time, the resistance-frequency curves of the sensor drift toward high frequency direction and the anti-resonance resistance value shows fluctuation changes. The Cement Hydration reaction process can be divided into different periods according to changes of anti-resonance frequency and anti-resonance resistance value of the sensor.
Jeffrey W. Bullard - One of the best experts on this subject based on the ideXlab platform.
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mechanisms of Cement Hydration
Cement and Concrete Research, 2011Co-Authors: Jeffrey W. Bullard, George W. Scherer, Hamlin M. Jennings, Richard A. Livingston, André Nonat, Karen Scrivener, J S Schweitzer, Jeffrey J. ThomasAbstract:The current state of knowledge of Cement Hydration mechanisms is reviewed, including the origin of the period of slow reaction in alite and Cement, the nature of the acceleration period, the role of calcium sulfate in modifying the reaction rate of tricalcium aluminate, the interactions of silicates and aluminates, and the kinetics of the deceleration period. In addition, several remaining controversies or gaps in understanding are identified, such as the nature and influence on kinetics of an early surface hydrate, the mechanistic origin of the beginning of the acceleration period, the manner in which microscopic growth processes lead to the characteristic morphologies of Hydration products at larger length scales, and the role played by diffusion in the deceleration period. The review concludes with some perspectives on research needs for the future. Published by Elsevier Ltd.
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Mechanisms of Cement Hydration
Cement and Concrete Research, 2011Co-Authors: Jeffrey W. Bullard, George W. Scherer, Hamlin M. Jennings, Richard A. Livingston, André Nonat, Jeffrey Schweitzer, Karen Scrivener, Jeffrey J. ThomasAbstract:Abstract The current state of knowledge of Cement Hydration mechanisms is reviewed, including the origin of the period of slow reaction in alite and Cement, the nature of the acceleration period, the role of calcium sulfate in modifying the reaction rate of tricalcium aluminate, the interactions of silicates and aluminates, and the kinetics of the deceleration period. In addition, several remaining controversies or gaps in understanding are identified, such as the nature and influence on kinetics of an early surface hydrate, the mechanistic origin of the beginning of the acceleration period, the manner in which microscopic growth processes lead to the characteristic morphologies of Hydration products at larger length scales, and the role played by diffusion in the deceleration period. The review concludes with some perspectives on research needs for the future.
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a model investigation of the influence of particle shape on portland Cement Hydration
Cement and Concrete Research, 2006Co-Authors: Jeffrey W. Bullard, Edward J. GarbocziAbstract:Abstract The NIST Virtual Cement and Concrete Testing Laboratory (VCCTL) is used to simulate the influence of particle shape on the Hydration kinetics and setting of portland Cement. Building on previous work in reconstructing particle shapes from real Cements, real-shape particles are used to produce three-dimensional digitized Cement paste microstructures, and the Hydration of these microstructures is tracked using VCCTL. The degree of Hydration and percolation of solids is monitored and compared to experimental data at several water–Cement ratios. The simulations predict that shapes of particles influence Cement Hydration in two ways: the additional surface / volume ratio relative to spherical particles results in greater rates of Hydration, and the anisometry in shape influences the degree of Hydration at which the particles and Hydration products percolate to form a stiff three-dimensional network.
René Guyonnet - One of the best experts on this subject based on the ideXlab platform.
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HPMC and HEMC influence on Cement Hydration
Cement and Concrete Research, 2006Co-Authors: Jérémie Pourchez, Philippe Grosseau, Arnaud Peschard, René Guyonnet, Bernard Guilhot, F. ValléeAbstract:Cellulose ethers such as hydroxyethylmethyl cellulose (HEMC) and hydroxypropylmethyl cellulose (HPMC) are common admixtures in factory made mortars. Nevertheless, their use principally remains empirical, and no Cement-admixture interaction mechanism has ever been rigorously demonstrated. The main issue of this publication deals with the control of secondary effects generated by these admixtures such as the retardation of Cement Hydration. In this frame, a study of the impact of HEMC and HPMC molecule parameters on the modification of Cement Hydration was carried out. Minor influence of the molecular weight and of the hydroxypropyl or the hydroxyethyl group content was observed. On the contrary, the results emphasize that the methoxyl group content appears as the key parameter of the Hydration delay mechanism.
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HEC influence on Cement Hydration measured by conductometry
Cement and Concrete Research, 2006Co-Authors: Jérémie Pourchez, Philippe Grosseau, René Guyonnet, Bertrand RuotAbstract:Cellulose ethers are of universal use in factory-made mortars, though their influences on mortar properties at a molecular scale are poorly understood. Recent studies dealt with the influence of hydroxyethylmethyl cellulose (HEMC) and hydroxypropylmethyl cellulose (HPMC) molecular parameters on Cement Hydration. It was concluded that the degree of substitution is the most relevant factor on Cement Hydration kinetics, contrary to the molecular weight. Nevertheless, the major role played by the substitution degree has not been verified for other types of cellulose ethers such as hydroxyethyl cellulose (HEC), which generally possesses a higher Hydration retarding capacity compared to HPMC and HEMC. In this frame, a study of the impact of HEC molecular parameters on Cement Hydration was performed. A negligible influence of the molecular weight was observed. Moreover, the results emphasize that the hydroxyethyl group content mainly determines the delay of Cement Hydration.
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effect of polysaccharides on the Hydration of Cement paste at early ages
Cement and Concrete Research, 2004Co-Authors: Arnaud Peschard, Alexandre Govin, Philippe Grosseau, Bernard Guilhot, René GuyonnetAbstract:This work deals with the relative efficiency of polysaccharides and their influence on Cement Hydration. Several parameters such as the structure, concentration, average molecular weight, and soluble fraction value of polysaccharides were examined. Cement Hydration was monitored by isothermal calorimetry, thermogravimetry (TGA), and Fourier transform infrared (FTIR) spectroscopy. Results clearly show that retardation increases with higher polysaccharide-to-Cement weight ratio (P/C). Low-molecular-weight starch showed enhanced retarding effect on the Hydration of Cement. The retardation effect of polysaccharides is also dependent on the composition of Cement.