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George W. Scherer – One of the best experts on this subject based on the ideXlab platform.
Multi-scale observations of structure and chemical composition changes of portland cement systems during hydrationConstruction and Building Materials, 2019Co-Authors: Masoud Moradian, Mohammed Aboustait, M. Tyler Ley, Jay C. Hanan, Xianghui Xiao, Volker Rose, Robert Winarski, George W. SchererAbstract:
Abstract There is little agreement about the mechanisms and few direct observations of the transition of cement paste from a slurry to a solid. This paper uses four different imaging techniques at multiple length scales (from 15.6 nm to 1 μm) to follow the three-dimensional microstructural evolution of portland cement, and monoclinic tricalcium silicate (mC3S) paste over the first 16 h of hydration. Measurements of over 60,000 particles captured every 10 min were made at the micron scale. Nanoscale examinations of the structure and chemical composition are used to support this work. The results show that hydration products with an average Ca/Si > 3 form on and near the surface of the hydrating particles prior to the Acceleration Period that appears to control the reaction rate. These hydration products appear to change in chemical composition as more rapid dissolution of C3S and formation of hydration products occur during the Acceleration Period. The findings are used to provide insights into the origin of the induction and Acceleration Periods during hydration.
Materials & Design, 2017Co-Authors: Masoud Moradian, Mohammed Aboustait, M. Tyler Ley, Jay C. Hanan, Xianghui Xiao, George W. Scherer, Zhidong ZhangAbstract:
Abstract This paper follows the hydration of both portland cement and tricalcium silicate pastes between 30 min and 16 h of hydration. In-situ fast X-ray computed tomography (fCT) was used to make direct observations of the air-filled void formation in w/s of 0.40 to 0.70 with a micron resolution. The results show that over the first hour of the Acceleration Period the volume of air-filled voids reaches a maximum value and then decreases during the Acceleration Period and stays constant. The void distribution changes from a few coarse voids to a large number of smaller and more uniformly distributed voids. This behavior is suggested to be controlled by changes in the ionic strength that cause exsolution of dissolved air from the pore solution.
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.
You-li Chou – One of the best experts on this subject based on the ideXlab platform.
The Journal of orthopaedic and sports physical therapy, 1994Co-Authors: W.-l. Chen, You-li ChouAbstract:
The Acceleration Period that occurs during isokinetic tests may provide valuable information regarding neuromuscular readiness to produce maximal contraction. The purpose of this study was to collect the normative data of Acceleration time during isokinetic knee testing, to calculate the Acceleration work (Wacc), and to determine the errors (ERexp, ERwork, ERpower) due to ignoring Wacc during explosiveness, total work, and average power measurements. Seven male and 13 female subjects attended the test by using the Cybex 325 system and electronic stroboscope machine for 10 testing speeds (30–300°/sec). A three-way ANOVA was used to assess gender, direction, and speed factors on Acceleration time, Wacc, and errors. The results indicated that Acceleration time was significantly affected by speed and direction; Wacc and Eexp by speed, direction, and gender; and ERwork and ERpower by speed and gender. The errors appeared to increase when testing the female subjects, during the knee flexion test, or when speed …
Peiming Wang – One of the best experts on this subject based on the ideXlab platform.
Effects of super absorbent polymer on the early hydration of Portland cement highlighted by thermal analysisJournal of Thermal Analysis and Calorimetry, 2017Co-Authors: Guofang Zhang, Wang Yawen, He Rui, Peiming WangAbstract:
The effects of super absorbent polymer (SAP) on the early hydrhydration evolution of Portland cement within 72 h were investigated by isothermal calorimetry, thermal analysis and X-ray diffraction analysis. The results show that the SAP definitely affects the early hydrhydration process of Portland cement, increases the hydration heat evolution rate during the Acceleration Period and during the main exothermic peak, promotes the earlier appearance of the main exothermic peak, but does not affect the lengths of the initial reaction Period and the induction Period and the onset of the Acceleration Period. The SAP can accelerate cement hydration to increase the hydration degree within 72 h. But the dosage variation of SAP has minor influence on the hydration heat evolution and hydration degree. The SAP enhances the formation of Ca(OH)2 after 12 h to keep higher content than that in the reference paste. The SAP does not affect the maximum content of ettringite, but delays the conversion of ettringite to monosulphate to remain ettringite content higher at later hydration time. Besides, no new phases are found to have formed in cement paste with SAP.
Journal of Thermal Analysis and Calorimetry, 2014Co-Authors: Guofang Zhang, Zhao Jianbin, Peiming WangAbstract:
The effects of hydroxyethyl methyl cellcellulose (HEMC) on the early hydrhydration and main hydrates evolutions of Portland cement were quantitatively investigated by the isothermal calorimetry, setting times, X-ray diffraction analysis, and environmental scanning electron micrmicroscope analysis. The results show that HEMC definitely affects the early hydrhydration process of cement paste and retards the beginning of the hydration induction Period and Acceleration Period, but increases the length of these two Periods. HEMC decreases the hydration heat evolution rate during the initial reaction Period and the Acceleration Period, but increases the hydration heat evolution rate during the deceleration Period. HEMC decreases the hydration heat amount and hydration degree of cement paste at the early hydrhydration time, especially in the first thirty-six hours. There are good positive correlations between the setting time, the length of induction Period and the dosages of HEMC. HEMC also delays the formation of the hydrates and affects the morphologies of hydrates. Accordingly, HEMC remarkably retards the cement hydration at the early hydrhydration time, and with its dosage increasing, the retardation effect of HEMC enhances.
Huayong Yang – One of the best experts on this subject based on the ideXlab platform.
Tribology International, 2016Co-Authors: Yi Zhu, Jun Zou, W.l. Zhao, Xiang Chen, Huayong YangAbstract:
Abstract Cavitation erosion causes serious problems for hydraulic machinery. This study focuses on the influence of surface topography on the cavitation erosion rate of AlSi10Mg using an ASTM G134 test rig. Polishing, grinding, turning, and laser texturing are employed to finish the surfaces. The obtained cavitation erosion rates are presented, and the surface topography, cross-section, and surface parameters are analyzed. The results indicate that the laser textured surface demonstrates a higher cavitation erosion rate than other surfaces. Certain patterns on the surface affect the deforming behaviors at the Acceleration Period of cavitation erosion progresses. 3D surface parameters, Ssk and Sku, can be employed for predicting the time required for removing the original surface finishing marks.
Dean Paul Forgeron – One of the best experts on this subject based on the ideXlab platform.
A 43Ca and 13C NMR study of the chemical interaction between poly(ethylene-vinyl acetate) and white cement during hydration.Solid state nuclear magnetic resonance, 2011Co-Authors: Jennifer L. Macdonald, Ulrike Werner-zwanziger, Banghao Chen, Josef W. Zwanziger, Dean Paul ForgeronAbstract:
Abstract 43 Ca and 13 C NMR methods were used to study the chemical interaction of poly(ethylene–vinyl acetacetate) (PEVAc) admixture in commercial-grade white cement. From 43 Ca NMR it is shown both that PEVAc induces modest changes in the hydrated cement structure, and that hydrated commercial cement is significantly more complex than models that have been used for its structure in past work. The 13 C NMR results show that the PEVAc hydrolysis occurs early in the cement hydration Acceleration Period, with a rate well-fit by an exponential decay using a time constant of 6±1 days.