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Acceleration Period

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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 hydration
    Construction and Building Materials, 2019
    Co-Authors: Masoud Moradian, Mohammed Aboustait, M. Tyler Ley, Jay C. Hanan, Xianghui Xiao, Volker Rose, Robert Winarski, George W. Scherer
    Abstract:

    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.

  • Direct observation of void evolution during cement hydration
    Materials & Design, 2017
    Co-Authors: Masoud Moradian, Mohammed Aboustait, M. Tyler Ley, Jay C. Hanan, Xianghui Xiao, George W. Scherer, Zhidong Zhang
    Abstract:

    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.

  • Mechanisms of cement hydration
    Cement and Concrete Research, 2011
    Co-Authors: Jeffrey W. Bullard, George W. Scherer, Hamlin M. Jennings, Richard A. Livingston, André Nonat, Jeffrey Schweitzer, Karen Scrivener, Jeffrey J. Thomas
    Abstract:

    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.

  • Significance of Acceleration Period in a Dynamic Strength Testing Study
    The Journal of orthopaedic and sports physical therapy, 1994
    Co-Authors: W.-l. Chen, You-li Chou
    Abstract:

    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.

Huayong Yang – One of the best experts on this subject based on the ideXlab platform.

  • A study on surface topography in cavitation erosion tests of AlSi10Mg
    Tribology International, 2016
    Co-Authors: Yi Zhu, Jun Zou, W.l. Zhao, Xiang Chen, Huayong Yang
    Abstract:

    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.