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Journal of Zhejiang University SCIENCE A

ISSN 1673-565X(Print), 1862-1775(Online), Monthly

Stress relaxation properties of calcium silicate hydrate: a molecular dynamics study

Abstract: The time-dependent viscoelastic response of cement-based materials to applied deformation is far from fully understood at the atomic level. Calcium silicate hydrate (C-S-H), the main hydration product of Portland cement, is responsible for the viscoelastic mechanism of cement-based materials. In this study, a molecular model of C-S-H was developed to explain the stress relaxation characteristics of C-S-H at different initial deformation states, Ca/Si ratios, temperatures, and water contents, which cannot be accessed experimentally. The stress relaxation of C-S-H occurs regardless of whether it is subjected to initial shear, tensile, or compressive deformation, and shows a heterogeneous characteristic. Water plays a crucial role in the stress relaxation process. A large Ca/Si ratio and high temperature reduce the cohesion between the calcium-silicate layer and the interlayer region, and the viscosity of the interlayer region, thereby accelerating the stress relaxation of C-S-H. The effect of the hydrogen bond network and the morphology of C-S-H on the evolution of the stress relaxation characteristics of C-S-H at different water contents was elucidated by nonaffine mean squared displacement. Our results shed light on the stress relaxation characteristics of C-S-H from a microscopic perspective, bridging the gap between the microscopic phenomena and the underlying atomic-level mechanisms.

Key words: Calcium silicate hydrate (C-S-H); Stress relaxation; Ca/Si ratio; Temperature; Water content; Atomic simulation

Chinese Summary  <1792> 水化硅酸钙应力松弛特性的分子动力学研究

作者:耿志成1,汤盛文1,2,汪洋1,阿胡宝1,何真1,吴凯2,王磊3
机构:1武汉大学,水资源工程与调度全国重点实验室,中国武汉,430072;2同济大学,先进土木工程材料教育部重点实验室,中国上海,200092;3西安建筑科技大学,材料科学与工程学院,中国西安,710055
目的:水化硅酸钙(C-S-H)是波特兰水泥的主要水化产物,是影响水泥基材料粘弹性机制的主要成分之一。然而,人们还未能在原子层面上完全理解水泥基材料在外加变形作用下随时间变化的粘弹性响应。本文旨在通过建立不同钙硅比的C-S-H模型,以分子动力学模拟的方式系统研究不同因素对水化硅酸钙应力松弛性能的影响。
创新点:1.基于分子动力学模拟,获得C-S-H的应力松弛特性;2.研究应变状态、钙硅比和内部水含量对C-S-H应力松弛的影响,揭示其在应力松弛过程中所涉及的内部结构及能量变化。
方法:1.通过各原子基团的均方位移在应力松弛过程中考虑C-S-H层间区域的粘度变化;2.基于时间相关函数,在不同应变状态、钙硅比以及温度的条件下研究C-S-H层间区域涉及到的化学键断裂与重组;3.阐明氢键网络和C-S-H形态对不同含水量下C-S-H应力松弛特性演变的影响。
结论:1.在不同的初始变形条件下,C-S-H应力松弛响应均会发生,并显示出非均质特征;2.钙硅比的增大以及温度的提高会导致水分子、羟基和层间钙原子的运动加快,从而引起C-S-H层间区域的粘度降低,进而导致C-S-H的初始应力及残余应力降低;3.由于水分子会影响C-S-H的形貌以及层间氢键网络,所以C-S-H在不同水含量时展现出不同的应力松弛特性。

关键词组:水化硅酸钙;应力松弛;钙硅比;温度;水含量;原子模拟


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DOI:

10.1631/jzus.A2300476

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On-line Access:

2024-08-27

Received:

2023-10-17

Revision Accepted:

2024-05-08

Crosschecked:

2024-02-01

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