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Structure, Reactivity, and Mechanical Properties of Sustainable Geopolymer Material: A Reactive Molecular Dynamics Study
Frontiers in Materials ( IF 3.2 ) Pub Date : 2020-03-05 , DOI: 10.3389/fmats.2020.00069
Zhipeng Li , Jinglin Zhang , Muhan Wang

Sodium aluminosilicate hydrate (NASH) gel, the primary binding phase in geopolymer, determines the mechanical properties and durability of environment-friendly construction materials. In this work, the models of NASH gel were obtained through a two-step procedure: the temperature quenching method and Grand Canonical Monte Carlo water adsorption. The reactive force field (ReaxFF) molecular dynamics were utilized to investigate the structure, reactivity, and mechanical performance of the NASH gel with Na/Al ratio ranging from 1 to 3. Q species, the connectivity factor, shows that the increase of sodium content in NASH gel leads to depolymerization of the aluminosilicate network and more non-bridging oxygen (NBO) atoms. The adsorbed water molecules dissociate near the NBO with high reactivity in defective aluminosilicate structure. The newly produced hydroxyls associate with the aluminate species, contributing to the formation of the pentahedron local structure. The sodium ions distributed in the cavity of the aluminosilicate skeleton have around 4 7 nearest neighbors. Furthermore, with an increase in sodium, the molecular structure of the aluminosilicate skeleton is transformed from an integrity network to partially destroyed branch structures, which gradually decrease the stiffness and cohesive force of NASH gel, characterized by the uniaxial tensile testing. During the large tensile deformation process, the ReaxFF MD correlates the mechanical response with the chemical reaction pathway. The aluminosilicate skeleton is stretched broken to resist the tensile loading and the hydrolytic reaction of water molecules near the stretched Si-O and Al-O bond further accelerates the degradation of NASH gel. Hopefully, this work can shed light on the material design for a high performance of sustainable geopolymer at the nanoscale.



中文翻译:

可持续地质聚合物材料的结构,反应性和机械性能:反应性分子动力学研究

铝硅酸钠水合物(NASH)凝胶是地质聚合物中的主要粘结相,决定了环境友好型建筑材料的机械性能和耐久性。在这项工作中,通过两个步骤获得了NASH凝胶的模型:温度猝灭法和Grand Canonical蒙特卡洛水吸附法。利用反作用力场(ReaxFF)分子动力学研究NaH / Al比为1至3的NASH凝胶的结构,反应性和机械性能。Q物种(连接因子)表明钠含量的增加在NASH凝胶中的碳原子导致铝硅酸盐网络解聚和更多的非桥接氧(NBO)原子。吸附的水分子在有缺陷的硅铝酸盐结构中以高反应性在NBO附近解离。新产生的羟基与铝酸盐物质缔合,有助于形成五面体局部结构。分布在硅铝酸盐骨架腔中的钠离子具有约4 7个最近的邻居。此外,随着钠的增加,硅铝酸盐骨架的分子结构从完整性网络转变为部分破坏的分支结构,这逐渐降低了NASH凝胶的刚度和内聚力,其特征在于单轴拉伸试验。在大的拉伸变形过程中,ReaxFF MD将机械响应与化学反应路径相关联。铝硅酸盐骨架被拉伸断裂以抵抗拉伸载荷,并且在拉伸的Si-O和Al-O键附近的水分子的水解反应进一步加速了NASH凝胶的降解。希望这项工作可以为纳米级高性能可持续地质聚合物的材料设计提供启发。

更新日期:2020-03-05
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