基于反应力场分子动力学的水化硅酸钙水解弱化机理研究

Insights on hydrolysis weakening of calcium silicate hydrate:a ReaxFF molecular dynamics study

作为混凝土材料的主要胶结相,水化硅酸钙(C-S-H)凝胶的水解弱化是导致混凝土材料破坏和胶凝力下降的重要原因。本文通过反应力场分子动力学模拟研究了C-S-H凝胶中含水率对其分子结构、力学性能及动力学特性的影响。模拟研究结果表明:水分子的渗透加速了硅酸钙骨架的平移运动,这与整个结构稳定性的下降直接相关。C-S-H硅链上具有较高反应活性的非桥接氧有助于水解反应的发生,水解反应产生的羟基与未水解的水分子在C-S-H层间区域形成了复杂的氢键网络,使结构的薄弱区域逐渐由层内过渡到层间区域,降低了硅链在单轴拉伸过程中的重新排列程度;随含水率增加,C-S-H中出现更多的缺陷结构,导致C-S-H凝胶力学性能降低。

Calcium silicate hydrate(C-S-H)gel is the main cementing phase of concrete materials,the hy⁃drolysis weakening of which is an important reason for the failure of concrete materials and the decrease of cementing force.In this paper,the effects of water content on molecular structure and mechanical proper⁃ties of C-S-H gel are studied by molecular dynamics simulation(ReaxFF).The penetration of water mole⁃cules accelerates the translational motion of the calcium silicate skeleton,which is directly related to the decrease of the stability of the whole structure.The results show that the un-bridging oxygen in the silicon chain of C-S-H with high reactivity is helpful to hydrolysis reaction.Hydroxyl groups generated by hydroly⁃sis reaction and water molecules form a complex H-bonds network in the C-S-H interlayer region,which gradually transfers the weak area of the structure from the intralayer to the interlayer region and reduces the rearrangement degree of the silicon chain in the uniaxial tension process.With the increase of water content,more structures with defect appear in C-S-H,leading to the decrease of mechanical properties of C-S-H gel.