分子动力学模拟研究钙硅摩尔比对水化硅酸钙结构与力学性能的影响

水化硅酸钙(C-S-H)作为硅酸盐水泥基材料的主要结合相,对水泥基材料的耐久性、物理力学性能有显著影响。本文构建了钙硅摩尔比(Ca/Si)从1.1到1.9的5个C-S-H模型,并通过分子动力学模拟了C-S-H 模型沿x、y和z方向的纳米压痕测试,然后采用典型的Oliver-Pharr方法分别计算它们的压痕模量和硬度。模拟结果表明:随着钙硅摩尔比的增加,C-S-H的密度会逐渐降低,水硅摩尔比会逐渐增加,平均硅链长会有所降低;C-S-H的力学性能受钙硅摩尔比的影响很大,随着钙硅摩尔比的增加,硅链缺陷程度增加,钙硅片层状结构的稳定性会相应降低,C-S-H结构抵抗外界变形荷载的能力减弱,从而导致压痕模量和硬度降低。平行于钙硅层方向的压痕模量和硬度值比较接近,而垂直于钙硅层方向的值略低,C-S-H近似于横观各向同性结构。随着钙硅摩尔比的增加,三个方向的值逐渐接近,C-S-H具有从横观各向同性变为各向同性的趋势。

Effect of Ca/Si Ratio on Structure and Mechanical Properties of Calcium Silicate Hydrate via Molecular Dynamics Simulations

Calcium silicate hydrate (C-S-H), as the main binding phase of Portland cement-based materials, significantly effects the durability, physical and mechanical properties of cement-based materials. In this paper, 5 models with different Ca/Si ratios from 1.1 to 1.9 were constructed, and molecular dynamics was carried out to simulate the nanoindentation test on C-S-H models along x, y and z directions. Then their indention modulus and hardness were calculated by the typical Oliver-Pharr method respectively. According to results from present simulation, as the Ca/Si ratio increases, the density and the average silicate chain length gradually decrease, but the W/Si ratio gradually increases. The mechanical properties are greatly influenced by the Ca/Si ratio, as the Ca/Si ratio increases, the degree of the defect of silicate chains increases, and the stability of calcium silicate sheets is correspondingly reduced, resulting in the weakening of the ability of C-S-H structure to resist deformation and the reduction of indention modulus and hardness. Indention modulus and hardness values in the direction parallel to calcium silicate layers are closed, while the values in the direction perpendicular to calcium silicate layers are slight lower, C-S-H is similar to transversely isotropic structure. As Ca/Si ratio increases, values of both three directions are gradually closed, C-S-H changes from transversely isotropic structure to isotropic structure.