Dal Sasso Gregorio, Dalconi Maria Chiara, Ferrari Giorgio, Pedersen Jan Skov, Tamburini Sergio, Bertolotti Federica, Guagliardi Antonietta, Bruno Marco, Valentini Luca, Artioli Gilberto
Institute of Geosciences and Earth Resources, National Research Council of Italy, Via G. Gradenigo 6, 35131 Padova, Italy.
Department of Geosciences and CIRCe Centre, University of Padova, Via G. Gradenigo 6, 35131 Padova, Italy.
Nanomaterials (Basel). 2022 Jan 21;12(3):342. doi: 10.3390/nano12030342.
Calcium silicate hydrate (C-S-H) is the main binding phase in Portland cement. The addition of C-S-H nanoparticles as nucleation seeds has successfully been used to accelerate the hydration process and the precipitation of binding phases either in conventional Portland cement or in alternative binders. Indeed, the modulation of the hydration kinetics during the early-stage dissolution-precipitation reactions, by acting on the nucleation and growth of binding phases, improves the early strength development. The fine-tuning of concrete properties in terms of compressive strength and durability by designed structural modifications can be achieved through the detailed description of the reaction products at the atomic scale. The nano-sized, chemically complex and structurally disordered nature of these phases hamper their thorough structural characterization. To this aim, we implement a novel multi-scale approach by combining forefront small-angle X-ray scattering (SAXS) and synchrotron wide-angle X-ray total scattering (WAXTS) analyses for the characterization of Cu-doped C-S-H nanoparticles dispersed in a colloidal suspension, used as hardening accelerator. SAXS and WAXTS data were analyzed under a unified modeling approach by developing suitable atomistic models for C-S-H nanoparticles to be used to simulate the experimental X-ray scattering pattern through the Debye scattering equation. The optimization of atomistic models against the experimental pattern, together with complementary information on the structural local order from Si solid-state nuclear magnetic resonance and X-ray absorption spectroscopy, provided a comprehensive description of the structure, size and morphology of C-S-H nanoparticles from the atomic to the nanometer scale. C-S-H nanoparticles were modeled as an assembly of layers composed of 7-fold coordinated Ca atoms and decorated by silicate dimers and chains. The structural layers are a few tens of nanometers in length and width, with a crystal structure resembling that of a defective tobermorite, but lacking any ordering between stacking layers.
硅酸钙水合物（C-S-H）是波特兰水泥中的主要胶凝相。添加C-S-H纳米颗粒作为成核晶种已成功用于加速传统波特兰水泥或替代胶凝材料中的水化过程和胶凝相的沉淀。实际上，通过作用于胶凝相的成核和生长来调节早期溶解-沉淀反应期间的水化动力学，可改善早期强度发展。通过在原子尺度上详细描述反应产物，可以实现通过设计结构改性对混凝土抗压强度和耐久性等性能进行微调。这些相的纳米尺寸、化学复杂性和结构无序性阻碍了对其进行全面的结构表征。为此，我们采用了一种新颖的多尺度方法，结合前沿的小角X射线散射（SAXS）和同步加速器广角X射线全散射（WAXTS）分析，来表征分散在胶体悬浮液中的用作硬化促进剂的Cu掺杂C-S-H纳米颗粒。SAXS和WAXTS数据在统一的建模方法下进行分析，通过为C-S-H纳米颗粒开发合适的原子模型，利用德拜散射方程来模拟实验X射线散射图案。将原子模型与实验图案进行优化，并结合来自硅固态核磁共振和X射线吸收光谱的关于结构局部有序性的补充信息，从原子尺度到纳米尺度全面描述了C-S-H纳米颗粒的结构、尺寸和形态。C-S-H纳米颗粒被建模为由7配位钙原子组成的层状组装体，并由硅酸盐二聚体和链修饰。结构层的长度和宽度为几十纳米，晶体结构类似于缺陷托贝莫来石，但堆积层之间缺乏任何有序性。
