Investigation and modelling of alite hydration

目前每年生产和消费的水泥超过40亿吨。这一过程约占人为二氧化碳排放总量的8%，并与一次能源的高消耗有关。水泥被用来生产混凝土，这是建筑中最重要的材料。与材料的重要性相比，人们对硬化过程中的化学反应的了解还很不发达。了解硅酸三钙的水化机理将有助于减少对环境的影响，开发高性能的粘结剂和混凝土。以前的项目对理解硅酸钙在没有外来离子的情况下水化的基本机理做出了非常重要的贡献。首次证明了初始时间的动力学完全取决于C-S-H的沉淀速率。在定性论证的基础上，分析了界面速率、表面积、反应度和溶液组成等相关参数的定量数据，并将其提供给一个简单而稳健的动力学模型。该模型能够定量地捕捉无外来离子时硅酸三钙的水化过程，计算结果得到了实验数据的验证。用于模型验证的方法包括基于Rietveld方法的定量X射线衍射和应用外部标准(G因子)、量热法、孔溶液成分分析、热分析、29Si核磁共振光谱、电子显微镜和表面分析。目前的建议旨在将模型转移到阿利特在外来离子存在下的水化过程，因为许多离子以不同的形式改变了水化动力学。众所周知，不同来源的铝可以延缓主水化期，而溶解碱的存在则会加速主水化期。在本项目中，铝离子、硫酸盐离子和碱离子的影响将单独和结合进行分析。这也包括分析界面溶解和沉淀速率的基础研究，以获得关于外来离子如何影响反应性的机制的信息。这些数据可用于将目前的模型从纯硅酸三钙扩展到孔道溶液中存在附加离子时掺杂阿利特的水化。该模型可以使用与上一个项目中相同的实验方法进行验证。在基础研究成果的基础上，将通过模拟和实验研究探索修正水化动力学的新方法。这些努力的长期目标是了解和操作水泥水化。

More than 4 billion tons of cement are currently produced and consumed each year. The process contributes approximately 8% to the total man-made carbon dioxide emissions and is associated to a high consumption of primary energy. Cement is used for the production of concrete, which is the most important material in construction.Compared to the importance of the material, the knowledge about the chemical reactions during hardening is only poorly developed. Understanding of the mechanisms governing the hydration would enable the reduction of environmental impacts and the development of high performance binders and concretes.The previous project provided highly important contributions to the understanding of the basic mechanisms of tricalcium silicate hydration in the absence of foreign ions. It was proved for the first time that the kinetics in the first hours depends purely on the precipitation rate of C-S-H. Beyond this qualitative demonstration, quantitative data for relevant parameters such as interfacial rates, surface areas, degree of reaction and solution composition were analyzed and fed to a simple and robust kinetic model. This model can quantitatively capture the hydration of tricalcium silicate in the absence of foreign ions and the results of the computations are confirmed by experimental data. The methods used for model validation include quantitative X-ray diffraction based on the Rietveld approach and an application of an external standard (G-factor), calorimetry, analysis of the pore solution composition, thermal analysis, 29Si nuclear magnetic resonance spectroscopy, electron microscopy and surface analysis.The current proposal aims to transfer the model to the hydration of alite in the presence of foreign ions, as a number of ions modify hydration kinetics in different form. It is known that the presence of aluminum from different sources may delay the main hydration period whereas it is accelerated in the presence of dissolved alkalis. The impact of aluminum, sulfate and alkali ions will be analyzed individually and in combination in the present project. This includes also basic research for the analysis of interfacial dissolution and precipitation rates to obtain information on the mechanisms how the foreign ions affect reactivity. These data can be used to extend the current model from pure tricalcium silicate to the hydration of doped alite in the presence of additional ions in the pore solution. The model can be validated using the same experimental methods as in the previous project. Based on findings of the fundamental research, new methods to modify the hydration kinetics will be investigated by modelling and experimental research. The long-term of these efforts goal is understanding and manipulation of cement hydration.