The role of aluminium in C-A-S-H during chemical attack on concrete

在混凝土中使用外加剂，如飞灰、磨细的高炉矿渣或偏高岭土，在生态和经济上都是有利的。然而，这些材料会影响水泥水化过程中形成的相。由于材料的铝含量通常很高，相当数量的铝被束缚在C-A-S-H相中。在现场实践中，混凝土会受到硫酸盐、碱、酸和二氧化碳的化学侵蚀，具体取决于暴露条件。铝在C-A-S-H中的含量和溶解度对混凝土结构构件的抗化学侵蚀性能起着决定性的作用。例如，如果铝从C-A-S-H中释放出来，它可以与硫酸盐离子反应形成膨胀的钙矾石。碱的粘结，从而混凝土对破坏性的碱-硅酸反应的抵抗力，取决于C-A-S-H的铝含量。铝在C-A-S-H中的结合和溶解与其分子结构有关。本研究旨在揭示铝在混凝土化学侵蚀过程中C-A-S-H相中的作用。继续研究工作旨在回答开放和新的问题。除了C-A-S-H纳米结构中铝的结合外，混凝土的耐化学性还受到C-A-S-H中硫酸盐结合的影响。除了混凝土组件的耐久性外，这还会影响它们与环境的相互作用。因此，将研究硫酸盐侵蚀过程中C-A-S-H中硫酸盐键合的影响，特别是C-A-S-H相中硫酸盐离子的构型。其他研究涉及混凝土抗碳化性能的测试方法。将快速测试程序的结果转换为自然碳化混凝土组件的抗力的可靠性仍然是一个有争议的问题。在该项目的第一部分中，进行了二氧化碳浓度高达4vol.%CO2、储存期长达7天的实验。本工作旨在研究较高的二氧化碳浓度(高达10%)和较长的自然碳化时间对C-A-S-H相的影响，特别是反应动力学对C-A-S-H纳米结构变化的影响。

The use of additions such as fly ash, ground granulated blast-furnace slag or metakaolin in concrete is both ecologically and economically favourable. However, these materials affect the phases which form during cement hydration. Since the aluminium content of the materials is, in general, high, a significant amount of aluminium is bound in the C-A-S-H phases. In field practice, concrete is attacked chemically by sulphates, alkalis, acids and CO2 depending on the exposure conditions. The amount and solubility of aluminium in C-A-S-H is decisive for the resistance of concrete structural components to chemical attack. If, for example, aluminium is released from C-A-S-H, it can react with sulphate ions forming expansive ettringite. The bonding of alkalis, and thus the resistance of concrete to a damaging alkali silica reaction, depends on the aluminium content of C-A-S-H. The incorporation and dissolution of aluminium in C-A-S-H is related to its molecular structure. This research work aims to reveal the role of aluminium in the C-A-S-H phases during chemical attack on concrete.The continuation of the research work aims at answering open and new questions. In addition to the bonding of aluminium in the C-A-S-H nanostructure, the chemical resistance of the concrete is also affected by sulphate binding in C-A-S-H. In addition to the durability of concrete components, this also affects their interaction with the environment. Thus the effect of sulphate bonding in C-A-S-H during sulphate attack will be investigated, in particular the configuration of sulphate ions in the C-A-S-H phases.Other investigations relate to the test methods for determining the carbonation resistance of concretes. The reliability of transferring results from a rapid test procedure to the resistance of naturally carbonated concrete components is still a matter of debate. In the first part of the project, experiments were carried out with CO2 concentrations up to 4 vol.% CO2 and a storage period of up to 7 days. The present work intends to investigate the effect of higher CO2 concentrations (up to 10 vol.%) and longer periods of natural carbonation on the C-A-S-H phases, in particular the effect of reaction kinetics on changes in C-A-S-H nanostructure.