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

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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.