Carbonation of alkali-activated Binders and Concretes - Mechanisms and Implications (CaaB)

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Alkali-activated binders (AABs) and concretes based on these (AAB concretes) are promising building materials for a wide range of applications. To enable a safe use of these materials, however, several open questions regarding their properties have to be answered; this is particularly required for questions regarding their durability. A particular important aspect of durability is the response of these materials to access of carbon dioxide from the surrounding air, i.e. their carbonation and the protection that they provide against corrosion to embedded steel reinforcement when carbonation occurs. Contradictory reports regarding these issues exist in the literature, and important parameters influencing these processes are currently not well understood. In addition, it is not clear to what extent currently existing carbonation resistance testing methods are applicable to AAB concretes. The project contributes to the clarification of these issues by studying the early surface carbonation of these concretes and its consequences, the applicability of the phenolphthalein spray method, and the influence of carbon dioxide concentration, leaching and relative humidity on the carbonation of AAB concretes. To this end, AAB pastes and concretes with systematically varied calcium contents will be exposed to defined carbonation conditions and subsequently analysed using methods from construction materials technology as well as chemical and mineralogical analytical techniques. In particular spatially resolved methods, such as Raman microscopy and micro XRF, will be employed to account for, and study in detail, the advancement of the carbonation front. The principal aim of these investigations is to develop systematically for the first time mechanistic models of the carbonation of AAB concretes, considering also simultaneous leaching. Based on these models, recommendations will be given regarding meaningful accelerated testing methods for their carbonation resistance. In addition, potentials and limits of the applicability of AAB concretes will be identified.