Binder Chemistry – High-Calcium Alkali-Activated Materials

As mentioned in Chap. 2, the development and assessment of alkali-activated binders based on calcium-rich precursors such as blast furnace slag (BFS) and other Ca-rich industrial by-products have been conducted for over a century [1–3]. However, an increase in interest in the understanding of the microstructure of alkali-activated binders has taken place in the past decades. This has been driven by the need for scientific methods to optimise the activation conditions which give a strong, stable binder from a particular raw material, and consequently a high-performance alkali-activated material (AAM) concrete, while achieving acceptable workability and a low environmental footprint. A detailed scientific understanding of the structure of these materials is required to generate the technical underpinnings for standards which will facilitate their wider commercial adoption [4, 5]

Durability and testing – Degradation via mass transport

In most applications of reinforced concrete, the predominant modes of structural failure of the material are actually related more to degradation of the embedded steel reinforcing rather than of the binder itself. Thus, a key role played by any structural concrete is the provision of sufficient cover depth, and alkalinity, to hold the steel in a passive state for an extended period of time. The loss of passivation usually takes place due to the ingress of aggressive species such as chloride, and/or the loss of alkalinity by processes such as carbonation. This means that the mass transport properties of the hardened binder material are essential in determining the durability of concrete, and thus the analysis and testing of the transport-related properties of alkali-activated materials will be the focus of this chapter. Sections dedicated to steel corrosion chemistry within alkali-activated binders, and to efflorescence (which is a phenomenon observed in the case of excessive alkali mobility), are also incorporated into the discussion due to their close connections to transport properties