Page 406 - New Trends in Eco efficient and Recycled Concrete

Application of alkali-activated industrial waste 361

instability compared to OPC mortars in all curing conditions. Otherwise, the studies
on freeze thaw and chloride diffusion in alkali-activated slag (AAS) concrete
(AASc) applying the accelerated chloride penetration test showed that concrete
with AAMs present a similar behaviour to those made with OPC (Van Deventer
et al., 2012).
However, some authors (Ariffin et al., 2013; Sata et al., 2012) found that geopo-
lymers exhibit a minimal strength loss upon prolonged acidic environment exposure
to sulphuric acid in comparison with OPC concrete. The same trend is achieved
when geopolymers are exposed to a prolonged sulphate environment (Sata et al.,
2012) due to the low calcium content which renders it to be more resistant towards
sulphate attack (Bhutta et al., 2013).

13.2 New precursors and activators from wastes

During the past two decades there has been intense development of studies focused
on alkali-activated binders using traditional precursors, such as waste derived pre-
cursors like blast furnace slag or coal FA, and synthetic ones, such as MK
(Davidovits, 2015; Pacheco-Torgal et al., 2014; Provis and Van Deventer, 2014;
Shi et al., 2005).
Many investigations have been carried out based on the characterisation of the
molecular structure of cementing gels (NASH and CASH gels), their microstructure
in terms of porosity and transport mechanisms, the development of resistances in
different conditions and durability problems, among others. In many of these ana-
lysed systems activated with alkalis, the activating component was a highly alkaline
solution and was prepared from chemical reagents, mainly hydroxides and/or alkali
silicates (sodium or potassium) and in some cases carbonates. These are the tradi-
tional activators used in the manufacture of AAMs.
With the aim of expanding the knowledge and exploiting new raw materials in
alkali-activated binders’ preparation, several research groups are testing different
new wastes as precursors and activation reagents (Fig. 13.1). The availability of
new raw materials for the preparation of alkali-activated concrete will make this
technology more wide-spread and many people, including low-income groups, will
have more possibilities to manage waste and apply different cementing systems,
partially avoiding the dependence on the Portland cement industry. Also, several
new raw materials have been tested for preparing precursors and activating
solutions.
These precursors and activation reagents are prepared from different types of
waste from different urban, agricultural and industrial activities, or from natural
resources, mainly natural pozzolans such as pumice (Allahverdi et al., 2011), diato-
mite (Arbi et al., 2013), zeolites [clinoptilotite (Degirmenci, 2018), mordenite
(Baykara et al., 2017)], perlite (Erdogan, 2015) and volcanic ash (Djobo et al.,
2017), among others, and thermally activated clays (Dietel et al., 2017; Ferone