ABSTRACT
Portland cements to develop strength more slowly at early ages than Portland cement alone.
Recent research has shown that it is possible to use fly ash or slag as a sole binder in mortar by activating them with an alkali component, such as; caustic alkalis, silicate salts, and non silicate salts of weak acids (Talling and Branstetr 1989). There are two models of alkali activation. Activation by low to mild alkali of a material containing primarily silicate and calcium will produce calcium silicate hydrate gel (C-S-H), similar to that formed in Portland cements, but with a lower Ca/Si ratio (Bakharev and Patnaikuni 1997). The second mechanism involves the activation of material containing primarily silicate and aluminates using a highly alkaline solution. This reaction will form an inorganic binder through a polymerization process (Xu 2002). The term ‘‘Geopolymeric’’ is used to characterize this reaction from the previous, and accordingly, the name ‘‘geopolymer’’ has been adopted for this type of binder (Davidovits 1991). The geopolmeric reaction differentiates geopolymer from other types of alkali activated materials (such as; alkali activated slag/fly ash since the product is polymer rather than a C-S-H gel.
