2. Silica Fume as a Part of Precursor/An Additive

Due to the prospective properties of silica fume (SF), it is frequently used in Portland cement (PC) systems as a supplementary cementitious ingredient to improve the mechanical and durability properties. In recent developments, numerous studies have been implemented to obtain superior properties of various types of geopolymer by incorporating SF. In spite of SF can be incorporated into geopolymers in various forms, most of the past studies employed it as a part of precursor/an additive. However, recycling SF as a cementitious material (as a part of precursor) into various geopolymer types may have a positive effect or an adverse effect. This mainly depends on precursor/SF fineness, activator concentration and type, activator/binder ratio, testing age, curing condition, SF amount and Si/Al ratio. The target of this part is to review, summarize and analyse the past studies focused on the effect of SF, as an additive or a part of precursor, on workability, setting time, density, mechanical strength and different durability aspects of various types of geopolymer.