Introduction

Silica fume (SF) is a by-product of ferrosilicon alloys or the silicon metal industry. Due to its high fineness and amorphous silica, it is widely used in Portland cement (PC) systems as a cementitious material to enhance the durability and mechanical properties. In recent developments, numerous studies have been implemented to obtain superior properties of various types of geopolymer by incorporating SF. On the whole, SF can be recycled into geopolymers in three various forms: as an additive to the precursor or as a part of a precursor, as a part of an activator or as a foaming agent. Recycling SF 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 document is to review, summarize and analyse the past studies focused on the effect of SF, in its three various forms, on the properties of geopolymers.