3. Effect of Metakaolin on the Physical Properties of Geopolymers

The incorporation of metakaolin (MK) as a part of precursor may affect the physical properties of geopolymers. The density of the geopolymer may increase or decrease with the introduction of MK. This mainly depends on the type of precursor and MK amount. There are contradictory findings about the effect of MK on the water absorption and porosity of geopolymers. This typically depends on testing age, activator type/concentration, Si/Al ratio, MK ratio/fineness, precursor type/fineness and curing condition. When slag was used as the main precursor, most of the available studies reported an adverse effect of MK on porosity. When ladle slag was used as the main precursor, the incorporation of MK showed an adverse effect on porosity. Contrarily, when fly ash (FA) was used as the main precursor, most studies reported a positive effect of MK on porosity. The available limited studies agreed that the incorporation of MK decreased shrinkage when the main precursors were slag or slag/fly ash. The main aim of this chapter is to present a comprehensive review, summary and analysis of previous studies that have investigated how MK affects the physical properties of different types of geopolymers such as density, water absorption, porosity and shrinkage.