4. Effect of Metakaolin on the Mechanical Properties of Geopolymers

The incorporation of metakaolin (MK) as a part of precursor may have a positive or a negative effect on the mechanical properties of geopolymers. This typically depends on testing age, activator type/concentration, Si/Na ratio, Si/Al ratio, MK ratio/fineness, type of precursor, precursor fineness and curing condition. When slag was used as the main precursor, most of the available studies reported an adverse effect of MK on the compressive strength of geopolymers. Contrarily, when fly ash (FA) was used as the main precursor, most of the available studies reported a positive effect of MK on the compressive strength of geopolymers. When unconventional or blended precursors were used, inconclusive results of the effects of MK on the compressive strength were obtained. The findings on the effect of MK on the flexural strength of geopolymers are inconclusive, whilst the findings on the effect of MK on the splitting tensile strength and elastic modulus are too limited. The main aim of this chapter is to present an all-encompassing review, summary and analysis of previous studies that examined the effect of MK on the mechanical properties of different types of geopolymers.