Metakaolin Effect on Geopolymers’ Properties

There is a great deal of kaolin in the Earth’s crust, which can fulfil the global demand for ceramic, filler and paper industries. After suitable calcination, kaolin can be transformed into an amorphous material with pozzolanic activity known as metakaolin (MK). Due to its stable properties, fineness and reactivity, MK can replace part of Portland cement (PC) to improve its fire resistance, durability and mechanical properties. Due to its richness in alumina and silica, MK is widely used as a precursor for geopolymers. Recently, several experiments have been carried out to incorporate MK into different types of geopolymers to achieve improved properties. Incorporating MK into geopolymers could have either a beneficial effect or a detrimental effect. This primarily depends on precursor type/fineness, MK ratio/fineness, activator type/concentration, Si/Al ratio, Si/Na ratio, curing condition and testing age. This book aims to summarize and evaluate the available studies focused on how MK affects the properties of geopolymers.

Metakaolin (MK) is widely used as a part of precursor. The incorporation of MK in the geopolymer mixture can affect its fresh properties such as workability and setting time. The incorporation of MK in the geopolymer mixture may have a positive effect or a negative effect on workability. This mainly depends on the type of precursor, Si/Na ratio, activator type and MK amount. The incorporation of MK in the geopolymer mixture decelerated its setting time. The rate of deceleration depends on the precursor type, Si/Na ratio, Si/Al ratio and MK ratio. The objective of this chapter is to provide an overview, summary and analysis of previous studies that have examined the impact of MK on the workability and setting time of different types 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.

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.

The incorporation of metakaolin (MK) as a part of the precursor may have a positive or a negative effect on the durability of geopolymers. The findings on the effect of MK on carbonation depth and fire resistance are inconclusive. The incorporation of a suitable ratio of MK into geopolymers has a positive effect on surface resistance, sulphate resistance, acid resistance, rapid chloride permeability, alkali–silica reaction expansion and chloride binding capacity. The main aim of this chapter is to present an all-encompassing review, summary, and analysis of previous studies that have examined the effect of MK on different durability aspects of different types of geopolymers.

In this chapter, the general effects of metakaolin (MK) on the properties of different types of geopolymers mentioned in the previous chapters such as workability, setting time, water absorption, porosity, shrinkage and different durability aspects were summarized and compared. In addition, some statistics about the compressive strength, type of precursor and the percentage of studies about the effect of MK on the properties of geopolymers were reported.

Herein, the effects of incorporating metakaolin (MK) as a part of the starting material (precursor) on the properties of different geopolymer types such as workability, setting time, density, water absorption, porosity, shrinkage, compressive strength, flexural strength, splitting tensile strength, elastic modulus and different types of durability were collected, summarized and analysed. The general remarks can be briefed as follows: