**2. Aluminosilicates**

**1. Introduction**

240 Cement Based Materials

Geopolymer has an empirical formula of:

where M is cation such as K+

certain amount of SiO2

*Mn*{−(SiO2)*<sup>z</sup>*

amorphous to semi-crystalline. Tetrahedral SiO4

that is charge-balanced by cations (Na+

, Na+

hydroxides (NaOH or/and KOH) and silicate solution (Na<sup>2</sup>

**Figure 1.** Geopolymer systems based number of siloxo Si-O units [2].

In 1978, the word "geopolymer" was introduced by Davidovits [1]. In general, geopolymer is an inorganic polymeric material formed through the reaction between aluminosilicate sources and highly alkaline silicate solution, followed by curing at ambient or slightly higher

the amount of binding water. It has three-dimensional Si-O-Al polymeric networks ranging from

gen atom as shown in **Figure 1**. As refer to **Figure 1**, the terminology of geopolymers can be categorized into three forms which are poly(sialate), poly (sialate-siloxo) and poly (sialate-disiloxo). The Al is in IV-fold coordination [3, 4]. This leaves a negative charge in the IV-fold coordinated Al

by cations is important in determining the structural integrity and fragility of geopolymers [5].

The cations is usually contributed by alkaline silicate solution which is a mixture of alkali

alkali hydroxide is required for the dissolution of aluminosilicates while alkali silicate acts as binder, alkali activator and dispersant or plasticizer [9]. The alkali silicate solution contributes

for the geopolymerization reaction [10].

– AlO2} · *w* H2

and AlO4

, Ca2+, Ba2+, NH4+ and H3

or Ca2+; *n* is the degree of polycondensation; *z* is 1, 2, 3 and *w* is

SiO3

O (1)

are linked alternately by sharing oxy-

). The charge-balancing

) [6–8]. The

SiO3

O+

or/and K2

temperature [2]. The formation process is termed as geopolymerization reaction.

, K+ , Li+ The aluminosilicate sources are materials rich in alumina and silica content (e.g. ashes [11–14], clays [15, 16] or slag [17, 18]). Some other natural and artificial silicoaluminates such as zeolite [19] and magnesium-contained minerals [20] have also been used as an important source of Si4+ and Al4+ ions in the geopolymer binding system. Normally, the total composition of Al2 O3 and SiO2 is more than 70%, preferable in reactive amorphous phase [3, 21]. In this book chapter, the utilization of clay or clay minerals in geopolymer formation is discussed.
