**1. Introduction**

Geopolymers are a relatively new material [1–5]. Basically, this term is applied to material class that is chemically transformed from low-crystallinity aluminosilicates to three-dimensional inorganic polymers (tectosilicates). The resulting material has properties similar to natural minerals, so it is called artificial rock [3, 6]. Actually these materials exhibit chemical composition and mineralogical structure similar to feldspar, feldspathoid, and zeolites consisting of a polymeric Si–O–Al framework, with a microcrystalline or an amorphous structure. Geopolymers were termed for this group of materials by Prof. Davidovits [1].

The major aim of developing the geopolymers is to find alternatives to portland cement and thus to reduce carbon dioxide emissions during cement processing [7]. But in recent years, there has been an observable development in geopolymers and their applications, which have been used in various fields such as construction, waste management, art, and decoration [6, 8]. The precursors of geopolymers are characterized by the availability, whether earth materials such as kaolinitic soil or waste such as fly ash. Many geopolymeric materials are still under development, but some products are already commercialized and used in different fields.

Although geopolymers have attractive engineering and environmental characteristics, there are some challenges in commercializing these materials [9, 10]. In this chapter, these challenges will be addressed along with introducing the functional geopolymers as one of the effective approaches to commercialize these materials and make them economically feasible. Functional geopolymers are defined as geopolymers with more than one use at a time, such as use in construction and water purification or use in construction and passive cooling of houses [11].

#### **2. Functional geopolymers and their applications**

In the following sections, some of the most important functional geopolymers and their applications are discussed.

#### **2.1 Geopolymers for construction and water treatment**

This research approach is related to the use of geopolymers not only for construction purposes but also for water purification. The major interest is based on


#### **Table 1.**

*The chemical analysis of kaolinite and zeolitic tuff (ZK) [8].*


#### **Table 2.**

*Composition of geopolymers [8].*

the physical properties of materials as well as porosity. Therefore, in addition to the geopolymer porous matrix, natural zeolite is used as a filler or partial reactant.

Geopolymers were prepared using metakaolin, zeolitic tuff (ZK), and alkaline activators. The natural zeolitic tuff, mordenite, was collected from Kimolos Island, Greece. This mineral is associated with calcite and dolomite [8]. Metakaolin was prepared by calcination of kaolinite (Fluka, Germany) at 750°C for 3 to 4 h. The chemical composition of both the zeolitic tuff and kaolinite is reported in **Table 1**. Alkaline activators are prepared using sodium silicate solution and sodium hydroxide. The SiO2-to-Na2O molar ratio is 1, and the Na2O-to-Al2O3 ratio (from metakaolin) is 1. Finally the molar ratio of H2O/Na2O is 7. The zeolitic tuff is added in different ratios as reported in **Table 2**.

Geopolymers exhibit a nanoporous matrix gel as reported in **Figure 1** [8, 12–14]. This porous matrix assists in increasing the surface area and the physicochemical adsorption of micropollutants. The adsorption capacity of geopolymers with different zeolites/metakaolins was studied in terms of adsorption of Cu2+ ions at a pH of 3.

All the geopolymeric specimens exhibit high adsorption capacity of 8 mg Cu/g for samples G3 and G4 after 1 day (**Figure 2**). It is observed that the adsorption capacity of bulk disks of geopolymers is comparable with powdered zeolites in other findings [15]. **Figure 2** illustrates that increasing the zeolitic tuff percentages to 50% causes an increment in the adsorption capacity by several times. Therefore, this type of geopolymer can be used effectively in water treatment.

**3**

**systems**

*Adsorption of Cu (II) onto geopolymeric disks, pH = 3 [8].*

**Figure 2.**

**Figure 1.**

*Introductory Chapter: Case Studies of Functional Geopolymers*

**2.2 Natural fiber-reinforced geopolymers for construction and passive cooling** 

*SEM image of geopolymers. MK: Partially transformed metakaolinite. A: Geopolymer gel [8].*

In a recent research, vascular natural fiber is used to improve the properties of end products to be used for more than one purpose. The use of natural fibers such as *Luffa cylindrica* fibers (LCF) as reinforcements for geopolymers has several objectives. In addition to improving mechanical properties, these vascular fibers improve the microstructural properties of the resulting material. In this research,

*DOI: http://dx.doi.org/10.5772/intechopen.90363*

*Geopolymers and Other Geosynthetics*

LOI 11.8

*The chemical analysis of kaolinite and zeolitic tuff (ZK) [8].*

the physical properties of materials as well as porosity. Therefore, in addition to the geopolymer porous matrix, natural zeolite is used as a filler or partial reactant. Geopolymers were prepared using metakaolin, zeolitic tuff (ZK), and alkaline activators. The natural zeolitic tuff, mordenite, was collected from Kimolos Island, Greece. This mineral is associated with calcite and dolomite [8]. Metakaolin was prepared by calcination of kaolinite (Fluka, Germany) at 750°C for 3 to 4 h. The chemical composition of both the zeolitic tuff and kaolinite is reported in **Table 1**. Alkaline activators are prepared using sodium silicate solution and sodium hydroxide. The SiO2-to-Na2O molar ratio is 1, and the Na2O-to-Al2O3 ratio (from metakaolin) is 1. Finally the molar ratio of H2O/Na2O is 7. The zeolitic tuff is added

**Series Zeolitic tuff/metakaolinite weight ratio**

G1 0 G2 0.25 G3 0.50 G4 0.75

**Kaolinite Zeolitic tuff (ZK)**

**Compound Composition% Compound Composition%** MnO 0.01 MnO 0.04 Na2O 0 Na2O 0.77 CaO 0.06 CaO 14.66 K2O 1.05 K2O 3.42 MgO 0.93 MgO 2.76 P2O5 0.4 P2O5 0.05 Fe2O3 0.29 Fe2O3 1.36 Al2O3 33.57 Al2O3 11.04 SiO2 41.14 SiO2 58.35 TiO2 0.36 LOI 7.55

Geopolymers exhibit a nanoporous matrix gel as reported in **Figure 1** [8, 12–14]. This porous matrix assists in increasing the surface area and the physicochemical adsorption of micropollutants. The adsorption capacity of geopolymers with different zeolites/metakaolins was studied in terms of adsorption of Cu2+ ions at a pH of 3. All the geopolymeric specimens exhibit high adsorption capacity of 8 mg Cu/g for samples G3 and G4 after 1 day (**Figure 2**). It is observed that the adsorption capacity of bulk disks of geopolymers is comparable with powdered zeolites in other findings [15]. **Figure 2** illustrates that increasing the zeolitic tuff percentages to 50% causes an increment in the adsorption capacity by several times. Therefore,

this type of geopolymer can be used effectively in water treatment.

in different ratios as reported in **Table 2**.

**2**

**Table 2.**

**Table 1.**

*Composition of geopolymers [8].*

**Figure 1.** *SEM image of geopolymers. MK: Partially transformed metakaolinite. A: Geopolymer gel [8].*

**Figure 2.**

*Adsorption of Cu (II) onto geopolymeric disks, pH = 3 [8].*
