**3. Results and discussion**

Geopolymers and hybrid geopolymers or cementitious materials in general were synthesized using FAES activated by alkali solution and silicate sodium from sand from the dunes in southern Algeria. Results confirm that quartz is the main component in the different forms of the prepared geopolymers, along with calcite, hematite, mullite, and ferrite. These are the main elements responsible for networking in geopolymer matrixes. Thus, reactivity under alkaline conditions is affected only in the amorphous section of these reagents and acts as an indicator of geopolymer and a substitute for metakaolin.

#### **3.1 Analysis of geopolymers and hybrid geopolymers**

### *3.1.1 Analysis of different form of geopolymers*

The prepared geopolymers generally contain a large percentage of quartz in the form of silica (SiO2), which exhibits better resistance to external actions due to the hardness of the material. Local conditions and sources influence the chemical composition of geopolymers [15]. XRF is the most reliable technique for finding the lowest concentrations of the elements in a prepared sample, as shown in **Table 4**.

Ceramic materials can be prepared by geopolymers. The preparation and synthesis of our geopolymers is carried out by a chemical solution of alkali silicate. Solid aluminosilicates have been added from the source of the sand of the dunes. FAES is very rich in calcium, and with the presence of 13 M NaOH as an alkaline solution, the XRD models studied show remarkable differences in the influence of the fly ash samples on the geopolymers due to the position and shape of the quartz peaks and bumps (lower and upper) (**Figure 1**). The XRD diagrams of the geopolymer based on fly ash confirm that the geopolymer materials are essentially composed of an amorphous character under X-ray, knowing that the diffraction crystals are the same as the original materials (calcite, mullite, limine, hematite, and quartz). An amorphous peak was observed, as the value of 2θ on the diffraction pattern ranged from approximately 20 degrees to 69 degrees, given the presence of amorphous glassy materials [16]. With activation of the ash by NaOH (alkaline

**Figure 1.** *XRD patterns of geopolymers (GP1, GP2, GP3, and GP4) with a NaOH molar ratio variation of 13 M.*

solution), it was found that the diffractogram of the original ash was changed [17]. A slight shift of 19–50 degrees to 20–69 degrees (2θ) of the value of the peak attributed to the phase of the vitreous form of the original fly ash was observed. Ahydrate gel in the form of alkali aluminosilicate was formed as a result of this transformation. This hydrate gel is the main material that allows the initial reaction of geopolymerization of the geopolymeric materials mentioned in the diffraction diagrams [18]. With activation, the crystalline stages (hematite, quartz, calcite, mullite) observed inside the initial material remained practically without modification [19]. For the geopolymer model, the basic fly ash mineralogy does not change much, a result that agrees with the literature [20].

The SEM images shown in **Figures 2** and **3** show a change in morphology in most geopolymer samples compared to fly ash. Sodium silicate (Na2SiO3) was the most present element in all the samples studied (GP1, GP2, GP3, and GP4). In addition, after approximately 1 hour of preparation, a greater quantity of fly ash reacted positively. The microstructure of the geopolymers was heterogeneous and the matrix was full of loosely structured fly ash grains of different sizes, except in sample GP2, as shown in **Figure 3**, in which we observed a good microstructure. In the gel, several circular shaped cavities do not appear. Here, we suggest that a significant amount of spherically shaped fly ash reacts, and this result shows complete transformation within the system after only 1 hour and the reaction up to 78.93%. Finally, we found that the number of reactions taking place in a paste that forms the geopolymer develops as a function of the molar percentage of SiO2/Al2O3 and the reactivity ratio of the fly ash, which is rich in calcium (Ca). The "GP" geopolymers prepared by us have many characteristics that make them economical materials for construction [21]. The formation of geopolymer-type concretes is accomplished by the addition of water to a geopolymer, keeping in mind that the different shapes of geopolymers have a relatively porous structure. The water molecules limit the formation of gases

*Structural and Chemical Analysis of New Cement Based on Eggshells and Sand from Dunes… DOI: http://dx.doi.org/10.5772/intechopen.98346*

#### **Figure 2.**

*SEM of the foamed geopolymer according to the percentage of fly ash eggshell after 1 hour (GP1, GP2, GP3, GP4).*

#### **Figure 3.** *SEM of the foamed geopolymer according to the percentage of fly ash eggshell after 24 hours (GP1, GP2, GP3, GP4).*

before the gel hardens in the structure [22]. The geopolymer is formed when water is added to FAES in alkaline activation solutions. After adding FAES to the geopolymers, the number of gas-producing compounds is known, and they are trapped to produce a microstructure within the cured material [23]. When mixing water and geopolymers, the chemical reactions liberate different gases that are entrapped in the structure, especially CO2. When the oxides of silicone and calcium as well as metallic aluminum in an alkaline solution are conserved, carbon oxide and H2 are removed, creating aluminum hydroxide. Finally, the CO2 molecules will be blocked in the structure of the geopolymer, which means that the product is very reactive.
