**2.3 Synthesis of hybrid geopolymers**

The synthesized organic–inorganic hybrid geopolymers consist of FAES and Na2SiO3 from sand dunes (southern Algeria) activated by alkaline solution (13 M NaOH) in which a percentage of PET was incorporated. Four different formulations of hybrids were prepared and characterized, as shown in **Table 5**.

FAES and sand from the dunes were used as the principal sources of aluminosilicates because they are the cheapest aluminosilicates with a good degree of purity. Moreover, this raw material improves the mechanical strength of and reduces salts and CO2 in the final product. **Table 2** presents the compositions of the raw material. The mixture of fly ash and sand was sieved to obtain a fine powder with an average diameter of 100 μm. The powder was added gradually to an alkaline solution (NaOH 13 M) previously prepared by mixing a sodium silicate solution with SiO2/ Na2O ratio = 2 and sodium hydroxide with Na2SiO3/NaOH ratio = 1.5. The final


#### **Table 3.**

*Geopolymers synthesis procedure (GP).*


#### **Table 4.**

*Chemical composition of the synthesized geopolymer (GP-2).*

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


**Table 5.**

*Geopolymers hybrid synthesis procedure (GHP).*

composition of the synthesized geopolymer can be expressed as Si, Al, Na, and H2O. To synthesize geopolymer/PET hybrid systems, PET was also added in part to the alkaline solution as well as to the mixture of fly ash and sand dune during the mixing phase. The resulting product was stirred mechanically for approximately 30 min to reach good homogenization and then poured into plexiglass-clad molds and sealed. The molds were placed in an oven for 24 hours at 30°C to avoid any possible thermal degradation of the polymer and successively stored for 28 days at room temperature.
