**4. Conclusion**

The synthesis of a new geopolymer-type material using a hydrothermal process was carried out after the preparation of base materials such as silica and alumina. This work describes the synthesis and valuation of FAES in the raw and activated states as well as sand from the dunes of southern Algeria for the preparation of geopolymer mortars by alkaline activation. The characterization and preparation of sodium silicate (Na2SiO3) were carried out in specialized laboratories in Algeria. Chemical analysis by XRF shows that the sand of the dunes is very rich in quartz ranging from 90.04% to 99.16% silica; in addition, a low concentration of other oxides was observed. However, microscopic SEM observations of the sand revealed the presence of pores with differing morphologies (e.g., rounded, elongated, and angular). The influence of FAES is important with respect to water penetration, and this performance is better than that of ordinary Portland cement. In addition, we observed very good fire resistance with a reduction in CO2 emissions. SEM also revealed uniform and correct distribution of the eggshells over the whole matrix phase. It was also found that there is good adhesion between the sand particles and eggshell particles, due to the sand being rich in aluminum and silicon. From the alkaline activation of eggshells, it was found that FAES can be used with sand from dunes to obtain geopolymers and hybrid geopolymers that can be used as green and durable concrete.
