The field of engineering today, mainly civil engineering, given population growth and urbanization, is experiencing permanent changes, thereby implying the use of a sustainable and, above all, less polluting alternative. The present work deals with the study of the effects of the calcium-phosphate network in the geopolymeric matrix in an acidic environment (P2O5/H2O = 0.06 and 0.12) using metakaolin (MK) and calcined oyster shells (COs). Kaolin (K) and oyster shells (respectively heat treated at 700 and 900 °C), metakaolins and geopolymers (produced at room temperature according to the molar ratios P2O5/H2O = 0.06 and 0.12) have were characterized using chemical, thermal (TGA/DSC), mineralogical (XRD) analyzes and Fourier Transform Infrared Spectroscopic Analysis (FTIR). In addition, the physical and mechanical properties of the geopolymers (specimen appearance, setting time, linear shrinkage, water absorption and compressive strength) were determined. It was found that kaolin and oyster shells contain mostly kaolinite and calcium oxide respectively. However, the mineralogical analysis of MK shows a dome reflecting the presence of an amorphous phase favourable to geopolymerisation. From these results, we note that: the appearance of the geopolymer specimens is accentuated by the efflorescence and the presence of pores. The setting times of the pastes for the two solutions decreased with the addition of COs powder, due to the presence of calcium phosphate crystalline phases within the materials such as monetite and brushite which tend to accelerate network consolidation. Linear shrinkage also decreased with the addition of COs powder. On the other hand, with the addition of COs, the water absorption increase at the ratio 0.06 while they decrease at 0.12, due to the presence of pore within the geopolymers. As for the compressive strengths, they decrease with the addition of the COs powder, due to the weakening of the geopolymeric network by monetite and brushite. In conclusion, at high concentrations (P2O5/H2O = 0.12), COs (responsible for the formation of monetite and brushite in acidic environments) powder acts as a porogen. Given the presence of pores in the materials and their relatively high resistance compared to other studies, these materials could be used in engineering as sensors, insulators (thermal, electrical and acoustic).