## 1 Introduction
At the same time, the elastic modulus of concrete showed decreases of 10% and 25% when 20% and 25% of the oyster shells [19; 22] and mussel shells [15] were used, respectively. A mortar rich in calcite from seashells, which obtained a compressive strength of 22 MPa after 28 days of curing [30]. The use of scallop shells, with a particle size of 63 \(\upmu\)m as a partial cement in mortar achieved a compressive strength of 50 MPa with a 30% re-placement, indicating a 43% increase over the standard sample [31]. The use of acanthocardia tuberculate shells as a partial aggregate replacement reduces flexural strength due to the shells' water absorption, which adversely affects cement hydration [32]. Various researchers have discussed the advantages of replacing cement with alternative materials, as this can lead to a reduction in CO\({}_{2}\) emissions from an environ-mental perspective. For example, the use of 400,000 tons of coal fly ash in concrete con-tributed to an annual reduction of almost 250,000 tons of CO\({}_{2}\) emissions. They also noted that the production of one ton of calcinated clays, such as metakaolin, consumed 2.2 MJ/ton, which is 80% less than the energy needed to manufacture one ton of Portland cement. In contrast, cement is produced at temperatures ranging from 1400 \({}^{\circ}\)C and 1500 \({}^{\circ}\)C, while substitute materials like calcined clays (e.g., metakaolin) and natural hydraulic lime are obtained at temperatures below 850 \({}^{\circ}\)C to 1200 \({}^{\circ}\)C and from 450 \({}^{\circ}\)C to 900 \({}^{\circ}\)C, respectively. Regardingthe carbon footprint, the CO\({}_{2}\) emissions generated by the production of cement represent approximately 930 kg/ton, while materials such as natural hydraulic lime, limestone, and calculated clays, like metakaolin generate 335-568 kg/ton, 17 kg/ton, and 175 kg/ton, respectively [33]. Chile has a vast market of seashells; for example, in the year 2020, the following landings were reported: 400.30 tons of Mytilus chilensis bivalve mollusk; 11,288 tons of clams; 6314 tons of Aulacomya Atra bivalve mollusk; 3170 tons of Ensis Macha bivalve mollusk, among others, which have different dispositions, either for internal consumption or exportation, providing a wide opportunity for their use in research. In this way, the present research aims to develop and characterize a green mortar with Biobio region clam shells as a partial replacement for cement. The main novelty of the presented work lies in the use of clam shells from the Biobio region as a partial substitute for cement in mortars. The study focuses on evaluating the impact of 5% and 10% replacements of cement with calcined and non-calined shells, instead of conventional materials. This approach allows us to analyze their effect on the mechanical strength and properties of the mortar, something that has not been widely investigated in the Chilean context or with this species of shells. The distinction of this work from what is presented in the introduction lies in its specific focus. While the introduction covers previous studies on the use of different types of waste as a replacement for cement (including rice husk ash and seashell powder), this research narrows in on clam shells from a region of Chile, considering both calcined and non calcined forms. The findings provide a more localized and nuanced perspective, highlighting the unique mechanical properties of these mortars and addressing technical challenges, such as the reduction in strength attributed to calcification.