There are several methods of fire-resistant cladding used to protect buildings from fire. In the recent high-temperature fire of more than 1000℃, fire resistance performance is insufficient other than fire-resistant boards. However, fireproof boards are easily destroyed in explosive fires due to their high unit cost and weak strength. To address these shortcomings, research is underway to introduce oyster shells and eggshells into refractory materials. Oyster shell and egg shell are materials made up of with more than 90% of the ingredients. Oyster shell is biased in the timing and region of occurrence, but eggshells are characterized by evenly distributed timing and region. Due to various characteristics, it is believed that there will be advantages and disadvantages if used as refractory materials. Therefore, the purpose of this study is to provide basic data for use as a refractory material by comparing strength characteristics and fire resistance performance of mortar mixed with oyster shell and egg shell.

In this study, oyster shells and eggshells were processed in the same particle size. The physical and chemical properties were then analyzed, the experiments were manufactured according to the combination, and the strength and refractory properties were evaluated. The following conclusions are drawn from the study for the application of oyster shells and egg shells as refractory materials.

1. Oyster shell and egg shell are natural calcium carbonate materials consisting of 90% or more. Oyster peeling occurred more than 300,000 tons (as of 2019) and eggshells generated an average of 265 tons per day (as of 2019) on average. In terms of raw materials supply and demand, oyster shell usually occurs in the biased area of Gyeongsangnam-do during the winter season of the year. Egg shells are operated by 186 egg processing companies nationwide, and occur uniformly throughout the country 365 days a year regardless of the timing. Therefore, it is considered to be more advantageous than oyster shell in terms of supply and demand of raw materials.

2. Density was very similar for OSP and ESP. However, the absorption rate was about 5.34% higher, which is attributed to the large surface area due to the small pieces attached to the surface of the oyster shell. The mixture design shall be more water-rich than the existing mortar mix and secure the water required for hydration reaction of cement.

3. For the strength performance of mortar according to the mixture, the OSP-mixed mortar had a bending strength of about 2.6MPa greater than the ESP-mixed mortar, and the compression strength was about 16.58MPa greater. The reason why OSP has a greater flexural and compressive strength is that small pieces are attached to the surface of the corrugated shell in different directions, which are considered to have had a positive effect on the adhesion of cement baggage due to the rough surface. On the other hand, ESP are considered to have a relatively smooth surface, which is considered to be lower than OSP due to its adverse effect on surface attachment.

4. Mortar''s strength performance according to mixed materials was higher for both the bending and compression strength of OSP. The reason for this is that the strength of the oyster shell is higher than that of the egg shell, and the surface of the oyster shell is rough, which has a positive effect on the cement baggage attachment.

5. The difference in temperature behind 120 minutes of heating time of mortar according to OSP and ESP mixing rates was the greatest difference at 58.15℃ for 60% of the mixing rate, and 21.3℃ for 90% of the mixing rate. This is thought to be due to the fact that the egg shell consists of porosity and has more content.
6. OSP and ESP recited the thickness of the crack as the mixing rate increased. This is believed to be due to the increased mixture rate, which increases the amount of carbon dioxide escaping due to the de-carbonate reaction ().

7. Strength and refractory properties showed conflicting results. The strength of the OSP was measured at a higher value, and in the case of refractory properties, the refractory board mixed with ESP showed a lower Backside temperature of about 32.39℃ on average. However, both OSP and ESP showed lower strength and increased fire resistance as the mixing rate increased.

Therefore, experiments on the strength and refractory properties of mortar mixed with oyster shell powder show that oyster shell and egg shell can be selected and applied according to the purpose used.