Remaining Strength of Fireproof Mortar using the Oyster Shell as a Fine Aggregate

Abstract

This study classified oyster shells that produced as a industrial waste into 3 distribution by washing, drying and processing them. Mortar specimens with a constant ratio by using this to substitute fine aggregates were made, and the specimens were heated under the heating conditions of 300℃, 600℃ and 900℃ based on the 28-day age. On the age of 28 days, the plain flexural strength was found to be 9.2MPa, and in O 0.15, it was shown to be 4.4∼ 7.9MPa depending on the substitution rate. It was found to be 4.4∼7.7MPa in O 1.2∼2.5 depending on the substitution rate, and last but not least, it was shown to be 6.1∼8.8MPa in case of O 2.5∼5.0 depending on the substitution rate. In case of the compressive strength of the 28-day age, it showed the difference of 23.6∼43.2MPa in O 0.15 depending on the substitution rate, and 20.4∼45.1MPa in O 1.2∼2.5 depending on the substitution rate, and last but not least, 17.1∼40.4MPa in case of O 2.5∼5.0. As a result of measuring the residual strength through heating, in case of substituting fine aggregates less than O 0.15 by 100%, it showed the lowest strength reduction ratio, and it is expected that the heat-resisting property could be achieved through processing and proper mixing of oyster shells through these results.

Characteristics of Mortar Containing Oyster Shell as Fine Aggregate

“…These observations agree with previous studies and show that OSA is a lightweight material, considering that the generally known density of calcium carbonate is 2.93 g/cm 3 . At the same time, the density was measured in the absolutely dry state; thus, the measured values may be slightly lower than the surface dry density because of the micropores inside the oyster shells [ 5 , 10 ]. Water absorption is the highest (18.93%) for OSA0.6U, which has the smallest particle size and lowest density, and gradually decreases with increasing particle size, showing the lowest value (8.87%) for OSA2.5, which has the largest particle size.…”

“…However, for both wet and dry types, the damage to the structure is hard to prevent in case of fires accompanied by explosions and impacts exceeding a certain level because these materials do not possess sufficient durability. Therefore, fire-resistant boards with high strength that can withstand explosions and impacts are required [ 4 , 5 ].…”

“…Oyster shells have been confirmed to delay heat transfer and inhibit fire because of the endothermic decomposition of calcium carbonate at 800 °C. In addition, as shown in the following equation, calcium carbonate decomposes into calcium oxide and carbon dioxide, which has fire-extinguishing properties [ 5 , 12 ]. …”

“…Further research and analysis, however, are required to investigate the reasons and causes of the differences in fire-resistant performance for different particle sizes. Therefore, a method for selecting the appropriate particle size range for the required fire-resistant performance needs to be developed [ 5 , 6 , 12 ].…”