Combined effect of silica fume, metacaoline and fly ash in normal concrete exposed to high temperature

Today, various methods and materials are being investigated to increase the strength and durability of concrete and to minimize the loss of strength of concrete exposed to elevated temperatures. Mineral additives with pozzolanic properties are among these materials. In this thesis study, mechanical properties after elevated temperature of concretes composed with mineral additives (fly ash, silica fume, metakaolin) in different volumes were investigated. The proportions of mineral additives were determined as a result of pozzolanic activity tests. As a result of the literature research, 9 series containing 10% silica fume by volume in its main matrix, different fly ash percentages (10%, 20%, 30%) and different metakaolin percentages (10%, 15%, 20%), 10% silica fume A total of 11 different series were prepared, including one control series and one control series without mineral additives. Compressive and tensile strengths of the samples were examined at the end of 7, 28 and 90 days curing periods. In order to determine the strength losses after elevated temperature, 28-day-old samples were exposed to different temperatures (400, 600, 800 o C) in the high temperature furnace. At the end of the study, it was observed that the combined effect of 10% fly ash and 20% metakaolin additive increased the strength. It has been observed that the ultrasonic pulse velocity and porosity tests performed also support this result. When the compressive strength values after elevated temperature are examined, strength loss was observed in all series due to the temperature increase, while the series showing the highest strength differed depending on the temperature. As observed in previous studies at 600 oC, as the percentage of metakaolin increased, the rate of exposure of the series to high temperatures decreased. At 800 oC, as in previous studies, the highest strength was observed in the series where all mineral additives were optimally used (10% silica fume, 10% fly ash, 15% metakaolin).