At 800˚C, for normal concrete not only have surface cracks but also spalling.
At 400 to o C, they have surface crack and color changing brown to black brown for normal concrete, also white brown for RHA concrete. In addition, at 400, 600, and o C, the compression strength of normal concrete less decrease than that of RHA concrete Modulus elasticity of both normal and RHA concrete decrease after firing at 200 to o C. At temperature 200 o C, the compression strength of normal concrete lower than that of RHA concrete. The temperatures of fire are 200, 400, 600, and o C respectively with duration one hour. The test runs at 3, 7, 14, 28, and 90 days for normal concrete, and 90 days for after fire concrete.
They are 54 specimens, 30 specimens are used for compression strength of normal concrete at various ages, and the less 24 specimens are used for the compression strength of after fire concrete. The specimens are concrete cylinder with 15 cm in diameter and 30 cm height. The research would like to know the mechanical behavior and physical changing of after fire concrete with RHA. To anticipate that condition, in order to enhance the strength, the use of rice husk ash (RHA) as an additional material is an alternative. The temperature above 200 o C at fire can cause reducing of the strength of concrete.
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