Hideo Kasami

Effects of Mix Proportion on the Strength and Elasticity of Concrete Subjected to High Temperatures up to 800C

This paper presents the results of an experimental study on the strength and elasticity of concrete subjected to high temperatures up to 800C carried out to determine the effects of exposure temperature and the effects of mixture proportion of concrete. Cylinders made of 4 mixture of normal-weight concrete with the W/C of 50 and 60% and slump of 50 and 210mm were subjected to 13 phases of temperatures from 20 to 800C without seal at the age of 91 days. Exposure term was 91 days for exposure up to 300C, 60 days for 400C and 24 hours for higher temperatures above 500C. After temperature exposure, cylinders were tested for weight loss, compressive strength, dynamic and static moduli of elasticity and Poissons ratio at room temperature.Weight loss increased with exposure temperature, indicating greater loss below 110C and smaller loss above 300C. Compressive strength did not decline monotonously with temperature rise between 20 and 110C, but showed 10 % reduction at 35 to 50C and recovery at 80 to 110C, indicating the minimal and maximum points. The minimal point was associated with intermediate weight loss of 4 to 5 %. At temperatures higher than 400C, residual compressive strength showed greater reduction with temperature rise for smaller weight loss.As for the effects of mixture proportion, concrete with higher W/C and higher water content showed greater weight loss and greater strength reduction below 300C, while those with higher cement content showed greater strength reduction above 500C.Both dynamic and static modulus of elasticity declined monotonously with temperature rise, indicating higher reduction rate than compressive strength. And the relationship between the two moduli of elasticity was in good correlation. Poissons ratio did not show monotonous change with temperature, but showed discontinuity between elevated and high temperatures, indicating downward peaks at about 80C which associated with 2 to 5 % weight loss, and an upward peak at 200 to 300C, which was associated with about 7 % weight loss, and a rapid increase at higher temperature of 700 to 800C.

Effects of Exposure Term on the Strength and Elasticity of Concrete Subjected to Elevated Temperature up to 175°C

There are many papers on the effects of high temperature on concrete, but papers about properties of concrete subjected to lower elevated temperature such used in nuclear power plants are still limited. This paper presents the results of experiments conducted to determine the effects of term of exposure to elevated temperatures below the limit for concrete component in nuclear power plants. Sealed cured cylinders made of normal weight concrete containing ordinary portland cement were subjected to temperatures from 20 to 175°C without seal for 10, 30 and 90 days. After exposure, cylinders were tested for weight loss, compressive strength and static modulus of elasticity.