Shigeharu Nakamura

Influence of Mixture Proportion and Curing Condition on Contribution of Fly Ash to Strength of Concrete

To investigate the strength efficiency of fly ash in concrete, the contribution of fly ash to strength, k value was calculated with the equation: the strength difference between fly ash concrete and control concrete with no fly ash due to the different fly ash content divides by the strength difference between both control concrete with no fly ash due to the different cement content which equals to the former different fly ash content. The k values were organized with fly ash specific surface area, concrete curing condition and age of specimens. Based on a large number of data collected from several proceedings and journals published in Japan during 1981 to 2003, the influences of fly ash property, mixture proportion and curing condition on k value were investigated. Within the range of study the following observations were made: (1) When fly ash concrete kept in moist curing, the k value of fly ash with specific surface area from 250 to 500 m2/kg is averagely 0.5 to 0.6 or higher at an age of 91 days and later, whereas that of fly ash with specific surface area from 150 to 250 m2/kg is around 0.4 to 0.5, and with some cases contributing little to the strength. (2) In the range of a portland cement content of 250 to 450 kg/m3, the strength contribution tends to increase as the cement content increases. (3) The contributions of fly ash to strength at 91 and 364 days are 1.44 to 1.97 times as large as those at 28 days, respectively, by standard curing, but conversely decrease to 0.75 to 0.79 times those at 28 days by air curing.

Penetration Behavior of Chloride Ions into Concrete in Coastal Areas

Exposure test on chloride ion penetration behavior into Concrete in coastal area was implemented. The distances between concrete specimens and coast were changed in the range from 50 to 150 meters, and water-cement ratios (W/C) were 45, 55, 60 and 65 %. The total chloride ion content at each different depth from surface of concrete specimen was measured at the age of 1, 2, 3, 5, 7, 8 and 10 years. In this paper, apparent diffusion coefficient (D) and chloride ion content on surface of concrete (C0) were calculated by inverse analyses from the measured total chloride ion content, and the chloride ion penetration behavior was simulated using the calculated D and C0. As a result, the chloride ion penetrated in concrete with a W/C of 60 % at a point 50 m from the sea for 10 years was estimated approximately 0.2 kg/m3.