The Effects of Change in Fineness of Fly Ash on Air-Entraining Concrete

Abstract

Although the specific surface area of type-2 fly ash, specified to be not less than 250 m²/kg in Japanese Industrial Standard, type-2 fly ash manufactured and available range from 300 m²/kg to 450 cm²/kg in Japan. In order to make clear of the effects of change in fineness of fly ash on the properties of air-entraining concrete, 2 series of laboratory experiments were carried out using 6 kinds fly ash with the specific surface area in the range from 250 m2/kg to 440 m2/kg. In the series 1 experiment, mix proportion was the same for 6 mixtures of fly ash, regardless of the change in fly ash properties. Water binder ratio, unit binder content, fly ash replacement ratio and unit water content were constant for all mixtures as well as the dosage of chemical admixture. In the series 2 experiment, 5 mixtures of concrete with the same materials, with the same unit binder content, with the same fly ash replacement ratio and with the same water binder ratio as those in the series 1 experiment were examined. However, unit water content and dosage of air-entraining agent were adjusted to obtain target slump and target air content. The test results indicated higher slump and lower air content and higher dosage of air-entraining agent for fly ash with higher specific surface area than those with lower specific surface area. Compressive strength was found to increase with the increases of specific surface area of fly ash, while drying shrinkage and carbonation were found to show different tendency with change in fineness of fly ash.