Abstract
This paper presents the test results of a series of experimental studies on the effects of type and replacement ratio of fly ash on strength and durability of concrete. 3 types of fly ashes are used in this research, the specific surface area of which are 5070 cm2/g, 3760 cm2/g and 1970 cm2/g, respectively. They satisfy the requirement of Type-1, Type-2 and Type-4 fly ashes in Japanese Industrial Standard. Ordinary Portland cement, river sand, crushed sandstone, water reducer and air entraining agent are used as well. The results indicate that drying shrinkage of concrete is reduced when cement is partially replaced by fly ash. Comparatively, Type-2 fly ash's addition leads to a more effective drying shrinkage reduction, and those with replacement ratios result in larger dry shrinkage reduction. Carbonation increases with the increase of replacement ratio of fly ash, and concrete with Type-1 fly ash has higher carbonation than those with Type-2 and Type-4 fly ashes. The carbonation rate is found to be linear with water cement ratio regardless of replacement ratio of fly ash. Durability factor decreases with the replacement ratio of fly ash after 300 freezing and thawing cycles. Also, durability factor of concrete containing Type-1 and Type-2 fly ashes with replacement ratio of 25% to 55% is higher than 80%. However, those with Type-4 fly ash show lower durability factor after 300 cycles. Concretes with 70% replacement of fly ash are not durable in spite of the type of fly ash or specific surface area.
Highlights
Fly ash in Japan has been rapidly increasing with the increase of coal-fired power stations
The obstacles preventing fly ash utilization in Japan are that the permissible replacement ratio of fly ash is limited to 30% for structural concrete, and that only Type-1 and Type-2 fly ashes are usually specified, while JIS A 6201 Japanese Industrial Standard for Fly Ash Used in Conrete specifies Type-1, Type-2, Type-3, and Type-4 fly ashes
Type-1 and Type-2 fly ashes, and the replacement ratio is limited to 30% for structural concrete
Summary
Fly ash in Japan has been rapidly increasing with the increase of coal-fired power stations. The obstacles preventing fly ash utilization in Japan are that the permissible replacement ratio of fly ash is limited to 30% for structural concrete, and that only Type-1 and Type-2 fly ashes are usually specified, while JIS A 6201 Japanese Industrial Standard for Fly Ash Used in Conrete specifies Type-1, Type-2, Type-3, and Type-4 fly ashes. Japanese Industrial Standard for Fly Ash Cements requires that the portion of fly ash in the cementitious material is limited to 30% by mass. 1874-1495/13 the permissible Portland cement replacement with Type-1 and Type-2 fly ash is limited to 30% by mass, and JASS 5N for Reinforced Concrete Work at Nuclear Power Plants requires that the cement replacement should not more than. Type-1 and Type-2 fly ashes, and the replacement ratio is limited to 30% for structural concrete. The effects of type and replacement ratio of fly ash on mixture proportions, fresh concrete properties, strength development, drying shrinkage, carbonation and freezing-thawing resistance of concrete are widely discussed
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