Experimental Study on Effects of Type and Replacement Ratio of Fly Ashon Strength and Durability of Concrete

摘要

This paper presents the test results of a series of experimental studies on the effects of type and replacement ratioof fly ash on strength and durability of concrete. 3 types of fly ashes are used in this research, the specific surface areaof which are 5070 cm2/g, 3760 cm2/g and 1970 cm2/g, respectively. They satisfy the requirement of Type-1, Type-2 andType-4 fly ashes in Japanese Industrial Standard. Ordinary Portland cement, river sand, crushed sandstone, water reducerand air entraining agent are used as well. The results indicate that drying shrinkage of concrete is reduced when cement ispartially 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 ofreplacement ratio of fly ash, and concrete with Type-1 fly ash has higher carbonation than those with Type-2 and Type-4fly ashes. The carbonation rate is found to be linear with water cement ratio regardless of replacement ratio of fly ash. Durabilityfactor decreases with the replacement ratio of fly ash after 300 freezing and thawing cycles. Also, durability factorof 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 arenot durable in spite of the type of fly ash or specific surface area.