De-king Salt Scaling of Concrete Incorporating Different Types and Percentages of Fly Ashes

Abstract

This paper reports the results of an investigation on the effect of the water-to-(cement+fly ash) ratio, fly ash content, fly ash type, and curing compounds on the de-icing salt scaling resistance of concrete, and attempts to explain why fly ash, when used in large amounts in air-entrained concrete, reduces its resistance to the de-icing salt scaling. Fourteen air-entrained concrete mixtures were made in this investigation. The water-to-cementitious materials ratio of the concrete mixtures ranged from 0.32 to 0.45. Two ASTM Class F and one Class C fly ashes were included in this investigation, and the fly ash content ranged from 25 to 58% by mass of the total cementitious materials. Two control portland cement concrete mixtures with the water-to-cement ratios of 0.40 and 0.45 were included in this study for comparison. The type and the amount of fly ash used and the water-to-cementitious materials ratio of the concrete affect considerably the de-icing salt scaling resistance of concrete. In general, the resistance to the scaling decreases with increasing amounts of fly ash and increasing water-to-cementitious materials ratio. When cured with the curing compounds, both the control concrete and the concrete incorporating fly ash showed substantially less scaling than the concretes cured in the moist room. The water absorption of the moist-cured concrete seems to be related to its resistance to the de-icing salt scaling; the scaling increased with increasing water absorption. However, the concrete cured with the curing compounds had much less scaling than the concrete cured in the moist room even though the water absorption of the former concrete was higher than the latter. The microstructure of the cement paste at the on-set of the freezing and thawing appears to affect the de-icing salt scaling of the concrete.