RESISTANCE TO FREEZING AND THAWING OF STEEL-MAKING SLAG CONCRETE AND THE IMPROVEMENT

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  • 鉄鋼スラグ水和固化体の凍結融解抵抗性とその改善に関する研究

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Steel-making slag concrete consists of by-products at ironworks. The strength of steel-making slag concrete is 20-50 N/mm2 at 28 days. Ground granulated blast furnace slag is used as a binder. Steelmaking slag is used as an aggregate. Steel-making slag concrete doesn't use any natural aggregate, either. The calcium hydroxide leaching from steel-making slag acts as alkali activator of ground granulated blast furnace slag. Steel-making slag concrete can be hardened by itself without any cement. Resistance to carbonation of steel-making slag concrete and resistance to corrosion of steel rod in steel-making slag concrete are high for a long time due to calcium hydroxide leaching from steel-making slag. However, resistance to freezing and thawing of steel-making slag concrete is quite low. In this paper, the mechanism of low resistance to freezing and thawing was clarified. The method to improve the durability of steel-making slag concrete was shown. An entrained air by AE agent is formed by calcium ion. The paste just with ground granulated blast furnace slag cannot contain entrained air by AE agent because enough calcium ions cannot be produced by the hydration with water and ground granulated blast furnace slag. Big size air is formed around steel-making slag because of calcium hydroxide leaching from the steel-making slag. That's why resistance to freezing and thawing is low. In order to improve the resistance to freezing and thawing of steel-making slag concrete, it's necessary to use cement, fly ash and blast furnace slag sand. Cement is used to entrain the air by AE agent. Fly ash is used to consume the extra calcium hydroxide in steel-making slag concrete. Blast furnace slag sand is used to restrain the calcium hydroxide leaching from sand. Then, the resistance to freezing and thawing of steel-making slag concrete is as high as that of AE cement concrete.

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