• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.481-484
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• 2006

The purpose of this study is to present the recycling method of reject-ash. The reject-ash, a significant portion of the pulverized fuel ash produced by coal-fired power plants and rejected from the ash classifying process, has remained unused due to its high carbon content and large particle size. This study compared reject-ash with fly-ash by physical properties, the properties of fresh & harden concrete with cement replacement ratio of reject-ash and fly-ash, 0, 5, 10, 15, 20, 25(wt. %). The loss of ignition of the reject-ash is similar to fly-ash and is suited to the KS L 5405. When the replacement ratio of reject-ash is increasing the air content of reject-ash concrete is lowly decreased. The results of the compressive strength measurement of reject-ash tends to decrease by increasing the replacement ratio.

• Journal of the Korean Ceramic Society
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• v.52 no.4
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• pp.253-263
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• 2015

Ordinary Portland cement is a widely favored construction material because of its good strength and durability and its reasonable price; however, spalling behaviour during fire exposure can be a serious risk that can lead to strength degradation or collapse of a building. Geopolymers, which can be synthesized by mixing aluminosilicate source materials such as metakaolin and fly ash, and alkali activators, are resistant to fire. Because the chemical composition of geopolymers controls the properties of the geopolyers, geopolymers with various Si:Al ratios were synthesized and evaluated as fire resistant construction materials. Rejected fly ash generated from a power plant was quantitatively analyzed and mixed with alkali activators to produce geopolymers having Si:Al ratios of 1.5, 2.0, and 3.5. Compressive strength of the geopolymers was measured at 28 days before and after heating at $900^{\circ}C$. Geopolymers having an Si:Al ratio of 1.5 presented the best fire resistance, with a 44% increase of strength from 29 MPa to 41 MPa after heating. This material also showed the least expansion-shrinkage characteristics. Geopolymer mortar developed no spalling and presented more than a 2 h fire resistance rating at $1,050^{\circ}C$ during the fire testing, with a cold side temperature of $74^{\circ}C$. Geopolymers have high potential as a fire resistant construction material in terms of their increased strength after exposure to fire.