Eiji Maruya;Hidetoshi Misumi;Toshiyuki Takahashi;
<正>Industrial wastes and byproducts contain a relatively large amount of Al_2O_3.Therefore, increasing the amount of C_3A in cement clinker is an effective measure for expanding their use.The quality of such cement can be improved by adding small amounts of mineral admixtures(e.g.,blast-furnace slag or limestone powder),allowing the simultaneous utilization of industrial wastes and reduction of CO_2.In this study,we investigated the effects of C_3A content and addition of admixtures on the properties of cement pastes,mortars,and concretes,for cements with different amounts of C_3A.Cement clinkers were synthesized by using an electric furnace in laboratory or a rotary kiln in actual plant.The C_3A contents of clinkers were varied in the range of about 9 to 13 mass%with an unchanging C_3S content.Cement samples were prepared by adding gypsum and hemihydrate to clinker and adjusting the SO_3 content to 2.0 mass%.Hemihydrate prepared by heating gypsum(special grade reagent) in the atmosphere was used Some samples were prepared by adding blast-furnace slag and/or limestone powder.The amount of mineral admixture in the samples was set to 10 mass%. For these samples,apparent viscosities and setting times of the cement pastes, compressive strength and durability(Carbonation depth,drying shrinkage,Freezing and thawing resistance) of mortars and concretes were measured.When the C_3A content of clinker was 12 mass%or less,the fluidity of the cement paste could be improved to the same level as ordinary Portland cement by adding 10 mass%of mineral admixture.We found that the setting properties,strength,and durability of such cements were not much different from ordinary Portland cement.These results indicate that high C3A cement containing small amount of mineral admixture could be alternative to ordinary Portland cement. Originality The C_3A of cement clinker has a high rate of reaction.Hence,there is a concern that the qualities of concrete may decline as the C_3A content in clinker is increased However, there have been few studies on the qualities of concrete,such as compressive strength and durability,in cement in which the amount of C_3A and mineral admixtures exceed that in ordinary Portland cement.In order to develop the material design of such cement, we studied the various physical properties.
C_3A;;blast-furnace slag;;limestone powder;;durability
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