DESIGN AND DEVELOPMENT OF ADDITIVE FOR CO₂ FIXATION UTILIZING BY-PRODUCT CONTAINING Ca （1）

<p>In the use of by-products as raw materials of additive production whose main component is γ-C₂S, contamination of minor components is inevitable. This paper investigates the effect of Al₂O₃, which is contained several by-products （Waste concrete, sludge, slag, etc.）, to the properties of additive. The additives in this test ware prepared by adding 1 to 20％ of Al₂O₃ to the reagent of CaO/SiO₂＝2：1 （molar ratio）, burning at 1450℃, then milled to 4000-5000cm²/g of Blain’s surface area. By the increase of Al₂O₃, the ratio of C₂AS in the additive was also increased. Main component of all additives was γ-C₂S and small β-C₂S was confirmed. No or small effect of Al₂O₃ to prevent phase transition from β phase to γ phase wase confirmed. In the accelerated carbonation test of only additive, CO₂ fixation rate to the clinker was reduced by the increase of Al₂O₃, that means the increase of C₂AS which it non- reactive to water and CO₂. On the other hand, there was no tendency in the result of CO₂ fixation rate, amount of reacted γ-C₂S and total pore volume of hardened cement paste containing additives. This difference was caused by the reaction rate of γ-C₂S. In case of hardened cement paste, γ-C₂S was reacted faster than that only additive at carbonation of 1 day. On the other hand, the reaction of γ-C₂S in the hardened cement was stagnated after carbonation of 1 day, especially additive of high purity γ-C₂S. These results suggest that hardened cement is suitable to keep appropriate humidity and water content to the carbonation of γ-C₂S at early stage and then suppress the reaction of γ-C₂S by tightness of cement matrix and reaction layer on the surface of additive in long term.</p>