When hot weather concrete is utilized, the cooling methods of cooling pipe, liquid nitrogen, ice, etc., are used to prevent the poor consistency and cold joint due to high temperature. These methods, however, spike the production cost and energy consumption, and make quality control difficult. Among these methods is one that involves the use of a retarder. Although economical, retarder is caused difficulty of retarded hardening and setting time control due to inaccurate weighing and poor working condition. Therefore, how to make a tablet for hot weather concrete, as with the existing pharmacy and foods, is discussed in this study, including the following items: mortar setting time, flow test by elapsed time, physical and mechanical properties of concrete. As a result, gluconic acid is superior to lignosulfonic acid and the possibility of using them for such purpose without quality degradation was confirmed in this study, when retarder is tabletting.

Abstract-In this study, we evaluated the durability and the shrinkage of concrete mixes for constructing nuclear power plant structures, prepared by replacing some of the concrete with diverse admixtures. The experiment variables were the types of admixtures and the replacement rate, and mixing of the two-component and three-component system concrete was carried out. The parameters for evaluating concrete durability were compressive strength, salt damage resistance, and freezing and thawing resistance that are the major durability characteristics for nuclear power plant structures, and measurements were made till the material age of 91 days. Though most mixes showed freezing and thawing resistance performances equal to or better than that of the existing concrete mix for nuclear power plants, the freezing and thawing resistance was affected considerably by the air content of the concrete rather than by the types of the admixtures and the replacement rate. Further, the concrete produced by replacing some of the cement with fly ash was found to have better salt damage resistance than the concrete produced by replacing some of the cement with blast furnace slag. The measured durability of the concrete produced by replacing some of the concrete with blast furnace slag was found to be higher than that of the existing concrete mix for use in the construction of nuclear power plants.