2018 Volume 72 Issue 1 Pages 404-411
In Japan, the permitted amount of blending mixture in ordinary Portland cement（OPC）is limited to 5％ now. Increasing in the amount of blending mixture is one of the countermeasures for CO2 reduction. For example, OPC containing 10％ blending mixture is considered to be a candidate. However, keeping the qualities of cement（strength, heat liberation, fluidity, etc.）is required even if the amount of blending mixture increases. In this paper, the authors investigate the influence of tiny addition of superplasticizer on cement paste to compensate the decrease in heat liberation of 10％ blended cement. As the blending mixtures, blast furnace slag（BFS）, fly ash（FA）, and limestone powder（LSP）were used. Maleic acid type and methacrylic acid type polycarboxylate-based superplasticizers were also used. The dosage of superplasticizer was limited to 0.08mass％ of blended cement in consideration of the dosage of additives at industrial cement pulverization. OPC 95％＋BFS 5％, OPC 95％＋FA 5％, and OPC 96％＋LSP 4％ systems without superplasticizers were regarded as the current ordinary cements and OPC 90％＋blending mixture 10％ systems with superplasticizers were compared to the current ordinary cements. Cumulative heat liberations for 1day hydration were not increased by superplasticizer addition, independent of the mixture type. Maleic acid type superplasticizer showed the tendency to decrease the cumulative heat liberation and it should be related to the hydration retardation by superplasticizer. In contrast, cumulative heat liberations for 3 and 7days hydration were increased by superplasticizer addition, independent of the mixture type. When the dosage of superplasticizer was approximately 0.025mass％, the cumulative heat liberation became largest and the value was about 102.5％ of that without superplasticizer. For OPC 90％＋BFS 10％, OPC 90％＋FA 10％, and OPC 90％＋LSP 10％ systems, the cumulative heat liberations with 0.025mass％ superplasticizer were almost equal to those for OPC 95％＋BFS 5％, OPC 95％＋FA 5％, and OPC 96％＋LSP 4％ systems without superplasticizer, respectively. It means that the heat liberations are compensated by tiny addition of superplasticizer. Viscosity of paste was influenced by mixture blending, but the influence was not critical for viscosity. Even the tiny amount of superplasticizer（0.02mass％）decreased the viscosity, independent of the mixture type. Comparing to the pastes without mixtures, pastes with LSP showed lower viscosity. From a hydration simulation using Tomozawa’s equations, the increase in heat liberation with superplasticizer addition is considered to be related to the change in the diffusion coefficient of water in the hydrated layer.
