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The steam curing process is being applied to produce precast concrete to accelerate production cycle. A prediction of initial strength is required to determine optimized production cycle and provide economical mix proportions. As for this, the strength estimate by the Maturity method is being used widely so far. However, this method is pointed that the accuracy of the estimated strength of the concrete which has been steam cured is low. This is one of the problems on the precast concrete production. In this study, the relationship between initial strength at early age and effective material age calculated by Maturity method and Arrhenius's law was evaluated. As a result, it showed a higher estimation accuracy of the Arrhenius's law than the Maturity method. However, the accuracy of the prediction was different in each condition such as cement type, water-cement ratio, and steam curing temperature and material age.

The effect of early strength improvement of concrete with C-S-H type accelerator was studied for precast concrete efficient production under the steam curing condition. From the mortar test result, the effect of this improvement was confirmed to tend lager as the W/C is lower. This accelerator could short the curing time for 0.5-2.0 hours under the same temperature condition, and could reduce the curing temperature under the same curing time. Then the compressive strength was considered to be predicted by some formula, and it showed higher estimation accuracy of the Arrhenius’s Law than that of the Maturity Method.

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In recent years, concrete structures have tended to be taller and larger than before. With that trend, concrete as a material has diversified, and various kinds have been developed to meet differing quality requirements. In particular, the need for high-strength concrete is increasing. In general, high-strength concrete has a low water-binder ratio, so its workability is inferior to general concrete. Including admixtures such as silica fume is one way to remedy this problem. Previous studies have discussed the quality and hardening characteristics achievable using silica fume. Nevertheless, expected increasing demand for high-strength concrete dictates the need to understand not only its properties when fresh, but also to have an accurate picture of its vibration compaction properties on construction sites. In this study, the effect of adding silica fume on the workability of mortar was investigated by evaluating its fresh properties, plastic viscosity, and vibration propagation characteristics. Changes to mortar’s fresh properties due to pressure were also investigated to clarify its behavior in pumping environments. The study confirmed that the addition of silica fume decreases plastic viscosity and increases vibration propagation characteristics, and that increased plastic viscosity due to pressurization can be reduced.