2011 Volume 65 Issue 1 Pages 233-238
The main cause of cracks in reinforced concrete is drying shrinkage. Therefore, shrinkage-reducing admixture is used. The Architectural Institute of Japan has defined a shrinkage prediction equation in “Recommendations for Practice of Crack Control in Reinforced Concrete Buildings（Design and Construction）（2006）.” The equation considers external factors such as the volume?surface-area ratio and relative humidity, in addition to internal factors such as materials and mix proportions of concrete. However, it is necessary to confirm the validity of this equation by performing experiments.
In this study, an expansive additive and a shrinkage-reducing agent were used in the experiments. Using the drying-shrinkage prediction equation, the coefficient of mix proportion of concrete（K1）, coefficient of concrete age at initiation of drying（K2）, and coefficient of relative humidity（K3）were quantified. Experimental results showed that the shrinkage-reducing agent had a greater influence on drying shrinkage than the expansive additive. In addition, the coefficient of mix proportion of concrete（K1）was evaluated by effect of the type of admixture（γ3）. Therefore, it verified to focusing to γ3. In addition, the influence of the shrinkage-reducing admixture was evaluated using the drying-shrinkage prediction equation. Moreover, the individual influences of the expansive additive and the shrinkage-reducing agent, as well as their combined influence, were quantified.
